We're trying to make a mechanism that will allow for the
REPEATABLE lobbing of small projectiles over short (0-20 ft)
distances.
We've tried using a constant force with a variable launch angle
(higher for shorter).
And, a variable force with a constant launch angle (push harder
to throw farther).
The former seems to be easier to get repeatability. But, still
not great as it constrains HOW you develop the force to be applied.
A ferrous projectile would probably be easier to control
(think: rail gun) but then the projectile starts to become a safety
issue.
Now, we're looking at alternate ways of developing that propulsive
force -- e.g., controlled air or water (messy!) pressure. But,
I suspect qualifying the release valves' performance will prove to
be a stumbling point (and, how it changes).
Any other ideas, given latitude in the design of the projectile?
We're trying to make a mechanism that will allow for the
REPEATABLE lobbing of small projectiles over short (0-20 ft)
distances.
We've tried using a constant force with a variable launch angle
(higher for shorter).
And, a variable force with a constant launch angle (push harder
to throw farther).
The former seems to be easier to get repeatability. But, still
not great as it constrains HOW you develop the force to be applied.
A ferrous projectile would probably be easier to control
(think: rail gun) but then the projectile starts to become a safety
issue.
Now, we're looking at alternate ways of developing that propulsive
force -- e.g., controlled air or water (messy!) pressure. But,
I suspect qualifying the release valves' performance will prove to
be a stumbling point (and, how it changes).
Any other ideas, given latitude in the design of the projectile?
On 21/11/2024 07:04, Don Y wrote:
We're trying to make a mechanism that will allow for the
REPEATABLE lobbing of small projectiles over short (0-20 ft)
distances.
We've tried using a constant force with a variable launch angle
(higher for shorter).
And, a variable force with a constant launch angle (push harder
to throw farther).
Trebuchet is probably the method of choice. There is a bloke round here with one big enough to lob a watermelon about 100m. It is an impressive beast and flat packs into his pickup traler.
https://en.wikipedia.org/wiki/Trebuchet
He takes it around rural summer fetes to raise money for charity (and buying more water melons). They land with a very satisfying splat!)
One to throw a tennis ball 20ft would be a bit dangerous close to but very reproducible if that is what you want.
Bow and arrow?
That was actually meant seriously as the geometric arrantement of the
string acts as a variable-ratio transformer between the movement of the propelling spring (bow) and the increasing velocity of the load (arrow).
This means that if you charge the spring with a known amount of energy,
it will always be transferred with the same high efficiency into the
load.
By varying the starting point of the arrow, and hence the spring
tension, you have an accurate repeatable energy input.
On 11/21/2024 4:46 AM, Martin Brown wrote:
On 21/11/2024 07:04, Don Y wrote:
We're trying to make a mechanism that will allow for the
REPEATABLE lobbing of small projectiles over short (0-20 ft)
distances.
We've tried using a constant force with a variable launch angle
(higher for shorter).
And, a variable force with a constant launch angle (push harder
to throw farther).
Trebuchet is probably the method of choice. There is a bloke round
here with one big enough to lob a watermelon about 100m. It is an
impressive beast and flat packs into his pickup traler.
https://en.wikipedia.org/wiki/Trebuchet
He takes it around rural summer fetes to raise money for charity (and
buying more water melons). They land with a very satisfying splat!)
One to throw a tennis ball 20ft would be a bit dangerous close to but
very reproducible if that is what you want.
But how do you RELIABLY adjust the length of throw?
I.e., "I want THIS (repeatable object) to be tossed in a high arc
to land X (not Y or Z) feet from the launcher"
It is permissible to store "calibration factors" -- including
in *tabular* form. But, you should be able to use any of those
specified ranges with a reasonable guarantee that you'll strike
at the correct distance (the launcher won't be able to verify the
*actual* distance achieved)
The entire sequence has to happen without human intervention
(and, ideally, in a short enough time span that one can repeatedly
"get off rounds" without long delays)
On 11/21/2024 2:53 AM, Liz Tuddenham wrote:
Bow and arrow?
That was actually meant seriously as the geometric arrantement of the string acts as a variable-ratio transformer between the movement of the propelling spring (bow) and the increasing velocity of the load (arrow). This means that if you charge the spring with a known amount of energy,
it will always be transferred with the same high efficiency into the
load.
By varying the starting point of the arrow, and hence the spring
tension, you have an accurate repeatable energy input.
The "variable force constant launch angle" approach was
implemented on a similar principle: pull a spring back to
a particular amount of compression and then release.
(This is how a pinball is launched, hence my inspiration)
The "release" seems to be a big problem
Don Y <blockedofcourse@foo.invalid> wrote:
On 11/21/2024 2:53 AM, Liz Tuddenham wrote:
Bow and arrow?
That was actually meant seriously as the geometric arrantement of the
string acts as a variable-ratio transformer between the movement of the
propelling spring (bow) and the increasing velocity of the load (arrow). >>> This means that if you charge the spring with a known amount of energy,
it will always be transferred with the same high efficiency into the
load.
By varying the starting point of the arrow, and hence the spring
tension, you have an accurate repeatable energy input.
The "variable force constant launch angle" approach was
implemented on a similar principle: pull a spring back to
a particular amount of compression and then release.
(This is how a pinball is launched, hence my inspiration)
That is a less efficient system because a lot of kinetic energy is left
in the spring after it has lost contact with the projectile. The
bowstring method transfers much more of the energy.. The Roman ballista
and catapulta used a flip-over arm to bring the heavy beam to rest and transfer most of its energy to the projectile.
All those methods were designed during an energy-scarce era, something
we need to re-visit and learn from.
The "release" seems to be a big problem
That is a problem because if the 'catch' (of whatever type) moves to one side, it has the potential to introduce a variable factor. If it holds
onto the projectile along the axis of projection by friction, you have a different variable factor as it releases.
When faced with a similar problem in the past, I used a thin piece of
cotton to retain the projectile and snipped or burned it through to
cause the release, but this isn't really suitable for your application.
If you don't mind a slighly variable delay in the starting time, could
you retain the projectile with a clamp and a lead rod aligned on the
centre of mass. Releasing the clamp would put tension on the lead rod
which would 'neck' through and give a clean release. That method was
used for time-delay fuses in WWII.
Another release mechanism (which I have seen used in air rifles) is to
have three concentric components. In the centre is a rod attached to
the mechanism with a 'waist' machined in it. Arounf that is a sleeve
with three hole drilled radially at 120-degree intervals. In the holes
are ball bearingsa which engage with the waist when they move inwards.
Around the outside is a tube which keeps the ball bearing pressed
inwards.
When the sleeve is slid off, the balls move outwards and release the
inner rod. Because they are symmestrical, no unwanted displacing thrust
is applied to the rod.
