Specification for timing belt pulley on large CIM?

Subject says it all: What are the specifications of the belt that mates with the pulley.

On a related topic, where would I purchase belts and or blank pulley stock to match (3" in diameter, say, hmm, 21 inches long).


I’m bumping this thread. I’d also like to know the timing belt needed for the large CIM.

In another thread, Paul Copioli posted that the supplied timing belt pulley is 16 tooth, 3 mm pitch and 15 mm wide, matching the PowerGrip GT 2 Series available from Gates.

What FP product did this motor come off of, and how was it used? I am having trouble visualizing how the assembly would work installed in a power wheels vehicle. It seems if the belt breaks, the metal bar would slam into the
the shaft, and grind a nice groove while placing a no-no side load to the shaft.

Also, I was always taught that belts are fairly inefficient as a method for transferring power, especially for a vehicle. Maybe FIRST got all these motors
because they were recalled! :rolleyes:

But that aside, they look like they can do some heavy lifting. Gear these babies right, and you’ll be able to launch your entire robot through the center goal.

Well, the pulley it uses is for timing belt, greatly decreasing, if not eliminating the amount of slip on a conventional belt drive. What I’m having trouble envisioning is how they mounted the wacky thing. I can only imagine a cnc’d hole, with setscrews holding it in place.

  1. Timing belts have no slip and are very efficient, quiet way to transfer power. They don’t stretch either so they transfer shocks even more efficiently than chain - which is a design consideration - you might need torque limiters, for example.
  2. The large CIMs have less overall output power than the small CIM, look elsewhere in this forum for details. Their main attribute is 1/2 the shaft speed and probably a much higher sustained output before overheating.

the real question is why even a belt pulley??? most teams use chain and sprockets on thier robots, to much tension on the belts and they will rip. the only use i see for the new chips are for like trap door applications, or sliders, and other slow, but torquey situations.

Most belts are reinforced with a fiber or cable that makes them extremly torque capable. These are not sanding belts

Or dress belts

They’re are reinforced timing belts, meant to replace chain drives. And the MiniBike CIMs run at 2500 rpm, so its going to take a large bit of reduction to put them into a “slow, torquey situation”. Though they would work well for stating a flywheel…:wink:

ok i found the correct belt for this thing but how about the pulleys? where can i get 3mm pitch, 15mm wide pulleys?

neither mcmaster or grainger has them which is pretty amazing, because there arent that many things that neither of these two companies carry.

if thats not possible are there any gears or pulleys with a flat side, to put in place of the existing pulley on the big CIM?


Try Stockdrive Sterling NY. spd-si.com
Great people, good service, lots of hard to find stuff, :slight_smile:
They have pully stock too!
Have Fun!


I too love SDP, and this was the first place I looked for pulleys. However, unless I’m missing something the largest width pulley they offer in 3mm pitch is only 9mm.