= Eric's WideTrack Robot Page = http://home.austin.rr.com/elundquist/widetrack/P8170362_sm.jpg WideTrack at [http://www.armadillocon.org ArmadilloCon 24] Aug 16-18, 2002 == Background == I started the WideTrack project as an engineering experiment in "easy to build" tank tracks in early 2000. Typically robot tank tracks fall into 3 categories: 1. Custom machined links 2. Automobile Timing Belts 3. Hacked Toy Tanks None of these solutions appealed to me. I didn't want to learn to custom machine parts. Using timing belts didn't appeal to me and toy tanks are too small. I thought that there had to be an easier way to utilize an easy to work with material such as pvc pipe that would give me the results I desired. I wanted a material that was: a. readily available a. did not require special equipment or tooling to work with a. would work like a "real" tank track linkage a. would scale up to large sizes In my naivete, I thought I could knock something out in a couple of weeks. Two years later, I am still perfecting the design. In that time I have learned a few things about what works and a whole lot about what doesn't work. This has become a journey for me, not a destination. I thought that others may be interested in that journey too. This journey has not been entirely alone. I would like to thank Ed Gonzalez, Derek Bridges, Glenn Currie, Tom Davidson, Edwin Wise, Don Colbath, Tom Morin, Bill Craig, Aaron Lundquist, Catherine Lundquist and the rest of the [http://www.robotgroup.org Robot Group] for their help and support in getting me this far. Thanks! * Eric Lundquist * Austin, Texas * September 2002 * elundquist@austin.rr.com == What do the "Big Boys" do? == I started out by taking a trip with my camera to [http://www.kwanah.com/txmilmus/index.htm Camp Mabry]. Camp Mabry is the headquarters for the Texas National Guard and they have a great museum on base. If you ever get a chance to go there, it is definitely worth the trip. Of particular interest to me is their fine collection of WWII armored vehicles. They have everything from German half-tracks to American mud-buggies to Patton tanks. What was most interesting to me was that no two vehicles seemed to have the same track design. This taught me that there is no one optimal design for tracks. Clearly there was as much art as science in the design of track linkages. When I ran across this vehicle, I knew that this was something that I could copy and use for my purposes. http://home.austin.rr.com/elundquist/widetrack/PDRM0024_sm.jpg A ''Real'' Tank Track One interesting factoid that I discovered is that all of the drive sprockets seem to have an odd number of teeth. German and American, WWII and modern vehicles all seem to follow this rule. I am not sure why this is, but who am I to argue with the "big boys"? Here is my version of the above track design on an early frame. http://home.austin.rr.com/elundquist/widetrack/PB100006_sm.jpg == Building the tracks == An initial prototype of the "bogie" built entirely from cpvc pipe next to an intermediate design that still utilized cpvc for the axles. I eventually discarded the idea of the pvc in any of the framework simply because it wasn't strong enough. http://home.austin.rr.com/elundquist/widetrack/Tread_New&Old1_sm.jpg The sprockets are simply pine shelving that were hand cut with a skill saw. They were then epoxied together. Later, the exterior of the sprockets were covered with fiberglass cloth and epoxied for strength. This has worked surprisingly well throughout the entire project. It is one of the few things that has not had a material failure. In the background you can see that the pvc axles have been replaced by all-thread. At this point the only pvc remaining is the tracks and the motor support frame. The side panels are constructed out of plywood that has been fiberglassed on one side. http://home.austin.rr.com/elundquist/widetrack/PC070005_sm.jpg A couple of incredibly bad ideas I had was to use rubber tie downs as drive belts on wooden pulleys that I built using hole saws. The wooden pulleys ate rubber belts for breakfast and were very difficult to get tight enough. The drive mechanism was later changed to a chain drive. You can also see the [http://www.traxxas.com TRAXXAS] XL1 Electronic Speed Controller in the background that I used for a short time. I think I can confirm that they do not work well with 12V 70Amp wheelchair motors! After letting the "magic smoke" out of two of them and melting my 18 gauge [http://www.radioshack.com Radio Shack] wire, I changed to 12 gauge automobile wiring and built a simple mechanical h-bridge out of micro-switches and servos. In the foreground, the motors are still mounted to pvc. The entire frame had a tendency to twist when the motors engaged. The frame was later rebuilt using steel plumbing pipe (see ArmadilloCon photo at top). http://home.austin.rr.com/elundquist/widetrack/P2030089_sm.jpg == Track Coverings == I knew early on that I would have to cover my pvc tracks with something. The first material that I used was toolbox liner. This was a rubber mesh that was fairly strong and easy to attach to the pvc tracks with tie wraps. This worked ok for a short while but it quickly started to wear and I knew that something stronger was needed. http://home.austin.rr.com/elundquist/widetrack/Eric&Cath&Track1_sm.jpg While wandering around at the local Lowe's, I stumbled across a roll of carpet protector for $5.00. The stuff is very tough so I gave it a try. I spray painted one side and attached it to the pvc with pop rivets. It was better, but still not there. It just didn't hold up while driving around on the asphalt driveway in front of the Robot Group warehouse. Something even tougher was needed. http://home.austin.rr.com/elundquist/widetrack/P8010202_sm.jpg On one of the Thursday night get togethers, someone brought in a sample of the belting material used in conveyor belts and gave me the name of a local source. I went to Purvis Bearing. Once they got around the giggle factor of robot tank tracks, they were very helpful in locating a suitable material. Single ply pvc 120lb conveyor belt is what I needed. They ordered it from their San Antonio location and I had it a couple of days before ArmadilloCon. A couple of very late nights later, the new tracks were ready. http://home.austin.rr.com/elundquist/widetrack/P8170364_sm.jpg WideTrack and a couple of admirers at ArmadilloCon2002. A couple of other things of note here. Notice the addition of another battery on top. Going to 24V gave me full power on the wheelchair motors. Also notice the addition of the clear acrylic disks on the sides of the wheels. This helps keep the tracks from skidding completely off the robot when it turns. == Videos == I apologize for the QuickTime format. That's the way I get it out of my Olympus Digital Camera and I don't have a good format converter. Catherine driving an early 12V version of WideTrack (11.2MB QuickTime) Taking the 24V version for a test drive (6.6MB QuickTime) WideTrack Cruising at ArmadilloCon 2002 (7.5MB QuickTime) == Going Forward == I would really like to get rid of my simple mechanical H-bridges and replace them with a pair of [http://www.vantac.com Vantac] RET 713 Electronic Speed Controllers or possibly an OSMC. As soon as I can shake loose $300USD from the money tree I'll be sending in my order. An alternative may be to custom build a pair of controllers. Next will be the addition of sensors. Ultrasonic and IR rangefinders probably controlled by my [http://www.atmel.com Atmel] STK200 board connected via RS-232 to a laptop connected to an 802.11b network. == Making Contact == You can e-mail me at elundquist@austin.rr.com