3 questions about a basic robot arm design

[123laurens]

so I want to add a robot arm to my...well, robot, and I'm trying to make it cheap. I tihnk I'm going to use 2 of sparkfun's servo-medium for the base- for panning and lifting/lowering the arm, and another servo at the end of the axle to make the robot arm point down. kinda like this:

Code: [Select]

         O
       / |
     /   ||
   /     |
 /       |
O        *
with the bottom O being the base and the top being the pivot. I made it like this to make it easyer to control.
the || on the robot arm is where a rangefinder will go, to prevent the robot arm from trying to lift the robot, breaking either the robot or the arm. it's also the main sensor on the robot, as the arm turns and faces forward while the robot is moving and the arm not in use. it's final use is to detect objects near the robot to pick up while the arm is in use.

now, I have 3 questions based on the above:
1: robot grippers seem hard to make and expensive. is it possible that for my first robot arm, I use an electromagnet?I have one lying around from a fisher technic set, and I hope that that doesn't use too much power. would it bee a good idea to power this with the microcontroller's power? probably not. if not, how about a relay and have the electromagnet be powered by the servo power supply? if that is still too much power use, maybe a separate power supply for the magnet entirely? it is it just a bad idea?

 2: I still have sparkfun's servo-small witch I used to swivel the IR rangefinder around. is this thing strong enough for the final pivot (the top O in the drawing) and if not, would it work with a counterweight? or should I just get another medium servo?

3: finally, would this overall design actually work? is the medium sparkfun servos enough to move the arm, with or without counterweights? I'm trying to go for the cheaper approach, I don't have so much money and I've already spent quite a bit.

thanks in advance!

[rbtying]

All of this really depends on the length of the arm: remember that torque = F x r, and that the only source of torque on each part of the arm will be the servo. If you keep the arm segments short, then a servo might be able to handle it; if not, then you'll have to gear the servo down or do some other manipulations to make it work.

As for the gripper, it's fairly trivial to make a simple gripper from a servo and materials around the house. An electromagnet may not be able to pick up much, and you'd certainly need to run it through a relay or transistor from the unregulated power supply.