We’ve been working on an art collaboration, and have built a drawing machine based around a pantograph and a rotating turntable. It produces a Spirograph-style pattern, which can be tailored by changing the arm length, pivot point, rotor speeds and turntable speed. The build is a prototype, and can be replicated with power functions motors, rcx, Nxt kits, or even old school technics kits. A build video will follow, but check the time lapse for a quick overview.
We used the power functions speed controller remote so that we can control the rotor speeds and directions, as opposed to the digital remote which only allows full on/full off. If you were to replicate this build using NXT, you would have to set the Servomotor speeds in software, and then execute the program. You can see in the video above that Shorna changes the drawing pattern at 0.08 seconds in the video.