I just built this synthetic mechanical bear for SONIC BOOM record store here in Toronto. They were installing the static bear anyway and I happily got roped into making it move! This was the largest (physically speaking) project I have tried so far and it come with new exciting problems. The bear is made of hard-packed foam which is light (but heavy!) and fun-fur. We severed the head and arms and I placed surplus 12V power window motors in the armpits and neck attached to simple cams to create the movement. This allowed a single power-supply and was generally simpler than directly driving the arms with a bi-directional control system (we were on a budget). There is a 555 clock cycling two 4017B decade counters, one doing a full ten count and the other looping at seven. The chosen outputs (say 1 an 4 from the 10 counter and 2 and 6 from the 7 counter or whatever you like) pass through an inverter and then switch transistors on/off which in turn switch the IRF541 Mosfets which feed power to the motors. So there are 4 transistor/mosfet switching lines - head, jaw, left arm, right arm. The count sequence doesn't repeat until 70 movements due to the phasing of the 7 and 10 counts, so there is a lot of variety of movements making it seem less "dancing Santa" and more "sleeping Frakenstein". I am powering everything with a PC power supply (5V for the cmos and TTL stuff, 12V for the transistors and 5V for the motors). I used 5V for the motors instead of 12V to reduce the RPM as the bear was looking frantic and too ANGRY (also would have shaken itself to bits). The PC power supply I modifed is capable of providing 28A and that should be able to handle even the worst case scenario (all limbs stuck due to friction or human interference).
