A Continuously Variable Transmission (CVT) with mechanical tachometers.


This CVT was based on Zblj’s works. It enables a variable ratio on the output from 1:1 to 1:5. The CVT chooses the most suitable ratio functions of the resistive torque on the output. The principle is based on two differentials which are connected side by side with a first gear : 1:1 and a second gear on the other side : 1:5. The side with the 1:5 gear has also a friction pin in order to limit the rotation.


While there is not resistive torque (or low), the rotation goes through by the 1:1 gear because the 1:5 has locking torque thanks to the friction pin. When a torque is detected, the friction pin starts to spin and the rotation goes through the 1:5 gear which reduces the speed and increases the torque, the speed of the motor remains constant.

The two mechanical tachometers are not useful for the functioning of the CVT, they are useful to visualise the instantaneous speed of the motor (on the left) and of the output (on the right). Of course when the torque become too high, (around more than 5x motor torque), the speed of motor is reduced.

This CVT enables to have :

  • A constant speed of the motor (200 rpm)
  • A infinity of variable ratio between 1:1 and 1:5
  • A variable speed between 200rm (1:1) and 40 rpm (1:5)
  • A variable torque between 50N.cm (1:1 = motor torque) and arround 250N.cm (1:5)

Of course, some torque are lost because of the friction pin but the torque is increased by 5 so the loss is negligible regarding the increase.

Here is some pictures in order to re-built it. You can also download the ZIP file – 2mo.

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