On 21/11/2024 12:06, Don Y wrote:
On 11/21/2024 4:46 AM, Martin Brown wrote:
On 21/11/2024 07:04, Don Y wrote:
We're trying to make a mechanism that will allow for the
REPEATABLE lobbing of small projectiles over short (0-20 ft)
distances.
We've tried using a constant force with a variable launch angle
(higher for shorter).
And, a variable force with a constant launch angle (push harder
to throw farther).
Trebuchet is probably the method of choice. There is a bloke round here with
one big enough to lob a watermelon about 100m. It is an impressive beast and
flat packs into his pickup traler.
https://en.wikipedia.org/wiki/Trebuchet
He takes it around rural summer fetes to raise money for charity (and buying
more water melons). They land with a very satisfying splat!)
One to throw a tennis ball 20ft would be a bit dangerous close to but very >>> reproducible if that is what you want.
But how do you RELIABLY adjust the length of throw?
I.e., "I want THIS (repeatable object) to be tossed in a high arc
to land X (not Y or Z) feet from the launcher"
Ratchet mechanism and count the number of clicks or stepper motor.
It is permissible to store "calibration factors" -- including
in *tabular* form. But, you should be able to use any of those
specified ranges with a reasonable guarantee that you'll strike
at the correct distance (the launcher won't be able to verify the
*actual* distance achieved)
The entire sequence has to happen without human intervention
(and, ideally, in a short enough time span that one can repeatedly
"get off rounds" without long delays)
Speed of firing might be its main weakness. The thing depends on moving a heavy
counterweight up slowly to store the energy and letting it go in a single pulse
with mechanical amplification of the lever and sling.
Reproducibility was as I recall quite good.
On 11/21/2024 5:15 AM, Liz Tuddenham wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
On 11/21/2024 2:53 AM, Liz Tuddenham wrote:
Bow and arrow?
That was actually meant seriously as the geometric arrantement of the
string acts as a variable-ratio transformer between the movement of the >>>> propelling spring (bow) and the increasing velocity of the load
(arrow).
This means that if you charge the spring with a known amount of energy, >>>> it will always be transferred with the same high efficiency into the
load.
By varying the starting point of the arrow, and hence the spring
tension, you have an accurate repeatable energy input.
The "variable force constant launch angle" approach was
implemented on a similar principle:Â pull a spring back to
a particular amount of compression and then release.
(This is how a pinball is launched, hence my inspiration)
That is a less efficient system because a lot of kinetic energy is left
in the spring after it has lost contact with the projectile. The
But the spring is fully extended (decompressed) when the projectile departs. (?)
On 11/21/2024 5:34 AM, Martin Brown wrote:
Reproducibility was as I recall quite good.
But I suspect the forces involved in lobbing watermelons scores of
yards swamps the characteristics of the load -- so variations
would appear as "noise". Imagine how the same (scale) mechanism
might vary with a load like a tennis ball (over those distances).
On 11/21/2024 5:15 AM, Liz Tuddenham wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
On 11/21/2024 2:53 AM, Liz Tuddenham wrote:
Bow and arrow?
That was actually meant seriously as the geometric arrantement of the
string acts as a variable-ratio transformer between the movement of the >>> propelling spring (bow) and the increasing velocity of the load (arrow). >>> This means that if you charge the spring with a known amount of energy, >>> it will always be transferred with the same high efficiency into the
load.
By varying the starting point of the arrow, and hence the spring
tension, you have an accurate repeatable energy input.
The "variable force constant launch angle" approach was
implemented on a similar principle: pull a spring back to
a particular amount of compression and then release.
(This is how a pinball is launched, hence my inspiration)
That is a less efficient system because a lot of kinetic energy is left
in the spring after it has lost contact with the projectile. The
But the spring is fully extended (decompressed) when the projectile
departs. (?)
The mechanism must be able to be loaded, "cocked" and released
without humans being involved.
Another release mechanism (which I have seen used in air rifles) is to
have three concentric components.[...]
This seems to mimic the mechanism used to interconnect pneumatic quick release fittings (?).
I think re-SETTING that would be difficult.
The spring approach was relatively easy to mock up (despite being
a poor performer). I used a linear actuator to move the spring
(effectively shortening -- cocking -- it or "resetting" to the
uncocked position). The release mechanism could then stay stationary;
the spring pressing up against it while cocked and being retracted
(reset) once it had delivered its energy to the load.
Speed of firing might be its main weakness. The thing depends on moving
a heavy counterweight up slowly to store the energy and letting it go in
a single pulse with mechanical amplification of the lever and sling.
We're trying to make a mechanism that will allow for the
REPEATABLE lobbing of small projectiles over short (0-20 ft)
distances.
We've tried using a constant force with a variable launch angle
(higher for shorter).
And, a variable force with a constant launch angle (push harder
to throw farther).
The former seems to be easier to get repeatability. But, still
not great as it constrains HOW you develop the force to be applied.
A ferrous projectile would probably be easier to control
(think: rail gun) but then the projectile starts to become a safety
issue.
Now, we're looking at alternate ways of developing that propulsive
force -- e.g., controlled air or water (messy!) pressure. But,
I suspect qualifying the release valves' performance will prove to
be a stumbling point (and, how it changes).
Any other ideas, given latitude in the design of the projectile?
The "release" seems to be a big problem -- getting a (home
brewed) mechanism that cleanly releases so the stored energy
can be transferred to the projectile as a step function.
On 21/11/2024 12:43, Don Y wrote:
On 11/21/2024 5:34 AM, Martin Brown wrote:
Reproducibility was as I recall quite good.
But I suspect the forces involved in lobbing watermelons scores of
yards swamps the characteristics of the load -- so variations
would appear as "noise". Imagine how the same (scale) mechanism
might vary with a load like a tennis ball (over those distances).
One other thought you might be able to buy a tennis practice serve machine off
the shelf with high reproducibility.
One other thought you might be able to buy a tennis practice serve
machine off the shelf with high reproducibility.
Martin Brown <'''newspam'''@nonad.co.uk> wrote:[...]
Another thought would be a crossbow-like mechanism with a motorized
winding mechanism.
We're trying to make a mechanism that will allow for the
REPEATABLE lobbing of small projectiles over short (0-20 ft)
distances.
We've tried using a constant force with a variable launch angle
(higher for shorter).
And, a variable force with a constant launch angle (push harder
to throw farther).
The former seems to be easier to get repeatability. But, still
not great as it constrains HOW you develop the force to be applied.
A ferrous projectile would probably be easier to control
(think: rail gun) but then the projectile starts to become a safety
issue.
