[Diy_efi] Stepper Motor to drive mechaical speedo

Mike niche
Mon Oct 15 00:31:37 UTC 2012


The cheaper servos just have a speed feedback, thats all you need as your
primary output is speed, position feedback, in that application isnt helpful,
if however, it already has a quadrature angular position feedback output then just use
one channel and its frequency will be directly proportional to speed :-)
Mike

At 02:53 AM 15/10/2012, you wrote:
>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
>>
>>
>>
>>
>
>
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