Quote:
Originally Posted by UndergroundVoid
I would have to see some test data before i make any real judgment on things since the world is full surprises.
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While you can do a lot of engineering and material science related equations, there are a lot of good approximations and rules of thumb that high school students can use on FIRST robots. (Just don't use that practice IRL
).
Delrin (and UHMW) are both engineering plastics that have very low friction, and both work great for chain tensioners of various kinds. I prefer Delrin where possible since it machines very nicely (you can mill it
really fast too), but it does cost quite a bit.
But if you want proof of plastic chain tensioners, here's a photo from Team 228's 2007 robot.
The white plastic circles are either Delrin (back one) or UHMW (front one). You can also see a third Delrin one on the drivetrain through one of the chassis rail lightening holes in the back. These are really simple ones: plastic rod with an off-center hole. As you rotate it around, it varies the radius; and by cranking down the bolt, it will hold its position.
The Delrin ones held up the entire year (about five competitions and a lot of other random driving) with barely any noticeable surface scratches. The UHMW ones had small (about 1/16") grooves in them from the chain. (There was no particular reason why certain ones were Delrin and others UHMW; they just happened to be whichever our machinist mentor grabbed from the stockpile when making them.)