[Dick Linn]

Planning on jumping up on the platform from the 6" side, 4 WD otherwise, eh? My guess anyway.

Maybe a 12:35 on the 12.5 inch wheel and then come off that axle with a 15:12 to the 10" wheels to step them up 1.25 x. This should get you in the ballpark of 6-7 FPS (I seem to recall drills in low was around 360 rpm, maybe lower when accounting for friction & etc.) If you can find a dual-chain 12 tooth sprocket it wouuld be lighter. If you use separate sprockets, the 12 tooth sprocket on the drill tranny can be changed out to most any number of teeth from 10 on up to balance speed and pulling power. Make sure you get exact wheel diameters under the loaded conditions before finalizing the gear ratios. Tire pressure will be important.

Lots of sprockets = lots of weight.