im thinking of for my second animated prop to do a skull that rises up and down from behind a tombstone i have a windscreen wiper motor, skull and wooden tomb stone but not sure how to get the skull to rise up and down
A couple of ideas come to mind. You can use a crank arm like on a FCG, but sideways. Have the skull on a pole that is restrained by guides to move only up and down, the attach the crank arm to the bottom. This will probably require more torque than a cam.
In terms of the cam, there is no need for the cam to have a sudden drop off; it can have a smooth transition down, just like it has going up. May need to use a rocker arm to get enough range of motion up and down.
Finally, if you could figure out how to turn the windshield wiper motor on intermittently, that would be great...every 5 seconds or so here comes the skull head!