[Diy_efi] Stepper Motor to drive mechaical speedo

[wscowell at aol.com]

Hugh thinks there may be a problem linking the variable frequency of pulses from the speed sensor to PWM output for the speedo drive motor.  I think it will be very simple. Use a counter in the PIC to sense time between speed pulses, use a lookup table to create pulse durations for PWM +r an algorithm, which would be easier to tweak for accuracy.


Sent using BlackBerry? from Orange

-----Original Message-----
From: "Hugh Keir" <hugh at sol.co.uk>
Sender: diy_efi-bounces at diy-efi.org
Date: Sat, 20 Oct 2012 12:27:08 
To: diy_efi at diy-efi.org<diy_efi at diy-efi.org>
Reply-To: diy_efi at diy-efi.org
Subject: Re: [Diy_efi] Stepper Motor to drive mechaical speedo

Hi Mike,

I am not an electronics engineer, so have perhaps headed off on a tangent.

If you were able to post links to the pieces of kit that you would use,
that would be a great help.

I have a PICkit 3 programmer and am familiar with the principle of PWM,
but not how you would put it all together.

One of the biggest problems is tweaking the frequency output of the hall
sensor to drive the speedo at the right speed.

Perhaps some eBay links of the items you propose would help with the
global sourcing of parts.

Cheers

Hugh

Hi Hugh,
 From an electronic engineer's perspective a suitable dc motor is far
better, a cheapie
pwm radio/control type as someone else mentioned is ideal. However, some
years ago
I had to recalibrate the speedo on a vl calais turbo and found I could
move the
rotating magnet assembly further or closer to the reluctance wheel, so if
you have any pickup at all anywhere on the rear - or even front then you can
try this trick instead,
regards
mike

At 05:46 PM 20/10/2012, you wrote:
>I have tested a smaller stepper motor, but it was too slow.
>
>Have ordered a non geared stepper motor which has a spec sheet that says
>its good for 500 PRM and will try again.
>
>Stepper motors are torquey at very low RPM, so if this motor will turn the
>speedo, I will keep going with it.
>
>Be interesting to see whether the stepper or a DC motor system works best.
>
>Hugh
>
>
>
>
>Normally it's going to be 1000 turns\mile.  Dials out to be 60MPH as well.
>Some British speedos are different, but are usually marked in tiny script on
>the face.
>Jim
>
>-----Original Message-----
>From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org] On
>Behalf Of jayjunk at laserpubs
>Sent: Friday, October 19, 2012 9:23 PM
>To: diy_efi at diy-efi.org
>Subject: Re: [Diy_efi] Stepper Motor to drive mechaical speedo
>
>Ok - is there a standard revs/mile for a speedometer/odometer?
>The only thing I found so far is for a Vincent motorcycle!
>(1600 rev/mile)
>
>cheers...
>
>On 10/19/2012 5:04 PM, jayjunk at laserpubs wrote:
>> Funny- I was going through my garage and found my stash of gauges.
>> I found a 120 mph mechanical speedo (SW style) that will be just fine
>> for my mutant Corvair.
>> Now I need to look around for a DC motor with enough grunt to drive the
>> speedo!
>>
>> cheers
>> Jay
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