Introduction: How to Make an Animatronic Hand
In this Instructable I will be showing you how to make a moderately complicated Animatronic hand, using the kinds of techniques utilised by actual animatronics specialists. The system is effectively a complex puppet, with servos putting the 'strings' to operate the fingers. Unfortunately I could not figure out how to make the wrist move so at the moment just the fingers move.
I would like to credit http://vegard.hammerseth.com/2009/03/school-projec... as the source of visual reference for my project. I made modifications to their design to make it easier to create at home with fewer specialist tools and an easier to use servo controller.
The project took me just over six weeks of problem solving and actual making (hopefully as I have worked out most of the kinks in the process it should take anyone following this 'Ible a shorter period of time).
Even if you don't replicate exactly what's in this Instructable, don't be afraid to modify what's here. The first prototype I built was made from PVC pipes, blu-tak and drinking straws; instead of copper pipe, epoxy putty and bike gear cable tubing. It had three digits instead of five and was a lot larger than a human hand. This just demonstrates how a few techniques can be taken and applied to make a much wider variety things, hence why animatronic movie monsters can be so diverse in appearance.
If you don't want to add servos, the hand can be operated by hand as a puppet, with each finger operated by the puppeteers own fingers.
Step 1: What You Need
1. Copper pipe- I bought mine pre-cut from B and Q. These will make up each segment of each finger. For the full hand you will need 14 bits of pipe, I varied the lengths for each finger (e.g. three smaller lengths for the little finger and three larger lengths for the middle (longest) finger). I will re explain this later.
2. Bicycle gear cable and tubing- The cable is the 'string' used to operate the fingers. The tubing will be set within each finger segment to allow the cable to run through them. Using gear cable gives you greater dexterity and less strength, using brake cable gives greater strength but less dexterity. I found gear cable much easier to work with.
3. Small cabinet hinges- You need as many of these as you have finger joints/knuckles. I make the number 14 again.
4. Epoxy Putty- This fills the spaces in the copper pipe and allows the brake cable and tubing to be set within the fingers.
5. 50mm diameter Aluminium tubing- this forms part of the forearm, the cables run through these to the servos at the base. You will need about 2 metres of this as it will have to form 5 lengths of forearm
6. Sheet aluminum or steel- I used both, the harder steel for the palm of the hand and the softer aluminium for the supporting bracket for the forearm
7. 5mm thick MDF- This is what I used to mount the servos at the base of the arm
8. Super glue- Lots of it, due to being limited by not having a workshop of professional tools this is what most of the project is held together with. By all means if you are capable of joining the parts together any other way please post in the comments
9. High torque servos- I used Towerpro MG955 servos because there was an amazon deal for 75% off aa pack of four. I've heard they're not the best and tend to overshoot but I'm on a budget and not looking for incredibly precise movement anyway (unlike say, an RC plane hobbyist might)
10. A Pololu Maestro Servo controller- I bought the 12 channel version. This makes servo operation really easy as there is no programming involved. You just plug in the board to your PC and the software provides onscreen sliders to move the servos to the position you want https://www.pololu.com/product/1352
^NB: The pololu takes a standard USB cable, NOT A MICRO USB. This nearly caught me out but luckily I found one in the cable drawer
Step 2: Tools
1. A Dremel- With cutting disks and grinding wheels
2. An angle grinder
3. Scissors or tin snips
4. Permanent marker pens
5. A rule/ruler (not too sure what the correct English is anymore, people keep correcting both versions)
6. A work bench with clamps etc. - some of this work gets too hot and dangerous to hold by hand, so you will need to clamp things in place to prevent getting burnt
7. Safety Goggles (and possibly ear defenders depending on how old/loud your angle grinder is)
Step 3: The Fingers
To get the proportions for the hand right, I traced round my own hand onto a piece of paper. Keep hold of this as you'll need it throughout the making process as a reference.
Line up your bits of copper pipe on each finger- my order went as follows:
Little finger- 3 small bits
Ring finger- 2 large bits and a small bit for the fingertip
Middle finger- 3 large bits
Index- 2 large bits and a small bit for the fingertip
Thumb- 2 large bits
If you're working from a full length copper pipe, measure out the lengths of each finger and then cut to size with an angle grinder.
Step 4: Mitre
Next you need to mitre each part of the digits so they can bend once the hinges have been attached. For the fingertips you only need to mitre one end, this is both for image purposes and so the hand has a bit more grip. For te rest of the joints mitre both ends.
I clamped each section into my work bench and used an angle grinder to create the angles. Beware, the copper will get very hot so do not touch it immediately. I kept a spray bottle of water handy to cool it down and prevent it from scorching my workbench. For those of you with limited experience with an angle grinder, what I did was placed the flat face of the disk onto the copper and pressed down at the angle I needed (this was very much judged by eye), measuring it now the angle is about 45 to 50 degrees. The steeper the angle the greater the range of motion the fingers will have.
Do this to all of your joints until you have a full set.
Step 5: Add the Hinges
After numerous experiments in how to fix the joints together, I settled with good Ol' superglue. Just apply the glue to both sides of the hinge, being careful not to get any glue on/in the moving part of the hinge. Get your two joints and press them on to the hinge. Depending on how long it takes your glue to dry will then dictate how long you have t hold the pieces in place for. I used Loctite glue and didn't have to hold it for much over a minute.
If you do get any glue in the moving bit of the hinge, just wriggle it back and forth for a few minutes to loosen the joint again.
