I am trying to build a lego claw arm to pick up stuff that is out of my reach and I need some ideas on how to design it. I would like a mechanism to be able to open and close the claw from the opposite end of the arm.
If you're after a simple collapsible solution to reach those items just out of reach, you can start with the following setup:
You can extend this for quite some way, and use longer bricks or beams throughout if you wish.
To finish it off, I'd use a couple of longer bricks with some additional plates on the end to act as fingers, and add some handles (via axles) at the bottom. If you use longer bricks at the ends then the middle pin would need to be offset from the centre to keep it smooth.
I built a similar model to Zhaph's claw arm but with beams and a basic claw attachment:
I had a few problems operating the claw when I built it again with real bricks. If you collapse the beams too far, it can be difficult to open them again. When you try to pick up items with your tool, you also have to anticipate just how far the tool extends (try and possition the claw as close to the object as possible, the beams will push the object into the claws).