Quickest design information is from
http://www.york-ind.com/ They have easily downloadable synchronous belt design software. Here is the bottom line:
The belts are very strong...take one you are not going to use and give it a static test. For FiRST applications the drive limiting factor will be the sprocket to shaft attachment, not the strength of the belt. You must have at least 6 teeth in mesh with the pulley and the belt must be tensioned so it will not jump teeth under the most severe load it might see in service. Also, do not crimp (bend the belt tighter than the 16 groove pulley) or you will break the belt tensile member. Also, catalog belt ratings are set up for drives lasting hundreds of hours in industrial applications. A FIRST robot application can be run at least 3 times catalog ratings. Once again the shaft attachment and the tension is the limiting factor.