# Gearing down?

Hello my team is trying to gear down the chiapua to exactly 100rpm. Does anyone know how we could do this with the gears they have at McMaster?

We kept getting stuck at a number higher or lower than 100rpm.

What are you trying to do?

At what LOAD and at what VOLTAGE do you want the Chiaphua motors to run at 100 RPM’s?

If you want them to run at 100 RPM you could certainly put enough friction on the shaft at a low enough PWM value to have them run at 100RPM.

If you want there Free speed to be 100 RPM you need essentially a 55:1 gear ratio. This is not terrible hard to get, though EXACTLY that is a bit tricky but doable.

In the kit you already have a 44:9 ratio.

Try this:
(44/9)(72/16)(60/24)=55/1
Viola!

First stage:
44:9 36 DP from the motor and the gear cluster from Atwood

Second stage:
72:16 – use a 72T 32DP gear from McMaster and the 16 tooth gear connected to the 44T from the kit.

Third stage:
60:25 – use a 60T and a 25T 24 DP gears from McMaster.

I don’t know if you actually need the ratio you wanted but there you go.

Joe J.

P.S. The gears are sized about right to give you a nice long gear life – you may check the last stage, the stess on that one MAY be a bit higher than you would like.

Joe J., I hate to expose my level of ignorance in this area but are there any tricks to calculating which gears and how many stages you use to arrive at a desired rpm? Do the number of stages (ie. 5 vs 3) make a difference-- will more transmit less strain back to the motor? Do you pretty much just plug in a gear tooth size and do the math?

I ask these questions for two reasons. First, I saw the above post and wanted our Chiapua’s to ultimately turn a drive shaft @500 rpm’s free-load (assuming a 30% or so reduction with load). Doing the math I could probably figure out the gears but am not sure if I need “x” number of stages because of stress factors throughout the gearbox. Second, I don’t think that you want to be doing these calculations for even a small percentage of the 670 teams who would like the numbers.

Finally, THANK YOU for moderating and sharing as much as you do. You make it do-able for many who would otherwise be floundering at low tide!