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Servo / Stepper motor for DIY EGT gauge

Started by Kaellis991, December 05, 2021, 08:00:17 AM

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Kaellis991

I'd like to build a gauge for my home cockpit panel. The few gauges I have so far were all purchased from flight illusions. My switches are from real Piper aircraft and the autopilot is an INOP autocontroller III head I am repurposing. Which leads me to this idea. I'd like to try building an EGT gauge, for a new learning experience, out of an INOP real EGT gauge I found at an online salvage company and use the faceplate, bezel and part of the housing. The idea is to remove the guts of it, 3D print whatever I might need and use the 28byj-48 with the ULN 2003 to drive the needle. The physical building is the easy part for me, the Xplane programming will be the real challenge.
So is that stepper motor an appropriate one to use for an EGT gauge?

Mike.Powell

Yes. You can certainly make a gauge using the 28BYJ-48. You'll need a method to establish the needle zero position. For example, you could add a flag on the shaft that passed through an optical interrupter so the motor controller can learn where the needles points.

An X27-168 stepper motor is another choice. It's the type used in many automotive gauges. It's a much lighter weight motor that has its position initialized by rotating the motor up against internal stops. Its torque is low enough that it can't damage itself doing so. It has the further advantage that you don't necessarily need a driver chip. The outputs of an Arduino Nano can drive it directly.

Kaellis991

I take it you are the author of the book I just ordered... "Building Recreational Flight Simulators"...
Hopefully it will help me with this project. I'll go study up on the X27-168. Thanks.

Mike.Powell

The X27-168 steppers are cheap and easily available from multiple vendors through Amazon. Just search for "automotive stepper motors", and you'll get pages of options.

(And, yep, that's me.)

Kaellis991

December 05, 2021, 01:55:29 PM #4 Last Edit: December 05, 2021, 01:56:05 PM by Kaellis991
What's the difference between the 168 and the 589 motors?

Mike.Powell

The 168 motor has the shaft on the opposite side of the motor body relative to the electrical connection pins. The 589 has the shaft on the same side.

ame

I made a design for a 60mm gauge and talked about it here:
https://www.cockpitbuilders.com/index.php?topic=7836.msg56161#msg56161

I've left the driver as an exercise for the reader, but as Mike said you can drive them directly from a microcontroller.

bernard S

most excellent why because I have all these to do twice

Kaellis991

Quote from: Mike.Powell on December 05, 2021, 02:44:32 PMThe 168 motor has the shaft on the opposite side of the motor body relative to the electrical connection pins. The 589 has the shaft on the same side.

Just as you were posting this I found the info about the differences.

Kaellis991

Quote from: ame on December 05, 2021, 10:51:40 PMI made a design for a 60mm gauge and talked about it here:
https://www.cockpitbuilders.com/index.php?topic=7836.msg56161#msg56161

I've left the driver as an exercise for the reader, but as Mike said you can drive them directly from a microcontroller.

Even though I can do the 3d printing, I'd like to forgo most of that and use a real INOP EGT and then try to find a way to mount the stepper motor in it.

RayS

December 06, 2021, 01:23:10 PM #10 Last Edit: December 06, 2021, 01:27:07 PM by RayS
I'm going to shift gears here for a moment and say you don't need the stepper motor...

If it's like most engine gauges, it's got a d'Arsonval needle movement inside.

d'Arsonval movements only require 0v - 1v to drive them full scale. Simply take the gauge apart, locate the 2 wires going directly to the movement, and connect one side to Arduino Ground, the other to any PWM channel, but only AFTER you add a 5.6K resistor in series! (Otherwise you'll slam the needle to full deflection, possible breaking it.)

I use a 10k trim potentiometer in series with all my needle movements. They are calibrated by setting the PWM channel to "255", then adjusting the trim pot to full deflection on the scale.

Once that's complete it just a matter of writing the code.

There's a great plugin for X-Plane that allows you to connect a Teensy 3.2 directly to your sim computer and it will send/receive data to the Teensy with no middleware software to contend with.

You will need to exercise extreme caution when handling an open gauge, since the d'Arsonval movements are incredibly delicate. Breath on them wrong and it's destroyed.

You can find it here:
https://www.pjrc.com/teensy/td_flightsim.html

I use this architecture throughout my B1900D simulator, using about 20 Teensy 3.2 devices.

I have some code I can send you if you're interested.



Ray Sotkiewicz

Kaellis991

Ray,
It just so happens that I received Mike's book BRFS this afternoon and while looking through it I found his section on just that topic.
I'd certainly like to take you up on that offer.

Kaellis991

Quote from: RayS on December 06, 2021, 01:23:10 PMI'm going to shift gears here for a moment and say you don't need the stepper motor...

If it's like most engine gauges, it's got a d'Arsonval needle movement inside.

d'Arsonval movements only require 0v - 1v to drive them full scale. Simply take the gauge apart, locate the 2 wires going directly to the movement, and connect one side to Arduino Ground, the other to any PWM channel, but only AFTER you add a 5.6K resistor in series! (Otherwise you'll slam the needle to full deflection, possible breaking it.)

I use a 10k trim potentiometer in series with all my needle movements. They are calibrated by setting the PWM channel to "255", then adjusting the trim pot to full deflection on the scale.

Once that's complete it just a matter of writing the code.

There's a great plugin for X-Plane that allows you to connect a Teensy 3.2 directly to your sim computer and it will send/receive data to the Teensy with no middleware software to contend with.

You will need to exercise extreme caution when handling an open gauge, since the d'Arsonval movements are incredibly delicate. Breath on them wrong and it's destroyed.

You can find it here:
https://www.pjrc.com/teensy/td_flightsim.html

I use this architecture throughout my B1900D simulator, using about 20 Teensy 3.2 devices.

I have some code I can send you if you're interested.





Just received my EGT gauge and took it apart. It is definitely a d'Arsonval mechanism. There are some things in the case that I have no clue about.

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