Now, we're looking at alternate ways of developing that propulsive
force -- e.g., controlled air or water (messy!) pressure. But,
I suspect qualifying the release valves' performance will prove to
be a stumbling point (and, how it changes).
Any other ideas, given latitude in the design of the projectile?
Ideally, I would like the mass to STOP at the destination (not bounce
or roll away) but that's a secondary goal.
Don Y <blockedofcourse@foo.invalid> wrote:
[...]
The "release" seems to be a big problem -- getting a (home
brewed) mechanism that cleanly releases so the stored energy
can be transferred to the projectile as a step function.
A bow and arrow arrangement with two bow strings, one slightly longer
than the other. The shorter string is notched into the projectile and
the longer string is held back by a 'rolling nut' in a similar way to a mediaeval crossbow. The displacement caused by the rolling nut
releasing the longer string will not be communicated to the shorter
string or the projectile.
The mechanism must be able to be loaded, "cocked" and released
without humans being involved.
Have you seen the devices for throwing clay pigeons that are 'cocked' by
a crank on a lorry windscreen wiper motor tensioning a chest expander
spring. All very off-the-shelf stuff but not particularly accurate or efficient. (but bloody frightening when you are working on one and it
goes off unexpectedly).
I think re-SETTING that would be difficult.
In an air rifle it is allre-set by a mechanical linkage that operates
from 'breaking' the barrel to reload, with small auxiliary springs that
pull all the components into place automatically. The user is unaware
of any complication.
The spring approach was relatively easy to mock up (despite being
a poor performer). I used a linear actuator to move the spring
(effectively shortening -- cocking -- it or "resetting" to the
uncocked position). The release mechanism could then stay stationary;
the spring pressing up against it while cocked and being retracted
(reset) once it had delivered its energy to the load.
Not exactly off-the-shelf, but have you thought about a linear motor?
That would be eminently controllable as the speed of the projectile
could be measured and corrected as it accelerates.
Martin Brown <'''newspam'''@nonad.co.uk> wrote:
One other thought you might be able to buy a tennis practice serve
machine off the shelf with high reproducibility.
The tennis ball thrower seems promising if the projectile weight is
close to right.
Another thought would be a crossbow-like mechanism with a motorized
winding mechanism. Range could be adjusted by moving the limbs to
vary the preload on the string. Bulk can be reduced by using a
reverse-draw layout.
[electronics content]
Many years ago I worked on a project to build a fast (microseconds)
opening gas valve. Introducing a flying weight (essentially a hammper) between the first actuator and the rest of the control train improved reproducibility by sharpening up the trigger impulse. If you end up
using a pneumatic "gun" that would help regularize valve performance.
We used a pulsed coil accelerating an aluminum ring which then hit
the valve poppet to drive it off of its seat.
\[electronics content
A similar approach could be applied to a crossbow or catapult sear.
Thanks for reading,
bob prohaska
<bp@www.zefox.net> wrote:
Martin Brown <'''newspam'''@nonad.co.uk> wrote:[...]
Another thought would be a crossbow-like mechanism with a motorized
winding mechanism.
Apparently the technical term for the winding mechanism of a crossbow is "Crannequin", which sounds as though it could be quite naughty - so it
is a word we ought to use more often.
Don Y <blockedofcourse@foo.invalid> wrote:
Ideally, I would like the mass to STOP at the destination (not bounce
or roll away) but that's a secondary goal.
Apologies if I missed it, but what are the masses and accelerations in play?
On 11/21/2024 10:18 AM, bp@www.zefox.net wrote:
Martin Brown <'''newspam'''@nonad.co.uk> wrote:
One other thought you might be able to buy a tennis practice serve
machine off the shelf with high reproducibility.
The tennis ball thrower seems promising if the projectile weight is
close to right.
Another thought would be a crossbow-like mechanism with a motorized
winding mechanism. Range could be adjusted by moving the limbs to
vary the preload on the string. Bulk can be reduced by using a
reverse-draw layout.
The machine would have to move the limbs. Once fabricated (and
"loaded" with a supply of projectiles), a human doesn't interact
with it.
[electronics content]
Many years ago I worked on a project to build a fast (microseconds)
opening gas valve. Introducing a flying weight (essentially a hammper)
between the first actuator and the rest of the control train improved
reproducibility by sharpening up the trigger impulse. If you end up
using a pneumatic "gun" that would help regularize valve performance.
We used a pulsed coil accelerating an aluminum ring which then hit
the valve poppet to drive it off of its seat.
\[electronics content
A similar approach could be applied to a crossbow or catapult sear.
<frown> This sounds complex.
What sort of performance did you see from "unassisted" valves?Hammerless valves would start to leak millisconds before reaching
I.e., what made it so important to have such a fast action?
Boring, but think 'sling'. david and Goliath etc.
Rotating arm, center-fed ~ counterbalanced.
axle tilt, fixed length arm (rpm), angle of release,
Golfers would go for it.
RL
On 11/21/2024 5:52 PM, bp@www.zefox.net wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
Ideally, I would like the mass to STOP at the destination (not bounce
or roll away) but that's a secondary goal.
Apologies if I missed it, but what are the masses and accelerations in play?
The masses are negotiable. As is the acceleration (as long as you
can overcome gravity).
The goal is to PLACE a "thing" (projectile) at a specific location
relative to the launcher. And, to have it reach that location
with minimal interaction with anything located between the launcher
and destination.
E.g., If something was located immediately adjacent to the
launcher, the projectile's path should go OVER the obstacle
and not expect to be able to pass THROUGH it.
Imagine using a nerf gun to lob those little sponge balls
up, over obstacles -- but, being able to precisely control
the range so they land where planned (no farther nor shorter)
But, to do so completely under automation, without any human
intervention.
Don Y <blockedofcourse@foo.invalid> wrote:
On 11/21/2024 5:52 PM, bp@www.zefox.net wrote:Per projectile? All the same? Are they fragile? Same aerodynamics,
Don Y <blockedofcourse@foo.invalid> wrote:
Ideally, I would like the mass to STOP at the destination (not bounce
or roll away) but that's a secondary goal.
Apologies if I missed it, but what are the masses and accelerations in play?
The masses are negotiable. As is the acceleration (as long as you
can overcome gravity).
or variable? Grams per cc, or cc's per gram?
The goal is to PLACE a "thing" (projectile) at a specific location
relative to the launcher. And, to have it reach that location
with minimal interaction with anything located between the launcher
and destination.
What's the permissible error in position and landing speed?
E.g., If something was located immediately adjacent to the
launcher, the projectile's path should go OVER the obstacle
and not expect to be able to pass THROUGH it.
That's a mortar or howitzer.
