Path: ...!weretis.net!feeder9.news.weretis.net!news.quux.org!eternal-september.org!feeder2.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Don Y Newsgroups: sci.electronics.design Subject: Re: OT: Repeatably lobbing "projectiles" Date: Fri, 22 Nov 2024 22:57:47 -0700 Organization: A noiseless patient Spider Lines: 75 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Sat, 23 Nov 2024 06:58:00 +0100 (CET) Injection-Info: dont-email.me; posting-host="01962a914581412c1fe91addb5218a72"; logging-data="1687808"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/+N5m3TgM2jF02h+8l4wXH" User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 Cancel-Lock: sha1:wPJOBPKKzw/p+z4YjGINRXlL4ZI= In-Reply-To: Content-Language: en-US Bytes: 4558 On 11/22/2024 9:35 PM, Jasen Betts wrote: > On 2024-11-23, Don Y wrote: >> On 11/22/2024 7:08 PM, Jasen Betts wrote: >>> On 2024-11-21, Don Y 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)