I'll put in a good word for timing belts. On 1768, we used 23 belts on our 2016 robot with great success. We used exact center-to-center distance runs with no tensioners and had zero failures all season long (5 events, 86 official matches). We used a mixture of 6mm, 9mm, and 15mm wide belts, depending on the strength required in the application. We used 15mm belts on our 8WD (
picture) with 8" wheels and 60T versapulleys and never skipped a single tooth.
While chain certainly has its place (arms are a great example) and its advantages, properly used timing belts are lighter, quieter, safer, more efficient, require no lubrication, and are completely maintenance-free. Any ratcheting or failure is indicative of a design flaw, not of some unavoidable problem with belts. Whether used at exact distances like we did this year, or with tensioners as we have in the past, timing belts are fantastic for a variety of FRC applications.