Imagine using a nerf gun to lob those little sponge balls
up, over obstacles -- but, being able to precisely control
the range so they land where planned (no farther nor shorter)
Now you're talking projectiles dominated by aerodynamic drag.
Does your launcher need to take air movement into account?
But, to do so completely under automation, without any human
intervention.
Are you thinking of something like https://en.wikipedia.org/wiki/Girardoni_air_rifle
?
One could build a version to launch Nerf balls. Note that it
used a hammer to operate the gas valve and compensate at least
partly for pressure changes. You'd want a very low pressure
for 20 feet. Perhaps you want a toned-down potato cannon (I
think that was mentioned previously by someone).
We're trying to make a mechanism that will allow for the
REPEATABLE lobbing of small projectiles over short (0-20 ft)
distances.
We've tried using a constant force with a variable launch angle
(higher for shorter).
And, a variable force with a constant launch angle (push harder
to throw farther).
The former seems to be easier to get repeatability. But, still
not great as it constrains HOW you develop the force to be applied.
A ferrous projectile would probably be easier to control
(think: rail gun) but then the projectile starts to become a safety
issue.
Now, we're looking at alternate ways of developing that propulsive
force -- e.g., controlled air or water (messy!) pressure. But,
I suspect qualifying the release valves' performance will prove to
be a stumbling point (and, how it changes).
Any other ideas, given latitude in the design of the projectile?
We're trying to make a mechanism that will allow for the
REPEATABLE lobbing of small projectiles over short (0-20 ft)
distances.
The point is finding the right combination of mechanism
and projectile to get repeatability from the system.
Most "guns" just want to achieve a "maximum" (range,
load, etc.)
Don Y <blockedofcourse@foo.invalid> wrote:
Most "guns" just want to achieve a "maximum" (range,
load, etc.)
Not sure I understand what you're getting at here. On
the face of it that statement seems mistaken.
bp@www.zefox.net wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
Most "guns" just want to achieve a "maximum" (range,
load, etc.)
Not sure I understand what you're getting at here. On
the face of it that statement seems mistaken.
You are interacting with "Don Y". If you go review other postings
where "Don Y" has initiated a thread like this one you will find that
the "Don Y" poster quite effectively trolls the group every single
time. The initial post is always ambigious and seriously lacking in necessary details, such that 234+ wrong possibilities could be seen by readers. And as others in the group request details to try to gain an understanding from the vague, detail lacking initial post, they are
slowly tricked out over the course of days and plural postings from
"Don Y", intermixed with numerous random asides to maximize confusion. Meanwhile, as the supposed details are trickled out, the apparent requirements needed also shift as posters appear to gain any
understanding in order to keep the responders in the dark and allow the
"Don Y" trolling articles to continue to troll everyone who responds.
On 11/21/2024 5:52 PM, bp@www.zefox.net wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
Ideally, I would like the mass to STOP at the destination (not bounce
or roll away) but that's a secondary goal.
Apologies if I missed it, but what are the masses and accelerations in
play?
The masses are negotiable. As is the acceleration (as long as you
can overcome gravity).
The goal is to PLACE a "thing" (projectile) at a specific location
relative to the launcher. And, to have it reach that location
with minimal interaction with anything located between the launcher
and destination.
E.g., If something was located immediately adjacent to the
launcher, the projectile's path should go OVER the obstacle
and not expect to be able to pass THROUGH it.
Imagine using a nerf gun to lob those little sponge balls
up, over obstacles -- but, being able to precisely control
the range so they land where planned (no farther nor shorter)
But, to do so completely under automation, without any human
intervention.
On 11/22/24 03:55, Don Y wrote:
On 11/21/2024 5:52 PM, bp@www.zefox.net wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
Ideally, I would like the mass to STOP at the destination (not bounce
or roll away) but that's a secondary goal.
Apologies if I missed it, but what are the masses and accelerations in
play?
The masses are negotiable. As is the acceleration (as long as you
can overcome gravity).
The goal is to PLACE a "thing" (projectile) at a specific location
relative to the launcher. And, to have it reach that location
with minimal interaction with anything located between the launcher
and destination.
E.g., If something was located immediately adjacent to the
launcher, the projectile's path should go OVER the obstacle
and not expect to be able to pass THROUGH it.
Imagine using a nerf gun to lob those little sponge balls
up, over obstacles -- but, being able to precisely control
the range so they land where planned (no farther nor shorter)
But, to do so completely under automation, without any human
intervention.
You may want to look at marble machines on youtube. This one
seems much like what you're asking for.
https://www.youtube.com/watch?v=-AZMmg0qq4A
Jeroen Belleman
Most "guns" just want to achieve a "maximum" (range,
load, etc.)
Not sure I understand what you're getting at here. On
the face of it that statement seems mistaken.
Perhaps the most clever feature of the Giradoni mechanism
is pitting the momentum of the hammer _against_ the air pressure
bearing on the release valve. As the pressure goes down, the
valve opens farther, at least partially compensating for the
lower pressure.
Since you will have control of the exact pressure that particular compensation isn't needed. Still, if the valve opens differently
on timescales comparable to the departure time of the projectile repeatability will suffer and with it accuracy.
Opening the valve
poppet before the projectile moves is one way to help repeatability.
For the velocities you envision that shouldn't be difficult.
A pneumatic potato cannon seems like a good starting point.
But, to do so completely under automation, without any human
intervention.
You may want to look at marble machines on youtube. This one
seems much like what you're asking for.
https://www.youtube.com/watch?v=-AZMmg0qq4A
On 11/22/2024 1:21 PM, Jeroen Belleman wrote:
But, to do so completely under automation, without any human
intervention.
You may want to look at marble machines on youtube. This one
seems much like what you're asking for.
https://www.youtube.com/watch?v=-AZMmg0qq4A
While it appears to be repeatable, it is recycling the
same projectile. And, the same target distance (which
falls considerably short of the 20 ft mentioned in my post)
I.e., one would be surprised if it DIDN'T recapture the
projectile on each execution.
On 21/11/2024 07:04, Don Y wrote:
We're trying to make a mechanism that will allow for the
REPEATABLE lobbing of small projectiles over short (0-20 ft)
distances.
<snip>
I'd look at the way people throw pétanque boules. I imagine they've developed
an accurate technique.
On 11/22/2024 11:30 AM, bp@www.zefox.net wrote:
Most "guns" just want to achieve a "maximum" (range,
load, etc.)
Not sure I understand what you're getting at here. On
the face of it that statement seems mistaken.
A gun (in the sense of handgun) tends not to have a "range control".
You can use "light loads" (bullets with less black powder than a
"normal load") but that's not really intended to decrease the
firing range.
On 11/22/24 23:12, Don Y wrote:
On 11/22/2024 1:21 PM, Jeroen Belleman wrote:
But, to do so completely under automation, without any human
intervention.
You may want to look at marble machines on youtube. This one
seems much like what you're asking for.
https://www.youtube.com/watch?v=-AZMmg0qq4A
While it appears to be repeatable, it is recycling the
same projectile. And, the same target distance (which
falls considerably short of the 20 ft mentioned in my post)
I.e., one would be surprised if it DIDN'T recapture the
projectile on each execution.
Surely those are issues within range of your abilities?
You're free to scale and reconfigure the thing. If you
want an exact solution, at least specify your exact
requirements. Otherwise we'll think you're here just to
argue. You know how to state exact specs, don't you?
A long cylinder with recesses in its surface into which the projectiles
are loaded. It is spun rapidly inside a loose-fitting tube and
withdrawn at a steady speed.
The end of the tube where the projectiles
come out is shaped as a scroll with a lip so that the projectiles become
free at a definite angle of rotation.
The speed of rotation could be used to control the velocity and rotating
the outer tube to vary the position of the lip would change the launch
angle. The whole thing could be made with a screw thread traversing mechanism like the very earliest experimental Edison tinfoil
phonographs.
On 11/22/2024 9:03 AM, Clive Arthur wrote:
On 21/11/2024 07:04, Don Y wrote:
We're trying to make a mechanism that will allow for the
REPEATABLE lobbing of small projectiles over short (0-20 ft)
distances.
<snip>
I'd look at the way people throw pétanque boules. I imagine they've
developed an accurate technique.
Never heard of it. Seems quite like Bocci? But, that's a good point.
The goal in the toss is to place the ball at a specific spot, not
to attain maximum range.
Imagine a player doing so BLIND so no feedback from his prior attempts...
Ah, that suggests horeshoes or cornhole might also be worthwhile
models to examine! Thanks, that's another direction to explore!
Any other ideas, given latitude in the design of the projectile?
It sounds like you need a steel-spring crossbow mechanism as the
starting point.
On 11/22/24 20:36, Anass Luca wrote:
bp@www.zefox.net wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
Most "guns" just want to achieve a "maximum" (range,
load, etc.)
Not sure I understand what you're getting at here. On
the face of it that statement seems mistaken.
You are interacting with "Don Y". If you go review other postings
where "Don Y" has initiated a thread like this one you will find that
the "Don Y" poster quite effectively trolls the group every single
time. The initial post is always ambigious and seriously lacking in
necessary details, such that 234+ wrong possibilities could be seen by
readers. And as others in the group request details to try to gain an
understanding from the vague, detail lacking initial post, they are
slowly tricked out over the course of days and plural postings from
"Don Y", intermixed with numerous random asides to maximize confusion.
Meanwhile, as the supposed details are trickled out, the apparent
requirements needed also shift as posters appear to gain any
understanding in order to keep the responders in the dark and allow the
"Don Y" trolling articles to continue to troll everyone who responds.
That is unfortunately a rather accurate characterization, I concede.
Ah, that suggests horeshoes or cornhole might also be worthwhile
models to examine! Thanks, that's another direction to explore!
One pétanque technique which may not be obvious (or relevant to your requirements) is to give the balls some backspin, so that they don't roll on from where they land.
On 11/22/24 20:36, Anass Luca wrote:
bp@www.zefox.net wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
Most "guns" just want to achieve a "maximum" (range,
load, etc.)
Not sure I understand what you're getting at here. On
the face of it that statement seems mistaken.
You are interacting with "Don Y". If you go review other postings
where "Don Y" has initiated a thread like this one you will find that
the "Don Y" poster quite effectively trolls the group every single
time. The initial post is always ambigious and seriously lacking in
necessary details, such that 234+ wrong possibilities could be seen by
readers. And as others in the group request details to try to gain an
understanding from the vague, detail lacking initial post, they are
slowly tricked out over the course of days and plural postings from
"Don Y", intermixed with numerous random asides to maximize confusion.
Meanwhile, as the supposed details are trickled out, the apparent
requirements needed also shift as posters appear to gain any
understanding in order to keep the responders in the dark and allow the
"Don Y" trolling articles to continue to troll everyone who responds.
That is unfortunately a rather accurate characterization, I concede.
Jeroen Belleman
Any other ideas, given latitude in the design of the projectile?
On 2024-11-21, Don Y <blockedofcourse@foo.invalid> wrote:
Any other ideas, given latitude in the design of the projectile?
It seems that you are looking for a low friction (and thus repeatable) sear mechnism.
This is almost certainly a solved problem.
Possibly something involving an over-center mechanism and low friction bearings will be suitable.
On Fri, 22 Nov 2024 21:37:35 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 11/22/24 20:36, Anass Luca wrote:
bp@www.zefox.net wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
Most "guns" just want to achieve a "maximum" (range,
load, etc.)
Not sure I understand what you're getting at here. On
the face of it that statement seems mistaken.
You are interacting with "Don Y". If you go review other postings
where "Don Y" has initiated a thread like this one you will find that
the "Don Y" poster quite effectively trolls the group every single
time. The initial post is always ambigious and seriously lacking in
necessary details, such that 234+ wrong possibilities could be seen by
readers. And as others in the group request details to try to gain an
understanding from the vague, detail lacking initial post, they are
slowly tricked out over the course of days and plural postings from
"Don Y", intermixed with numerous random asides to maximize confusion.
Meanwhile, as the supposed details are trickled out, the apparent
requirements needed also shift as posters appear to gain any
understanding in order to keep the responders in the dark and allow the
"Don Y" trolling articles to continue to troll everyone who responds.
That is unfortunately a rather accurate characterization, I concede.
Jeroen Belleman
You give up too easily. Most people can solve an engineering problem
if they are given accurate specifications and objectives. In my
limited experience, I've never received all the necessary information.
In the few times when I did receive accurate specifications and
objectives, the client was made endless changes and "enhancements"
until little clue as to what he wanted and somewhat less on what I was expected to accomplish. Over the years, I've deduced that this
typical and that Don Y is a good model for my typical client.
Still, something can be done with the muddle. The first step is to
determine what problem Don Y is attempting to solve. Don Y does a
tolerable job of providing a partial solution, but without a clue what problem his partial solution is intended to solve, his partial
solution is at best a moving target. My guess(tm) is that it does
nothing useful, so this initial step can be ignored.
The next step is to determine what we have to work with. Since there
are no specifications except for 20 ft range, the launcher and
projectile can be almost anything. A 40 ft diameter ball would do the
job and never miss the target. However, that's probably not what Don
Y is expecting.
A smaller ball, with a 20 ft steel wire attached,
would also work. The 20 ft steel wire limits the flight distance to a
20 ft radius. Then the steel wire become taught, the small ball fall straight down and into the target receptacle.
