sprockets

[Harrison]

I'm curious where you're using the plastics Joe?

Personally, I would for sure never use them in a drive system. Maybe for pick-up or something...?

[Lauren Hafford]

finding a 5/8'' bore: it's uber easy to drill out the center of a gear, especially a spur gear with a hub. but sprockets have hubs, just mount them in the lathe hub inwards in the chuck and put a drill bit in the tailstock. for drilling out steel i would run it reallly slowly. that's if you can't find cheap sprockets to your desired bore.
BTW, we have steel spur gears and turned off most of the hubs (so we can still have a setscrew) and the weight was almost cut in half. If that helps.

lauren

[Dick Linn]

It's all engineered, folks. Glass-filled sprockets of the correct diameter can work just as well as steel if you figure it out. Just don't count on a 10-tooth plastic sprocket if you have high torque and poor alignment and don't drive conservatively. It all depends...

On the other side of the equation, picture this. Last year, we had 60-tooth #35 chain sprockets that needed serious lightening to make weigh. I didn't like it, but I had to spend about 2 hours with a 4 1/2" angle grinder and a very thin cut-off wheel to gouge about 1 1/2 pounds of out of the solid steel "pancakes" because we had no access to a mill. Not fun and definitely bordering on the dangerous in trms of possible mishaps. The good part was that these were off-the-shelf go-kart parts that were really cheap. And the drive-train was completely reliable. No breakage, no spares, no hassle. And no chain tensioning during the regional or the final at Epcot.

[Mercutio]

I'm seeing a lot of hostility towards plastic sprockets on this thread. I can't say I've ever seen plastic sprockets, but we are using a lot of plastic as a structural component on our robot this year. We haven't done any formal tests, but after trying to file it, bend it, break it, and punch a hole in it with a hammer, I got the impression that it's very strong. One definite advantage of plastic is that blocks of it can easily be formed into complicated-shaped parts. This is the first time we've ever used plastic, so stay tuned... if Team 1213's bot falls apart, you'll know plastic is no good! ^_^

[RobDeCotiis]

I think you may be refering to gears made of pressed powdered metal like the old chiaphua gear cluster. If you want a good idea of how hard that thing was, try to grind it off. The lathe wouldn't even scratch it.

i had to saw through one of those.. by hand..it took me 45 minutes with a CARBIDE BLADE!!!
lord, that sucked royally

[Maxzillian]

Another idea would be to make the teeth section steel, and then mount that to an aluminum hub.

[Cory]

I was pondering that idea myself. It would work pretty well too. A system like this was just introduced in the bicycling industry. A steel braking surface for disc brakes is bolted to an aluminum carrier that then attaches to the hub. It saves quite a bit of weight, but im not sure how easy it would be to implement this in FIRST. It would take quite a bit of machining and a lot of work. I dont think it would be strong enough for drive sprockets either.

Cory