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Car motors for speedometer, fuel-meter, etc.

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banh

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I opened up a few speedometer, fuel-meter on the car dashboard, and found that what controls the indicator's movement are actually motors.

All motors for this purpose are same type: they have copper coils + 4 poles...

i wonder what type of motor are they and how to control them..
 

Hi banh,

It’ not really a motor it has similaritys but it is a ”Moving coil meter”: **broken link removed**
Hope this will help you!
 

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    banh

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thanks,
i'll check it out again.


for these kind of devices, how do we know the starting point (i.e. the 0 point of the needle ) ?

inside my speedometer, fuel-meter, there's no "spring" to pull it back to the beginning. it's like free rotating.

so I just guess the starting point is when the magnetic field of the coil "align" with that of the magnet attached to the needle -> hence they don't force against each other.
 

banh;

Some of them have a return spring and some do not, they rely on the magnetic field to get a starting point just like you assumed!
 

Ante said:
Hi banh,

It’ not really a motor it has similaritys but it is a ”Moving coil meter”: h**p://chem.ch.huji.ac.il/~eugeniik/instruments/test/galvanometers.htm
Hope this will help you!
Click to expand...


more exactly, they are air core meter:
**broken link removed**
 

In most recent cars, with use CAN protocol, these actuators are bipolar stepper motors. FIAT car's, like Palio, Marea and Stilo; use this type of motors in dashboard.
 

leomecma said:
In most recent cars, with use CAN protocol, these actuators are bipolar stepper motors. FIAT car's, like Palio, Marea and Stilo; use this type of motors in dashboard.
Click to expand...

thanks. Do you have any links/resources about this?

I guess when using stepping motor, microstepping is needed.
 

Look this site:
**broken link removed**

If the coils have a commom point, this motor is unipolar, if not, two independent coils, the motor is bipolar. In half step mode (microsteping) you have more precision, and less torque. National, TI, Infineon have good drivers for this type of application. L293 is most commom and it support 600mA continuous.
 

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