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VDO Cockpit International Electronic Speedometer, with dual scale.
Supports both 12 Volt and 24 Volt systems with bulb changes.
100 mm diameter.

The drive for this display system is a stepper motor, comprising a permanent magnet rotor within a crossed winding arrangement. A zero backlash gearbox at the output ensures a high drove torque and fine resolution. The gearbox has a reduction ratio of 43.2 : 1 and an internal mechanical stop. The stepper motor drive was developed specially by VDO for this product.

The drive produces a bipolar sinusoidal variable voltage using digital pulse width modulation. There is a 90
phase difference ( sine-cosine ) between the voltages on the two motor coils. This rotates the electromagnetic field through equidistant angular steps with a constant length resultant vector (sin2 + cos2=1).


The motor torque is therefore constant at each step with zero cogging. At the pointer one motor step equals 0.065.


The stepper motor parameters and the design of VDO control-driver electronics are carefully matched to ensure reliable operation of the system under all conditions. Optimised control algorithms ensure a visually smooth pointer motion.
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