Low Tech Prototyping
In my earlier VanSpoof prototyping posts I was working with circuit boards designed for testing and debugging, but not really suitable for installing on to the bike. They're too big and the wrong shape to fit in any of the any wee nooks or crannies around the bike, so I need to come up with something smaller and find somewhere to install it.
A chap called Max reached out and suggested that we could possibly design a board that could fit inside the frame tubes, but I'm not sure if the current STM32 chip is small enough to fit through the existing hole used by the e-shifter cable. There are other, smaller, chips available but I don't know if they've got the right peripherals on the correct pins for our purposes.
Instead, I looked at the device replaced with my VanSpoof, the e-shifter itself!
Taking the shell apart reveals a series of gears driven by a motor. Taking out the gearset shows the PCB within the e-shifter. It's a pretty convoluted shape, with cutouts for the gears' bearings and it has been heatstaked in place, so a 1:1 replacement is off the cards. Removing the motor leaves a mostly rectangular area which could give us enough space to fit all our components.
Due to the awkward position of the space and the surrounding case, taking direct measurements with my callipers proved tricky. Its jaws weren't quite long enough to prevent the body from fouling on the case. This is when I returned to one of my favourite low tech prototyping methods. 1:1 scale models from paper, card, or board! Using some thin MDF sheets I recovered from old picture frame backings, I cut and trimmed a piece until it was a snug fit in the space.
I could then pop that piece back out of the space and measure it instead.
Measurements of 31.45 mm reducing to 27.45 mm were taken for the width of the cavity.
The depth of the space was found to be 21.55 mm reducing to 18.20 mm.
Transferring these measurements to KiCAD let me throw together a quick design to see if all of the components are likely to fit. I still need to work out if everything is routable within these new constraints, but my early tests are hopeful.
I believe the incoming cable, with Orange, Black, Brown and White wires, is terminated with a JST-SH connector. This hopefully means that I can use a JST-SR header, probably a BM04B-SRSS-TB, and make the VanSpoof a drop-in replacement part for X3 and S3 owners.
2025-03-22