[Diy_efi] Stepper Motor to drive mechaical speedo

[bhu678 at gmail.com]

Try looking at a modern 'analog' gauge.  They're mostly digital with 
only the analog needle left from days gone by.  I'm currently looking at 
using a speedo and tach from a '95 Maxima to drive the old analog faces 
in my '74 260Z.  If you rlly want to spin your old school speedo, use a 
Mabuchi slot car motor w/ a PWM speed controller on it, DC motors are 
made for spinning fast.  Stepper motors don't spin, they step.  They're 
made for precision movement, not speed.  Anyway, use a freq. to volts 
converter to read the driveshaft speed, then use volts to pulsewidth to 
drive the DC motor.

Scott B


On 10/14/2012 1:28 PM, Milosz Kardasinski wrote:
> 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
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