I recently moved a dozen or more plastic spaceship models that I built in my 'teens from one house to another. Some were slightly broken and some were very broken. I saw a webpage with Lego Mindstorms robots on it that looked like fun. Then I realized that if I had built all those ships out of Legos, I could have re-used the parts. Or I could have fixed them easily. Legos have been around for a long time and the current shapes allow you to build almost anything. And have you looked at the prices of model kits these days? They are very pricey for something you can't play with or make more than one thing with. So I bought a lot of lego kits to see what I could do... (and if I ever get tired of Legos, I can give them to my granddaughter - they last almost forever).
LeoCAD file for this assembly.	I got a Spybotics S45 kit without the treads or common parts so I stuck a couple wheels on it to see it go. It ran into things often and I didn't want it to break so I worked up a bumper for it. It is mostly DDK parts with one shock absorber. Now when it hits, it triggers the touch sensor as well. Most of the force is absorbed by the spring and released when it backs up. If it hits really hard, the bumper hits the floor. I found this worked okay except if the spybot got wrapped around a table leg so I added the fenders in front of the wheels. They are put on upside down because the top ones have slots cut in them for lego panels while the bottom ones have smooth edges. Now the spybot can run around for quite awhile without getting stuck.
LeoCAD file for this assembly.	I saw a website showing a robot with a Synchro drive. I designed this one based on it, but with one important difference - rotation. I haven't connected any motors to it yet as I'm working out the bugs. The concept is that the robot can drive forward or backwards. Then it changes the position of the wheels by 45 degress using the worm gears and it can rotate left or right. With enough freedom, it could even shift the wheels by 90 degress and go left/right without rotating. I originally conceived of this with each wheel powered and the platforms independent of each other. That took four indepently controlled motors (Lego doesn't make anything to run four motors using just one controller though). To change modes, just make the motors work against each other and the axles would move. The worm gears limit some of the flexibility, but add needed stability and alignment. This should now work with only 3 motors: one motor for left, one for right and one to drive the worm gears. The front/rear wheels will need to be linked with a differential as they move opposite directions when the mode changes. The motors have to be for left and right to do the rotation. Front and back motors won't work. I was also thinking about having floating gears where the axles would connect to one set at 45 degrees and another set when going straight. If I could figure that out, I could get it down to just two motors and no differentials. I would lose the possible 90 degree mode though. I have a better design than this. It takes less bracing, no differentials, and has a lower center of gravity once the motors are added. It has a choice of either 4 wheel drive or having the 90 degree mode. Unfortunately, it won't work with both. The new design also has better wheel alignment than the old one. Perhaps I'll take pictures of them both and put on this page.
LeoCAD file for this assembly.	This is my second design (my first was boring). It's not easy to build as the center beams are all pressure fit. I was originally going for a different look with a pair of motors back to back on the bottom floor, but it kept falling apart. Now it doesn't come apart without working at it.
LeoCAD file for this assembly.	I ordered some parts direct from the Lego website and I received a dozen of the 50th anniversary gold bricks. You can't make much with them by themselves so I put them together in a pyramid. Then I needed a building to house my gold brick. It seemed natural to replicate the gold repository at Fort Knox. I started this using real bricks, but I ran out of white ones before I had finished the front wall. So here is a model I worked up. It's not complete - the back wall is open and it has no internal support. This is due to the lack of pictures showing those areas. I wanted to model it in LDD (official Lego Factory software), and then I could order it. The problem is that they don't give me the 384 white bricks that it takes to work with. I received email stating they were going to compensate for that in the next revision (to make it more like the former revision). I also checked and Lego doesn't make the 3x3 plate (without corner) in white so I can't build it anyway.
LeoCAD file for this assembly.	This is the smallest drive unit I have built that can carry an RCX unit. It uses two motors for extra power. The cables are added between steps 8 and 9. They go straight out between the two plates (which keep them from getting caught in the gears). It can go up about a 45 degree incline inside of 4" diameter PVC pipe.
LeoCAD file for this assembly.	And here we have a push-pull drive train followed by the RCX secured tightly to a sled. The sled just fits vertically in the pipe. The two drive assemblies are identical and connected so that they can pivot as they go around corners.