Major problems with tank tread drive

[dlavery]

Originally Posted by Lord Nerdlinger

We finally hooked up our drive system today, and we can only go about 2 feet before the treads fall off the wheel. The treads are flat on aluminum rollers and they have no grove. We have a pulley that's flanged and 2 other flanged rollers (one in the front and one in the back).

The flanges are about .1 inches, and the rollers/sprockets are 2 inches wide.

Are we totatlly screwed? Or is there anythign we can do?

Would attaching circular plates onto the flanged wheels to make a really big flange do anything?

Help plzz!!!

Ohh, do we feel your pain! Sounds exactly like our experience last year, which was ugly enough to make us swear off treads. The problem is that as you start to turn, the side forces are pushing the treads across the face of your pulleys, and into the flanges. The side force is strong enough that one of three things has to happen (we went through them all):
- the tread climbs up the flange, and off the pulley (if the tread is loose enough)
- the tread rips and tears on the edges of the flange (if it is too tight to climb up the flange)
- the tread crushes the shape of the flanges and makes them useless (if the treads are very tight and the flanges are weak or damaged)

None of these are good conditions, and all of them will cause the robot mobility system to sieze up and stall. At this point, it is a virtual certainty that you will not be able to get new treads with self-centering ridges on the back (which is what you really need to use), unless you are incredibly lucky and can find a team with a spare set. Short of that, here are a few suggestions:

- make sure the "line" of your treads is bowed down. In other words, look along the area where the treads make contact with the floor. Ideally, the ends of the treads should be slightly higher than the middle (like a flatter version of the rocker on a rocking chair). This puts most of the weight of the robot near the center of the contact patch, where the side forces from scrubbing the treads during a turn are the smallest. This allows the ends of the treads (potentially where the side forces are greatest) to "float" a little and hopefully reduce the side forces.

- increase the size of the flanges. This will help, up to a point (if your treads are too loose they will still climb up the taller flanges and thereby increase drag on your drive motors as the tread material scrubs against the larger surface area of the flange).

- make sure you have sufficient tension on your treads. Again, this will help, up to a point (if they are too tight, the increased loading on your pulley bearings will result in extra friction in the system, and potentially could fail the bearings).

- can you convert to wheels in the next four days? If the above suggestions don't help enough, you need to take a serious look at this option. I have seen teams completely re-build their drive system in two days, so know that it can be done.

Good luck!

-dave