Here’s a tutorial for the simplest possible method:
Cut a piece of cardboard. Make sure the corrugated ribs are going across the strip, not up and down the length of the strip. Fold the strip every inch or so.
Cut short segments of plastic straw. Tape them lengthwise, one per section of the cardboard.
Thread a string through all the the straw segments. Tape it down at one end, and leave a loose end hanging out the other end. Pull on the loose string to bend the “finger joints.” Optional – add a handle to make it easier to hold on and pull the string.
Variations: Put straw segments on the front AND back of the cardboard. Run string in a loop – tape on the back, then run it through all the straws on the back, over the end, then through all the straws on the front, and leave the string hanging on the front. This led to a better / tighter curl when the string was pulled. (See photo of curled finger at top of post.)
Pincer grasp: take a flat square of cardboard (whoever made this one reinforced it with a couple popsicle sticks to make sure it couldn’t fold.) Then add a couple “spacer” pieces of cardboard. Then tape on your “finger” with the straw side DOWN toward the other cardboard. (First picture.) When you pull the string, the finger curves up against the lower cardboard, forming sort of a pincer grasp. (Second picture.) It can pick up small objects like this red Lego piece.
This is a fun, easy, hands-on project for kids that we may use in either our “Skeletons” class or our “Robots” class. And it fits both our tinkering aesthetic and our pulling materials from the recycling bin approach.
When we got home, I searched for other examples of similar projects online.
Kiwi Crate has a Straw Fingers project, where they just use straws and string – they cut notches in the straws to allow them to bend. You can choose to make five and tape them to cardboard for a hand.
On Carolina, to model a human hand, they take the notched straw idea, but then tape them onto a hand-shaped piece of cardboard, then score the cardboard so it will fold everywhere there is a joint.
RIT has a full lesson plan on bio-engineering, which includes a how-to on how to make a finger with wood, rubber bands, tape, string, straws, and cardboard.
Science Buddies has a fully detailed tutorial on how to make a robot hand from straws. Their directions include an evaluation of ways to improve the process. They use straws, string, polymer clay and plastic rings. Each finger has three rings, one for each joint so you can bend the joins separately. On Prezi, there’s a vaguer description (with no pictures) of something that sounds like a similar process… might be some tip you could glean from there.
Weird Science Kids uses a hand-shaped cardboard, bendy straws and string, and “glues” the straws down to the cardboard with clear silicone caulk (like you use to seal seams in a shower.) It looks complicated to me… and takes a couple days as you have to wait for the caulk to dry / cure.
PBS Kids has a “design a robotic arm” challenge.
All these examples inspire a lot of ideas for projects we could do. If working with younger children (preschool age – 3 – 4 or so), I would likely have them build just a single finger, either using the PacSci method I describe, or the straw from Kiwi Crate. For early elementary school age children (age 5 – 8), I would teach them a simple method for building a finger, then encourage them to figure out how to build a hand. For older children, I’d just show them this post, and let them decide how they wanted to build a hand.