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Peter Elsler
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SYNCHROS "SELSYNS" as Output Devices -

In this case, the SYNCHROS or “SELSYNS, “AUTOSYNS” are used as “motors” to drive the exact position of indicator needles or discs on aircraft instruments, such as on the RADIO MAGNETIC INDICATOR (RMI).

In my example of the shown RMI, there are the following devices:

3x   Bendix AUTOSYN – Types No. AY 20362B and AY 20191B

      Rotor:      1 Phase  26 V            400 Hz  -  2 cables

      Stator:     3 Phases  11.8 V       400 Hz  -  3 cables

    

1x   Bendix AUTOSYN – Type No. AY 503-...   (the smaller one)

       Rotor:      1 Phase  26 V            400 Hz  -  2 cables

       Stator:     3 Phases  11.8 V       400 Hz  -  3 cables

 

1x   Bendix LOW INERTIA MOTOR – Type No. LK-/006-78

      4 cables: red + black,  blue + orange

 

In case of the AUTOSYNS, I want directly connect the 3 stator coils and the rotor coil to 4 H-Bridges per SYNCHRO and drive them by the ARDUINO, using the PWM-Mode.

In first tests that I tried with PWM signals, I could drive the coils even at lower voltages between 7.5 V and 12 V. I have no idea of the apropriate Arduino (UNO or MEGA) program code to realize the 360° needle movement on the instrument, with the required resolution of minimum 1º. Therefore, I ask you, the Arduino specialists on the forum, for help.

As shown in literature, 400 cycles are used in aeronautics and naval industry to reduce the size of electronic parts and diameter in cabling to reduce weight. Therefore 60 Hz signals cannot be used to drive these instruments, otherwise the small coils would burn because of current increase.

 

Any help would be appreciated.

In advance, many thanks.

 

Peter

RMI 01
RMI 02
RMI 03
RMI 04

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Peter Elsler
(@peter-elsler)
Active Member
Joined: 3 months ago
Posts: 19
Topic starter  

SYNCHROS "SELSYNS" as Output Devices - In this case, the SYNCHROS or “SELSYNS, “AUTOSYNS” are used as “motors” to drive the exact position of indicator needles or discs on aircraft instruments, such as on the RADIO MAGNETIC INDICATOR (RMI).

Good descriptions of all types os Synchros can be found on the internet, such as:

https://www.tamagawa-seiki.com/products/resolver-synchro/synchro-about.html

https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1947/05/page50/index.html

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-13/selsyn-synchro-motors/

In the following, I want to explain the approach that I would prefer, if possible:

In case of the AUTOSYNS, I want directly connect the 3 stator coils and the rotor coil to 4 H-Bridges per SYNCHRO and drive them by the ARDUINO, using the PWM-Mode. I want to use PWM square waves from the arduino to create magnetic fields in the coils, one permanent magnetic field in the rotor and 3 changeing magnetic fields in the stator coils, depending on the position of the indicator needle.

SYNCHRO with H Bridges big

I have no idea of the appropriate Arduino (UNO or MEGA) program code to realize the 360° needle movement on the instrument, with the required resolution of minimum 1º. Therefore, I ask you, the Arduino specialists on the forum, for help.

 

Any help would be appreciated.

In advance, many thanks.

 

Peter


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Peter Elsler
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PLEASE DISCONSIDER THE FIGURE IN THE FIRST UPLOADED POST. HERE COMES THE CORRECTION

 

SYNCHROS "SELSYNS" as Output Devices - In this case, the SYNCHROS or “SELSYNS, “AUTOSYNS” are used as “motors” to drive the exact position of indicator needles or discs on aircraft instruments, such as on the RADIO MAGNETIC INDICATOR (RMI).

Good descriptions of all types os Synchros can be found on the internet, such as:

> https://www.tamagawa-seiki.com/products/resolver-synchro/synchro-about.html <

> https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1947/05/page50/index.html <

> https://www.allaboutcircuits.com/textbook/alternating-current/chpt-13/selsyn-synchro-motors/ <

In the following, I want to explain the approach that I would prefer, if possible:

In case of the AUTOSYNS, I want directly connect the 3 stator coils and the rotor coil to 4 H-Bridges per SYNCHRO and drive them by the ARDUINO, using the PWM-Mode. I want to use PWM square waves from the arduino to create magnetic fields in the coils, one permanent magnetic field in the rotor and 3 changeing magnetic fields in the stator coils, depending on the position of the indicator needle.

Synchro H Bridges 60 180 300
Synchro H Bridges  0 90 270

 

I have no idea of the appropriate Arduino (UNO or MEGA) program code to realize the 360° needle movement on the instrument, with the required resolution of minimum 1º. Therefore, I ask you, the Arduino specialists on the forum, for help.

 

Any help would be appreciated.

In advance, many thanks.

 

Peter


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robotBuilder
(@robotbuilder)
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@peter-elsler

May I ask where you obtained the above schematic?

So you have two selsyns connected, one as a manual input tx and another that follows the manual setting rx and you want to replace the direct connection with electronics?

To enlarge images right click mouse and choose Open in new window.

image2

Now my understanding is that the selsyn output follow the selsyn input and that information is in the form of voltages on s1, s2, s3. Could you just read those values into the Arduino and leave the two devices to work as normal?

image3

 

This post was modified 3 months ago 2 times by robotBuilder

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Peter Elsler
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Hi, robotBuilder.

 

Many thanks for your post and your interest to help me solving the problem with the Synchros.

To answer your first question, where I obtained the schematic in my post:

It´s not from the internet. I did some previous test with the Exhaust Temp. Indicator and the Amps Indicator of the Auxiliary Power Unit Module (APU), seen in the picture below.

