Instructables
Picture of Science Fair - Articulated Hand < $20
My niece Sydney needed help for a 7th grade Science Fair project. I helped another friend's daughter (Kaitlin) build an articulated hand for a project in the past and suggested we resurrect the project. The build is fun for the kids and I wanted to try some enhancements on the original idea.
 
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Step 1: Materials, Tools & Time

Picture of Materials, Tools & Time
Materials:
You can get everything you need at Lowe's or Home Depot.
1 - 3/4" hardwood dowel
1- 4" x 1" Pine plank (I'm calling it '1x4' here)
5 - bags of #216-1/2 small screw eyes (eyelets)
1 - roll of braided nylon string (one color for ligaments. We used yellow)
1 - roll of braided nylon string (another color for tendons. We used pink)
1 - bag of 1/4" wide rubber bands (like the Post Office uses)
1 - cup hook (open eyelet)
1 - can of white spray paint
2 - 3/4" sheet rock screws

Tools:
Various hand tools (you already have them if you are a maker! :)
We used a small drill press, 4" side grinder, jig saw (my Dad taught me this was called a "Saber saw") and a chop saw with a trim blade. These are time savers, but you could do it all with hand tools if you can spend the time.

Time:
Assuming you have the power tools, you should be able to easily build a hand in about 8-10 hours. That includes taking time to teach your young experimenter how to safely use tools.
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JimmyL 10125 days ago
Can this model pick up things
kzerpa made it!2 months ago

My son made this over the weekend for a school project on the hand. The project takes a bit of time but it's so worth it! His won't pick up anything heavy or oddly shaped although it will pick up lighter things. Either way it's pretty awesome and he's very proud of it. He can't wait to present this in class.

hand.jpg
lulucrazy10 months ago

I need to have the variables for the science fair and I don't really know what they would be. Can you help?

jayotte lulucrazy7 months ago

your manipulated variable could possibly the weight of an item you try to pick up with the hand (possibly using a water bottle and different amounts of water for different weights) or the position you use to pick up an item?

Wow this is amazing, you inspired me to make my own Instructable! Thanks.
grogg343 years ago
Sorry it took so long - here is my hand - your instructable got me 1st place in the fair!
IMG_0609.JPGIMG_0675.JPG
rgraylint (author)  grogg342 years ago
Hey Grogg34. Congratulations! And thanks so much for posting your photos! I really am pleased to see our project help other students. It's especially fun to see pix. I like your "How does this grab you?" line. That is a great idea. Good job.
Oh.... ( Sorry for bothering again...) I forgot to mention what a great job you did!!!!
It looks so professional and just amazing!!!!=)
Hey=)
So I'm in seventh grade too and our teacher just assigned this as our next big project. Needless to say, I was pretty nervous; as the way he explained it it seemed very hard. So I went online to look for some ideas and plans, and I found this lovely design. I feel so much better, it doesn't look as hard as I imagined, although I may be underestimating its difficulty. Thank You so much, I intend to use this for the project, and (with any luck) get an A! Although this is a great design, I think I'll put a little spin on it.... do something extra or crazy like I'm always doing =) Anywhooo.... Thanks again. Thank You Thank You Thank You!!! =)
This amazes me every time I come to instructables. My best friend and I are going to make this for our science fair, if you don't mind. It's gonna be called "Movement of the Hand" and we are already talking about making it. We are actually compromising it right as we speak! I think we might end up giving it to the science or health teacher so we don't fight over it... Creepilish! I love this, and have been planning it since the last summer! Make more instructables please! Maybe one for next years science fair? ;)
baybay19964 years ago
what is the lenght of each finger bone? i know you said they are all the same length but how long is that?
rgraylint (author)  baybay19964 years ago
We built our design based on the size of my hands, which are pretty big. I figured a bigger hand would be easier to build. It turns out my hand was just about the right size. The middle segment of my middle finger is 1 5/16". The same segment of my little finger is 3/4".

But we didn't make different segment sizes for different fingers. You could do it, but it would be a lot more trouble to get all the right ones in the right places. So in the end we just made all our joint segments the same length - 1 1/4".

Good luck and I hope this helps...
I NEED URGENT HELP!!! What would i be testing if i used this for my science fair, like what should i name it? Im in 8 grade
rgraylint (author)  Purepwnage5755 years ago
Hi I'm not exactly sure I understand what you mean by "What I would be testing...". Do you mean what does this project demonstrate? If so you could say it shows how the skeletal and tendon structure of the hand works. You could also talk about how our muscular system is made up of flexor and extensor muscle pairs. Meaning one muscle pulls a body part one way (flexor) while another extends (extensor) to allow the movement. Then the roles reverse to move the body part the other way. I hope this helps you. Let me know if you have any other questions... Good luck!
I also have the same problem but you awnsered it. My teacher is making me say how this relates to science, any help? And do you have any tips on how to make a glove controller? Thanks. This is amazing.
I believe this is a demonstration of animatronics, I've tried to make one of these out of a coat hanger and some aquarium tubes but it didn't go so well, hopefully this time it will. I'm in the 8th grade too, except i was home schooled up until now so i know a lot more than I should.
Roxy 1434 years ago
Good
DubRunner4 years ago
nice instructable just the thing i was looking for wanted to incorporate this to a halloween costume back pack puppet just wondering what is the grip strength on this as i want movable hands on it. Plus how do you think that it would perform inside a heavy plastic monster glove thank you.
astrong04 years ago
i made mine out of bicycle chain :)
grogg344 years ago
1st place in science fair thanks!!!
rgraylint (author)  grogg344 years ago
Congratulations!  I'm really happy to hear it.  :)
2nd place at the district science fair !!! thanks
rgraylint (author)  grogg344 years ago

That is fantastic!  Thanks so much for letting me know.  I'm really glad our ideas helped inspire you.  Good luck!

TFElite4 years ago
I'm making something somewhat akin to this. It's made from the kind of pipes that people use to rout wires through walls. If that turns out well, I may very well try this. The only problem is, I don't know how I will be able to cut the pieces because being a 14 year old really can't get you anywhere in terms of something that cuts like this... Anyways, do you have any tips otherwise?
rgraylint (author)  TFElite4 years ago
I understand your trouble with limited tools.  That is frustrating.  You can actually build this project with just regular hand tools but to be honest I'm not patient enough to do that either.

The conduit idea is a good one.  I'm not sure if you mean metal or plastic conduit.  Since your tools are limited maybe you should consider using that blue plastic conduit (some people call it smurf tubing).  It is cheap (at Home Depot) and easy to cut with a hacksaw.  If you cut a triangle out of it where where the joints go it might bend like a finger.  You would have to cut it almost all the way through leaving a small piece of the plastic at the top/knuckle. 

My concern is that the plastic might be too stiff and/or brittle.  It might bend a few times then break. You could experiment with the same kind of idea on different types of materials.  Try some rubber and plastic hose - also cheap at Home Depot..  An old water hose might even work.  It would have to be a soft one though.  1/2" PVC water pipe is easy to work too.  It won't bend like a hinge but maybe you can work out a plan for that.  Cardboard or even rolled up and glued paper could work too.

If leaving a small bit of plastic or rubber at the knuckle doesn't make a good hinge, you could consider cutting your triangle all the way through and separating the fingers at the knuckles.  Then drill/poke a couple of holes maybe 1/4"-3/8" apart where the knuckle would be.  You could basically stitch the 2 finger segments together at the knuckle with a couple of pieces of stiff wire (like 12 ga house wire) or even some tywraps. The idea here is to make a hinge that moves easily. You could also try gluing a strip of fabric (blue jean denim?) along the top of the finger segments to make a hinge.  Just leave the glue out of the bendy parts.

The next challange is how to run the strings to operate the fingers.  The thinge we found is that you must have the strings at the far edges (top and bottom) of the fingers for them to  have enough leverage to move the fingers.  So the strings need to run along the top of the fingers (back of the hand) and you have to work out a way to keep them from sliding off when the fingers bend.  The wooden version allowed us to screw in eyelets.  But you can't really do that with a rubber or plastice finger.  Maybe you can bend part your finger joint hinge wire to not only act as a hinge, but also stick up a bit and make a loop for the top string to thread through.   If you used fabric for the hinge you could stitch (needle and thread) some kind of bead (check the beading store) to the fabric and leave enough room in the hole for the tendon string to fed through and slide easily.

The strings on the palm of the hand also need to be near the skin surface.  You could get some small, stiff plastic hose and tywrap it inside each finger segment.  Put them where they are against the palm side of the fingers.  You could poke 2 holes at each end of the finger segment and thread tywraps through the hole, then around the thin hose and back out the other hole. Do this at each end of each finger segment and you have a path for your palm side strings/tendons.  The trick will be to get these small tubes to all line up properly so your string doesn't bind.  It might not be a problem if your hinge is loose enough to allow a little wiggle in the joints.

These are just some ideas to get you started.  I would like to see someone put a workable hand design together that would be easy to build with hand tools (get it - "hand" tools :)  OK, that was lame.  Anyway - good luck with your experiments and don't get discouraged.  If you come up with something you like please share a picture with us.

- Robert
grogg344 years ago
this is an awesome idea for the sf!!!
rgraylint (author)  grogg344 years ago
Thanks! :)  We had a lot of fun with it.
Chrisdalton4 years ago
I don't know if it is in your budget but here are a couple suggestions for a better model
- instead of rubber bands use surgical tubing
- make a latex hand mold and put it around the hand to make it look more realistic
- make a hand grip so that it follows the movement of your hand
if you actually did some of this it would be pretty cool
rgraylint (author)  Chrisdalton4 years ago
Those are some pretty cool ideas.  It would be interesting to see someone implement some of them.  We have talked a few times about making a hand grip like you describe.  That shouldn't be too difficult.  We have put a glove over the hand to make it more realistic.  It works pretty well. 

Are you thinking about building one?  Please share some photos if you do...
tigers086 years ago
What a great project- I'm going to try it for my SF project next year! Good Luck!
rgraylint (author)  tigers086 years ago
Thanks. If you build it for your SF please let us know how it works out.

yay im doing the hand this years sf it wil be awsome i will let u know if u subscribe

TechDante5 years ago
made a simple mock up of something like this yesterday while waiting for stuff to dry, only had time for one finger but using the cord is a much easer why than I had planned (carving joints out in the band saw), one question, one sudgestion.
question: how durable is the hand.
Sudgestion: instead of having lines from the tips of the fingers to the rubber bands why not just have the band run from the top of the fingers to back of the hand where your knuckle would be

rgraylint (author)  TechDante5 years ago
I'm glad you like the string/ligament design.  I started out thinking about carved joints too.  But that would be way too complex for a young student without a lot of shop skills to build. 

Re your rubber band suggestion, my final design that wasn't my original idea.  But sometimes we have to change on the fly.  :)  I originally intended to drill the string/ligament holes slightly away from the edge of the finger joint slope (meaning more toward the center of the flat area between each joint.  Then I could just put the rubber bands on the ends of the ligament strings and pull them tight to straighten the fingers. I hope that explanation is clear. Sadly it didn’t work out like I expected. Even with my (own) hand pulling the ligament strings tight it would just barely straighten the fingers out. Part of the problem was it is too difficult to get the holes to come out just where you want them. The thin bit drifts as you drill through the length of a finger joint. You start with the hole in the right spot going in, but it often pops out too close to or actually on the sloped surface. So when you pull the ligament tight it doesn’t have enough leverage to pull the fingers straight. The string/lever action is too close to the center of the finger (the fulcrum). So we added the back of the hand tendon strings to move the pull (lever action) further from the fulcrum. 
 
When we first made this change I think we actually tried just putting the rubber bands on the back of the hand as you suggest. But without eyelets on the back of the fingers the bands slide off and slip between the fingers when you close the hand. That locks the fingers in a death grip :). We added eyelets to keep the bands on the back of the fingers, but the friction of running the rubber bands through the eyelets caused trouble with binding. It was getting late on the end of our long build day so we just switched to string in the eyelets and put the rubber bands on the string. 
 
There might be a more elegant way to work out that problem. Maybe thread a very light bungee cord through the eyelets instead of using rubber bands and string? We were just pressed for time so when we found a way to make it work we never looked back. I do appreciate the suggestion though. If you work out some alternative way to handle the issue I’d love to see what you come up with.
 
Have fun with it!
Robert
yes that is very informative thank you for your explanation of your process. may work on trying pinao hinge in my next prototype
rgraylint (author)  TechDante5 years ago
Forgot to answer your question. They are all still around and working.  The rubber bands get old eventually.  Other than that the hands are pretty solid. 
McGyver25 years ago
You should make a video of you using it
rgraylint (author)  McGyver25 years ago
That's a good idea.  Maybe we'll find time over the holidays...
ea4225 years ago
Graeat job! I set up stations like you did and let my kids (13) make one for their science class. A+    Thanks!
rgraylint (author)  ea4225 years ago
:)  I really makes me happy to hear feedback like that.  Thanks for sharing.  I'd love to see a pic of all your kids with their hands - if you can still get them all together. That would be very cool to see...
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