Crab Claw Improved Design

Mon, 25 Nov 2013

After a few frustrating day struggling with dead hard drives and faulty motherboards I’m finally back to paper craft. Just remember folks, back up, early and often. I was glad I had!

I’m happy to return to the crab project. The good thing about being elbow deep in backups and restores is the time for reflection as the progress bargraph creeps slowly across the screen. I’ve thought of a couple of changes to try out. First of all, I’ve decided to fix one of the claws rather than having both moving. The tendon now pulls against the larger claw. The other change is to the tendon placement.


Currently the tendon runs through the centre of the arm. Here’s the problem. Because the tendon is flat against the joint there is no leverage. Pull the tendon and the movement of the claw is sudden and jerky. I’ve solved this problem in earlier projects by lifting the tendon from the centre line using triangular section blocks at each joint. That said, I’m always on the look out for ways for simplifying mechanisms.


How’s this? I’ve woven the tendon under/over/under along the upper side of the arm.This keeps the tendon high up away from the hinge line thus increasing the leverage at each joint.


The result, smooth, even movement as the tendon is pulled and the arm raised.