Pretty sure speed 700s are high revving. As in, vastly higher than the clone s900s you had in there before. Also not sure if they are happy beyond 12v, they're optimised for that voltage range. Also they are timed for one direction, I think. I'd be surprised if they ran the robot at all happily. Torpedo whatchacallsits would be a safer bet, possibly cheaper and unless the bolt pattern is different to s900s essentially plug-n-play.