Electronics > Projects, Designs, and Technical Stuff
Aircraft instrument servo motor
duak:
Just last week I was showing one of my sons a few old aviation instruments and trying to get him interested in building something with them, but no luck. Anyway, I looked into synchros a bit.
Here are a few links to drivers on this site:
https://www.eevblog.com/forum/projects/driving-a-synchro-from-a-uc/
https://www.eevblog.com/forum/projects/driving-a-synchro-from-digital-logic/
Analog Devices has a fairly detailed writeup on how it could be done using one of their products:
https://www.analog.com/media/en/training-seminars/design-handbooks/synchro-resolver-conversion/Chapter4.pdf
An Arduino should be able to generate the low level signals for a 3 or 4 channel power driver. Note that it doesn't matter too much whether the sychro is three phase or two phase. There is a mathematical transform to convert from one to the other and it's a matter of the appropriate voltage and phasing of the windings.
It would be interesting to try DC on the reference winding and try to turn the rotor with some AC signals. I expect it will turn but it will also require an encoder so the driver can supply the correct drive to build up the power angle. IOW, it will be easy to stall the motor otherwise.
Cheers,
georges shed:
Thankyou for the comments, They sparked a long 4 hour deep dive into syncros and some old blog posts from 2006. It all seems very complex and outside of my current technological ability so this project is going to be shelved for a while but will always be taunting me in the back of my mind so will definatley be revisited. I think the jist of it is figuring out a way to generate 26v 400hz sine and cosine signals and the various control methods to vary their amplitudes.
georges shed:
some of the best sites i found during my reaserach, if youre intrested :)
https://www.electro-tech-online.com/threads/3-phase-syncrhos.142595/
https://www.avrfreaks.net/forum/avionics-instrument-motor
http://www.ddc-web.com/documents/synhdbk.pdf
http://mikesflightdeck.com/oldnews/oldnews_2006.html
http://www.pdp-11.nl/viperpit/altimeter/altimeter.html
https://forums.eagle.ru/showthread.php?t=145264&page=4
http://www.scottbouch.com/aircraft-cockpit-instrument-simulation.html
Martinn:
I don't think you should give up already. I am not sure how this instrument works, but my guess would be that you don't need the 400 Hz AC signal. I would think that if you connect the reference to some fixed DC value, you can use the two phase coils to drive it like a brushless or stepper motor.
Why don't you simply connect reference and one of the drive coils together and apply a small DC voltage (lab supply, start slowly from 0 V) and see what happens.
duak:
Martinn asked a good question so I looked it up. A synchro or resolver has an additional set of windings called the Rotary Transformer than gets around needing slip rings, but can only pass an AC signal to the reference winding. see https://www.amci.com/industrial-automation-resources/plc-automation-tutorials/what-resolver/
It occurs to me that if the indicator has slip rings instead of a current transformer then DC could be applied to the reference winding. It's still worth trying a DC signal to see what happens. Since it's an altimeter that's inside a closed loop, it might be a simplified design.
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