How about using linear actuators to drive a robot arm instead of stepper motors or servos? The big 340+ oz/inch servos cost a fortune and are incapable of lifting a measly five pounds with an 18 inch arm length.
12V actuators are down to $59 on feeBay and that's less than the price of the large servos.Of course an actuator would weigh a lot more than a servo but so what - they lift 300 pounds. Heck, you could jack up your car with it.
Caveats I see is actuators are a lot slower and eat current. Full extension on an actuator is maybe 45 secs and they can draw 5 amps but I suspect that lighter loads would not consume so much.
Any thoughts on this infallible idea?
Pokey.