motor and controller circuit
This is the motor and control circuit for my setup.
The main function here is to provide super-slow motion to the dolly. This is achieved with both a gear box and a pulse width modulation (PWM) circuit.
I used a Tamiya gearbox for my gearing ($15). My particular gearbox allows for 6 different speeds by swapping out gears. In practice however, the speed is more or less fixed as it means taking apart the whole thing to change out the gears. I have mine set on the lowest speed (using all six gears that came with the kit). This gave me the slowest output, and great torque. Further speed control was achieved through the PWM circuit.
The PWM circuit helps reduce the motor speed even more and provides speed control through the knob on the left. The circuit slows down the motor by breaking up the voltage into short pulses. By changing the width (or duration) of those pulses, you can change the average voltage to the motor, thus changing the speed. All the PWM parts were picked up from Radio Shack for about $20. Eventually this should all probably be soldered down, but for now it still on the breadboard.
I learned about PWM circuits from the following video (nerd-alert warning): www.youtube.com/watch?v=YmPziPfaByw
The pen on the right is used to wind up my string. It is not very high tech, but it was free and has served me very well thus far.
You can also see the aluminum guides I have mounted on track edges to keep my dolly inline. These were home depot items and cost me about $10. Most of the wood here is scrap, but I did spend around $12 for a 6' length of 1x8 for the track itself.