For stepper motors of that size, RS and Farnell can supply them. However the these robots often use the same servos the you will find in any hobby grade RC cars and come in a variety of sizes, torque ranges and turn speeds.(those pictured above appear to be futaba by manufacture) I too would love to build one of these. I was trained as a mechanical engineer, my other hobby is RC cars and have a good understanding of the power systems and motors used for this,and have previously built a cybot just for fun... http://lpilsley.co.uk/cybot/graphics/robo-mag.gif My problem has always been that whilst I have the mechanical understanding to build the machine, I still don't fully grasp the software to operate these things. I still have my cybot and would love to have the n900 control it. Shame they never released the software for it.