Mechanum wheel mount for pib.rocks

During the Februrary 2024 pib hackathon, we assembled a mobile base for pib.

Here are the improvised 3D-Printed parts we used for mounting the wheels.

We used mechanum wheels 150mm diameter, 46mm wide and a 25mm diameter mounting hole in the center.

The motor shafts are 8mm D-type, but only 18mm long.

To make this fit, two Pololu Mounting Hubs (https://www.pololu.com/product/2693) were used on each motor shaft. (On the front wheels only one flange and one printed dummy, as we ran out of flanges :-))

The flanges had an outer diameter of 25.4 mm, which was machined down to snugly fit inside the center hole of the wheels.

The wheels are held in place with a collet made out of PETG. Very unusual design, but works astonishingly well, even when excceding the rated load per wheel of 15kg. We loaded ca. 25kg, and nothing broke.

The collet is pressed onto a cone by 3 M4 screws, 40mm long. The collet expands and binds into the center hole of the mechanum wheel, holding it firmly in place. The outer disk on the collet is probably not even necessary, but may add some extra stability.

The cone is printed in 6 wesge shaped parts, three of which are mirrored version. This is done to allow printing the wedges sideways, so that layerlines run from top to bottom of the cone. this way, the layer lines of the collet and the cone are perpendicular and don't bind into each other when pressed.

The motors are 24V types and rated at 35W. They come with a planetary gearbox which outputs a nominal 150 rpm.

As the motors are plain open loop DC, we added an encoder for postion feedback. https://www.tinkerforge.com/en/doc/Hardware/Bricklets/Rotary_Encoder_V2.html

The gear train is a clip on ring gear, that snaps into some holes on the side of the mechanum wheel and a smaller pinion that goes on the encoder shaft. The encoder PCB is attached with a printed bracket to the aluminum frame.

Category: Robotics