[magnets]

Good point about the counterbalancing.

You'll still need to worry about bearings and loads from hitting the arm sideways. If you can find any good pictures from 2005, when we had to lift those heavy tetras, you'll see some pretty cool double-tetra arms. There were also plenty of bad arms too.

A few pieces of advice:
I agree with Adam about getting a good fit. You don't want a sloppy fit anywhere in the big pivot. If your pivot is huge, you can use SilverThin bearings, which are pretty neat.

How the bearing is retained by the frame is just as important as the bearing itself. You should try to get the entire length of the bearing supported. It puts a lot less load on races. That being said, most of the bearings you'll look at are much stronger than they need to be, so you might be able to get away with only partial support. If your arm is very long, you'll have to worry about people pushing on it from the side. There can be an incredible amount of force down at the pivot. You may want to use thrust bearings here. This was a killer in 2005, when teams got tangled in the towers.

A common mistake seems to be making pivots that are well supported for carrying weight, but are very weak when pushed on from the side. They often "parallelogram", or just twist and deform due to inadequate support.

Check out CAD models from 1114 and 118, who both had great claws.