Date   : Mon, 18 Oct 2004 16:02:28 +0100
From   : Ben Newsam <ben@...>
Subject: Re: BBC buggies and robot arms

In message <00c901c4b519$4c1a0500$7dc3033e@...>, Charles 
Blackburn <charlesb@...> writes
>you'll probably find that any rubber ring will do as long as the size 
>(ID and OD) are correct.

Exactly. We found that the best tyre to use had to be stretched slightly 
to fit the wheel and thus the diameter was not as predicted. That meant 
that the hardness of the rubber had to be specified as well. The 
hardness of the rubber also affects the size of the "footprint" of the 
tyre on the running surface, which should be as narrow as possible 
within reason. Because both requirements were in conflict (if you see 
what I mean), we[1] chose a hydraulics O-ring to use as a tyre because, 
although they look it,  the profile of the tyres is not actually 
circular, but tends to a slight "point" at the outside.

[1] When I say "*we* chose", the engineer did the choosing, and I merely 
agreed with him that it worked better from a software point of view.
-- 
Ben Newsam