Elevation and azimuth
can be stabilized by spinning the ball, switching to pointed
projectile, or both. Using two steel wires to form a triangle, will eliminate the need for spin or fin stabilization.
At this point, I usually would present my worst and most ludicrous
ideas to the client, who would immediately being crying, screaming or yelling. Since that clients endless changes and meddling have dragged
the estimated delivery date far too close to the deadline, the client
has to select something.
It's at this time that he gets serious about
defining specifications (with my assistance). The rest of the project
is comparatively easy and consists mostly of lost weekends and lack of
sleep.
I could go on, but it's raining, the lights are flickering, and I
suspect that I'll loose power shortly.
On 11/22/2024 7:08 PM, Jasen Betts wrote:
On 2024-11-21, Don Y <blockedofcourse@foo.invalid> wrote:
Any other ideas, given latitude in the design of the projectile?
It seems that you are looking for a low friction (and thus repeatable) sear mechnism.
This is almost certainly a solved problem.
Possibly something involving an over-center mechanism and low friction
bearings will be suitable.
So, are you suggesting sticking with the initial compression/extension spring approach and just "fixing" the release "catch"?
On 2024-11-23, Don Y <blockedofcourse@foo.invalid> wrote:
On 11/22/2024 7:08 PM, Jasen Betts wrote:
On 2024-11-21, Don Y <blockedofcourse@foo.invalid> wrote:
Any other ideas, given latitude in the design of the projectile?
It seems that you are looking for a low friction (and thus repeatable) sear mechnism.
This is almost certainly a solved problem.
Possibly something involving an over-center mechanism and low friction
bearings will be suitable.
So, are you suggesting sticking with the initial compression/extension spring
approach and just "fixing" the release "catch"?
If that's the problem and not the temperature of the spring, or some
other uncontrolled property of the aperatus.
I haven't seen any suggestions yet that don't have the same release
friction problem, except perhaps the rotating arm in sleeve,
But, isn't that just RL's "sling" with an "autoloader" built in?
I.e., can't I just have a "throwing arm" fed by a hopper with
a collection of projectiles? (likely balls of some sort)
Engineering is not just about solving problems but, rather, about identifying the problem to be solved.
Don Y <blockedofcourse@foo.invalid> wrote:
[...]
But, isn't that just RL's "sling" with an "autoloader" built in?
I.e., can't I just have a "throwing arm" fed by a hopper with
a collection of projectiles? (likely balls of some sort)
Yes, it was just an alternative that might have had some of the characteristics you need.
Another possibility is a variant on a pea-shooter that has a steady jet
of compressed air entering a long tubular barrel through a port in the
side. A continuous line of 'peas' is slowly pushed up the barrel and as
each one passes the port, it is accelerated by the air stream. You only
need to control* the air steam continuously, there is no need to
micro-mange each pulse.
[* The source pressure (voltage) and restrictor valve setting (source impedance). One will control the acceleration rate and the other will restrict the ultimate velocity; they will interact if the barrel is too short.]
Don Y <blockedofcourse@foo.invalid> wrote:
Engineering is not just about solving problems but, rather, about identifying
the problem to be solved.
We have been told the range is about 20ft (but no accuracy limits) and
there have been hints about what the projectile must not do (bounce or
injure bystanders) but the main constraints on the projectile were not
known at the outset and this was mainly what was making the problem more difficult than it needed to be.
The sorts of properties that make a huge difference to the design are:
Rigid , flexible, floppy or completely shapeless like a bag of water?
If fairly rigid: spherical, cylindrical or some other shape?
Approximate range of mass?
Homogenous or made from bits of widely differing density?
There is a vast difference between trying project a
quarter-inch-diameter lead ball 20ft and trying to do the same with a bucketfull of cows guts.
So, by NOT specifying either of these, I've given you the freedom
to pick whichever is easiest. Presumably, some identifiable
characteristic of your choice will be a hint as to other "compatible" projectiles to exploit your design.
On 11/23/2024 3:50 AM, Liz Tuddenham wrote:[...]
Another possibility is a variant on a pea-shooter that has a steady jet
of compressed air entering a long tubular barrel through a port in the side. A continuous line of 'peas' is slowly pushed up the barrel and as each one passes the port, it is accelerated by the air stream. You only need to control* the air steam continuously, there is no need to micro-mange each pulse.
Now that's a "different" approach! But, the air exiting the barrel doesn't create a vacuum that drags "unwilling" peas into it? Or, is the space "behind" the peas closed, limiting any displacing air from being drawn
in prematurely?
The actual problem isn't important. If you can't think in abstractions,
then reify my stated problem to something that you can wrap your head
around -- to overcome the limitations of your imagination.
On Fri, 22 Nov 2024 19:24:06 -0700, Don Y
<blockedofcourse@foo.invalid> wrote:
The actual problem isn't important. If you can't think in abstractions,
then reify my stated problem to something that you can wrap your head
around -- to overcome the limitations of your imagination.
I didn't consider designing a fantasy projectile lobber. Replacing my engineer hat and with my computer game player hat, I now have a better
idea of what you're trying to accomplish. The processes you describe
are very similar to writing a computer game using "the hero's journey"
as a template:
<https://en.wikipedia.org/wiki/Hero%27s_journey> <https://www.novel-software.com/heros-journey-examples/>
What you've done is setup a fantasy playing field that is 20 ft long.
Various SED (sci.electronics.design) members are invited to design a
poorly defined machine which will lob projectiles repeatedly and
accurately. The extent, size, composition etc of the playing field
are not defined. Similarly, the composition of the projectile is not defined.
Due to the lack of design criteria, the objective of the game is not
to design something that will function in a defined manner. Rather,
it's for the participants to determine what the game-master (Don Y)
has in mind. To do this, each player is allowed to ask questions and
offer suggestions to the game-master. He may choose to help, explain, provide detail, offer clues, or he may choose to hinder, confuse,
wander off into the weeds, or provide useless clues. He may also
criticize and pass judgment on suggestions. His choice.
So far, the game only follows a few of the 17 stages suggest by Joseph Campbell. For example, a knowledgeable mentor might appear in SED to
offer experience and suggestions.
From what I've seen so far, the game continues until everyone involved
is terminally frustrated and gives up. However, the game does have possibilities. Normally, such a game has a built in reward system,
where the players are granted "points" for successfully achieving intermediate goals. To prevent player frustration, some kind of prize
or reward system much be implemented. Without keeping score, the game
is largely brainstorming, which usually ends with an argument between
those claiming credit for the best solutions. Therefore, some kind of scoring system should be implemented. There's also the problem of
dealing with unacceptable and ludicrous solutions. The scoring system
much include a way to exclude these solutions. Anyway, some changes
in the game rules will need to be made to prevent player frustration. However, I'm frustrated, so I'll give up now.
