Inspired by viih's ffbeast mount model. My mt6701 is an i2c board 23mm on a side and didn't fit. It needed to be mounted outside of the bell with a wheel spacer that could hold a 4mm magnet.
In the end, I separated the spacer from the magnet holder because of its utility and the ability to print it without supports.
To install the sensor, wires need to be soldered to the back of the mt6701 board and routed through the channel in the shaft of the pcb holder. The pcb holder is then inserted into a 6.5mm hole drilled into the motor shaft. Note, the motor shaft needs to be drilled through to route the wires. This can be any size to fit your wires, but the outermost part of the shaft needs to be 6.5mm to a depth of at least 10mm.
I'm using 30g wire wrap wires to save volume, but any wire that fits should work.
The pcb holder has screw holes to align with the sensor, but I just dropped a little bit of superglue onto the board instead. I secured the wires into the channel with a drop of hot glue for strain relief.
The motor bell has to be assembled with the magnet cap (4mm magnet glued into the depression) and the spacer before reassembling the motor. The spacer uses a standard 6 hole pattern for steering wheels.
The author marked this model as their own original creation.