Re: OT: Repeatably lobbing "projectiles"

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 admit my prototype was quite crude; I was more interested in seeing
what was possible than coming up with a final solution.
I used a linear actuator (from an electric wheelchair -- so it
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".
I would move the spring assembly away from the release to
ensure the free end of the spring was "below" the catch.
Then, let the catch fall into its "holding" position.
At this point, a projectile (plastic ball similar to a "whiffle
ball" -- but without the holes) could be placed on the
"far side" (out side?) of the catch.  The spring is never in that
area until after firing so it is "safe" for loading.
When commanded to a specific range, I would drive the linear
actuator "forward", into the catch, compressing the spring,
until a desired displacement was achieved (the actuator
has positional feedback built in).
When commanded to "fire", the catch mechanism would be released,
allowing the spring to expand to its uncompressed length,
launching the ball.
With the free end of the spring now PAST the catch, I would have
to retract the spring *assembly*, again, as above.
The first "catch/release" I tried was just a solenoid.  Then,
a BIGGER solenoid as the side forces bound the plunger so that
the electromagnetic force was not sufficient to withdraw the
plunger.
I later replaced this with a screw driven mechanism (another
linear actuator).  This resulted in a slower release as the
mechanism moves slower (I suspect I need a more "abrupt"
mechanical transition on the catch AND the spring's carriage)
Martin's Trebuchet might be more tolerant of a "slow release"?
A colleague (another discussion, elsewhere) is suggesting
"skinless water balloons" (i.e., "slugs" of water ejected
from a pressurized nozzle).  I'm going to try that, next,
as it avoids the whole issue of scattered "debris" from
previously fired projectiles and the mechanism reduces to
a valve and pressurized water chamber (similar to the air
gun solutions proposed)