I'm looking for suggestions on a Halloween project I'm working on. I want to combine a talking skull with a tombstone popper. I have the prototype of the talking skull working but I want to give it a bit of a twist. When triggered (by a parallax PIR sensor) I would like the head to pop up from behind a gravestone then say something, then pop back down to hide. The jaw servo is being driven by a Scary Terry audio servo controller board with audio supplied by a VMusic2 usb mp3 player.
The mechanics of a gravepopper that makes a full up/down cycle can easily be accomplished by using a windshield wiper motor. But pausing the cycle in the up position for the time required to deliver his saying is what's a problem for me. A pneumatic piston would work but I'd rather stay all electrical if possible as I'm much more comforable there. So my question is has anyone done anything similar to this and can offer advice?
My best idea at this stage is to drive a 12vdc motor with two limit switches (one for the up position and one for the down position). Imagine something like a wheel with a bump on it to activate the switch. The wheel would have to be connected to a piston of course for the up/down linear motion. That might work and it would avoid having to reverse the motor - just turn it until one of the switches were triggered. The weight of the skull I think should be under a pound and I only need a displacement a little more than the height of the skull - maybe 10" or so.
My second thought would be to use a stepper motor. This would give me greater control over the prop but would require a bit more programming up front. BTW I am controlling everything with a PIC18F4550 so I've got plenty of I/O and programming space - I just want to keep it as simple as possible.
Any advice or suggestions are appreciated.