The ARM (Auckland Version) #2

August 25, 2024

The ARM (Auckland Version) #2

Hoho the next update is HERE!

Play "Tadow (Extended Version)" by "Masego & FKJ" to see this post.

Welcome back to the 'roh'bot center, so we have the first finger all assembled. The wires and cables are not shown in the pictures because I am working on assembling the mechanical components first.

The whole thing started in 2022, "they" told me to create an arm. I made a few concepts but before making the concepts I made the EXACT skeleton of my palm and I mean EXACT EXACT EXACT, OUI OUI EXACT, en fracaise le "exact" cest exact.

The hospital told me, well you can't get a X-ray of your hand just because you want to. You need a doctor's approval. Even though I said "sil vous plait" they said "non monsieur non, cest pas possible." Sad but defiant I returned and made some boiled apple jus and stired in one shot of double oak bourbon and half table spoon of lemon jus.

So how is this exact EXACT? I took my vernier callipers, sharpened it a little bit and started finding the end of my bones in the fingers, took 10 - 15 measurements each matched it with the rough fibonnaci pattern and made the whole 3D model, printed it and took the difference of flesh and the height of each finger bone set and then matched it in real life. VOILA! Belle demoiselles et monsieur.

Here are the different concepcións.

Concepción - Bone Structure

The bone stucture was mainly made with the idea that the bones are rods with bulb heads on both extremes. The bulbs are the width of the correspoding fingers and the distance beween the two extremes is the height of the corresponding finger.

This thing can best be printed in off whitish - yellowish resin using a SLA printer. Here's a 3D model of it to develop understanding.

One of the fingers are colored to represent Metacarpals, Proximal Phalanges, Intermediate Phalanges and Distal Phalanges.

3D View Of The Bone Structure Assembly

Concepción - Joint Test

This concepción was concieved to basically invent a robust joint system using off the shelf ball bearings, rods and rings. The principle was that both the finger plates will have a bearing which locks them in place to the joints with a retaining ring. The fingers themselves were made by just flattening the actual bones from the previous concepción and drilling holes in the extremes.

This thing can be best printed in PETG using a 0.02mm nozzle and a FDM printer. Using a metal powder 3D printer or a stamping machine would be amazing. Make sure you press fit the ball bearings.

3D View Of The Joint Test Assembly

Concepción - Grove Test

This cconcepción was made for testing an idea for embedded groves for the strings to pass through. It was mostly successful HOWEVER a bunch of work was to be done to make sure the strings actually engage with a pulley so that it does not hand there freely doing nothing. I have some strong ideas for that but cant show that since "CoNfiDenTIaliTy". This concepción was the final piece of hand that was printed and tested. It worked quite good. The palm was a problem becasue I didnt have enough time to come up with something but now its looking good. I hope I can setup my workshop to make it.

Here's a 3D model to see what really went on.

3D View Of The Grove Test Assembly

Concepción - Auckland Version

The finger joints are very easy to understand, they are basically pulleys, both fixed and free ones, the top joint (distal interphalangeal) has a fixed pulley which is wound around by a string that passes to two free pulleys to maintain independent angle to both middle and lower (proximal interphalangeal and metacarpophalangeal) joints. The middle joint has again a fixed pulley, however only one free pulley beneath it. The lower joint is a direct joint with one single pulley.

You can see in the pictures the different components for each joint, the joint feedback potentiometer, the special shaft which I painfully made one by one by grinding the brass shafts to have a 1mm shaved off top part.
The picture with a vice in a seal able bag? yeah I just didn't want to clean the metal dust in my room afterwards. Lazy people really do take amazing decisions sometimes.

3D View Of The Auckland Version Assembly

Hoho Bye

This hand is slowly getting made due to minor funding and technical issues. Keep an eye out for the next post if you are ever interested in my big toys.

Here's a little video - YOUTUBE

Originally posted on Linkedln

- Made in A.U.T. Room 1552, New Zealand by RolandThsive

Have a nice day,

- Rohit