23 Aug 2003 EdwardRupp   » (Journeyer)

I've been working on a home made Ultra Sonic ranger. Its working very nicely now. The original hardware worked perfectly from the start. I originally had trouble with the time of flight measurement. Proved to be the way I was trying to count the time for the trip back. Pic Basic's Pulse in apparently counts the time between pulse's, not from the time the command is issued to the arrival of the first pulse. So I just look for a logic level state change in a tight counter loop. Works great with excellent repeatability and little noise.

The range is only good to about 15" but most small robot stuff needs only about that anyway. Super simple only a couple surplus transducers, a pic, Op Amp and a couple trimmer pots. Maybe $5.00 worth of parts.

Last year at the Critter Crunch (held in Denver Co, every October) my robot couldn't see it's opponent very well. We both had painted the robots flat black. So the idea is a major rebuild of the robot to use ultra sonic ranging sensors. The cost will be low enough to put a transducer pair in each corner, for nearly 360 degree view. Now my Critter Crunch robot will be able to see those black panted stealth bots!

The robot originally had a tank toy for a drive train. All that's been eliminated with only the original rubber treads, cogs and idler wheels. I very carefully chucked the coged drivers in the lathe and machined a alignment feature to mount RC servo horns. This way I can use RC servos which have much better power and speed characteristics than the original toy motors. I had some .100" thick aluminum brackets that were originally for some old hard drive mounts. With some drilling and use of a nibbler they have proven perfect for mounting the motor, drive cogs and idler wheels.

Now I just have to wait to decide the battery pack voltage. Its looking like I'll be close or exceeding the 2 pound limit if I go with a 12 volt AA pack. A 9.6 volt will probably be ok. It all depends on how much the still unknown weight of the new sonar and rebuilt upper casing will weight. Being I'm greedy to have the extra performance of the higher voltage I try to see if I can find weight to save. Until I get the actual batch of sonic transducers I'll have to make some mockups to determine geometry and possible weights.

I'm hoping to have the robot going for the next FRR (Front Range Robotics) meeting in Fort Collins. The hope is seeing a working Critter Crunch robot might stimulate some robot building in time for the actual event in Denver in October.

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