British Science Week: How to make a mechanical arm
Craft an arm with fingers that can grip using objects from around your home
1. Make the arm
First, cut an arm shape out of a piece of thick, corrugated cardboard around 40cm long, with a hand at the end. Try to have the corrugated lines perpendicular to the arm’s length. At the elbow end of the arm shape make sure the arm widens slightly (your hand will need to fit here later). Then cut two more pieces of cardboard – one that’s 4 x 32cm and one that’s 4 x 35cm.
2. Hold your hand
You now need to decide whether you want to create a left or right hand. If you want to use it as a right hand, place the card ‘palm down’ on the table and stick the shorter strip of card that you cut onto the arm to strengthen it. Then turn it back to the arm side and stick the longer strip to the wider part of the arm near the elbow. This is your handle.
3. Finger grips
Now use a ruler to bend the fingers in three places. These are the joints of your mechanical hand. Now cut out eight small, 1cm sections of a plastic straw. Use thin strips of strong tape to attach these between the joints in the fingers. Then cut four longer, 3cm strips of straw and attach them to the palm so that they line up with the fingers.
4. Thread your fingers
Next, cut four lengths of thread, each around 40cm long. Wrap the end of one over the top of each finger on the model and tape them firmly to where the fingernail would be. Then feed the threads back over the top of the fingers and push them through the straws on the fingers and palm. They should reach your hand grip.
Make a loop at the other end of each piece of thread big enough for your finger to fit through and tie a knot in them to secure it. Put your hand through the grip you created, then put your fingers in each loop. When you close your hand on the grip the fingers should close on your mechanical hand too!
The thread here acts like the muscles in your forearms. The muscles are attached to strong, flexible bands of connective tissue called tendons. When you flex your muscles the tendons pull your finger joints inwards to close your hand – just like you’re doing when you pull the threads on your mechanical arm!
For more fun science activities, download your free British Science Week activity packs here: https://whf.cm/2OrCa3e
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