2 Oct 2001 EdwardRupp   » (Journeyer)

I've been observing the behavior of my new walking robot and want to improve it. The design is a classic 3 motor, 6 leg robot.

One motor is used for lifting by moving the center legs. This motor is the one that requires the most power. About half the time it spends trying to hold half of the robot up in the air for that sides corner legs to move forward. This requires a large holding current. It would seem a great solution to use a servo motor that had a worm gear in it. The lovely thing about worm gears is its very hard for loads to transmit back though them. Thus the motor lifts the robot, at the top of the travel it should be able to "relax" and the load will lock the worm gear, thus keeping the side of the robot in the air without further need of power.

I haven't been able to find a ready made solution so I converted a cheep worm gear box motor with a hobby servo just the other weekend. Works pretty well. I used a Tamiya worm gear kit bought at the local hobby store. Gutted a old Futaba servo. Used the pot, controller and the motor. The cheap worm gear motor was very inefficient so did some machining to adapt the Futaba motor, it was worth it. It works pretty well!

The walker design is based on the two center legs being mounted directly to the servo output shaft, no connecting rods. I'm thinking of trying a separate pivot for each leg and a connecting rod system. However it still wouldn't really solve the power lifting problem. This is because I want my robot to have a variable walk that will lift the legs only as far as is necessary to clear the ground for a fast walk. Then using sensors of a still undetermined nature, detect that the ground ruffness needs for a higher leg lift for clearance. Thus slowing the walking speed.

This weekend I finished the designing for a SIMM based motor control board. The board has two 16F84 processors controlling two L293 dual H-bridge chips. It also has a 7 channel Darlington transistor array. Totally this board can control four DC motors, five servo motors and 7 high power outputs, which could also be DC motors or a unipolar stepper. Also the four DC motors could be replace with two bipolar steppers. Lots of capacity! It also takes a long time test! The layout didn't prove as neat as I hoped. This ones defiantly a prototype. The next one will use double sided PC board. I had planed on double sided but ran out of stock and its hard to find .047'' PC board. Everyone seem to sell .062'', which won't fit in a SIMM socket.

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