Dear All,
I was wondering if I could enlist some help and/or advice.
I am undertaking a project where I am transplanting a more modern engine and transmission in a 1990s Mercedes.
The old transmission uses a mechanical drive cable to drive the mechanical speedometer. This is the 'eddy current' type speedometer. This mechanical drive also drives worm wheel setup for the mechanical odometer.
The new transmission uses a Hall sensor and trigger wheel to generate pulses.
Essentially I want to utilize the hall sensor AND the appearance of the old mechanical speedometer and odometer.
I have envisioned 2 ways of doing this.
Option 1
Driving the speedo directly with a dc motor whose speed is controlled by an Arduino. The pulse signal from the hall sensor dictates the speed of the DC motor.
This would be fairly simple option however I am unsure whether there is an easy or practical way to control a DC motor over this wide RPM range.
From my research to date 1000 revolutions of the speedometer drive = 1 mile.
e.g. 1000 (revolutions per hour) = 1 MPH
1000 / 60 = 16.66 RPM
Therefore the DC motor would have to turn smoothly at speeds from 16 RPM (1 MPH) up to 2500 RPM (150 MPH).
Does anyone have any experience with using motors over this wide RPM range. I have seen that NEMA 17 stepper motors can be driven upto 4000 RPM or so but is this difficult to do so? What kind of motor do you think would be best for the job?
Option 2
Scrap the old internal workings of the speedometer and have a servo motor controlling the speedometer needle directly, pointing to a particular position/speed on the gauge according the rate of the pulses received from the hall sensor.
This would be most simple however the mechanical odometer would no longer work. I have thought about replacing the mechanical odometer with a small 16X1 (or similar) LCD display which could be done fairly discretely.
I would love to hear peoples opinions and advice on which option they think would be best.
The DC drive motor VS the Servo & LCD.
As you can tell I really want to keep the original look of the car so for me replacing the entire speedometer with an LCD is not an option !
Any comments would be appreciated !