Latest picture and update on my real 727 engine gauges working

[737NUT]

The EPR gauge is servo driven, Fuel Flow is driven by servo on a pot producing a 0-5Vdc output driving an old gauge set-up from Beta Innovations. The digital mechanical N1, N2, and EGT are driven off the PIC boards Mike Powell and I built and designed. VSI gauge is stock internals with a gutted servo driving the stk dc motor w/ feedback from the stk pot in gauge. All are interfaced thru OC servo cards and SIOC. ALL are working flawlessly now with over 100hrs of operation. The wiring is a little messy as this is a temp set-up in my apartment.

[twisted8]

Impressive! that looks sweet!

[Matt Olieman]

Impressive Rob

[737NUT]

Thanks Matt! It sure does enhance the flying on the sim. My next project is the radar altimeter.

[choffmann]

Hats off! This must be a very subtle and difficult work! Are those gauges original ones, or replicas? They look marvellous! What i/o cards do you use?
Chris

[737NUT]

The gauges are the real deal, using SIOC, Opencockpits servo cards, and custom built interface for the digital gauges.

[crashdog]

Hello,
my name is Gery and I am new to this forum. I'm building an MD80 simulator with as many real parts as I can get and use.
www.md80.ch. Currently I'm working on my overhead panel where I have a similar if not the same gauge to interface. I'm wondering if I can use the same approach as you did. But actually I'm not shure if the gauge really has a DC motor or if it's something else.

Here's a picture of it. It's the APU percent indicator. The same kind of gauges have being used for N1 and N2 as well.
There are 3 cables coming from the motor one red, one blue and a white one. Possibly this motor is a stepper or aircore ? I also have OC servo cards and also OC stepper motor cards. But would not know how to connect this one. From the pictures of the DC motor card it seames that only 2 cables go to your N1 gauges.?. Hope you could help me on to the right track here...

Kind Regards,
Gery

[Anderson/SBSP]

Your cockipt is amazing!!!

[737NUT]

Hello,
my name is Gery and I am new to this forum. I'm building an MD80 simulator with as many real parts as I can get and use.
www.md80.ch. Currently I'm working on my overhead panel where I have a similar if not the same gauge to interface. I'm wondering if I can use the same approach as you did. But actually I'm not shure if the gauge really has a DC motor or if it's something else.

Here's a picture of it. It's the APU percent indicator. The same kind of gauges have being used for N1 and N2 as well.
There are 3 cables coming from the motor one red, one blue and a white one. Possibly this motor is a stepper or aircore ? I also have OC servo cards and also OC stepper motor cards. But would not know how to connect this one. From the pictures of the DC motor card it seames that only 2 cables go to your N1 gauges.?. Hope you could help me on to the right track here...

Kind Regards,
Gery

You have a Synchro which operates on 400Hz AC power. Don't fret though as it is easy to convert! Remove the rear housing, remove guts of synchro, mount micro servo and use a coupler from servo city or make your own to go from servo to the needle shaft. Piece of cake!

[Leo Bodnar]

This is not a synchro and it does not operate on 400Hz.
The APU % indicator pictured uses 3 phase synchronous AC motor with permanent magnets rotor and unlike synchro uses only three wires.
Operation is achieved by spinning the motor at a speed proportional to APU speed. The airgap magnetic coupling causes the needle to deflect in proportion to the rotor RPM.
To drive this and similar RPM gauges you need to supply 3 sinusoidal signals shifted 120 degrees to each other somewhere in the region of 12V or possibly more.
There is no position or speed feedback (the AC motor works in open loop mode) so you have to figure out what voltage is enough to keep rotor moving up to speeds producing full scale deflection.
Because you are varying the drive signal frequency make sure you don't use the full voltage for very slow speeds effectively slowing down to have DC voltages on the coils. In such case there is no inductive impedance and motor coils can easily overheat.
What I mean is that if you find out that motor works reliably to full scale at e.g. 24V AC then don't allow 24V to remain on the coils when APU stops. Cut it off at e.g. 10% speed or ideally you can decrease driving voltage simultaneously with RPMs arriving at about 5V at zero RPMs.

So this is one of the simple gauges to drive, just excercise a little bit of caution and planning

Here is a picture of similar one running without any internal alterations. It also demonstrates how magnetic flux coupling works.
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