[Diy_efi] Stepper Motor to drive mechaical speedo

[Hugh Keir]

Hi Guy's

I have been trying to sort out a stepper motor to drive a mechanical
speedo on a TR7.

The problem started after an engine and gearbox change from a car with no
mechanical speedo drive and also a change of diff ratio.

As a first step, I bought a 28BYJ-48 12V stepper motor from ebay plus a
controller with on board frequency generator to drive.

The first problem I have faced is that the stepper motor is not capable of
spinning fast enough to drive the speedo.

It seems to peg out at about 160Hz measured at one of the stepper motor
phases, any faster on the input and the stepper motor freezes.

The declared stepper motor frequency is 100pps with a step angle of 5.625?
and a step reduction of 1/64 on the gearbox which I calculate should be
2.5 RPM. I reality I am getting 18RPM, either way this is not fast enough.

I intend using a GT101 hall sensor on the propshaft to feed a digital
pulse to an as yet to be sorted stepper motor control board.

I wonder if anyone has attempted anything similar?

Thanks

Hugh