Older blog entries for EdwardRupp (starting at number 1)

The Front Range Robotics club meet this Saturday, unfortunately the turnout was light, so my new walker didn't have anyone to compete against. Also there was only one other sumo robot for my sumo's to go against, and that one was still having problems. However it was still enjoyable to see fellow robo folks again and exchange ideas. Next Sunday the 28 is the Critter Crunch in Denver. For more info see http://www.milehicon.org/. Some of us plain to be there to see the robots compete and we will be doing a sumo demo, and show our other robots off. I've never been to one of these events before, from what I've been told the competitions there are mostly remotely controlled robots similar to Robot Wars or Battle Bots in nature. Only these bots are much smaller, 20 and 2 pound classes. This event has been going on even before the more famous shows by about ten years. Should be a lot of fun!

Front Range Robotics meets on the third Saturday of the month at the Coffee Connection, on the corner of Drake and Shields, next the Pulse fitness center in Fort Collins, Colorado. Meeting starts at noon and goes tell we can't talk no more! The email list serve is FrontRangeRobotics@yahoogroups.com.

Also at the meeting I showed my prototype SIMM based motor control board. This board I call the kitchen sink motor control board, because it is one very busy board! It has 2 dual H-bridge controllers, 2 16F84 processors and a 7 channel power transistor array. It worked very well for the demo. I had 4 brush motors, 5 servos, a small fan and a bunch of LED's going through a simple test program. The next version I hope to make double sided as the present single sided board has way too many jumper wires!

I finished converting a hobby worm gear kit with a servo motor and controller. It works well, but could use some more work. The walker is moving very nicely now. Speeds up to a smooth run and turns nicely. If it sees something straight ahead or if the bump switches hit something, it will slowly backup and turn on its axis an then speed up going forward again. I'll definitely have to continue my Idea of multiple processors, because just the code to make it walk uses up all the memory of the 16F84. My plan is a dedicated SIMM style sensor board with its own processor, separate boards for a central processor and modify the existing program for a processor board dedicated to only moving the legs.

The center lifting legs motor is very stressed by this design. To keep the motor from burning out I've cut off the back case of the servo. Glued copper strips to the control chip and to the motor case, then use a very tinny fan to help cool the thing! My plan is to continue to work on a worm gear drive and also some linkage system to help reduce the stress on the system.

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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