Re: OT: Repeatably lobbing "projectiles"

Don Y <blockedofcourse@foo.invalid> wrote:

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.  (?)

But one end has considerable mass and is moving, so it has kinetic
energy.


[...]

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).

[...]

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 (?).

Yes, that's exactly the same idea.
[...]

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.


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