Home Chapter 16 DC Servo Motor, muscle wire, Pneumatics and rubber muscles
DC Servo Motor, muscle wire, Pneumatics and rubber muscles

Servo motors are wonderful motors that can provide a high level of torque and precise control. Servo motors can rotate in both directions generally from 0 degrees to 180 degrees though they can also be purchased with more limited range of rotation of 60 degrees or 90 degrees. They can also be modified for continuous rotation though you can purchase them premodified for continuous rotation. A DC servo motors shaft is positioned through sending a coded signal. As the signal to the motor varies so the shaft rotates to a new position. For their size, servo motors are quite powerful.

When searching for a DC servo motor you must consider the weight of the motor, the torque of the motor rated in ounce-inches, the shaft speed, the voltage, maximum current and the life or numbers of rotations it will withstand.

Current refers to the max current that can activate the motor without overheating the motor coils. Torque is the rotational power of the motor under continuous conditions where the shaft is under load.


3D model of servo motor


Muscle Wire

Nitinol is an alloy wire material that expands when given electricity and contracts when it does not receive the electricity. It is effective for moving applications but not so good where the speed of the system is critical though it can move relatively quite quickly. When muscle wire is activated, you can move it back into position faster by pulling it back with another muscle wire or you can use a spring. The wire will consume more current based in the width.


Pneumatics use compressed air to move and control linear actuated valves. Compressed air can drive linear piston cylinders as well as drills, automatic doors, and hammer drills.

The cylinders can convert compressed air into motion and a piston is pushed by the compressed air. One type of cylinder is a single-acting cylinder (Below), which has one air outlet.


Single-acting cylinder


Double-acting linear actuated valves have two connections to outlets.


Rubber muscles

The FESTO rubber muscle robot that started this chapter is a beautiful figurative sculpture. Festo is a large company that specialized in rubber muscles and artists like Stelarc have used these to create large walking robots.
The artist David Foster has constructed his own pneumatic rubber muscles and has given us the recipe below.


David Foster


David Foster


Note these parts are not part of the kit you received, but can be obtained from the sources below.
This homemade muscle will contract by 20% at 75 PSI.

  1. Cut Manosil rubber tubing 10% shorter than polyester sleeving
  2. Insert hose barbs into ends of rubber tubing.


Rubber tubing below polyester sleeving


  1. Slide rubber tubing with hose barbs through polyester sleeving.
  2. Move hose clamps over the hose barbs and crimp.
  3. Add necessary hardware.
  4. Fabricate and attach fasteners.


Tubing inside polyester sleeve