Best amount of sprocket teeth

We are optimizing our drive train and we would like to see your opinion on the best amount of teeth on a sprocket for a 6WD drive train.

We have right now 26 and 12 teeth…

James,

It may help to provide some other details about your drive train such as # of motors and diameter of your wheels. Generally, there is more to it than the sprocket reduction after the gearbox. To help you, JVN from 148 updates his calculator every year. Play with the #'s so they match what’s on your robot, and tell us what your final speed is. Be careful when gearing for high speed though – there IS a trade-off.

Finally, don’t let anyone tell you that 2 CIMs on a drive train is a bad idea – if it’s geared properly, it works just fine (and you can still be very successful).

After you’ve found the desired ratio, use as few teeth as possible so that the weight remains low.

Or use as many teeth as possible so the stress in the chain remains low. :wink:

Remember its not really about the number of teeth… its about the diameter of the gear.

In matched gears this can be equated to the number of teeth.

You want to figure out the ratio you need between motor and output and then figure out a way to get that mechanical advantage…

You don’t have to use gears or teeth at all…you may also have to use several gears to get where you want…(ie gear box…)

Better to think of it as the ratio you want…and not the number of teeth…

Good luck with your design!!

I’m going to go ahead and do that - “geared properly” for a 2 CIM drive with Kit wheels is under 8 feet per second - not very fast.

not sure where you got your number. 4.7:1 gearbox and 2.1:1 sprocket ratio and 6 inch wheels gives you a 13 feet per second top speed.

2 CIM’s can be very effective. My team’s rookie year (2007), we were highest rookie seed, and one of the more effective defensive bots. You don’t need to have a ton of pushing force to be a good bot (offensive or defensive).

4CIM’s is no doubt going to produce a stronger drivetrain.

Everything is a trade off. 4 CIM drivetrain=more pushing ability, but no CIMs are available for other purposes. 2 CIM drivetrain=not pushing anybody around the field, but those 2 motors are freed up to work elsewhere.

I won’t even get into 2009 where less was actually more.

Make sure your chain catches at least 120 degreees of every sprocket. And in general tooth/diameter ratios of more than 3:1 are problematic.

Beyond that just choose sprockets that fit and give you the gear ratio to generate the required torque and/or speed.

I am saying that is not a proper gear ratio for a good performing drive with only 2 CIMs. Of course it is technically feasible with the KoP to gear a CIM faster - I just don’t think you’ll really be able to do anything over 8 FPS.

4 CIM drivetrains, plz

4 vs 2 CIM’s is not about pushing power. It’s about available torque and how you choose to use that torque. You can gear for speed with 2 but will you ever be able to reach that speed, or you can gear for power but can you effectively be able to get the motors spinning up fast enough to apply that power?