Android 12 REV B Leg Modifications 2
This page is about Android 12’s Revision B leg parts, check out the project index for the rest.
This page continues from the REV B leg modifications page to show the replacement parts for Android 12’s legs. All the REV B parts will be printed in red plastic.
As I mentioned in the last part, the original knees look a bit weird, and also now I can control the joints properly I’ve found that they don’t hinge in the right place. Mostly the leg doesn’t get any shorter when the knee bends because it ‘drops down’ due to the off centre hinge, and also they don’t bend far enough.
My plan now is to use an additional linear actuator on the back of the thigh, so I can use one actuator for the thigh and one for the knee. The new knee has the hinge point slightly forward of the studding that makes up the leg, and also plenty of clearance for the actuator lever:
I also found that the chains in my linear actuators won’t stand up to the forces required. After a little testing I found a couple of the chains had apparently stretched – a few of the links had opened up and some had buckled. I’m now going to try steel reinforced toothed belts. This requires a re-design to the carriage part of the actuator as well as new sprockets/gears for the servos. The front thigh linear actuator now operates the knees with an additional lever:
Here are the pieces printed and installed:
And the whole assembly: