Optimal Gear Box For Motors

How might one calculate the optimal gear ratio for a task. For example our team is making a “tennis ball shooter”. We will be using the standard 217-2000s that came with the kit, but how do you calculate the best ratio for it to work? (rookie team here).

I’m not sure if you’re asking for an explanation on how gear ratios work or what gearboxes work for different things. Could you please clarify?

Figure out how fast you want to perform the task, then use that to figure out how fast something needs to move or spin. Then compare that speed to the motor speed, and assume that you want the motor to run at about 80% of it’s “free” or maxium rpm, so it will be operating efficiently and not loaded too much. Then calculate the ratio needed to do that.

often you will have some type of chain or belt drive involved, and that means you need to figure out the size of sprockets or pulleys also.

It’s a complicated process, and gets easier with experience. If you provide a lot more details about what it is you’re trying to do, we could probably help you better. Don’t worry about someone stealing your ideas…if they’re good ideas, then imitation is the sincerest form of flattery. If they’re lousy ideas, we’ll let you know, so you can work on finding a better idea. win-win!

First, look at the motor data sheet FIRST provides:
http://www.usfirst.org/sites/default/files/uploadedImages/Robotics_Programs/FRC/Game_and_Season__Info/2014/2014_Motor_Information.pdf

Then figure out, for your design, what the final speed you want to go… the final ratio you want is the multiplier that makes the free speed about the same as your desired speed (but please note… free speed <> speed under load. If you want it to be that fast under load, give your self a buffer and gear it for a faster free speed than you really want it to go).

Also for reference, 217-2000s are usually referred to by their name, CIM motor. The same for the mini-CIM (217‐3371) and the BAG (217‐3351) motors.

Another thing to note that the “217-2000” motor that you are referencing to is usually referred to in FIRST as the CIM. It’s a lot easier to ask for “CIM gearboxes” than “217-2000 gearboxes,” since many people will have to look up what motor corresponds to that part number.

Other than that, heed the advice given by others on this thread. Andymark and Vex Pro both have a wide selection of gearboxes that can suit your needs well.

[EDIT]: Jon Stratis beat me to it. Darn me for having to consult the rule book.:smiley: