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Alekseev_D

Robot arm or foot

by Alekseev_D Apr 6, 2011
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I like this! Well done. Most robotic arms on this site seem to keep the servos at the joint. That adds extra weight, and thus lifting power. So I set out to make an arm with the weight at the base. Imagine my surprise when I found you have already done this. Hurrah!

Looks cool in the video!

What size of servo is required and where are the original CAD-files you exported the STL from?

the youtube video looks really interesting, really looking forward to the instructions. I'm curious how you ran the strings to get that motion, but I can wait... :) Nice work.

Well done Alekseev

Correct me if I'm wrong...

There are loops around each pair of pulleys. Since the pulleys on the arm are all the same size, all of the pulleys that are looped together will keep the same orientation relative to the ground. So the red pulleys all turn in unison when the red servo moves. The green
pulleys respond to the green servo. The thing that makes it look magic, is that the red pulleys don't rotate, even as the green pulley moves the green joint.

The pulleys on the servos are larger than the pulleys in the arm, this was probably by design. It makes it so that the arm joints have a larg
er range of motion than the servos.

Pretend that the strings around the blue pulleys are blue.

If there was a set of pulleys that went all the way to the foot, then the foot would keep the same orientation too. This would look cool. Not sure it would be useful.

Fish line (strings) loops only joint 2 pulley transit.

Others are connected as shown in the photo.

When turning the green joint need rotate red servo that-be the angle between the red and green joint has not changed. Larger diameter servo pulley to do just that.  

 Yes strings around blue pulleys should be blue.  

 Servo removed from the arm - it was interesting and may be useful. Robot walking through puddles   :)