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Author Topic: airsoft gun motor causing servos to twitch  (Read 986 times)
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I bought this autonomous airsoft sentry gun from realsentrygun.com http://www.realsentrygun.com/Paintball%20Airsoft%20Turret%20Kit.htm . It works great but I wanted to put a different airsoft gun on it. When I put my own airsoft gun on it and wire it up, the left/right direction servo has like a big twitch when the airsoft gun fires. It didn't do this with the original airsoft gun though. They built it with 'ceramic disk capacitors' going along the wires that power the airsoft gun's motor. When I put my airsoft gun on it, I didn't use them because I didn't understand why I needed to. I've also noticed that the further the airsoft gun's motor is from the servo, the less the servo twitches when the airsoft gun fires. Can anyone explain WHY I need those capacitors, SPECIFICALLY what they do to prevent the interference caused by the airsoft gun's motor, and what I can do to get rid of the interference problem completely?
« Last Edit: March 06, 2013, 11:07:39 am by David82 » Logged

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EM noise is a big subject and I suggest you read up on it if you're interested in understanding the problem.

I suppose that you have worked that the first step needs to be putting back those components that you removed. Does that cure the problem?
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not really. The new airsoft gun has a bigger motor. The solution is simple I would think. We just need the right expert to stumble upon this post. Then he would say, "oh, you need to completely shield the motor by placing blah blah blah in such-n-such way" or "oh, you need to ad caps of this type in this specific configuration". See, that's what I'm hoping for. An actual experienced expert on the topic.
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If you want specifics, you better start giving some.
What motor was originally installed and what capacitor?
What currents were involved?
What motor dis you install?

The solution might be simple, but none of the experts you hope to come are psychic, well most of them in any case.
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hehe, airsoft motors messing with your electronics. I used to have that problem.

Just wondering though, You upgraded to a new gun on the sentry correct. Might I recommend looking into a fullmetal gun or at least one that has a metal box around the motor. If this box is grounded, it will go a long way to removing interference. Also shielding the wires like you said would do a bit to help. Putting the control board in a box to protect that too could help a bit too. But I'm not an expert. This is just the crap that I've done to make my guns not interfere with my own electronics. YMMV though because of the design of the turret.

You might also consider though that the new gun is too heavy for the mount though, and has more recoil (yes the recoil on airsoft guns is high enough to cause problems, if your moving from a cheap $50 uzi to a $300 rifle. My best suggestion to you though would move to a propane driven rifle though. Since you have the added bonus of a stationary turret, it would be easier to just have a camping grill bottle of the stuff onhand by the turret to drive the gun. And then you have no EM interferance. (people can find it by the smell though. well theres always plusses and minuses)
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The new gun is similarly sized and has a similar weight. If I wanted to use a heavier, larger full metal airsoft gun I would've bought their "Heavy Turret" product instead. The new airsoft gun is just better quality (not that there was anything wrong with the original gun). The new gun is still plastic though. So what do I specifically do to shield it?
« Last Edit: March 06, 2013, 12:19:22 pm by David82 » Logged

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The new gun is similarly sized and has a similar weight. If I wanted to use a heavier, larger full metal airsoft gun I would've bought their "Heavy Turret" product instead. The new airsoft gun is just better quality (not that there was anything wrong with the original gun). The new gun is still plastic though. So what do I specifically do to shield it?

What kind of gun is it. Personally Id say if you dont mind, make yourself a metal sleeve that fits around the area with the motor, and then tie that into ground. That should get rid of some of it. If I knew the make of the gun I might be able to check my airsoft store for one and examine it better for better advice.

Also I wonder somethign else. So the little control board. SO that controls the pan, tilt, and sends a firing command to the gun. The guns running its motor off its own internal battery correct. How's it activate the trigger? is there a motor up there that you hook in the trigger cage and it presses the trigger, or does your control board get wired into the motor directly?
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I didn't use them because I didn't understand why I needed to.
The ceramic capacitors are more than likely used to quiet down the interference from the motor.  Read up on a decoupling capacitor for more information.  As PeterH had said, have you tried putting them back into the circuit?
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A decoupling capacitor is a capacitor used to decouple one part of an electrical network (circuit) from another. Noise caused by other circuit elements is shunted through the capacitor, reducing the effect they have on the rest of the circuit.
http://en.wikipedia.org/wiki/Decoupling_capacitor
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not really. The new airsoft gun has a bigger motor. The solution is simple I would think. We just need the right expert to stumble upon this post. Then he would say, "oh, you need to completely shield the motor by placing blah blah blah in such-n-such way" or "oh, you need to ad caps of this type in this specific configuration". See, that's what I'm hoping for. An actual experienced expert on the topic.

Well, until your expert stumbles across this thread I suggest that you simply put back the existing protection that you removed because you didn't understand it, and see if that helps. Maybe you'll need to do more to cure the problem, but at least do the no-brainers first.
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From Wikipedia:
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Another kind of decoupling is stopping a portion of a circuit from being affected by switching that happens in another portion. Switching in subcircuit A may cause fluctuations in the power supply or other electrical lines, but you do not want subcircuit B, which has nothing to do with that switching, to be affected. A decoupling capacitor can decouple subcircuits A and B so that B doesn't see any effects of the switching.

This describes the problem in general but doesn't give an example of specifically where the best place to put them would be. You can put one near the gun, on the servo power lead for each servo, on the power lead for for servo controller, at the relay that switched the gun on, at the power supply for the gun, etc. See the problem? I need someone who understands this stuff to say, "oh, the best place to put the caps would be at _______".

Then there's also the idea Nakarus was talking about:
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make yourself a metal sleeve that fits around the area with the motor, and then tie that into ground.
is it best to place it around the gun motor or around the servo motor instead? is this supposed to function like some sort of half-*** faraday cage?

See the 3 different options for caps and diodes that are applied to the motors in the image below?:

Aren't they there to prevent the same problem I'm experiencing? Which configuration would be most effective?

« Last Edit: March 06, 2013, 06:45:01 pm by David82 » Logged

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DC motors have commutators in them, and when the brushs pass over them, they sometimes hit a gap. This gap cause the motor to loose power for less than a hundredth of a second (depending on speed) and will cause fluctuations in the current. These capacitors help reduce the fluctuations by temporarily acting as a load, and keep the current consistent. Motor diagrams 1 and 2 are both good to use, but I sometimes combine the two diagrams, if needed.
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DC motors have commutators in them, and when the brushs pass over them, they sometimes hit a gap. This gap cause the motor to loose power for less than a hundredth of a second (depending on speed) and will cause fluctuations in the current. These capacitors help reduce the fluctuations by temporarily acting as a load, and keep the current consistent. Motor diagrams 1 and 2 are both good to use, but I sometimes combine the two diagrams, if needed.
THANK YOU. That's the most competent answer I've seen yet.
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The new airsoft gun has a bigger motor.

Are you trying to power it and the servos with four AA batterys?
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The new airsoft gun has a bigger motor.

Are you trying to power it and the servos with four AA batterys?
no.
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