Details: I've previously featured Sariel's first "hand" model, but he has now created a second one. This one makes use of the WeDo Educational Software. LEGO WeDo is only sold through the LEGO company's educational division (see http://www.legoeducation.us/store/), and is designed to work directly with the Power Functions motor system. A USB hub allows a computer to directly control two of the PF motors. Up to 3 hubs can be controlled with the off-the-shelf software, and 2 hubs were used for this particular model. One motor controls the pneumatic hand itself and the pneumatic compressor for that hand, using an autovalve. Two more motors are used for the turntables (one per turntable) to power the wrist and the base of the arm. The fourth motor controls the elevation of the hand through a linkage that does not tilt the hand. Software-wise, there's a task programmed for the arm and the ability to use the keyboard to control the motors individually.
Details:
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.
Details: Here's a nifty LEGO MINDSTORMS NXT-based robotic arm. It uses a slider mechanism to keep its hand at the same angle at all times (which makes it easier programming-wise to determine the hand's locations). I'm surprised by the way that the center-of-gravity is kept in place by a wheel-based counterweight instead of with an actual LEGO® counterweight brick.
I've previously featured Sariel's first "hand" model, but he has now created a second one. This one makes use of the WeDo Educational Software. LEGO WeDo is only sold through the LEGO company's educational division (see http://www.legoeducation.us/store/), and is designed to work directly with the Power Functions motor system. A USB hub allows a computer to directly control two of the PF motors. Up to 3 hubs can be controlled with the off-the-shelf software, and 2 hubs were used for this particular model. One motor controls the pneumatic hand itself and the pneumatic compressor for that hand, using an autovalve. Two more motors are used for the turntables (one per turntable) to power the wrist and the base of the arm. The fourth motor controls the elevation of the hand through a linkage that does not tilt the hand. Software-wise, there's a task programmed for the arm and the ability to use the keyboard to control the motors individually.
-based robotic arm. It uses a slider mechanism to keep its hand at the same angle at all times (which makes it easier programming-wise to determine the hand's locations). I'm surprised by the way that the center-of-gravity is kept in place by a wheel-based counterweight instead of with an actual LEGO® counterweight brick.
