We are using 4 CIMs (2 in each Toughbox). According to the AM TB specs, the gear teeth go 14, 50, 14, 50. The sprocket on our output shaft has 15 teeth and the sprocket on our wheel has 28 teeth.
I was wondering if I filled in the chart below correctly, because if so, we are going to need a lot more speed lol.
what range of speed are you looking for? 10-12 fps?
at least, hopefully closer to 15 (we are using a car steering mechanism so we won’t have to slow much during the match)
It looks right from what you described as your set up. But to get the correct torque values you need to change your weight and your coefficient of friction if you haven’t already. While that won’t change the FPS calculation it could cause problems as well.
Ok thanks Phyrxes 
If I remember correctly from my students doing our transmission math the standard output shaft speed is around 9.5 fps so if you were going for say 15 fps you would need around 2:3 ratio on your output shaft to wheel gears/sprockets.
You will probably need a larger output sprocket on the transmission to get the speeds you want. Last year, we used the AM single speeds (same ratio as the ToughBoxes) and had to go up to a 21T sprocket from Small Parts on the output to get to ~8ft/s. To get to 15ft/s you would actually need to gear up from the transmission output to the wheel. Something like a 1.73:1 gear up should work for that.
1.73:1 is a decently sized gear up (well, at least for going from the tranny to wheels), so you may want to consider going to larger wheels. If you want to stick with 6" wheels, an aluminum output sprocket is probably in order (a steel one large enough to get that gear-up would be really heavy); unfortunately, aluminum sprockets with 1/2" bores and 1/8" keyways are hard to find (assuming you’d rather not broach your own keyway). To that end I’ll leave you with links to two parts that can solve that problem, but how to do it is left as an exercise for the reader (it’s not that difficult, you just have to think creatively) Link 1 Link 2.
thanks much Luke
we have a meeting tomorrow morning and I’ll show our team these
We’re removing the second reduction stage in the KOP transmissions, so it is only a 3.57:1 reduction, and adding more reduction on the chain drive.
The change seems to be easy to make, you have to flip over the aluminum plate (to get the right size bearings in the correct place) and punch new holes in it to clear the ends of the CIM shafts, and add a washer next to the roll pin to keep the big gear on the output shaft from moving sideways too much. Looks like a common modification.
Interesting idea any chance you have pictures you can post?
look at the pictures that 1662 recently posted of their robot, they did this too…
Today we threw our 42 teeth aluminum sprockets on the output shafts and kept the 28’s on the wheels. Calculations show that we should get about 14 fps, and that’s about what we got in testing today
Thanks for all your help