Incidentally, the power stayed on during last nights rain. In my
haste, I forgot to proof read and spell check my previous message.
Sorry(tm).
Don Y <blockedofcourse@foo.invalid> wrote:
On 11/22/2024 3:35 PM, Jeroen Belleman wrote:
You're free to scale and reconfigure the thing. If you want an
exact solution, at least specify your exact requirements. Otherwise
we'll think you're here just to argue. You know how to state exact
specs, don't you?
What specs are missing from my original post?
Your original post (message id <vhmm2k$hpg1$1@dont-email.me>) omitted
(at least) any statement of the requirement for:
From Message-ID: <vhn9jc$klsd$2@dont-email.me>
The mechanism must be able to be loaded, "cocked" and released
without humans being involved.
Which was only revealed after two sequential posts from Liz and one intervening reply from you.
Don Y <blockedofcourse@foo.invalid> wrote:
On 11/23/2024 3:50 AM, Liz Tuddenham wrote:[...]
Another possibility is a variant on a pea-shooter that has a steady jet
of compressed air entering a long tubular barrel through a port in the
side. A continuous line of 'peas' is slowly pushed up the barrel and as >>> each one passes the port, it is accelerated by the air stream. You only >>> need to control* the air steam continuously, there is no need to
micro-mange each pulse.
Now that's a "different" approach! But, the air exiting the barrel doesn't >> create a vacuum that drags "unwilling" peas into it? Or, is the space
"behind" the peas closed, limiting any displacing air from being drawn
in prematurely?
If we are allowed to specify the shape of a projectile (within limits) a ball-shaped projectile may look like the obvious choice, but it is not particularly aerodynamic and may have errors induced by erratic
turbulence I would suggest that the projectiles could be tear-drop
shaped to give them the best aerodynamics, with slightly spiralled tail
fins that engage with rifling in the barrel to spin stabilise it in
flight.
If you don't want it to bounce on arrival and would rather not use hard
solid material which might cause damage, you could use a shaped
thinwalled polythene bag full of sloppy semi-liquid that would be firm
enough to take up the spin but would cause the bag to burst on impact.
In flight, semi-liquid droplets tend to take up the shape of a teardrop naturally, so the bag need not be particularly stiff, but it would need
some sort of hoop around its point of largest diameter to ensure that it sealed well in the barrel. The fins could extend from the hoop
backwards along the body to rigidise it and impart the spin.
The barrel needs to have multiple ports around the circumference where
the air is injected, supplied by a 'manifold' in the form of a collar surrounding the barrel. At least two projectiles would have to be
waiting in the barrel, they could be pushed forward by a positive displacement plunger so as to drive the hoop of the first one past the
air ports, the second one acting to block the barel and prevent the
escape of air backwards.
The plunger would then be moved backwards and another projectile
introduced into the space through a slot in the side of the barrel.
There is no need for a sealed 'breech' as the second projectile acts as
a breech block. That sort of loading mechanism lends itself to
automation or even gravity feed from a vertical magazine.
To reset the mechanism, the carriage moves to allow the electromagnet
to reengage with the "back/innermost/moving" end of the spring, awaiting instruction as to how much the spring should be extended for the
next cycle?
On 11/22/2024 9:35 PM, Jasen Betts wrote:
On 2024-11-23, Don Y <blockedofcourse@foo.invalid> wrote:
On 11/22/2024 7:08 PM, Jasen Betts wrote:
On 2024-11-21, Don Y <blockedofcourse@foo.invalid> wrote:
Any other ideas, given latitude in the design of the projectile?
It seems that you are looking for a low friction (and thus repeatable) sear
mechnism.
This is almost certainly a solved problem.
Possibly something involving an over-center mechanism and low friction >>>> bearings will be suitable.
So, are you suggesting sticking with the initial compression/extension spring
approach and just "fixing" the release "catch"?
If that's the problem and not the temperature of the spring, or some
other uncontrolled property of the aperatus.
I haven't seen any suggestions yet that don't have the same release
friction problem, except perhaps the rotating arm in sleeve,
I used a linear actuator (from an electric wheelchair -- so itWhat if I do this mechanism BACKWARDS?
could handle large forces, given that people weigh hundreds of
pounds) to move the *spring*. I.e., the spring was attached to
the "carriage" that the actuator moved forward and back.
A stationary "release" (catch) was mounted on the fixed portion of
the assembly adjacent to the moving carriage. So, any connections
to it -- mechanical or otherwise -- wouldn't be "traveling".
On 11/23/2024 1:49 PM, Liz Tuddenham wrote:[...]
Don Y <blockedofcourse@foo.invalid> wrote:
On 11/23/2024 3:50 AM, Liz Tuddenham wrote:
If we are allowed to specify the shape of a projectile (within limits) a ball-shaped projectile may look like the obvious choice, but it is not particularly aerodynamic and may have errors induced by erratic
turbulence I would suggest that the projectiles could be tear-drop
shaped to give them the best aerodynamics, with slightly spiralled tail fins that engage with rifling in the barrel to spin stabilise it in
flight.
Do you think that would actually be significant on such a small scale? "Rifling" in a gun barrel seems to be an improvement to maintain
controlled flight over REALLY LONG distances and at high muzzle velocities.
... I had assumed "water" just because it "flows" once the bag hasruptured.
(the ruptured bags represent minimal litter and the water will
eventually evaporate.
What if there was a "plunger" that provided the seal, with the "payload" sitting ON the plunger, while loaded? E.g., like a linear catapult.
Could a "gate" behind the ONE projectile not serve the purpose of the
second? Or, the plunger I mentioned, above?
Use ice for the projectile, there would be no litter at all. If it were pointed and had the right aerodynamic properties it would embed
point-first in the ground and not bounce - but it could be dangerous if
it hit anything other than soft ground.
... I had assumed "water" just because it "flows" once the bag hasruptured.
(the ruptured bags represent minimal litter and the water will
eventually evaporate.
Use ice for the projectile, there would be no litter at all. If it were pointed and had the right aerodynamic properties it would embed
point-first in the ground and not bounce - but it could be dangerous if
it hit anything other than soft ground.
What if there was a "plunger" that provided the seal, with the "payload"
sitting ON the plunger, while loaded? E.g., like a linear catapult.
Yes, that would work. The critical point is that the air flow and
maximum obstructed pressure are already established before the
projectile enters the accelerating region, so there is no need for
accurate valve timing.
How about a spherical bag (toy balloon?) full of water sitting in a polystyrene cup which maintained its shape as it was accelerated up the barrel. The cup and balloon would separate in the air, with the cup
falling near the launch point where it could be retrieved and re-used.
