Sunday, February 12, 2012

Week TechVideo, 2012 #06 - LEGO Prosthetic Arm

It is not the first time we share magnificent attempts to replicate the human hand (with or without the respective arm) by several builders, using LEGO Technic or MINDSTORMS [1, 2, 3].

Today just another great example, which takes the challenge some steps further, with amazing results.

As the author (Max Shepherd) explains in the video description,

- Hand movements and wrist abduction/adduction are controlled with LEGO pneumatics.
- Wrist pronation/supination, wrist flexion/extension, and elbow flexion/extension are controlled with LEGO motors (Power Functions).

The main purpose of this project was to accurately mimic the full range of motion of a normal human arm and hand. The secondary goal was to maximize speed and power, yet maintain a consistent ratio between the two for demonstration purposes. It is important to note that it was designed as an above elbow prosthesis, and the yellow shoulder is only meant to act as a static model.


Marin said...

Too bad we didn't see any "cool" signals like \m/ and the finger but that fist bump in the end was great.

TechnicBRICKs said...


santi said...

Quite impressive!! I see that for some movements, the author selected linear actuators, whereas for some others, pneumatics was used. Of course, for fingers, pneumatics is a better choice, since you avoid all the space for axles and gears. But I'm curious as to why did he choose pneumatics for some of the pistons that can be seen in the arm

Jetro said...

My guess is that it is to do with response times, forces and precision. The fingers appear to work as a single continuous mechanism powered by pneumatics alone and so this choice makes much sense.
For the wrist movement, with LAs it is a lot easier to get precision control.
I'd love to see how exactly it is all controlled.

nockawa said...

I wish TLG would make motor with more power/efficiency to make this kind of MOC yet more real...
Congratulation to the author!

Allanp said...

Awesome model, I think it just needs a better compressor and one or two tweaks to the fingers but I love robotic arms/hands because there are so many different movements you have to make happen and so it's a good challenge. He accomplished it very well, one of the best i've seen.

Max Shepherd said...

Thanks for the nice words guys.

I chose pneumatics for the radial/ulnar deviation because not as much precision was needed; the range of motion was relatively small. The wrist flexion/extension, however, has a range of motion of about 130 degrees, so for every small step of the linear actuator, a relatively large step is taken. For the elbow, six pneumatics and two linear actuators were used together, with the linear actuators helping with the control and the pneumatics adding more power. One of my goals was to get the motors as far away from the hand as possible since they are so heavy.

The fingers have the same "self-actuating" mechanism as the one that is shown squeezing a blue air tank (the old site that explained it no longer exists) except that these have three joints, not just two.

As you could probably see, the abduction/adduction is controlled by an XL, the wrist by two mediums, and the elbow by two mediums (plus those pneumatics).

I did not do an advanced control system since this is a model prosthetic arm, and real prosthetic arms are controlled with biopotentials (or related) and not but some guy moving his arm also. That's more Raytheon Sarcos type stuff (also cool).

Let me know if you guys have any other questions, this and Tinkernology are really all I follow.


TechnicBRICKs said...


Thanks for coming here and giving these explanations.

Keep the great work!

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