My team is considering creating a rack and pinion drive for this years competition. It seems that this kind of drive has not been used often and we have had difficulty finding information in the forums. Does anyone know the pros and cons of this drive system and any potential problems that could occur during construction?
Many teams used it last year, since it allowed fast cornering. If you search for “Ackermann”, you should find many mentions on here.
My team used a rack and pinion drive system for all four wheels in the 2008 overdrive competition. It was very maneuverable but very difficult to program. In fact, we couldn’t even have an autonomous that achieved so much as one line because it was so difficult getting the wheels strait and keeping them that way. It was also very difficult to keep track of the wheel orientation when trying to program a closed loop steering algorithm without the wheels overshooting and searching for the desired position until they narrowed in on it. These problems weren’t so much the problem of the old controller being slower, but in the design of the rack and pinion itself. In the picture below, we are using a rotary potentiometer with two pulleys and a rubber band, but we later moved to linear potentiometers. The full length of travel from one end to the other was only a few turns of the window motor and this was one of the major issues. If we had had a smaller gear or some other means of making it take more turns to get through its travel it would have made control a bit easier. Honestly, while it would probably take forever to get from one limit of travel to another, a threaded rod probably would have been best for moving the wheels rather then the way we have it set up below. All in all, a rack and pinion drive system has the potential to be an excellent solution, but do take the time to think a little further forward in your design than we did with ours and remember that it becomes tricky to keep track of wheel positions if your trying to get anywhere in autonomous.
