A tendon-driven prosthetic hand is a model that uses strings to copy the way tendons bend human fingers. In this school project, a glove acts as the hand shape, while strings, guides, and attachment points turn a pulling force into finger motion. The design helps students connect anatomy, engineering, and physics in a hands-on way.
It also shows how assistive technology can improve daily life for people with limb differences.
Each string works like a tendon because it transmits tension from the wrist or palm area to a finger segment. Pulley loops guide the string so the finger curls in a controlled path instead of pulling sideways. By changing tendon attachment points and pulley placement, students can compare grip force, finger curl, and pinch precision.
Testing the hand with objects of different sizes and masses helps students use evidence to improve the design.
Key Facts
- Tension is a pulling force in a string, and it can transmit force around bends when guided by pulleys.
- Torque = force x lever arm, so a tendon farther from a joint can create more turning effect.
- Work = force x distance, so pulling the tendon farther can move the finger through a larger curl.
- Grip force can be measured by pulling or squeezing a spring scale, with force recorded in newtons.
- Pinch precision depends on thumb position, fingertip alignment, and repeatable tendon motion.
- A good engineering test changes one variable at a time, such as tendon attachment point or pulley placement.
Vocabulary
- Tendon
- A tendon is a strong cord in the body that connects muscle to bone and helps move a joint.
- Tension
- Tension is the pulling force carried by a string, cable, or tendon.
- Pulley guide
- A pulley guide is a loop or small channel that changes the path of a string while keeping it close to the finger.
- Torque
- Torque is the turning effect of a force around a joint or pivot.
- Prototype
- A prototype is an early working model used to test and improve a design.
Common Mistakes to Avoid
- Attaching the tendon too close to the joint, because this gives the string a very small lever arm and weak finger curling.
- Letting tendon strings rub freely across the glove, because friction wastes force and makes the finger motion inconsistent.
- Changing several design variables at once, because it becomes impossible to know which change improved or worsened the hand.
- Testing only with one object, because a hand that grips a large cup may not also pinch a small pencil accurately.
Practice Questions
- 1 A student pulls a tendon with a force of 8 N, and the tendon acts 0.03 m from a finger joint. What torque does the tendon create at the joint?
- 2 A prosthetic glove lifts a 0.5 kg object. Using g = 9.8 m/s^2, what minimum upward grip force is needed to support the object without accelerating it upward or downward?
- 3 Two teams build glove hands. Team A places pulley guides close to each finger joint, while Team B uses only one guide near the palm. Explain which design is likely to give more controlled finger curling and why.