The diagram shows the drive system of a small robotic arm used to sort medicines into boxes. A d.c. motor rotates a pulley, pulling a cable to raise the arm...
Question 1 Report
The diagram shows the drive system of a small robotic arm used to sort medicines into boxes. A d.c. motor rotates a pulley, pulling a cable to raise the arm. The motor coil is inside a magnetic field and the controller can reverse the battery connections. A limit switch stops the current when the arm reaches the top. The engineer explains that the motor effect changes electrical energy into useful mechanical energy, although some energy is dissipated by the resistance of the wires and by friction in the pulley.
(a) What is the useful output energy of the motor? [1]
(b) Which two energy transfers are unwanted in this system? [2]
(c) What change to the electrical supply makes the arm move down instead of up? [3]
Answer Details
(a) The useful output is kinetic, or mechanical, energy [1], because the motor produces rotation that raises the arm.
(b) Electrical energy is transferred to thermal energy in the wires or coil because of resistance [1]. Energy is also transferred to thermal energy and sound because of friction in the pulley [1]. [2 marks]
(c) Reverse the battery connections, or polarity [1]. This reverses the current in the coil [1], reversing the motor-effect forces and the motor rotation, so the cable unwinds and the arm moves down [1]. [3 marks]
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