Attempting the impossible

Originally Posted by ratdude747

from experience, chain tends to have always worked, but belts tend to be way too much trouble.

one of our mentors used to be on a wisconsin team (fondy fire). being from there, he told us something we should have followed: "team 93 once tried to use belts. there is a reason why they never have since."

better yet, i found that someone from there said it here on CD on another thread:

The only belt failures I have come across in FIRST are an improperly tensioned, aligned, or designed system. Belts can be stronger and more precise than chain when correctly executed. Please run some numbers, and examine the use of belts in applications other than FIRST, as we tend to be a fairly trigger happy bunch at discarding solutions.

reasons to ban the belt from your drivetrain;

1. belts have a lesser surface of contact. therefore, they skip and slip under less torque

A correctly designed belt (the ones for high torque applications, ie part # 6486K116 from McMaster) will hold about even, if not more than equivalent sized chain (#25 in this case).

2. related to #1, belts are harder to tension as belts stretch at a faster pace.

Incorrect. A Steel Belted belt (ie anything by Brecoflex) will not stretch under FIRST loads. Examine Outback Tracks as an example.

3. weight- belt sprockets are HEAVY. unless you have access to a CNC or a very precise mill and operator. if not, you will pay a weight penalty.

Again, false. SDPSI sells aluminum pulleys that are fairly lightweight, and can be hand lightened if need be. Proper design of a robot (ie proper weights set during design, and so on) should allow decently heavy pulleys (up to 1lb) without penalty. Being overweight is a result of sloppy design, and nothing more.

4. length- chain can be made shorter and longer, belts cannot.

This one has merits, but again points back to design. If you need that much variance in the design, you shouldn't even be looking at belts.

in the long run, it seems that belts are better in high speed, low torque situations. Chain is for lower speed higher torque situations. unless your wheels are <2" diameter, you can almost always count on high torque. and hence why belts never worked for us.

I've built a 200lb robot that has pulled a FORD F150 in first gear (engine off) that ran entirely on McMaster timing belts. High torque can be achieved with belts.