Let's Make Robots!

Hobby Servo and then...how are large robotic arms actuated?

I'm working on several robotic arms as a hobby.  I've used Hitec robot servos to good results, but I'd like to construct an arm that is strong: capable of lifting 10+ lbs from a 24" arm.   Obviously, hobby servos aren't going to work.

What kinds of servos (are they stepper motors?) are used in larger scale robots?

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Get a windscreen wiper motor and fit a pot or encoder to the output shaft.  The wiper motors from trucks and busses are 24V and have very strong, durable gearboxes.

Wipre motors have the advantage of being relatively cheap, almost silent in operation, have a worm drive gearbox that can hold the position of the arm without power being applied (with the condition that the load does not strip the gears). The only drawback is that they need high amperage motor drivers and that raises the cost greatly.  

http://www.scary-terry.com/wipmtr/wipmtr.htm

The guy says they have 13 to 17 pound-feet of torque.

That seems to be in the range that you want.

An easy way to make a strong servo like that is to modify a cordless screwdriver. You should look at something with at least 250in-lbs. You might need to gear down a normal screwdriver to get that kind of torquet though. If screwdrivers aren't enough, try window motors or windshield wipers.

All of the industrial robots I've worked with have servos that are built into the robot itself. They might be somewhat standardised, but they're not the kind of thing you can just pick up at the shop and use straight out of the box =)

In the end they're just servos made with high quality motors, high precision encoders and very smooth, low backlash gearboxes.

If you need more power you can always build your own servo - find the motor you need to drive the load, add an encoder to get the position feedback, and then add a controller to drive the motor until the encoder says that the target has been reached.
You can do a lot to improve the control system software from there, but in essence that's all there is to a servo.

Take a look at this example for some inspiration.