I've been working on designing and building a heated build platform controller that would work as a standalone device, as well as integrating into the RepRap or Makerbot electronics. It's meant to control up to 400VAC and about 1000W of power using an optically isolated triac which is also protected by a changeable fuse. Temperature feedback is through a Type-K thermocouple being read by a MAX6by Jeremydeath - Controllers
The makerbot (popular rep-rap derivative) currently runs off of a geared DC motor without an encoder, so it is definitely possible, as long as the gearing is high enough. Basically, with the makerbot, you always run the motor at a constant voltage/PWM. This causes the speed to be constant enough that the filament generally comes out at a constant rate and a constant amount. Then, to change the thby Jeremydeath - General
You may also want to consider an Isaac here: . It's a milled derivative of the Mendel, and to me at least it looks like a really good alternative. The parts are made out of a sort of plastic-wood that seems to be really strong. It's still a work in progress, but hey, everything here is.by Jeremydeath - General