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Re: Most Powerful FIRST Team created T-Shirt Cannon
Why not just have feedback through whatever processor is already on the robot?
Mount the pot and motor (or a sprocket chained to the motor) on the shaft of the cannon. If there is no place for the pot it can be on a sprocket on the motor chain as well. If the shaft is hollow, you can put in a plastic (HDPE, Delrin, etc.) plug with a set-screw for the pot, and mount the pot with a piece of folded sheet metal.
Then, wire the pot to an analog input, and the motor, through a speed controller, to a PWM output.
You can then have fun writing and tuning PID code. If it dosen't have a whole lot of mass to it then P would work fine, if it can't get to the setpoint without overshooting you can add a little bit of I to help it along, and if it has a giant amount of mass (e.g. a big steel pipe) you can add D to help with momentum.
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