[Diy_efi] Stepper Motor to drive mechaical speedo

[Chris McKinnon]

Assuming you can't find a fast enough stepper, my suggestion is to look 
at DC servo motors as they have a position sensor in them for feedback. 
A tiny one should work fine since you don't need any real torque. You 
can either run them from a real servo amp or just feed them with PWM.

Chris

> 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
>
>
>
>