Wooden Robot Hand Part 1

This is one of my most recent projects: a wooden robot hand.
The fingers are controlled through 5 servos pulling on 2 pieces of fishing line each, one on the front of the finger and another on the back. When the servo moves it releases one side of the finger and tighten those other. I chose this method because at the time, it sounded pretty simple and cheap to achieve.
The drawback to this design is that the fingers are extremely weak and cannot grasp anything. So until I get around to figuring out how to make the fingers curl around tighter, the hand will probably never hold anything.
I have since seen some videos of other servo robot hands that seem to achieve hand strength, but I haven't really looked into how they did it. But in my defence, I think my hand looks more hand-like than the others that I've seen. Also, none of their's "flips the bird"!

The servos are controlled using an Arduino Mega 2560. Obviously my choice of Arduino is a bit of an overkill (since only 14 I/O's are required), but it is all I have available for now. Eventually I'll replace it with an Arduino Uno or Nano. The whole thing is fed from a 9V battery. The servos get their 5V from 3x 1A voltage regulators. I'll get into the wiring and what-not on another day.

So here's a run down of how I made the hand:

I started with tracing out my left hand and marked out the design that I was going use to build the hand itself.
I first measured out and cut the segments to make the fingers and thumb. I used 12mm dowel. I chose to make my own hinges because anything at the hardware store was either too big, too flimsy or simply split the dowel in half when I tried to put screws in! So I ended up making the hinges by cutting up some sheet metal into a two hole mechano-like piece. I used two of these metal pieces for each pivot point with a 1/8" brass screw holding it all together. The small ring hooks are for the fishing line to thread through and tie off at the end of each finger, front and back.

After redrawing several times, I decided upon this design for the palm. It allowed room for the servos to fit and kept the palm pretty strong.
The palm is made up of 2 separate parts that screw together later; the main section which holds all 5 servos and 4 of the fingers (attached with the same sheet metal hinges) and a small section that holds the thumb. The smaller section is angled roughly 45 degrees down.

This is how the palm turned out (thumb piece not built yet!)

After assembling all of the fingers and the two palm pieces, I gave it all a quick once-over with some stain and varnish (just to be fancy).
As you can see in the photo, I then mounted the 5 servos.


I got the 5 servos for AU$30 on eBay. Heaps cheaper than at the hobby shops in Adelaide!

Now the reason I used 12mm ply in the construction of the palm becomes a bit obvious in this photo. I matched the width of the servos to the ply wood width so I could attach some aluminium sheet on both sides of the servos. Two reasons; it prevents the servos from falling out (they weren't screwed in too well) and it looks kinda cool!











I'll continue with the construction of the wrist and the wiring on another day.