A cardboard robotic claw is a fun way to explore how machines help us grab, lift, and move objects. The project uses simple materials like cardboard, popsicle sticks, brass fasteners, string, rubber bands, scissors, and small spools or pulley wheels. By building the claw, students can see how a small pull from a hand can create motion at the claw tips.
This matters because the same ideas are used in robot arms, prosthetic hands, factory grippers, and space tools.
The claw works by combining levers, linkages, pivots, string, and elastic force. When you pull the string, it moves through a pulley path and pulls the claw arms inward to grip a ball or cube. Rubber bands can pull the arms back open when the string is released.
Careful spacing of holes, smooth pivots, and balanced claw arms make the motion stronger, smoother, and easier to control.
Key Facts
- A lever turns around a pivot, also called a fulcrum.
- Mechanical advantage compares output force to input force: MA = output force / input force.
- A longer handle can make a lever easier to pull because torque = force x distance.
- String tension pulls along the direction of the string, so pulley placement controls the direction of motion.
- Rubber bands store elastic potential energy when stretched and can help reopen the claw.
- Friction at pivots and pulleys can waste energy, so holes should be neat and fasteners should not be too tight.
Vocabulary
- Lever
- A simple machine that turns around a pivot to move or lift something.
- Pivot
- A fixed point where a part can rotate, such as a brass fastener through cardboard.
- Linkage
- A set of connected bars or sticks that transfers motion from one part of a machine to another.
- Pulley
- A wheel or spool that guides a string and changes the direction of a pulling force.
- Tension
- The pulling force carried by a stretched string, cord, or rubber band.
Common Mistakes to Avoid
- Making the pivot holes too tight stops the claw from moving smoothly because friction blocks the rotation.
- Using uneven claw arms makes the claw twist because one side moves farther or faster than the other.
- Tying the string in the wrong place gives weak closing motion because the pull may not create enough turning effect around the pivot.
- Skipping the rubber band return can leave the claw stuck closed because there is no force pulling the arms back open.
Practice Questions
- 1 A claw handle is 12 cm from the pivot, and a student pulls with a force of 4 N. What torque is applied to the pivot using torque = force x distance?
- 2 A string pulls a claw arm with 3 N of force. If the claw tip pushes on a foam cube with 1.5 N of force, what is the mechanical advantage using MA = output force / input force?
- 3 If a robotic claw closes but cannot lift a foam ball without dropping it, explain two design changes that could improve its grip and why they would help.