This project was originally inspired by my granddaughter's interest in Wednesday Addams. I thought it might be interesting to build an animatronic "Thing". The main challenge that was of interest to me was how to get at least 2 finger joints to be controlled by a single actuator. The design I came up with can be extended to operate 3 joints from one actuator, but 2 joints are sufficient to prove the concept. I did need to implement all 4 fingers and a thumb to prove that five motors could fit in a hand at the correct angles, but the main objective was getting the finger mechanisms to have the right geometry to work properly.
I also decided to do some voice acting and hand acting to make the project a little more entertaining. This was my first time doing these kinds of effects so I can't promise stellar results. To make it even tougher, all shots were done in one take and nothing was cut from any of the footage. That is all I had time to do.
I should have asked my black cat to pose for this shot....
The Wednesday Interview
The Design & Build
This is one of those projects where it was prudent to test the geometry calculations with some test prints of linkage parts. It took a few tweaks to get the geometry working the way I wanted.
Finger Geometry Explanation
3D Printed Hand Parts
Hands and fingers are very complex shapes and the joints are also very complex. They are not simple hinges. I found it very hard to measure my hands well enough to understand the bone dimensions and even the joint locations. To get a really accurate hand and joint motion model would take many months of work, but I am happy with the animatronic hand I designed and the way it functions. In particular the finger joints work just the way I envisioned at the concept stage. It was great that the small little servo motors had enough power to easily operate the fingers. It was quite disappointing that the motors did not arrive in time to make all fingers work at the same time, especially since they were ordered before the contest officially started. However, it was fun to work through the technical challenges and come up with a workable system. I do have an Arduino and a multi servo driver that can be used to control the whole hand if and when the motors come in.
Doing voice acting, hand acting, writing scripts and choreography for that type of video was new for me, but fun to try.