Tuesday, March 14, 2006

Lead by Nose Programming

Here are a pair of 3-DOF legs. All I need to do now is add the servo controllers. I've made the limbs in such a way that it is possible to dissengage the motor and potentiometer just by removing two screws. Using this method it is possible to program the robot "Lead By Nose style". So in order to program my robot to perform a specific repeatable motion all I have to do is dissengage the motor and pull the joints to whatever position I like. The potentiometer is still engaged so it will track where I pull the joints to. I can then simply record which positions I like, re-engage the motor and play back the joint trajectories and Bob's your uncle!

Here are some pics of the two legs together..

High Power Servo Electronics

Now Ive made a pair of 3-DOF legs I have only to attach them to each other. I am literally building this robot from the bottom up. I intend to use standard Picaxe 18 chips as positioning servos for each of the robot joints.

Here is the schematic in jpeg form. IC1 is a standard Picaxe 18 chip. I will use it to read in two streams of standard 1-18ms PWM from a servo controller and convert that into positional output for two motors.

Ive used this circuit on older robots and coupled with the Como 810:1 motors you have quite a powerful servo. In theory each servo will have a torque in the region of 3.3Nm at 12v over a travel range of about 180 degrees.

The H-bridge is only a bipolar one but should be good for about 60 watts. I might use MOSFETs later on depending on how well it performs.