Repeat this for each finger. You want 3 hinges per finger and two for the thumb (you'll probably get a better idea from the pictures). The last hinges on each digit will have one side free, this is so they can be attached to the palm later on. If anyone has a better suggestion as to how to join the sections together please let me know, however with my limited toolage glue was the only proper solution.
Step 6: Create the Palm
Hopefully you kept the hand cutout you used to get the finger proportions right, if not just trace out another one.
Cut out the palm and trace it onto a piece of sheet metal. I used some 2mm steel I found, it was the casing for a PC disk drive. Again I used the angle grinder to cut out the shape (don't forget to clamp your metal in place first).
I used the sanding wheel of the Dremmel I smoothed off the sharp edges around the palm, this wasn't completely necessary, but I did it for neatness and so I didn't cut up my hands when working with it.
To give it a bit of 3D shape, I hammered the edges up a bit, but tried to keep the central palm flat (this is necessary for the attachment of the aluminum tubing later). The slight curve to the palm also helps with grip.
Do not attach the fingers to the palm yet, otherwise it makes a later step more fiddly.
Step 7: Create the Forearm
Here you will cut out and assemble the tubing that each cable will run through (going from the fingers to the servos).
Measure from the middle of your palm to your elbow, this will be the length of each of the five tubes for each finger. Mark up the lengths on your piece of aluminum and use an angle grinder or hacksaw to cut them out. You need one length of tube for each digit, so for the hand I made I used five.
I bent each tube to a different angle to match up to where each finger would sit on the palm. This is a bit difficult to communicate in writing so hopefully the photos should help.
Step 8: Put Together the Rest of the Forearm
I bent some very thin, flexible aluminium sheet (the kind used in computers etc. I found it in my old xbox 360) into a curved bracket shape. It was cut to about the same length as the aluminum tubing (I tidied up the lengths later with my Dremmel). Leave extra length so it can be attached to the palm.
I attached the bracket to the wrist first (using the ever faithful super glue, I would have used a pop-riveter if I had owned one at the time). After that I glued the aluminum tubing to the bracket and the palm. The bent ends of the tubing should come to about half way up the palm (see the photos).
Step 9: Prepare the Tubing
Take the tubing that covers your gear cable and remove the cable. Use the cutting disk of a Dremmel or angle grinder to cut small lengths of about 4mm. You'll need one length per section of copper pipe, so 14 in total.
Take your 5 lengths of gear cable and thread the bits of tubing on to each cable (three bits for the fingers and two bits for the thumb)
Step 10: Attach the Cables
This is a pretty vital stage of the process, as it is what allows the fingers to contract.
Start with the tip of the finger, mix a marble-size piece of epoxy putty and wrap it round the very end of the cable (there should be a metal 'nub' to stop the tubing slipping off the cable). Push this into the fingertip, smoothing down the putty as you work (depending on the putty it may dry quite quickly). Let this dry and make sure it stays adhered to the inside of the finger.
Slide the next bit of tubing into the second piece of copper tubing, again surround it with putty and push into the joint. This time, make sure the cable can move freely within the tubing, don't let the putty close the ends of the tubing. Pull the cable back and forth to make sure it can move. Do this again for the third bit of tubing.
Repeat this for all the other fingers and the thumb. When you pull the cable the fingers should contract.
Step 11: Attach the Fingers to the Palm
Now the fiddly bit is done, thread each cable through its corresponding aluminium tube so all the digits line up with the palm. Dab some super glue on each hinge and hold in place until each finger is attached
Step 12: Make the Servo Mount
For the mount I used a 4mm sheet of MDF as it was the only thing I had available. Ideally I would have used some slightly thicker MDF or metal.
Get out your servos and place them on the MDF. I configured them in a staggered way to prevent the servo arms hitting each other. Unlike in the photos above I also left some horizontal space between the servos to stop the cables snagging on each other. I used my Dremmel, scissors and a craft knife to cut out the spaces where the servos will sit. Once that was done I cut out a square around the spaces with a rectangular ledge to then be glued to the forearm.
Thread each length of cable through its corresponding servo arm. Make sure the arm is at the end/beginning of a rotation (this is so you get the maximum contraction in the fingers when the servos are active). Once you're happy with the cable length, loop it through the opposite end of the servo arm, this should lock it in place (if you need any clarification about this step please ask, it took me a while to figure it out).
Optional: Trim the cables once you're done for convenience. I haven't bothered with this bit as of yet, I just tied up the slack with food bag ties.
Step 13: Connect the Pololu Servo Controller
That's it! The building bit is done! Now for the control.
I used a Pollollu 12 channel Maestro servo controller to move my servos. It is pretty much a plug and play kit, I had zero problems with it.
Connect your five servos to five of the channels on the board, plug the board into your computer and then connect the power (I used 4 AA batteries, giving me 6v. The operating range of the servos I bought was 4v to 7v. Be sure to check your servo specs before choosing a power source). Open up your software and select the channels you've plugged the servos into. You should then be able to control each finger's movement individually.
^This is the link to the 12 channel controller. The website also features incredibly helpful instruction videos that will probably explain the set up a lot better than I will.
Step 14: Finished!
You're all done! And hopefully you have an awesome working robot hand that you can impress people with.
If I had more time and money I'd liked to have made a latex or silicone appliance to put over the hand like they do for movie VFX. If I ever do I'll add it to the instuctable.
Hope you guys and gals like the project, embedded (hopefully) is a video to show how it works in real life.