Re: OT: Repeatably lobbing "projectiles"

Don Y <blockedofcourse@foo.invalid> 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).
 
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?

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.

--
~ Liz Tuddenham ~
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www.poppyrecords.co.uk