Attachment for speedometer speed sensor (FreeCAD)

The original mount for the speed sensor of my Sigma BC 14.16 STS CAD speedometer has a very small joint. While being mounted on the front suspension strut of my velomobile, it broke…

The replacement sensor is now glued onto my new holder. The contact area is about 1 square inch and I used industrial glue (Sikaflex) – so I'm pretty sure that this will last. 😁 The holder is attached with two cable ties, a piece of old butyl inner tube prevents it from twisting around the strut. The sensor now has a perfect orientation towards the magnet. 

You can alter values in dim spreadsheet in FreeCAD to make the holder fit to your needs. Parameters most likely to be changed are marked bold:

• D_Federbein – diameter strut
• Dicke_Gummi – thickness anti–twist rubber
• Offset_Sender_Federbein – how far the tip of the sender stands out (sideways) from the strut (see 2nd image)

Altering some of the values may break fillets and chamfers so you have to re–model (or just remove) them.

The distance from the tunnels for the cable ties to the bottom / top of the holder is chosen so that in printing the tunnels connect to the top / bottom surface for extra stability with less infill.

In the image above you also see the correct orientation of the cable ties, so that their head sits perpendicular on the flat surface. This prevents the ties from buckling. The yellow "dummy strut" helps glueing the anti–twist rubber in place.

Printing

PETG, 0.4 mm nozzle, 0.25 mm layer height, 2 perimeters, 30 % lightning infill, arachne, no supports

Assembly

Cut away that link from the speed sensor.

Then you can glue it onto the holder and also glue the anti–twist rubber in place as shown above. After the glue is dried you can cut away the protruding rubber.

Finally, take two cable ties and attach the sensor to the suspension strut. 

Bonus

1. The new holder even weighs about 1 gram less than the original. 😎
2. In the first part of this video I show how to make a better magnet for the speed sensor from 1 neodym magnet, a cable tie and some heat shrinking tube:
    

… Happy riding!