I should have known that this would open up a can of worms :) Unfortunately, for confidentiality reasons, I can't give all of the details. However, I can say that we have already tried most of these alternative suggestions. These robots need to operate in the customer's environment with minimal modification of the floor. Some of our customers have terrible floors - one customer has a floor which has a half-inch wide expansion gap in the concrete every 10 feet. We've tried dragging chains, wires, etc. and all of them have eventually managed to get caught in such gaps and ripped off. The ESD generation is not due to the reversing loads but rather, we think, due to friction between the main wheels (not the casters) and the floor. There are some maneuvers which the robot does which involve rotating in place and this produces some slip between the main wheels and the floor (due to the wheel not being an ideal thin disk). One version of this robot uses neoprene wheels and doesn't have this problem (ESD) when running on concrete. A larger, heavier version, though, uses urethane wheels due to the necessary hardness, and these have the problem. We have not been able to find a commonly-available alternative material for the main wheels which can handle the loads, although we are looking at getting conductive additives for the urethane. We are also looking at dragging a conductive neoprene strap, but some of our testing has indicated that it will wear significantly due to the very large distances traveled by these machines (they pretty much move at 1 meter per second constantly, 16 hours per day). It seems like a conductive or dissipative caster with a fairly hard material would be a good option because it would not wear nearly as much as something which is dragging. Because there are direction reversals very often, I suspect that dust build-up on the caster would not be a huge issue (we don't really see it on our existing casters). Sean On Thu, Mar 25, 2010 at 10:39 AM, M. Adam Davis wrote: > On Thu, Mar 25, 2010 at 10:08 AM, Sean Breheny wrote: >> We have a robotics application which puts fairly high reversing loads >> on caster wheels. > > >> We are looking for a source for heavy-duty casters >> which are either conductive or dissipative (we can deal with roughly >> anything from 0 ohms to 10^9 ohms from hub to floor) to counter some >> ESD generation problems that we have. > > So the high reversing loads are causing the ESD (Van De Graaff between > floor and cart)? > > Or are you merely trying to reduce ESD by using the wheels as the > discharge path? > > If the first, then you might look into other wheel materials (and > possibly floor coverings/coatings) to reduce the generation of the > electrostatic energy. > > If the latter, I'm sure such wheels exist, but my understanding is > that it's more common to have a dangling conductor (or sprung > conductor) in constant contact with the floor. =A0You have much greater > control over the discharge resistance and path, and since the wheels > don't "wipe" they can become less effective over time due to dirt, > oil, etc coating them. =A0A wiping ground contact can be made that will > self clean, won't mar or mark the floor, won't catch on minor ground > imperfections (cracks, concrete stress releif joints, etc), and will > wear well. > > However, I think the search terms that you need are "condutive wheels" > and "anti-static wheels" > > http://www.google.com/search?q=3Dconductive+wheels > > http://www.google.com/search?q=3Dantistatic+wheels > > And they appear to be widely used in, for instance, the medical industry. > > -- > http://chiphacker.com/ - EE Q&A site > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist