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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: OT: Repeatably lobbing "projectiles"
Date: Fri, 22 Nov 2024 16:41:18 -0700
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On 11/21/2024 12:23 PM, Joe Gwinn wrote:
>> 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.

The fact that this keeps coming up is interesting.
ISTM that it would be harder to electronically control
such a stiff mechanism; you'd need something strong
enough to counter its force to "cock" it and something
to ensure it is cocked to a particular tension
(strain gage or position transducer).

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]

The barrel can be anything that "fits" the projectiles
(likely something round so loading it doesn't require
a particular orientation and facilitates "dispensing"
from a "magazine"/hopper)

A linear actuator to adjust the elevation of the barrel.
(note the compressed air tank can be coupled to the barrel
via a semi-flexible conduit so it need not be moved
with the barrel)

This then boils down to how repeatable a valve I can find.

Calibration can then just be done empirically:  set the
elevation and vary the pressure -- tabulate results.
Lather, rinse, repeat.  Analyze data for variance.
Tweek mechanism.