So I dug out this project. I never actually intended to abandon it for so long, but somehow that's exactly what happened. Today I started preparing for the PyCon.PL confernece, and looked at the shelf, and there it was. We are going to do some Micro:Bit hacking at the conference, and I thought: "Hey, it's a good thing to connect a Micro:Bit to!" So I took it out, blew the dust from it, replaced two broken bolts (those acrylic bolts are delicate when you tighten them too much) and added a bunch of wires to the servos:
Every servo has now two extra wires: one going to the center tap of the pot, and one going to the motor. Why? Because I want to be able to do position and force sensing! Probably not right now and not with the Micro:Bit, but I really want to do some experiments with complain motion and such.
One of the more important challenges in the design of MeArm is making it as light as possible, especially at the end of the arm, where there is the longest lever and the inertia is the worst. But if you look at the robot, it has 10 metal bolts in there, which are quite heavy. So what can be done without laser-cutting my own version of the gripper that would use fewer bolts?
When I was looking for bolts for the #Talk Ranking Machine, I stumbled upon those acrylic bolts. They are like completely normal nuts and bolts, except they are made out of acrylic, instead of metal. And they are light. Sure, they are not as strong as metal bolts, but they are as strong as the rest of MeArm, so it doesn't matter. They fit this project perfectly:
Now, there is a trick to using them. You will need one normal metal bolt, to thread the holes first. Preferably several times, and make sure you get all the way through, because if you don't, you are going to break the acrylic bolts trying to force them in. After screwing the bolt in and out several times, you can screw in the acrylic bolt, and cut it to size with wire clippers. Easy.
You can see on the picture that I didn't replace one bolt inside the robot, and the four bolts in the base. The bolts in the base are longer than the acrylic bolts I had, and they don't matter for the weight of the arm itself anyways, and the bolt in the middle was just too hard to get to without disassembling the whole robot first, so I let it be. It's close to the center of gravity anyways, so it shouldn't matter that much.