Thursday, March 4, 2010

Mechanical Arm

Name of Model: The Hand
Created by: Sariel
Found at:
This human-size arm is an extremely unusual feat. Done entirely with off-the-shelf LEGO Technic parts, it holds it's own weight and can maneuver well enough to pick up objects. You can get an idea of the strain on the parts by looking at the overhead view - extra battery packs are acting as a counterweight, and you can see how just one linear actuator holds the weight of the arm. The video is what really makes this model so dramatic - you can see that the parts have little problem handling the loads. Frankly, as nice of a model as this is, it almost feels like an advertisement for the newer Power Functions motors, linear actuators, and pneumatic parts. The older pneumatic parts show up in the hand itself, used as a way of closing fingers while limiting the amount of force used to grip. While the claim that this was built in one weekend might appear suspect, I'd argue that this is clearly an example of what you can do quickly if you've built up a decent collection of parts and have a good idea of each how to appropriate us the various elements. The use of the strong linear actuators in certain places allowed this arm to be much more stable and powerful than it would have been with geared joints or pneumatic actuators in the upper arm. Using pneumatics to limit the amount of force for the grip was a pretty clever trick, but not one quite as intuitive as using torque-limiting gears.

The important skill that allows people to build models like this quickly is knowing the strengths of each part. There's really no replacement for just messing around with elements you're not familiar with and seeing what they can do. That, kids, is what you should tell your parents when they ask why you never did finish building that big Technic kit.
No, seriously - I learned how to use pneumatic parts in the first place by "failing" to "correctly" assemble an 8868 Air Tech Claw Rig. Ironically, my parents weren't convinced it was a good idea until I built my first large mechanical arm - which couldn't be mounted in a human manner because pneumatics wouldn't be able to handle that much weight.

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