[Diy_efi] Stepper Motor to drive mechaical speedo

[Milosz Kardasinski]

I have experimented with a speedometer from a Jeep. I used a Nema 8
200steps/rev motor direct coupled to the speedo.

I came to the conclusion, that microstepping is unnecessary. Stepper
drive voltage is directly proportional to max speed, with a 12v
drive...selecting a motor with the lowest possible winding inductance
is key to higher RPM.

MK.

On Sun, Oct 14, 2012 at 11:14 AM, Hugh Keir <hugh at sol.co.uk> wrote:
> 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