I'd like to build a robotic arm capable of lifting five pounds. The shoulder and the forearm will each be 24" long. It's to be run by a friendly PIC 16F628.
I like the idea of using RC servos to move the arm but the strongest servo I can find is the Hitec HS-805BB which only has 343 oz/inch of torque. I discovered that this means it will lift 343 ounces of weight with a one inch lever. Since my robot arm will be 24", that means it will be capable of lifting 343/24 = 14.29 ounces which is less than a pound - far short of my five pound goal.
Assuming my calculation is correct, what I need are some suggestions. These big servos are pretty expensive, about $50 a piece shipped. I did come across a servo gearbox for $50 that would give it a 5:1 increase in torque. That would get me close but that's another $50 for the gearbox and I would need two - one for the shoulder, one for the forearm.
I've not had much luck locating gears.
What have the arm builder's on this group done to solve this problem on the cheap? Or have you all shelled out $200 on servos? Or have I miscalculated the torque needed to drive the shoulder and/or forearm?