motor/gear ratio

if i wanted to make our robot really fast do i gear it up or do i find a different motor?

You probably want to gear it up, and if you only have one CIM motor per side you probably want to add one more per side (assuming you don’t have any more of them on the robot already, because you can only have 4 maximum). If you’re using the kit Toughbox transmissions, it’s not too difficult to remove the second stage of gear reduction, then play with the drive chain sprocket sizes to get the overall ratio just right.

There are a few ways to make your robot go faster:

-Larger (though not necessarily wider) wheels
-Gearing up, either in gears or (probably easier) sprockets

That said, there are upper limits on that. You’re always trading off top speed for acceleration abilities, and demanding too much torque from your motors (read: more than they can put out at stall) is a sure-fire way to trip breakers. The often-used rule of thumb around here is that a robot should be able to slip its wheels when pushing against a wall on carpet. If you want to be able to go faster than that condition allows, you’ll need to integrate a multiple-speed transmission.

If you’re really up for number-crunching, try JVN’s spreadsheet on the topic. Ask around on anything that’s fuzzy, and you should get the answers you need.

Doing this took us about an hour while pits were closing on Saturday of Silicon Valley. AM made it very easy to remove that second stage.

If you want to know how I can go over how to do it from memory

here what we use, to 1:6 ratio in tough box, out of tough box a 24:36 ratio to the wheels, our wheels are 8 inches in diameter, 2 cim’s per tough box, we get good accleration, and a descent top speed, we would be better but were to wide…

A. John’s white paper rocks, although I prefer his earlier one (http://www.chiefdelphi.com/media/papers/1469) because it provides plots for acceleration, velocity, distance, current draw and such.

B. Be careful in speeding up the drive train a lot because it’s very easy to make a drive train the won’t turn. The exact number is dependent on the type of wheels being used and where they are located. I’d suggest that upwards of about 10 fps and you need to put conscious thought into this problem. This white paper on turning is quite helpful http://www.chiefdelphi.com/media/papers/1443
If it’s a 4x4 drive train this supporting spreadsheet may be helpful http://www.chiefdelphi.com/media/papers/1917

C. Finally, with super high gearing it is very easy to give up some initial acceleration to win the 30’ lane sprint… for the first half of the match. The second half of the match can be spent motionless with a dead battery. Again this is extremely dependent on the type of wheels and their location, but I’d suggest that anything higher than 15 fps starts to run this risk.

D. Go Fast, Turn Left!!!