Wood Flexible Wheel for the Thymio Robot

These instructions show the design of a flexible wood wheel for the educational Thymio robot.

Version en français ici

I tested many wheel designs. The one chosen for this example is based on two flexible elements oriented perpendicularly. The two flexible elements are on two different diameters and are separated by rigid rings (in green). One internal flexible element (in blue) ensure the horizontal (in the image) flexibility. The two semicircular arms allow to avoid the rotation of the central element. The external flexible element (in red) just reproduces the same mechanism rotated by 90 degrees. The two flexible elements have not the same dimensions, and therefore need to have a different thickness to have a similar flexibility. This can be calculated but I will not enter in the details here, but this is a nice topic for study :-)

The Thymio robot has three contacts points to the ground. Two are ensured by the wheels, one by a contact point to the ground. This third point should also be flexible. Therefore a frame clips to the Thymio body to provide a flexible contact point. The flexibility is made by a long spring (wood) lever.

Here you can find the SVG file for cutting the elements on a 3mm thick plywood.

The frame is not trivial to assemble, please have a look to the video. The frame is hold in place by some elements clipping to the buttons and the pen hole of Thymio.

The wheels are assembled with 4 pins each.

The testing showed in the video has been done with three experiments:

1. Crash test into a wall. This is at low speed and the flexibility is hard to observe directly. In slow motion one can see the oscillations.
2. Impact of an object. This is also better visible in slow motion videos, but the effect of the flexible element is visible directly.
3. Falling robot. This is the most impressive experiment, but a too high fall, higher than 15 cm, can brake the wood wheel. This type of high is not an issue for the robot, that is very robust.