Team 48 has used tank tread drive trains of various designs with great success since '04. As a team that loves to play defense, we utililize the traction and stability that tank treads provide. Examples of our past tank drives:
2004 - triangular design to climb the vertical side of a 6" high platform
2007 - combined with 2-speed transmission, provided superior pushing power
2008 - a year where no one in their right minds would have thought to use treads, we wanted them for stability around the corners while carrying the trackball
As for the issue with turning, we were able to solve that with a couple methods:
- including one or two bogey wheels located under the CG point that could be lowered 1/8" to 1/4"
- instead of full-length treads, use a half-track system with omni wheels, such as our '08 robot shown above. A more typical method is moving the treads to the rear of the robot and a pair of omnis at the front. You maintain your pushing power, but the turning is much smoother.
Also, drivers need to develop "tank steering". With older tanks, you don't often see one turn on the fly--often they drive in a straight line, then stop forward momentum to turn with one tread going in the opposite direction of the other in a zero-radius turn.
For belt tensioning, our shop teacher developed a system that tensions the dead axle of the non-powered outer wheel. This was used in all of our systems and can be seen in the pictures above.
One of the biggest issues we had to deal with was the sheer stress on the belts brought on by side contacts, as our driver liked to interfere with another robot by drivng in front of it perpendicularly. If your robot is pushed from the side, the belt can twist (sometimes right of the tread wheels) or sheer a steel-reinforced belt in half--and that's not pretty when the belts run between $150-300 each. You have to have a system in place that keeps the entire length of the belt in contact with the carpet (or at least at minimum intervals) from sliding sideways, be it with bogey wheels, slider blocks, etc. Keeping the belt in line is critical in a successful tank drive. With a half-track system, we found that the side stress were much less due to the shorter length and extra lateral support was not needed.
Please feel free to PM me about this.