yea the educational tamiya stuff is ok, but not real durable if your looking to move some heavy material. Could look at some gear head units or depending on the size of the machine these gearboxes we use in 1/16 r/c tanks are real nice. Sabertooth ESC's work well and have different models.
https://www.servocity.com/motors-act...ty-gear-motors
http://robotmarketplace.com/products/motors_geared.html
http://www.etoarmour.com/product_det...?productID=S04
http://www.dimensionengineering.com/...bertooth2x12rc