how to select sprocket size for gearing

[diver]

If a motor turns 3300 rpm and one has a 24 inch wheel that one wants to be at 800 rpm. what size tooth for the driven gear and drive gear have to be. Is there a way for the not so smart person to figure this out with out buying and installing sprockets to get the right RPM of the 24 inch wheel by trial and error.
thanks again

 

[HAL9000v2.0]

Rear sprocket must have 4,125 times more teeth than front one (12 on motor, 50 on rear wheel). But I think that 3300 is no load rpm. So if you want to have exactly 800rpm with load i'll say go with 6 or 7 times bigger rear sprocket if your motor have enough power.

 

[frodus]

well.... you want 3300 in and 800 out

3300=800* x where x is the ratio.

3300/800 is 4.125 ratio.

If you have a 50 tooth rear sprocket.... you'd need a 12 tooth to get roughly 4.16:1 ratio. 3300 in is 793rpm out

if you have a 60 tooth rear sprocket.... you'd need a 14 tooth to get roughly 4.28:1 ratio. 3300 in is 771rpm out.

66 and 16 gives you 4.125:1, so does 33 and 8, but 8 might be too small.

Basically you have to play around with ratios of sprockets. Don't go too small on the front, it can bind and its noisy. Also don't go too big on the rear, as it might get in the way of the frame, or it might be so large that it adds too much rotational weight to the wheel.

Just get as close to the ratio as you can, its not an exact science, unless you're trying to make sure 3300rpm goes EXACTLY XX distance.

 

[Jeremy Harris]

It's also a really good idea to have an odd number of teeth on one sprocket, just to even out the chain wear. The chain will last a lot longer on something like a 13/48 set up than it would on a 12/48 arrangement.

Jeremy

 

[Drunkskunk]

800 rpm on a 24 inch wheel works out to just shy of 60mph. What exactly are you building?

 

[diver]

800 rpm on a 24 inch wheel works out to just shy of 60mph. What exactly are you building?

Im building a rear wheel drive three wheeler at 48 volts . going to use and etek motor and a alltrax controller. I just bought the motor and already have the controller. this will also be a pedal bike just so i can sort of still be legal here in the sunshine state. I don't plan to run 60 just want the tq . our three wheelers now run nice but they are heavy and I have just to many controller problems and very little starting torque. I would like to just gear it so i only 40 or so but by looking at the sprockets you guys figured for me that might be hard to do. Im just found out that my motor is back ordered. it wasn't when i ordered it on line yesturday..lol this is the motor i bought http://www.robotmarketplace.com/products/ETK-ETEKR.html
thanks again

 

[Link]

You might cancel that order and try an Etek-RT. It's got 50% more winding, so it will be torqueyer and won't have to be geared so low.

Plus if you got it from RobotMarketplace you didn't get the best deal, I think. Electric Motorsport and I think Falcon-EV have them for like $450. $525 for the Etek-RT.

 

[diver]

You might cancel that order and try an Etek-RT. It's got 50% more winding, so it will be torqueyer and won't have to be geared so low.

Plus if you got it from RobotMarketplace you didn't get the best deal, I think. Electric Motorsport and I think Falcon-EV have them for like $450. $525 for the Etek-RT.

wow you are right. i will call them first thing in the morning, since the other one is back ordered. I think i will stick with robo as the are just down the road from me in case i need more help from them
thanks for the help guys

 

[diver]

Crap, i think the rpms are not enough at 48 volts for the high tq motor. Its 2200 verses 3700 for the plain Etek

 

[Drunkskunk]

Crap, i think the rpms are not enough at 48 volts for the high tq motor. Its 2200 verses 3700 for the plain Etek

Looks fine to me. the regular with the gearing toy wanted put you at 60MPH. you want 40, and that would mean a motor RPM of 2500 or so, roughly (unloaded) so thats only a small change in the output gearing.

 

[diver]

Hi Diver,

I bought my Etek-R from Robot Market Palace and having it, is very pain full. If you can buy it directly from electric motorsport (RMP distributor for Etek-R and Etek-RT). You have a better service from Todd. Or you can buy it from Thunderstruck people, Brian he's very usefull and don't bother with RMP if you can.

Have a nice day!
Bikeraider

what do you mean by pain full . I can just cancel my paypal and order it from one of the other supplyers if need be. thanks for heads up

 

[diver]

I was able to cancle with robo, in fact they were great about it. I placed an order with mars. He said it should be here on weds of next week.He said they are selling as fast as they can make them.

 

[Jeremy Harris]

You'll find John at Mars Electric a great guy to deal with. I bought an ME0709 from him (the "Etek RT") and not only did he go out of his way to do a good deal on shipping to the UK, but also sorted out a minor shipping damage problem very quickly indeed.

I'd not hesitate to buy from him again. As the guy that designed, and makes, the motor he's best placed to offer advice and service. His direct sales prices are also either the same as, or slightly better than, some of the resellers.

Jeremy

 

[diver]

I just found this great place for gears and other stuff
http://www.bmikarts.com/1-sprockets-chain-clutches-torque-converters.shtml

 

[Dr. Shock]

I just found this great place for gears and other stuff
http://www.bmikarts.com/1-sprockets-chain-clutches-torque-converters.shtml

And don't forget McMaster-Carr.
http://www.mcmaster.com/