Jury Rigging a Servo to Drive a Low Voltage Motor (DIY ESC)

Every good maker has used a servo at sometime or another. Whether it was for a RC car or an Arduino powered robot arm. I was working on building an Arduino powered tank. I tried using continuous rotation servos as the drive motors, but it was much too slow. I knew how to interface a servo with an Arduino, so I really wanted to stick with this and didn't want to pay the money for a motor shield. Then I got creative....

I designed this device to allow me to control a motor with an RC receiver/transmitter setup, but the same system can be used with an Arduino! It has full motion control, going both forward and backward, and speed can be controlled. For the RC minded, this is just a cheap, DIY Electronic Speed Controller, much like those in Rc airplanes and Helis!

NOTE: When using with Arduino:
Program this with the servo library as you would program a continuous rotation servo.
This can be used with Arduino as long as a seperate battery is wired, it may draw too much power from the Arduino if ran directly off the Arduino's 5 volt pin! 

Step 1: Parts and Tools

For this project you will need:
Materials:

Servo (I used a Parallax servo avaliable from Radio Shack

Dc motor (mine is in a gearbox)

Hookup wire

Tools:

Soldering iron and solder
Desoldering pump or braid
Needle nose pliers
Small screwdriver

Step 2: Open the Servo

Use the screwdriver to remove the 4 long screws on the back of the casing.
Remove the top with the servo arms. Then, take the gears and fittings out. Next, unscrew the servo arms so you are left with the top part of the casing that has a hole in it where the servo axle came out. When the screws came out, the bottom of the casing should have fallen off along with it. If not, just pop it off. You should be able to see the pcb that controls the motor. Use the small screwdriver to unscrew the motor from the top of the servo there should be two small screws. Then use the screwdriver to pry out the pcb and the motor, which is directly mounted to it. BE EXTREMELY CAREFUL NOT TO SNAP THE CIRCUIT BOARD! I did, then tried to solder it back. I made magic blue smoke! :(

Step 3: Where We Are So Far

We ahould have the motor control board and the case. Locate the potentiometer. We need to put this in the exact center position to trick the controller board. This will allow us to use the motor as though it was a continuous rotation servo. Be careful not to move this piece, as you will have to readjust it again.

Step 4: The Soldering

Locate the two leads that power the motor. Carefully desolder it and remove the motor. Use the pliers to help you. Two pieces of of hookup wire need to be cut, about four inches each. Solder one to each of the leads from the motor. Thread these through the small screw holes used to hold the motor in before we removed it. Then, put them through the hole in the top of the case.

Step 5: Finishing

Almost Done! Screw the case back together. Hook up the two loose wires to the lead of any other low voltage motor. Hook it up to an Arduino, RC reciever or anything else that can control a servo, and let 'er rip! The last image is it hooked up to my Tamiya gearbox and motor, and it works great! Good luck, and please tell me about anything you make with it!

Also, I'm entering this in the Macgyver contest, so if you like this project, a vote would be much appreciated!