• Determination of the input and output speed ratio and the torque distribution.
  • Study of the efficiency.
  • Study of the use of a differential as a simple transmission system.
  • Visualization and demonstration of the behaviour of a differential when used as a means to provide a drive.
  • Verification of the gear ratio.


  • An input pinion.
  • A crown-wheel.
  • Three gears, named sun gears.
  • Two gears coupled to the shafts of the wheels, named planetary gears.
  • Three pulleys with protractor.

The unit includes a differential group consisting of:

  • Input pinion (Z = 21).
  • Crown-wheel (Z = 63).
  • 3 sun gears (Z = 16).
  • 2 planetary gears (Z = 32).

When a vehicle takes a curve, the external wheel must travel a greater distance than the internal wheel. The shaft is divided to enable the wheels of a same shaft have different speeds, guaranteeing the coupling of both parts with the differential. It is difficult for many students to visualize the action of a differential when used to provide a drive from the gearbox to each shaft, allowing at the same time an independent motion between the shafts. The unit has been designed to demonstrate the action of the elements of a differential: the crown-wheel and the pinion. The unit, simulates a differential mechanism. The function of the differential mechanism is to enable the drive wheels rotate at different speeds, regardless of whether they are the front or rear wheels. When the vehicle is travelling in a straight line, the differential must behave as if it were rigid and make both wheels rotate at the same speed. It means that in this situation the sun gears do not spin around their own axis, in other words, they act as wedges to transmit the motion of the crown. Therefore, the differential allows to provide the torque to either both wheels or only one wheel. When both wheels have the same load the differential supplies the same torque to both of them, but when one of them supports a greater load than the other, then motion is distributed uniformly. The input pinion transfers the power to the crown. That motion of the crown drives the sun gears and they, rotating together with the crownwheel, transfer the power to the planetary gears. The planetary gears at the same time transfer the power to the output shafts, allowing. Them to rotate at the same or different speed. The unit is mounted on a frame consisting of aluminum profiles with panel made of painted steel, with legs that enable to locate it on an appropriate surface. On the other hand, it also includes brackets that allow to hang the unit on a wall. Gears are distributed on different shafts (input shaft, right output shaft and left output shaft), which are mounted on ball bearings that will allow low inertia and a decrease of the losses due to friction. Both the input shaft and the output shafts have pulleys equipped with protractors with the aim of enabling the student to determine and verify the torque and speed ratios. They are made of aluminum and their radius is 40mm. In order to carry out some of the practices with unit, 3 sets of weights “B” type are required. (See “required accessories” section).