Building a 5DOF robot arm 2

Here’s a shot of my workbench right now.

I went through three different wrists before I got the measurements right. The bevel gears were brushing against the forearm or the mounting screws. I also reprinted the wrist gears with a smaller center hole so they can hold the 5mm bolt that runs across the center. I need to find a way to attach that bolt to the wrist. A nut, a lockwasher, and another nut? Double nuts? Seems to work on the Prusa 3D printer hobbed bolt.

In the next version the elbow joint will change to increase the range of motion. In the current version there’s little or no room to add braces across the bicep pieces. Braces are needed to keep the bicep from twisting along it’s major axis. I haven’t worked out how to drive power to the elbow rotation yet. I’d like to put the stepper motor down at the shoulder again, but I might have to put it up near the elbow. Try it and see!

I’ve also started to plan the limit switches. In the Arm3 the switches are very close to the shoulder. There is less opportunity for error the further out they move. An error of 0.1mm near the point of rotation can turn into many mm out at the far end.

The total length of the forearm is something like 235mm. Once the tool changer goes on the end the distance from elbow to tool changer will be 250mm.

We got a mention in MAKE at the tail end of Robots Week. Thanks, Caleb! Please keep sharing with your friends. All my marketing is all done through word of mouth – usually my own. Your help drives sales, which gives me the resources to keep designing.