HOW TO Use X27-168 and X40 Steppers

The X27 stepper motor is a miniature stepper developed primarily as an indicator drive for dashboard instrumentation and other indicator equipment. It has a "Lavet" type stepper motor and two step gear train which reduces the rotation by a factor of 180 whereby a full step driving pulse results in a one degree rotation of the pointer shaft.

As the “Lavet” stepper motor needs 6 steps for a full rotation, one full rotation of the pointer shaft will need 1080 steps. Although this value is great for pointer resolution, the PS Cockpit System will not achieve the enough speed to drive the stepper motor for fast dials (i.e. Altimeter, FTIT, Rpm,…). In these cases Aircores motors are recommended.

Nevertheless, the X-27 stepper motor can be used in the PS Cockpit System for slow rotating dials (EPU fuel, Cabin Press,…) and the X40, which is basically to X-27 stepper motors in a train with double shaft, can be used in the watch and fuel gauges:

 

The X27 stepper motors can be connected directly to the 16/40 I/O expanders of the PSCockpit system in 4 consecutive outputs as the maximum current draw of these steppers is 20mA. Of course, the X40 will need 4 more outputs for a total of 8.

The configuration of the stepper motors in the PS Cockpit software is done in the same way as the unipolar stepper motors. See section “Configuring the stepper motor” in the following post:
PS Cockpit System - How to use steppers

The only difference is that “X27 168” has to be selected in the pull down list:

 

Edited on April 11th, 2016
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Typical connection for X27 and X40 stepper motors are as follows:

 

Please refer to your stepper motor datasheet for confirmation.

 

The connection between the stepper motor and the 16 I/O or 40 I/O expanders is straight forward: Select 4 consecutive outputs of the expander and connect them directly to 1 to 4 pins and avoid using outputs between two separate octo-inputs. This means that the four selected outputs have to be between 0-7, 8-15, 16-23, 24-31 or 32-39.



Be aware that X27 and x40 stepper motors do not admit different scales so the gauge you want to drive needs to have the same scale in the full range.

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Regards,

Shep