Motor enclosure – part 2

Firstly, I have to apologise that I’m slipping behind my (self imposed) schedule of weekly updates. I’ve been a bit short of free time recently, so progress has suffered somewhat…

Since last posting, I’ve turned a first prototype pulley on my woodworking lathe. It’s made from a scrap of nylon sheet, and attached via a standard servo horn. (Hobby servo output shafts are splined, and I couldn’t see a way to machine my pulley to mount to the splined shaft directly).


I’ve opted for 20mm internal diameter on the cable channel, which is where I wanted to be in respect to maximising the leverage against the cable resistance, but will need to see whether the bend radius is a bit tight for the cable. My concern is that there is very little spring tension on the cable when the Tacx trainer is at minimum resistance, so if the cable takes on any curve from the pulley when unwound, it may have an impact on accuracy when returning to this position.

pulleyI’m just waiting for a delivery of some tiny M2 nuts and bolts to fasten the pulley to the servo horn. Once I have these, I’ll be able to start some further testing.

If it does prove to be a problem for the standard cable, I’ll increase the bend radius of the next prototype. There would be one unforeseen advantage to this. The servo horn itself has a 21mm diameter, which means the current 20mm cable channel has to be ‘stacked’ on top of this – further away from the servo body, resulting in more leverage & stress on the servo output shaft and bearings.

If the cable channel diameter is increased to something like 25mm then I’ll be able to cut in a much deeper recess for the servo horn, bringing the cable channel in closer to the servo body and reducing the leverage on the output shaft.

More updates soon…