I started roasting coffee a couple of months ago on my Kitchenaid gas grill. The K/A rotisserie kit works well, but it's too slow for roasting coffee, and the beans can get roasted a little too much if you're not careful.
I found this rotisserie motor on Amazon that seemed to be the fix for this problem. It arrived today. It's a variable speed motor that runs from 13 to 55 rpm's. And it fits perfectly on the standard Kitchenaid mounting bracket. It seems a well built moderately heavy unit, and it worked flawlessly on my first attempt with it this afternoon, roasting some green Columbian beans very evenly. It can turn 30 pounds on a balanced spit, more than I'll ever need to spin.