Some years back I was talking with a friend at work about LEGO robots and he mentioned this synchro drive robot platfrom concept. Some of the really fancy professional robots are built this way and he was already working on a LEGO version. What is interesting about this type of bot is the way that it turns, or doesn't turn ... The orientation of the base itself never changes. Instead, all of the wheels turn in unison to change the direction of motion. One nifty feature of these platforms is that the wheels are not 'scrubbed' in place as they are turned in a different direction with the main drive off. Instead, each wheel just travels in a small circle while the bot as a whole does not move at all. This is accomplished by offsetting each wheel from the center of it's mount and using appropriate bevel gears to compensate for differences in wheel radius and wheel offset. One of the benefits of this arrangement is a turning radius of zero. It is also very easy to keep track of direction and distance traveled. So, this is my attempt at a synchro drive LEGO robot. It has four wheel units with the wheel offset set equal to the wheel radius for a nice 1:1 bevel gear ratio. The basic design was completed within a few days back then but was never motorized until now. Enter LEGO Mindstorms. After building the simple tracked bot with obstacle and table-edge avoidance it was time to re-visit the synchro drive robot base which was collecting dust. Now it has an RCX to control it and two angle sensors to keep track of distance and direction. I will be adding another sensor or two soon but for now I was only trying to get the base working properly. And it does . :-) I only have it running in a square pattern for now but still it's pretty cool. Lots of work still to do but here are a few images of the synchro drive base with and without the RCX.
Click on any image for a larger view.
November 1998
Here is the same bot with full 360 degree bump detection using four touch sensors and some rubber bumper elements. The whole bumper is suspended on four small spring shock absorbers so it can move in any direction horizontally. Also, the RCX and light sensor, which is multiplexed with the bump sensor, rotate and 'look' in the same direction as the bot is traveling. So, if the bot runs into something, it can back up a small amount and 'look around' for the offending obstacle and choose a new heading. Both rotation sensors are still used for motion control but the one used for steering drive feedback now can also be used to keep the wires going to the RCX from getting too wrapped up.
December 1998
Some details of the rotating head and bumper assemblies.
Now the RCX is stationary and only the light sensor rotates to follow the direction of travel.
October 1999
November 2001. This model's 'head' currently has an IR LED brick and light sensor connected through a rotating electrical connection to keep the wires free from tangles.
