Wednesday, June 15, 2011

Electronics Project: Animatronic robot head (EAP)

A few weeks ago, I was contacted through a friend about helping out with building a robot for an indie short film. Since then, I've met with the other robot builder and the producer, and I've started work on the animatronic control for the robot head. The robot is named EAP, and he's going to be part of the short film Joanna Makes a Friend.

Yesterday, I picked up a 4 channel RC Airplane control and receiver, which I'll be using to control the animatronics. I temporarily mounted a couple servos with some speaker wire as eyebrows, to see how it looks when it's animated:


I'm pretty happy with how that worked out.

The eyes need to rotate both directions as well. Right now, they have motors attached:

(It's hard to concentrate on aiming the camera while trying to hold two wires in the other hand, and touch them to the diode chain. Also, since the camera was aimed straight down, the rotation sensor ended up deciding the video should be upside down.)

Unfortunately, those motors aren't controllable directly from the RC receiver. The motors rotate in one direction when positive voltage is applied, and at different speeds depending on the voltage, and rotate the other direction with negative voltage. Continous rotation servos, however, use PWM to indicate a rotational speed, and direction, but the voltage is always positive. Those can be controlled directly from the RC receiver:


I have a couple options for the eyes at this point:
  1. Use the motors, and an Arduino to read the PWM from the RC receiver, and output a positive or negative voltage to run the motor. This has the advantage of being able to spin the motors quite quickly, and not needing to do any cutting or modifying to the mechanical bits of the reel-to-reel machine.
  2. Remove the motors, and mount the eyes on continuous rotation servos. This has the advantage of being controlled directly from the RC receiver, so no fancy Arduino wiring needed to handle reverse voltage. However, it does mean cutting up the reel-to-reel machine to mount the servos.

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