Animatronic Balsa Wood Hand




Introduction: Animatronic Balsa Wood Hand

About: Carnegie Mellon Design + HCI
here is something i built 3 years ago over the summer. All it really does is open and close the fingers of the hand but it also shows  how tendons work in a real human hand. It really is a quite interesting project and can start you with some basics of programing basic stamps in P-Basic language. Feel free to subscribe to the YouTube channel also.

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Step 1: Materials List:

1. Plywood board 12 inches long and 5 inches wide or bigger.
2. A standard servo preferably from Parallax.
3. Any kind of Stamp preprocessor that you know how to use. If you are using Parallax sample code will be provided later on.
4. Pins/Needles, 100 pins should be enough... you only need one sewing needle.
5. A spool of thread.
6. 6, 3-4 foot pieces of balsa wood. about a quarter on an inch wide and a sixteenth of an inch of thickness. (you will probably have extra)
7. Two to four screws.
8. A small spool of copper wire. (should not be insulated, preferably thick gauge.
9 super glue, and hot glue.

 Optional: Dental rubber bands 

Step 2: Cutting Balsa Wood to Length

Use your chopper of choice there are very nice ones on the market, but an X acto will do fine:)

1. Six 2 inch pieces.
2. Eight  2 1/2 inch pieces.
3. Six 1/2 inch pieces.
4. One 1 and 3/4 inch piece. 
5. One 1 and 15/16 inch piece.
6. Two 1 and 14/16 inch piece.
7. Twenty Seven One inch pieces.
8. Two 1/4 of an inch pieces.

This is not very accurate but should be a good bare minimum for this project

Step 3: Building Fingers

The fingers are the most delicate part of the hand and should be treated with great care to prevent the fingers from hyper extending i added a cap on the top of the knuckle so to stop it from moving back to far. of course there is a trade off and you have to round the edges of the fingers to improve its maneuverability. 

1. the first thing you want to do is obtain these pieces.
Twelve 1 inch pieces,  the 1 3/4 piece, the 15/16 piece, and the two 14/16 pieces.

2. Think of the twelve 1 inch pieces as the outside digits of your pointer, middle, ring, and pinkie finger. Then think of the 1 3/4 piece, the 15/16 piece, and the two 14/16 pieces as the inner digits of your finger. (the ones closer to your hand) For times sake i am going to show you how to make one finger and just do the same for the rest :) now line the pieces up like in the photo and then push pins into balsa at connection points, example in photo below. all of this is not including the thumb.

Step 4:

As you can see in the photo illustrated below there are two little comers of wood that come out when ever the finger is bent. To fix this you have to take apart each of the fingers and sand down the corners for a smooth semi circle at the end. When put back together the finger should have no corners peeping out. You have to do this because with out the edges the hyper extension plate does not limit the fingers movement.

Step 5: Hyper Extension Plates

5. Now that you have the basic joint system you need to put an anti hyper extension plate on top. Use one of the one inch pieces as followed, if one inch does not work go ahead and make it a tad bit longer. Go ahead and place glue on where the black markings would be on your piece of wood be very careful to not be messy. (stray glue could kill the joints movement.) USE PHOTOS AS REFERENCE. Repeat these steps for each finger besides the thumb.

Step 6: Basic Palm Frame

You will need.

Seven 2 1/2 Pieces, four 2 inch pieces and pre-built fingers, go ahead and use 12 half inch pieces for the separators that you see in the photo.

1.The first thing you want to do is assemble each section that will hold the fingers separately and then put it together at the end.

2.After making each slot install the fingers so that they are similar to the hinges of the mid digits and have sanded edges. 

3.On the top after installing the finger into these slots you want to take the 2 inch balsa wood strip and apply it there. it will prevent hyper extension in the fingers and 3 two inch pieces completely surrounding the bottom of section x one on each side

The photo below should show a good display of the grid of the palm of the hand.

Step 7: The Thumb

Honestly i can not give any instruction on how to make this thumb, go ahead get creative you can even put another servo in to control it separately. I will show what i did in the photos below. A lot of hot glue was used and it is not practical at all. hopefully you can get a good idea of how the tendons and everything els works in my model so you can make yours from the images below.

Step 8: The Tendons Pt. 1

The first thing we need to do to begin the tendons is make certain that they don't slide off the finger and give us odd results.In my case i bent copper and made guide rails for it i will show a few photos and examples but this step is pretty self explanatory after viewing the photos. make sure you have your guard rails at the base of the hand so they all come together. Remember there needs to be tendons on the bottom of the hand.

Step 9: The Tendons Pt. 2

You should get about 10 inches of string for each tendon, you will need exactly ten strings. For this step you will need a thread and needle, first thread a small piece of thread through each of the gaurd rails for each finger. at the tip of the finger you want to thread it through the wood so it does not come loose like in the images below. Do this for each of the fingers (to be exact 2 tendons for each finger, one on top one below) When you have your set of all 10 try using the hand as a puppet just to test out if the joints work. 

(in the photo below i threaded the string through the wood and then kept it secure with a dab of crazy glue.( I'm not sure why but my image notes are not working.)

Step 10: Platform

Your Animatronic hand needs a steady base i used a plywood base and gently hammered in needles with pads under them so that my hand stood at a 45 degree angle. use your imagination i will provide you with a photo for a guideline.  This is not what i would have done if i did this project again. Also you might want to try a different method of mounting you r servo.

Step 11: Connecting Man to Machine

Here we will connect the servo to the actual threads. The first thing you want to do is take all of the threads from the top and bottom and cut them all just enough so that they are they same length. Now split each set apart (top from bottom) and glue the set together so the 5 on top and the five on bottom. The hand should be in an open hand position. now take the servo and make sure it is aligned to the thread and in its clockwise maximum position. Now tread the top thread through the top horn and the bottom thread to the bottom horn of the servo. You can go ahead and glue these in if nothing els works. Make sure all of the tendons are very tight or els the hand will have a very choppy motion.

Step 12: Programing

 I will supply the code for parallax basic stamp. But not to worry for all of you using Arduino and other platforms the program is very simple and is just a time executed code.

Parallax Code:

' {$STAMP BS2}
' {$PBASIC 2.5}

counter VAR Word
control VAR Byte

FOR control = 1 TO 10

DEBUG ? control

DEBUG "pulse width increment by 8", CR

 FOR counter = 500 TO 850 STEP 5
   PULSOUT 14, counter
   PAUSE 7
   DEBUG DEC5 counter, CR,CRSRUP
   DEBUG CR, "pulse width decrement by 8", CR

   FOR counter = 850 TO 500 STEP 5
   PULSOUT 14, counter
   PAUSE 7
   DEBUG DEC5 counter, CR, CRSRUP

 DEBUG CR, "Repeat", CR



Step 13: Sit Back and Watch in Amazement

Well its a useless project, but it all turns out to be pretty interesting

oh and yes the photo below is for lack of a better one:)

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    6 Discussions


    9 years ago on Introduction

    This is cool, but it would be even cooler to see a short video of it in action.

    (Upload it to YouTube, then embed it here, and the video will drive views to your project as well.)


    Reply 9 years ago on Introduction

    i did try to embed the video im not sure why its not working
    there is a link below


    Reply 9 years ago on Introduction

    You have to use the "old" embed code:

    <object width="480" height="390"><param name="movie" value=";hl=en_GB"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src=";hl=en_GB" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="390"></embed></object>

    Which gives you: