Introduction: Mechanical Hand

Picture of Mechanical Hand

Students will make a simple mechanical hand with a trigger connected to a hinge. Once complete, students can test the ability of their hand by trying to pick up as many straws as possible. Extra class time (and there should be plenty!) can be devoted to further testing and redesigning to make the best mechanical hand possible!

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Step 1: Materials

For this design, you will need:
(and extra for redesigning)

15 Craft sticks
8 Craft cubes
4 Round cube beads(larger pack size)
Part of 1 Straw
2 1/8" dowels
2 Rubber bands
Tape
Hot glue with safety nozzle

And a box of straws for the challenge!

Step 2: Build the Hinge

Picture of Build the Hinge

Cut two 1/2-inch pieces of straw. Wrap tape around the end of a skewer and thread the round cube beads and the straw pieces onto it as shown. Wrap tape around the other side and cut off the excess. 

The straw pieces act as spacers to prevent the fingers from colliding.

Step 3: Make the Fingers

Picture of Make the Fingers

Create the center finger as shown in the picture. The half-sticks are glued onto the side of the cube at a 45-degree angle.

The two other fingers are built similarly on either side of the center finger. Make sure that the half-sticks on the outside fingers are glued on at an angle that is inverse to the center finger.

On the 'back' of the hand, glue a half-stick to the two outside fingers. These two fingers will be actuated at the same time.

Step 4: Make the Arm

Picture of Make the Arm

The arm is an extension of the center finger. Sticks are glued together with at least 1-inch of overlap to ensure a nice strong bond. The arm can be any length, but longer than 6 or 7 sticks is not recommended because it is more difficult to lift objects that are further away from your body. The arm also may not be able to support it's own weight if it is extremely long.

Once the arm length is determined, add a handle and a thumb rest at the end. The handle and thumb rest that are pictured are very minimal - there is a lot of room for innovation and customization.

Step 5: The Trigger

Picture of The Trigger

A trigger is anything that activates a mechanism - it's not a term just used for operating a gun. The trigger is what transfers the movement from the user's hand to the mechanical hand.

Place two skewers end to end such that the pointed ends are facing each other. Firmly wrap a 4" piece of tape lengthwise around the skewers. Attach one end to the 'back' of the hand with several layers of tape as shown in the picture.

Make the trigger as shown in the second picture. Thread it onto the skewer.

The mechanical hand needs to be calibrated to match the user's finger length. Hook your thumb around the thumb rest and place the handle against the base of your thumb. Extend the other 4 fingers and place the trigger just under the first digit of the user's hand. Wrap tape around either side of the trigger to hold it in place and cut off the excess. This can be tricky to do by oneself, so encourage students to help each other during this step.

Loosely tie a cable tie to hold the trigger in place. And finally, attach a rubberband to each of the outside fingers to the arm using a hitch knot. These will automatically open the hand when the user is not squeezing the trigger.

Step 6: It's Alive!

Picture of It's Alive!

Operation is simple. Hook your thumb over the thumb rest and place the handle at the base of your thumb. Wrap your fingers around the trigger and try it out! Try to pick up some everyday objects. What kind of things is the hand good at picking up? Where could it improve? How would you modify it? Ask yourself and your students these questions.

The placement of the trigger is important for easy operation. You may need to adjust the trigger by as little as 1/2-inch to achieve optimal range of motion. Avoid using hot glue to secure the trigger since it is more difficult to adjust.

Step 7: Tips and Troubleshooting

Picture of Tips and Troubleshooting
This project offers a lot opportunities to customize and redesign. Give your students at least two hours to: receive instruction, build the hand, and then redesign it while participating in the challenge.

Conducting the challenge is easy. Open a full box of straws and have your students take turns trying to pick up as many as possible and move it into a separate container. Any straws that are dropped in transit don't count. Have your students count their straws and keep a record. Straws will fall out and make a mess, so tell your students that they are responsible for any straws that are dropped during their attempt.
  • This project has many steps and some small but important details. Having an example or two for your students to refer to will help tremendously. 
  • If a student has a small hand, then it will be more difficult to get a good range of motion. There are two ways to solve this. One is to lower the skewer that is attached to the back of the hand. This will bring it closer to the hinge. Smaller movements near the center of the hinge have a greater effect. Another solution is to not cable tie the trigger to the arm, and instead use two hands to operate it: one hand holds the arm, and the other hand operates the trigger.
  • Some students may want to make enormous mechanical hands and super-long arms. Although I encourage novel designs, you may want to gently encourage your students to refrain from extremes. In my experience, ultra-large-scale designs are more susceptible to breaking under it's own weight, and there sheer amount of time required to build it leaves little time for testing and redesign.
  • If the hand is difficult to open, try manually stretching the rubberbands to gain more slack.
Did you try this project and find some new ideas or encounter a design issue? Let me know! Send me a message or email to Lance@TheWYE.com

Comments

tncb (author)2016-02-26

What size craft cube would you recommend?

LanceMakes (author)tncb2016-06-11

1/2" cubes are used in this example

MeredithLopez76 made it! (author)2016-04-20

I helped my 7-year old make this for his school science fair. While I do wish the supply list were more detailed - including the sizes for things, and how the craft sticks, cubes, and beads should all be the same width - the two of us managed to put this together in about an hour and a half, which includes letting the hot glue dry between steps. Even though ours isn't pretty, and the fingers aren't perfectly even or nice and neat, this thing still has grip! My son demonstrated this by picking up a "lightsaber" made out of a foam pool noodle.

The instructions and photos were straightforward enough that my son understood what to do, and once it all started coming together he had no problem figuring out how it all worked together.

FWIW, we used regular Scotch tape to hold the trigger and hinge in place and duct tape to attach the skewer to the back of the hand. Instead of buying wood skewers I cut some wire hangers to the lengths we needed. We didn't have a cable tie, so I used a Velcro wrap to keep the skewer on the arm. The craft sticks we used are 4 1/2 in. long x 1/2 in. wide, and we used half-inch rounded craft beads for all the joints instead of blocks. The arm is 3 sticks long, which is perfect for my 7-year old.

Wow, thanks for sharing! I'm glad to hear that you super successful!

ijazzahir (author)2015-07-08

fantastic idea...its quite helpful especially for the elderly people, so thumps up..!!

_makerbot_ (author)2015-06-10

does this actually pick things up? Is it a lever?

ericesquivelbr made it! (author)2014-06-29

It was great to do it, and I made one only enhacement, that I took a picture. Thank you... I have a lot of fun...

Wow, this is awesome! Thanks for sharing - it's really cool to see others actually make use of these project plans :)

mohesh (author)2014-02-23

extremely awesome

TTSS (author)2014-02-20

Simply Wonderful.

pickleman1234567890 (author)2014-02-17

That's awesome

craft-n-genius (author)2014-01-20

Awesome! This would work great for a puppet hand :D thanks for sharing!

rimar2000 (author)2014-01-17

Good work! Maybe you could add a video.

audreyobscura (author)2014-01-16

So great!! Thanks for posting.

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Bio: I'm a writer, maker, and educator. For free lesson plans and teaching materials, check out LanceMakes.com.
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