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From: Martin Brown <'''newspam'''@nonad.co.uk>
Newsgroups: sci.electronics.design
Subject: Re: OT: Repeatably lobbing "projectiles"
Date: Thu, 21 Nov 2024 12:34:30 +0000
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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.

-- 
Martin Brown