Thymio as steelyard


This page includes the script of the video. Sentences in italics are those presented in the clip


Opening credits

Question about Thymio

  • Thymio can be used to weigh things. But how?

General concept presentation

  • Principle
    • Different types of scales exist, but we will explore only one type: the steelyard.
    • The steelyard exists since the 2nd century BCE. It is made of 2 unequal arms: the one on the side of the mass we want to measure has a fixed length and the other one has a variable length.
    • Indeed, we are not trying to balance the system by equalising the masses but by changing the lever's length. The arm with the counterweight is graduated so as to directly indicate the weight of the object.
  • Example
    • To better understand how this works, here is an example.
    • If we want to weigh a 20g object with a 20g counterweight, both masses must be at exactly the same distance from the fulcrum.
    • However, if we want to weigh a 40g object with a 20g counterweight, the counterweight must be twice as far from the fulcrum as the object. All that is important is that the moments defined from the fulcrum balance out.

Concept presentation with Thymio

  • We have built a small Lego steelyard with our robot Thymio II. Indeed, this robot has an accelerometer which lets it measure its tilt according to gravity. This makes it possible to know if the robot is horizontal or not, therefore if the arm is tilted or not.
  • When Thymio detects that it is not horizontal, it moves along the arm with the help of a rack-and-pinion and the motorization of one of its wheels.
  • When the system is balanced out, Thymio stops and turns green. We can then know the object's weight compared to Thymio's weight by observing the arms' lengths.

Closing credits

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License