sprockets
 

I just wanted to get peoples opinions, which do you think is better, Aluminum, Steel, or Plastic sprockets?? My team is having a minor problem in agreeing ....Some want to use Steel (which I believe is over kill and if you are tight on weight its not a good idea.) and then some want to go with AL and or Plastic.

assuming you are talking about drive gears
i dont think steel is much of a problem as long as its not to big, aluminum would be the best , but i would never use plastic. it will break or strip out way to easily.if your budget allows it i would use the aluminum gears , evn though they are more expensive.

I would just cut out the idea of aluminum or steel sprockets. Because drive gears/sprockets are under constant force and stree during the match, you want to use steel or cast iron. It's heavy, I agree, but it is the best choice. Our team gets sprockets/chains/gears machined by Borg Warner people and realize they make 90% of the world's small car chains and 80% of the larger automobile chains... such schweet quality.

Steel is best. If you're willing to buy extras and replace them periodically, aluminum may be worth it if weight is that important. Never plastic. Never.

:)

Definately Steel.

Weight however is an issue, which is why you pump it full of holes. You can even lathe down the hub in many cases (since often it is not needed, or at least doesn't have to be as big as it is). Generally, we manage to cut at least half the weight off our steel sprockets (and some of the gears too).

the teachers, engineers, and some knowledgable students on my team (myself hopefully included) all shudder and spasm at the idea of plastics sprockets when we saw them in the big blue book. its scary, those things - in a 130 lb robot - that will be ramming into things at top speeds? AAHHHHHHHHAHHHHHHHHHHHHHHAHHHHHHHHHHHH ahh ah

lol. *pictures total annihialation as little bits of plastic shrapnel come flying out of a robot*
okay mabie thats a little overdramatic bot SAY NO TO PLASTIC

Aluminum is fine, and is a lot lighter. Racing go-carts and motorcycles use aluminum sprockets, and they have a lot more horsepower! Anyone know of a source for aluminum sprockets with a 5/8" bore?

Try Small Parts or Mcmaster Carr.. I would say look into Mcmaster Carr first.

If you mount, and use them properly, plastic will work just fine, at least for wheel driven robots. The important thing is how you transmit the load from the shafts to the sprockets. If you get the chance, stop by our pits and check out our plastic sprockets.

Cast iron? That is a little brittle and extremely heavy if I remember correctly. 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.

Aluminum is just fine
 

We've used aluminum sprockets for the last couple years (manufactured on our shop's CNC). We've had no problems and saved (literally) pounds of weight vs. steel.

Just don't have 5 subsystems and the weight should be fine. We use standard issue (formed powedered metal?) black steel sprockets from SPI or McMaster.

SPI is way overpriced though.

plastic is good enough for me...
 

I don't want to change anyone's mind but I can tell you that I am using a LOT of plastic sprockets this year.

Plastic is not as strong as aluminum and steel, but in the right application with the right design, it can be better than metal.

Your mileage may vary...


Joe J.

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...?

hubs and bores
 

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

Sprockets
 

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.

Plastic... material of the future or angel of robotic death?
 

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! ^_^

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

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

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