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DIY DC Servo

A DC servo is an electric motor used by robots and radio-controlled planes, boats and cars. These motors are designed to rotate to a specific degree, as instructed by the circuit board. This allows the robot's arms to move and airplane flaps to operate. A typical DC motor is modified into a servo with the addition of an encoder to the rear shaft. This tells the circuit board the exact position of the drive shaft, allowing it to determine how to move the motor.

Things You'll Need

Calipers
Center punch
DC motor
Drill press
Electric tape
1/4-inch drill bit
1/16-drill bit
1/4-inch metal rod
Vise
Hacksaw
Cyanoacrylate glue
Encoder
#4-40 machine screws

Instructions

- 1
  Measure the width of the rear drive shaft, with a pair of calipers. Divide this measurement in half, and adjust the calipers to that dimension. Use the calipers to determine where to mark the center of the drive shaft, with a marker.
- 2
  Place the center punch in the middle of the marking, and push down until the center punch makes a small dent in the middle of the drive shaft.
- 3
  Adjust the calipers to 0.570 inches, and mark this distance from the end of the 1/4-inch drill bit. Wrap the drill bit in electric tape at this marking. This assures the proper depth of the drilled hole.
- 4
  Align the DC motor under the drill press, so that the 1/4-inch drill bit is centered on the middle of the rear drive shaft. Drill the 1/4-inch hole 0.570 inches deep, by rotating the drill-press' handle clockwise.
- 5
  Adjust the calipers to 1.31 inches, and mark this distance on the 1/4-inch metal rod. Place the metal rod in the vise, and tighten to hold it in place -- with the cut line about 1 inch outside the vise's jaws. Cut along the marked line with a hacksaw.
- 6
  Apply a dab of cyanoacrylate glue to the drilled hole in the rear drive shaft. Center the cut metal rod over the drilled hole, and gently tap into the hole with a hammer.
- 7
  Place the encoder over the metal rod, and mark its two mounting holes with a marker. Remove the encoder by pulling it off. Place the center punch in the middle of each marking, and push down until it leaves a dent.
- 8
  Align one of the mounting holes under the drill press, and drill a 1/16-inch hole. Repeat this process to drill the other mounting hole. Be careful not to drill too deep into the motor, as this may damage its internal components.
- 9
  Apply a dab of cyanoacrylate glue to the 1/4-inch metal rod, and side the encoder over it while aligning its mounting holes with the drilled holes. Secure in place by tightening two #4-40 screws with a screwdriver.

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