Introducing the Resolver

Introducing the Resolver

What is a resolver? Simply put, a resolver is a transformer with a fixed input winding and two rotating output windings placed orthogonal (90 degrees) to each other. Like a transformer, a resolver only works with AC voltages.

If a third output winding is added and they are spaced 120 degrees apart instead of 90, then the resolver becomes a synchro. So, synchros and resolvers are closely related and are often referred to as synchro-resolvers.

They are used in for instance robots, tools, weapons, ships, and airplanes as they are not only very precise but also extremely robust and reliable. They support wide temperature ranges and can handle shocks and vibrations. Resolvers excel in harsh environments.

If you put an AC voltage on the input winding of a resolver, a voltage develops on the output windings. However, as the output windings can rotate, the amplitude of the output voltage depend on the angle between an output winding and the input winding. One amplitude follows a sine wave, the other a cosine wave. From these amplitudes the angle between the rotating and fixed windings can be calculated. It is also possible to determine rotation direction and speed.

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[kwgm]

I too, a former electrical engineer, had no idea what that device was for. Thank you for the informative presentation. That's a clever little device, useful for many applications

[danielduncan]

When I was in high school I got a pair of synchros (also called selsyns) at an electronics surplus store. The single windings were rated at half the US standard AC line voltage, so I put them in series, then connected the triple windings in parallel, and made a rather strong repeater. I had a lot of fun with that myself, and later while teaching physics and electronics. If I ever get the garage cleaned out I will probably find them, and have some more fun now that I am retired.

[LousyPainter]

Awesome introduction! Thank you my friend. Looking forward to watching more on these and their applications.

[farhanaumar]

After a lot of videos, I found this to be most helpful

[alkodjdjd]

GREAT VIDEO you made something complicated into something simple and practical, God bless you for it

[andypughtube]

Resolvers are fairly easy to read with an Arduino or similar. They don't particularly care about the excitation voltage, and (perhaps surprisingly) work fine with square-wave excitation. So you just need to measure the two voltages and use the atan2 function to get the angle out when excited with a 5V or 3.3V square wave from a 50% duty cycle PWM generator.
You need a phantom baseline voltage at half Vcc, but you can create that with a zener.

[krishnasa]

Thanks a lot for Introducing the Resolver with a great explanation.

[simonbaxter]

These are used extensively in the aerospace industry and many aircraft systems rely on them!

[alzalame]

Very good explanation, thank you very much , i am going to search the web to get some of these resolvers .

[VoltaicoDevelopment]

Thank you for this video!
I have a question: why does the resolver rotor have 2 windings? Isn’t one enough to measure the rotor angle?