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Spinning Bolt

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#1 Shadow 92

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Posted 04 May 2008 - 03:17 PM

I'm trying to build a paintball/ nerf gun that uses an electric motor to spin a bolt and close a breach. I planned out most of the stuff I need, I just need help with the motor.

I was browsing Radio Shack and I saw, this motor, and I was wondering if it would provide enough torque to spin a 1.75" long PETG bolt. I also need to figure out a way to make the bolt spin to the sealed position every time I pull the trigger. Finally, is there a way to control how fast the bolt spins and how long it stays in the sealed position?

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Posted 04 May 2008 - 03:42 PM

I wish I could help you with the torque question, but I do have some advice. Is the gun semi- or fully automatic? If full, then use the motor. If semi, then you may want to look into using a sliding breech and a solenoid actuator instead, as it will be far more reliable. Trying to get the gun to fire single shots with a motor will need precise timing.

Perhaps you could use the motor to flip the switch for the actuator. This would allow you to fire in fully automatic mode as well. Attach a wheel to the motor shaft with notches cut into it so that the rotation of the wheel will push the button, let it reset, and then push it down again.

Edited by SHADOW HUNTER ALPHA, 04 May 2008 - 04:27 PM.

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#3 Split



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Posted 04 May 2008 - 09:28 PM

Any basic motor will turn a light piece of plastic if there's no resistance (including being well lubed). The radio shack motor will do. There is another problem though. Basic electric motors free spin. This means that once you stop putting power through to the motor, and it stops spinning, the momentum/un even weight of your "bolt" could just make it move again.

Also, if there will be a load on the "bolt"" (this is an incorrect term, but I know what you mean), then you will need either a higher torque motor or a gear head motor (which has has enough torque to spin no matter what basically). Gear head motors will also solve that free spinning problem, as they lock into place when they stop. Think of a power car window, since that's a typical application for them. However, these types of motors are usually large and less cost effective (if you know what I mean).

To vary speeds, change the voltage to the motor. To vary the voltage you could buy a variety pack of resistors and test them out to what you like, or you could buy an adjustable one. Be aware that Radio Shack stores mostly do not carry electronic pieces anymore, but there are some. If you do end up buying off of the internet, just use allelectronics.com . The shipping is constant no matter how much you buy, and the prices are great, and even better with bulk discounts.

Use a "momentary switch" also if you were wondering which to get.

/end semi-helpful rantish post.
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#4 Snazzy Q

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Posted 05 May 2008 - 10:54 PM

In response to splitlip's suggestion of buying a variety pack of resistors, you would need to make sure you get resistors rated for enough wattage or run a LOT of higher value resistors in parallel. The resistors you would get in the variety pack are either 1/4 or 1/2 watt, so if there's any real load on the motor they will quickly get hot and fail. It might work for a quick test, but I'd suggest buying a power resistor once you know how many ohms you need for the speed you want.
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