3 Jan 2002 EdwardRupp   » (Journeyer)

Robotics can have such distractions! My major project is still to build 3 identical robots who's ultimate task is to cooperatively collect and sort colored M&M candies, peanut M&M's specifically. Thus I'll be able to state that I eat the labors of my robots! Also along the way, design these robots are do other interesting things such as compete in the Trinity fire fighting contest. However my efforts have been slowed a bit by a I/O board design that proved to have a great deal of noise on it and cross talk on the serial lines.

Then to soothe my great disappointment (it was a heck of a lot of work!) I bought a little toy walking robot bug. My thoughts were ``this looks like a nice quick weekend project!''. How wrong I was.

The toy bot in question was the model I.B.34 Insecto-Bot. A little fellow so ugly it has to be cute. I mistakenly assumed this toy would use two motors on cams to move the legs and thus allow a fairly simple brain transplant to more intelligently control them. Unfortunately it turned out to only have one motor. True to classic cheap toys (it after all, only cost $15) it used a blizzard of gears and a cleaver set of gears that engaged when the motor reversed. Thus it could walk forward quite well and very badly turn left only. Thus to make the little guy move I bought three $20 mini servo motors.

I now have new respect of Dremel style motor tools! I've done a tremendous amount of surgery on the little beast, and I must say its coming out very nicely. Two big problems were of course coming up with motor mounts and connecting rods and cranks to the legs. The second big problem, the battery compartment!

The most evident of the modifications, the original battery compartment only had 3 AAA batteries. For my application I needed to have two independent batteries. This is due to a walking robot having to do a lot more movement with the motors. That uses a lot more draw current, and generates more noise. A wheeled bot, with careful design can get along just fine with one battery pack. Also I needed four batters for each pack because the rechargeables have a lower voltage. Thus the need to stuff EIGHT batteries where only three had lived before! Lots of careful mototool work and cleaver hinge design latter, they fit. Though he now has a bit of a beer belly.

Next I have yet to build is the PC boards to control the little guy. One thing I decided early on was I wanted him to do something more interesting than the usual run around and avoid bumping into things. I found a little recording module at Radio Shack. It can record up to 20 seconds. The thought is to have the bot walk up to something and attempt to circumnavigate it. Then conclude the shape of it, and vocally announce it. I'll give it a simple vocabulary of words and have the processor start the play back and blank the audio for only the words needed. This will make for a stilted speech, but should be useful.

The sound module itself didn't produce enough volume to be heard well but very close up. I happened to have a little 1 watt amplifier kit I had never assembled. It works well with the output from the recorder. And as luck would have it the little speaker in the toy robot (he originally made random sounds)is just the right eight ohms the amp needed. Now the little bot can down right shout!

I hope to have the electronics done in the next few weeks, in-between the usual work on the other robots. Presently my CNC is cutting out a sensor array board for the more complex robots.

The sensor array board idea uses IR and ultra sonic. The ultra sonic section is a Devantech SRF04. Latter designs I hope to build my own ultra sonic hardware directly into the board. The IR section is the new idea. It uses 4 IR sensors and 3 IR LED's Using hardware PWM to adjust the brightness of the LED's. The twin IR sets are pointed 45 degrees from the board, producing a large field of view. The upper IR's are sensitive at 38khz and the lower set at 56.9Khz. One IR LED is centered between the IR sensor sets with the other IR LED's flanking either side of the IR sensors. With this setup it is possible to see seven possible angle hits. Along with the crude changing of light level I hope to use in software, a system where the number of pulses returned verses transmitted is also used to give a ruff calculation of distance. I realize it will be very crud and heavily influenced by the color of objects but should still be useful. If the idea works I'll use a simpler one frequency, IR only setup for the walker.

I hope all of this isn't interpreted a crowing. I like to hear and hope to hear more about what others are doing, and hope my writing is also interesting.

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