stumped on a seemingly simple problem, ive been making hybrids of coilguns and railguns for a good while, works great with current config.

stumped on a seemingly simple problem, ive been making hybrids of coilguns and railguns for a good while, works great with current config. problem is, instead of using optical sensors or whatnot ive been using a thin aluminum brush which activates the coils. this works incredibly well to my surprise however somewhere between 100-800 cycles the brushes need replaced and thats a problem. my goal with the hybrid projects is to increase efficiency and reliability and ive very much improved on some areas however pretty much flopped on the sensor aspect. i have no idea how to get the proper sensors, or what they would be called. searched "optical sensor" on digikey to no avail, and apparently no yt videos on that. ive googled articles several times but its all the same general description but nothing fundemental, just a overview for people who don't actually want to learn about the technology. i was considering maybe just making some pv cells and hope they saturate/desaturate fast enough but thats a lot of work for a test as semiconductors assides from bismuth are not something i'm used to making stuff out of and as such will take hundreds of attempts. i couldn't find any for sale small enough for the application on digikey either. what do you think PrepHole?

  1. 3 weeks ago
    Anonymous

    phototransistors seem like the most likely, a while back i picked some up from a freind who had extra MTRS9520s he had ordered from digikey for a unrelated project. they didn't work, either that or they don't work like i think they do, saturating the gate with light instead of electricity.

  2. 3 weeks ago
    Anonymous

    Let me give you a tip anon. Instead of trying to set up "gate" style sensors that are activated as the projectile proceeds down the barrel, put an LED + photodiode at the back of the barrel (where the bolt would be in a normal firearm) and use the quantity of reflected light as a proxy for the position of the projectile. Naturally, the light level will start off very bright (since the back of the projectile is directly in front of the LED) and fall off as it is fired. If you calibrate this properly, I think you can get the position data you need. You can even crank up the LED power as the projectile gets farther away in order to increase the signal to noise (as long as you adjust your calculations to compensate for the increasing LED intensity).

    > t. spent a lot of time building brushless linear motors and thinking about coil-based accelerators

    • 3 weeks ago
      Anonymous

      like this

    • 3 weeks ago
      Anonymous

      I would recommend IR leds and IR sensors instead. Tho you gotta remember what material blocks IR and what doesn't.

      • 3 weeks ago
        Anonymous

        What are you talking about? There was no wavelength specified. The point is, you can determine the position of the projectile with a single LED/sensor pair at the rear of the barrel instead of having "gates". The question of what wavelength to use is a secondary concern.

    • 3 weeks ago
      Anonymous

      https://i.imgur.com/CPLOcIX.png

      like this

      op here, took a lot of work but i stayed up overnight making a prototype using this. i figured out i was actually just using the phototransistor wrong, but making the prototype took a incredibly short ammount of time. the software, however was much more difficult. i ended up brute forcing it with a lepotato to change parameters, shoot, gather the data and a machine learning algo i made on main pc to get the timing juust right.3 3.7-4vdc coils plus a 300vdc 3.5 inch rail propels a standard copperhead .17 bb at 1300-1400 fps.total barrel length 9.5 inches. im going to bed now, thank you and have a good one. i feel happy with the results.

      • 2 weeks ago
        Anonymous

        bruh was a typo or are you seriously getting 1400fps with an airgun bb? lmao
        I always thought my phototransistor idea was interesting but never got around to building it. I gotta see what you built, post pics.

      • 2 weeks ago
        Anonymous

        >1300-1400 fps.total barrel length 9.5 inches

        Wtf, is this a thing now?

  3. 3 weeks ago
    Anonymous

    I can't tell what you want the sensor to do.

    • 3 weeks ago
      Anonymous

      He wants the sensors to tell him that the projectile has passed a particular coil so it's time for that coil to turn off and the next one to turn on. This is a bit sloppy since coils in this use case tend to have non-negligible rise & fall times (so if you wait until the projectile is between coils, it's probably too late to be optimal) but for better or worse that's what he's trying to do.

      Better approach IMO:

      Let me give you a tip anon. Instead of trying to set up "gate" style sensors that are activated as the projectile proceeds down the barrel, put an LED + photodiode at the back of the barrel (where the bolt would be in a normal firearm) and use the quantity of reflected light as a proxy for the position of the projectile. Naturally, the light level will start off very bright (since the back of the projectile is directly in front of the LED) and fall off as it is fired. If you calibrate this properly, I think you can get the position data you need. You can even crank up the LED power as the projectile gets farther away in order to increase the signal to noise (as long as you adjust your calculations to compensate for the increasing LED intensity).

      > t. spent a lot of time building brushless linear motors and thinking about coil-based accelerators

  4. 2 weeks ago
    Anonymous

    Don't leave us hanging OP, did you really get 1400fps? Even 140fps would be neat

  5. 2 weeks ago
    Anonymous

    Nobody else finds it intriguing that OP claims to have made a 1400fps coilgun?

    • 2 weeks ago
      Anonymous

      Yes, that would be remarkable. I'm not huge into coil guns but my understanding is most of them can fire a projectile at somewhere between 200 and 300 fps. 1300-1400 would be a major accomplishment, even for a BB.

Your email address will not be published. Required fields are marked *