Could a "gate" behind the ONE projectile not serve the purpose of the
second? Or, the plunger I mentioned, above?
Yes. I was following on from the 'row of peas' already stored in the
barrel, but if you have a magazine on the side you could load one at a
time. That could get messy if the projectiles were water-filled bags.
On 11/23/2024 2:13 PM, Edward Hernandez wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
On 11/22/2024 3:35 PM, Jeroen Belleman wrote:
You're free to scale and reconfigure the thing. If you want an
exact solution, at least specify your exact requirements.
Otherwise we'll think you're here just to argue. You know how to
state exact specs, don't you?
What specs are missing from my original post?
Your original post (message id <vhmm2k$hpg1$1@dont-email.me>)
omitted (at least) any statement of the requirement for:
From Message-ID: <vhn9jc$klsd$2@dont-email.me>
The mechanism must be able to be loaded, "cocked" and released
without humans being involved.
Which was only revealed after two sequential posts from Liz and one
intervening reply from you.
Gee, my bad.
I also didn't mention that you couldn't use a professional basketball
player as the launcher.
Or, that explosives as propellants would likely not be acceptable.
Or, a specific accuracy *or* repeatability.
Or, a cost, weight, size, etc.
Feel better?
Couldn't the plunger be "polystyrene cup shaped" so it stays behind
for reuse, automatically?
Don Y <blockedofcourse@foo.invalid> wrote:
[...]
Couldn't the plunger be "polystyrene cup shaped" so it stays behind
for reuse, automatically?
No - because the cup has to be in contact with the projectile to
maintain its shape while it is accelerated up the barrel. That means
the air pressure must be behind the cup.
The cup could be stopped rapidly at the mouth of the gun by some sort of >obstruction, but that would risk damaging it and/or fouling the
projectile.
Don Y <blockedofcourse@foo.invalid> wrote:
[...]
Couldn't the plunger be "polystyrene cup shaped" so it stays behind
for reuse, automatically?
No - because the cup has to be in contact with the projectile to
maintain its shape while it is accelerated up the barrel. That means
the air pressure must be behind the cup.
The cup could be stopped rapidly at the mouth of the gun by some sort of obstruction, but that would risk damaging it and/or fouling the
projectile.
On 24/11/2024 11:30, Liz Tuddenham wrote:
<snip>
Use ice for the projectile, there would be no litter at all. If it were
pointed and had the right aerodynamic properties it would embed
point-first in the ground and not bounce - but it could be dangerous if
it hit anything other than soft ground.
Snowballs!
On 11/24/2024 7:36 AM, Liz Tuddenham wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
[...]
Couldn't the plunger be "polystyrene cup shaped" so it stays behind
for reuse, automatically?
No - because the cup has to be in contact with the projectile to
maintain its shape while it is accelerated up the barrel. That means
the air pressure must be behind the cup.
I don't understand. What's the difference between the cup BEING
the top of the plunger (which has air pressure behind it) and
leaving the barrel WITH the projectile?
Don Y <blockedofcourse@foo.invalid> wrote:
On 11/24/2024 7:36 AM, Liz Tuddenham wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
[...]
Couldn't the plunger be "polystyrene cup shaped" so it stays behind
for reuse, automatically?
No - because the cup has to be in contact with the projectile to
maintain its shape while it is accelerated up the barrel. That means
the air pressure must be behind the cup.
I don't understand. What's the difference between the cup BEING
the top of the plunger (which has air pressure behind it) and
leaving the barrel WITH the projectile?
The plunger has to stay behind the air inlet so as to block the back end
of the barrel.
I think I'm going to explore the air solution, next.
I figure I can use a surplus oxygen tank (they come in
smaller sizes for portability) so I know it will
handle any sort of pressure I might apply without
rupturing. I can probably fashion an inlet port
and outlet valve to mate to it via the single
opening available (so I don't have to pierce the
vessel to allow for the introduction of pressurizing
air).
I'm *guessing* that a battery powered "inflator" that
one might use to fill tires could achieve whatever
pressure I need (?). The chamber acting as a reservoir
to allow a larger volume of air to be expelled than
the inflator could supply in a short interval.
[The "reload time" may become an issue. But, a larger
inflator -- or a real *compressor* -- should address
that shortcoming]
This then boils down to how repeatable a valve I can find.
What if I do this mechanism BACKWARDS?
I.e., use a spring in extension mode. Let the "carriage" STRETCH
it to a desired length (storing energy). HOLD the "free" end of
the spring in place ELECTROMAGNETICALLY (!).
On 11/23/2024 6:20 PM, Don Y wrote:
What if I do this mechanism BACKWARDS?
I.e., use a spring in extension mode. Let the "carriage" STRETCH
it to a desired length (storing energy). HOLD the "free" end of
the spring in place ELECTROMAGNETICALLY (!).
THIS is the solution! One can purchase electromagnets that can
hold 40+ pounds (some operating at up to 100 pounds) for ~$75 (QTY1)
and operate them from a 24V supply with << 1A.
This has got to be the easiest way to avoid the mechanical mess
that comes with other "launch" schemes!
Maybe I can replace the spring with something else, at the same
time. If the release/catch issue is out of the way the rest
should be easy!
On 2024-11-26, Don Y <blockedofcourse@foo.invalid> wrote:
On 11/23/2024 6:20 PM, Don Y wrote:
What if I do this mechanism BACKWARDS?
I.e., use a spring in extension mode. Let the "carriage" STRETCH
it to a desired length (storing energy). HOLD the "free" end of
the spring in place ELECTROMAGNETICALLY (!).
THIS is the solution! One can purchase electromagnets that can
hold 40+ pounds (some operating at up to 100 pounds) for ~$75 (QTY1)
and operate them from a 24V supply with << 1A.
Or for the scrap value of a microwave oven transformer.
This has got to be the easiest way to avoid the mechanical mess
that comes with other "launch" schemes!
There will be magnetic friction as it lets go, but this should be
repeatable if the armature placement is repeatable,
Maybe I can replace the spring with something else, at the same
time. If the release/catch issue is out of the way the rest
should be easy!
Some sort of "springboard" perhaps.
On 11/23/2024 6:20 PM, Don Y wrote:
What if I do this mechanism BACKWARDS?
I.e., use a spring in extension mode. Let the "carriage" STRETCH
it to a desired length (storing energy). HOLD the "free" end of
the spring in place ELECTROMAGNETICALLY (!).
THIS is the solution! One can purchase electromagnets that can
hold 40+ pounds (some operating at up to 100 pounds) for ~$75 (QTY1)
and operate them from a 24V supply with << 1A.
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