# *Project* Building electrical (robotic) arm. Need help!

## Main Question or Discussion Point

Hello, I'm an electrical engineering student and I've decided to build a robotic arm as a final project for one of my classes.

Basically, my skills as far as building circuitry and solving electrical problems are at an intermediate level at this point, however, I'm not too familiar with the mechanics of building a movable arm.

Anyways, before I start anything I want to simply build a clamp that closes and opens with an electrical circuit. More specifically, I want to create a motion that is similar to a toilet seat rising up and coming down.

I think using hydraulics to achieve this would be best, but any other suggestions are more than welcome.

So anyone with any tips as to where I can start or how I can go about making the clamp... please share!

(By the way, if something like what I described is available to purchase online and someone has a link to it, then it would make things much easier for me just to buy it!)

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Danger
Gold Member
Welcome to PF, Milkisgood.
Unless you need significant power, hydraulics is probably not the best way to go. It's expensive and bulky. You'd be better off using electric servo motors.

The easiest way to go is using a servo, and generate a fitting PWM wave to control the circuit, you can use a 555 timer to hack a pwm together, or if you want something fancy, you can get a PIC18f4331, those have about 8? if i remembe correclty PWM's.

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I can't imagine a servo being powerful enough to lift a loo seat up directly!
It depends on the control you want and the speed.

If you're happy with a slow action, a motor with a either a rack and pinion arrangement or a worm gear would suffice. For accurate control, use a stepper motor.

If you want a fast open or shut then a powerful electromagnet may do the trick. There's a lot of overhead to running hydraulics or pneumatics, but they would certainly give you the power and the speed to catapult a sitter a fair distance :-)

If you can reduce the angular momentum of the thing you're moving, the less torque you'll need to get it moving.

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Oops, just reread your post, and I think I got the wrong end of the stick regarding size.

Have a look at 123 robotics experiments for the evil genius by Myke Predko. Not a great book, and a bit dated, but from scratch he shows you how to build a robot arm using servos, including the grabby thing.

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Danger
Gold Member
While it might not be big enough for the intended purpose, I've successfully used a bicycle brake caliper as a gripper (it even has a non-slip contact area). The 'opening' spring needs to be removed, though.

Oh god, sorry, another mistake. The book I meant was PIC Robotics: A Beginner's Guide to Robotics Projects Using the PIC Micro by John Iovine.