HOW TO MAKE THE GIANT ROBOT FINGER

NOTE: There are 3 levels of difficulty - -from a simple one-piece finger, to a whole hand -- depending how far you go in the instructions. Going to Step 4 will give you a basic finger with one tendon. That's enough to get the point about how tendons work. Going on to Step 5 will get you a finger with opposing tendons. If you make 5 fingers (they don't have to have opposing tendons), Step 7 will show you how to make them into a hand.

What you need:

string

You will need about 2 feet per finger.

thin cardboard

I use cereal boxes to recycle them, but you can use "poster board." You will need 2 or 3 cereal boxes if you make the whole hand, 1 box for just a finger.

scissors, tape, (ruler, optional)

Either clear tape or masking tape will work.

Step 1

Cut out the cardboard using the pattern,

Click here and print out the pattern page. Some browsers--especially Netscape--change the scale and the size of the printed pattern. If the printout says something like, "Scaled-60%" try another browser. Also, the printout has a scale check. It says 2" line to line or 5 cm line to line. Make sure it's accurate. Rough-cut (bubble-cut) it out, separating the two patterns. The following instructions apply to the pattern that looks like this:

Roll 4 pieces of tape into circular "doughnuts" with the sticky side out. Tape them to the corners of the blank side of the pattern. Then tape the pattern to a piece of cardboard, avoiding any creases within the pattern.

Notice that there are two kind of lines on the pattern: solid lines (shown in blue in the illustration) and dashed lines (shown in green in the left illustration). The orange indicates the cardboard the pattern is taped to.

Cut on the solid lines. Do NOT cut the dashed lines. Do NOT remove the pattern when you are done cutting.

Step 2

Fold on the dashed lines.

Use the sharp edge of a table or a ruler or some other kind of straight edge to make the folds straight. When you've finished folding, peel off the pattern and tape.

 

Step 3

Shape and tape into a 3-dimentional object.

Bring the edges together and tape them. In order to press the tape on really hard, push down and to one side to fold the assembly flat on the table. The bottom of the 3 illustrations at right shows a top view of one of the segments bent flat. Alternately, you can stick a ruler inside to back up the cardboard.

 

Notice that--unlike a real finger--there is nothing to prevent the assembly from bending both ways. If you continue on to step 6 and 7, we will deal with that issue.

 

Step 4

Tape on the string.

Take a look at the finger. Notice that the segments at one end are smaller than those at the other end. The small segment will be the finger tip.

Roll the assembly upside down so the un-notched side is up, as shown on the right. This is the only side that has no cuts in it. Tape the end of the string onto the tip. Thread the other end of the string into the finger tip and out the other end as shown on the left.

You can try out your finger so far. Simply hold the base, pull on the string and watch it curl like a real finger. Doctors call this "flexion", and the mechanism that does it is very much like a real finger. Notice that when you release the string, the finger straightens, but not all the way. To get it to straighten all the way ("extension"), you can build the other half of the finger and add another string, just like a real hand. But you don't have to. Just stopping here is the easiest version of this project. It models how our tendons going to our fingers allow them to close.

Step 5

Adding an opposing tendon.

In this step we will add another string to make the fingers straighten, another step closer to a real hand. We will also add a structure to the finger that keeps it from bending too much the other way, which is also like your real hand unless you are extremely double jointed.

Tape the other pattern onto cardboard as you did the first. Once again, cut on the solid lines. Last time, all the solid lines to cut on were on the perimeter (outline), but this time three solid lines cut into the pattern (remember to stop when you get to the dashed lines).

Once again, fold on the dashed lines. Tape the edges together as before.

Notice that--although it looks somewhat similar to the first assembly--it only bends one way, as shown. Once it straightens, it does not bend over the other way (assuming you are gentle with it).

 

Once again, tape the end of a string to the tip (the smallest segment), making sure you tape it to the only side that does not have any cuts in it. Thread the other end of the string through the assembly to the other end. When you pull the string, it should tend to straighten rather than bend.

Step 6

Tape the two parts together.

Make sure when you put the two halves of the finger together to be taped that they are paired as shown in the illustration. The sides that have no cuts, but do have string taped to them, will be touching each other. Try it out. You can stop here or go on and make a hand.

 

 

 

 

 

 

Step 7

Make a hand.

Although you will have to make 5 "fingers" (one will fill in as a thumb) to make a hand, I suggest that you only make the curling half (steps 1 through 4). The fingers will spring back part way. Furthermore, keeping track of 10 strings is very hard. Click here to print out a double pattern of the curling part of the finger. Some browsers--especially Netscape--change the scale and the size of the printed pattern. If the printout says something like, "Scaled-60%" try another browser. Also, the printout has a scale check. It says 2" line to line or 5 cm line to line. Make sure it's accurate.

The palm of my hand was simply the side of a cereal box with the top and bottom flaps left on for a little extra length. It was about 7 1/2" by 14". Whatever you use for cardboard, fold it in half and tape it to double the stiffness.

Notice how the fingers are taped onto the palm. The bottom segment is taped on while the 3 finger segments hang out. I used 4 pieces of tape to secure each finger, as shown in the front and back views.

MORE ABOUT HANDS AND FINGERS

For explanations, activities and cool links related to hands and fingers click here or on the picture.



Back to the robot finger introduction page.


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Copyright © Slater Harrison, 2003/04
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