Dan, the `mechanical slop' is gear "backlash" and steering linkage. As someone else pointed out, you really need a platform with two motors to do what you want. R/C `racer' cars are really not suitable for real robotic experiments. Again, all I can do is go forward and backwards, and based on mechanical and IR sensors, steer one way or the other while navigating. Again, I was bored one day and hacked up this car... Heck, I'm a `pack-rat' and the front bumber sensors is a SPACE bar from an old VT-100 terminal with two keyboard switches at each end ;-) So far my PID is fairly crude. It does P and I but not D... Given that this thing is suppose to wander around the house and it's around 14" long, it tends to rely on bumper switches more than the IR to get out of trouble ;-). I've reached the point, and have the level of interest, that I want to go forward with a new platform with two motors for steering. Again, as someone mentioned, it would be nice to rotate around a point. A little more on my `crude' sensors; I needed several interrupts. I ended up using a simple 74x30 8-Input NAND gate with pullup resistors. The output went to RB.0. So when I get an RBIF, I read port B and to determine the source of the interrupt. Since these sensors relate mostly to position, `race' conditions were not a problem. In my case I have 4 bumber switches and two IR sensors right now. The IR sensors use the simple Sharp module at 40KHz. I modulate four IR LEDs at an offset of about 30 degrees from the front and rear. The first problem I had was that it was too sensitive. It turns out that it's easier to just reduce the modulation frequency so that the IR receiver only demodulates the signal at a shorter range. I too have the same goals as you as far as a platform for adding sensors and studying control methods (ie: Fuzzy Logic and others). I realized I would not be able to do that with this platform. Still, it has allowed me to study things I've long been interested in such as H-Bridges, PID, and sensors related to an autonomous platfrom which I can apply later. Ya know... Given the talent in this group, I wonder if we could form a company to bring simple robotics down to a reasonable price-level? Parallax's pricing is ridiculous... As most have noted, buying a simple platform with gears and motors is ridiculous... Anyway, just a thought... - Tom At 12:18 PM 11/10/00 -0500, Dan Michaels wrote: >Hi Tom, > >[hmmm - I don't need a robot to freak the neighbor's cat - squirrels >in my backyard drive it crazy already]. > >By "slop", you mean backlash in the drive mechanism, or something else ???? > >Am not sure this would be a big problem for what I would like to do >- mainly obtain a mobile platform that I could add a few sensors to, >and which would form the foundation for playing with "higher" functions, >such as rudimentary learning, fuzzy logic control, neural net learning, >etc. > >Idea would be to have the thing traipsing around on its own and sorting >out behavior that favors survival. Basically, something patterned after >Rodney Brooks' work - simple robust platforms with multiple layers of >control arranged hierarchically, and which co-opt lower level functions >as they are added: > >http://www.ai.mit.edu/people/brooks/paperlist.html > >"A Robust Layered Control System for a Mobile Robot" >"A Robot That Walks; Emergent Behaviors from a Carefully Evolved Network" >"Intelligence for Miniature Robots" >"Elephants Don't Play Chess" > >[I figure multiple PICs headed by a king-Scenix - he, he]. > >Also, another reason I like the RC-car idea is that you could have 2 >RC transmitters on different frequencies, put the 2nd one on the car >itself, and use it to xmit status info back to the base station >chimputer. Now that xmas/crazybuyingtime is here again, and new >RC-cars are on the shelves, it's time to look around again. >=============== > > >> Speaking of Parallax, I can't believe the price they charge for that >>little robot... As far as web sites, I only found one a long time ago and I >>forgot where it was. I was looking at R/C servo hacks to give them >>continuous rotation. I found a lot of info on that subject. >> > >Yeah, I have always wondered how Parallax can stay in business at >the prices they charge, but ha - they're lots richer than me. Also, >I have looked at a number of mobile platforms for sale from robo-sites, >but they are all all extremely to-heavy designs, simple platforms on >wheels, and selling for >$250, or tiny little things. > >Don't know if you caught this link, but this is an interesting mobile >job, albeit a little steep at $5000 -[and somehow connected with >Brooks]: > >http://www.irobot.com/ir/index.htm > >Still haven't found anything on RC-car robo-hacks. > >best regards, >- Dan Michaels >Oricom Technologies >http://www.users.uswest.net/~oricom ------------------------------------------------------------------------ Tom Handley New Age Communications Since '75 before "New Age" and no one around here is waiting for UFOs ;-) -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.