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Building a robotic arm? Answered

In Science next term, we've been told that we'll need to build a robotic gripper.
All it has to do is pick up a cup.

I've been having a look around, and the balloon idea isn't practical because if the cup was full it wouldn't work. And I'm okay with spending a little money, but I'd rather not spend $100 or anything on a kit.

So what's a good idea for me?


In the rcx manual it shows you how to make a robot arm out of legos earn paypal money online to get this cheap on ebay.

My son built a robotic arm for a science fair a good 6 years ago, and he based the "hand" portion on a generic "long arm" grabber. His arm uses threaded rod (coupled to electric motors) and sliding nuts to do all the actuation.

His "arm" has a total of 5 axis: torso rotation (L + R), shoulder lift (up + down), elbow bend (close up  + extend out), wrist rotation (L + R), and hand grip/release. For the hand grip/release, he ended up using threaded lamp tube to allow the actuation rod to move back and forth while letting the wrist spin. Structure was built from perforated metal strip, bought at Sears Hardware, bent to shape and held in place with bolts/nuts (most of the "hardware" came from Sears). Motors and couplers, switches and battery packs came from Jameco. All in all, I think the total was about $80. If you only need a hand and shoulder, you can cut the cost way down.

If you want more info, PM me.


the jamming baloon idea ...does...work with a cup full of liquid - and can lift several pounds; problem?

Wooden hand operated by pulling strings - you can even do this with cardboard assuming the cup will be paper or plastic. all you need is the gripper

see here http://www.sciencetoymaker.org/robothand/assembl.html