Exhaust Temp Ind ARDUINO

Both are ampere meter like indicators!  They only have one coil as rotor and a permanent magnetic stator. The needles of both run very fine at the full range of the scale, when driven by an PWM input. Of cause, I was using an protecting flybackdiode in the circuit, to avoid the inductive voltage pulse on turnoff.

I tried this approach on the RMI, too. I applied a constant PWM signal on the rotor coil and applied another PWM at least on one of the three stator coils. The needle of the indicator moved reasonable well inside the 120° sector. Inverting the polarity of the stator coil, resulted in the inverted position of the needle.

From this results, I designed my simple schematic idea, applying it on the three stator coils of the Synchros. I added the H-bridges to invert the direction of the current in the coils in order to obtain inversion of the magnetic fields in the stator. The rotor should remain always be connected in the same way, without of changeing the direction of the magnetic field.

You are right, robotBuilder, I have two selsyns connected, one as a manual input TX and another that follows the manual setting RX and I want to replace the direct connection with electronics. Your image2 is exactly, what I want to do (only without the direct wiring between both).

The Arduino receives the signals from TX and “transmits“ them to X-Plane 11 Flightsimulator. The flightsim „commands“ the output on the RX. It´s important to note that I have many instruments / indicators, that have no TX and only receive their signals for indication from the X-Plane FS and not from an co-pilots backup instrument.

Now to your image3 and your question, if I could just read those values into the Arduino and leave the two devices to work as normal? I have no suitable 400 Hz sinus generator. Considering that I have a lot of indicators, I would need a lot of such generators. Some of the videos on the internet show much of noise emission by these inverters / 400 Hz generators. I dond´t know, if generating a magnetic field on the TX rotor with PWM and transmit the induced electrical signals on the 3 wires that connect to the RX stator coils, would result in right positioning of the indicator needle?

Therefore, your image2 schematic seems to be more feasible for me.

Finally, I want to remark that I have less wires, at least no ground wire, on my synchros, different to your schematic.

Most of them have 3 stator wires and 2 rotor wires. Only the Synchro Differential Resolver on the Set Altitude Indicator has a rotor with 3 phases and 4 wires  and a stator with 2 phases and 3 wires:

CLIFTON SYNCHRO DIFFERENTIAL RESOLVER – Type CDSH-IO-QS-4/F321

   Rotor:      3 Phases  11.8 V       400 Hz  -  4 wires   black - red – blue - yellow

  Stator:     2 Phases  26 V          400 Hz  -  3 wires   black/white - blue/white -   yellow/white

 

At this moment, I dond´t understand, why there are 2 phases in the stator. That´s still an open question for me.

 

Thank you very much for your post.

 

Peter


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robotBuilder
(@robotbuilder)
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@peter-elsler

Is it possible to replace the tx selsyn with a POT and the rx selsyn with a stepper motor or servo motor?

On one of the web pages I noticed some equations which might be the ones you want the Arduino to output to turn the selsyn to some given angle?

To enlarge image right mouse click image and choose open link in new window.

selsyn9
This post was modified 3 months ago by robotBuilder

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Peter Elsler
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Hi, robotBuilder.

Many thanks for your post and your help.

I have just thought to use of a potentiometer and servo / stepper motor combination, but I want to avoid it.

I put in a poti in the MODE SELECTOR to the PITCH CMD. But a poti has some disadvantages: smaller lifetime, less precision and, of cause, it occupies a lot of space that I often don´t have.

 

Mode Selector

Important limitation is, that I do not want to alterate the mechanical arrangement of these high precision instruments and their fine mechanical construction. Therefore I want to keep their original configuration, maintaining the synchros functional and work on electronic and  programming part to reach a solution.

I remember having seen the article with the scheme and equations you mention in your selsyn9 picture. But I confess, I don´t have the experience and expertise to create the right Arduino sketch for it.

At this point, I want to discuss a little modification, that I made in my model, how to put in the PWM signals to the coils. I want to discuss the most simplest model, a Synchro with 3 wires for the Stator and 2 wires for the Rotor.

For example the the TX Synchro in the RMI:

CLIFTON CONTROL TRANSMITTER– Type No.  CTH-IO-QS-4/F323  

   Rotor:      1 Phase  23.5 V         400 Hz  -  2 wires   black/white - red/ white

  Stator:     3 Phases  11.8 V       400 Hz  -  3 wires   black – yellow – blue

 

Also, a very good example is the COLLINS old style indicator of the Distance Measuring Equipment (DME) with it´s 3 Synchro Receivers:

CLIFTON (Litton Company) SYNCHRO RECEIVER– Type No.  HRC-10-AS-1/B057

   Rotor:      1 Phase       26 V       400 Hz  -  2 wires   red - white

  Stator:     3 Phases  11.8 V       400 Hz  -  3 wires   black – yellow – blue

 

DME 01
DME 02
DME 03

I want to discuss the following scheme, how to interact to the three stator coils using the H-Bridges and PWM inputs:

Synchro H Bridges

60° Position:      Applying PWM signals (always via two H-Bridges) from S2 to S1 and S3 to S1, the Stator should go to the 60° position.

180° Position:    Applying PWM signals from S1 to S2 and S3 to S2, the Stator should go to the 180° position. Important that in this case, S2 should be negativ (-) and S1 and S3 should be positiv (+).

300° Position:    Applying PWM signals from S1 to S3 and S2 to S3, the Stator should go to the 300° position. Important that in this case, S3 should be negativ (-) and S1 and S2 should be positiv (+).

ALWAYS THE COMMON WIRE BETWEEN TWO ACTIV COILS MUST HAVE THE SAME POLARITY.

 

Varying the duty cycle of the PWM signal on one, or on both activ coils, one increasing and the other decreasing, should move the Stator clockwise or counter clockwise in the activ 120º sector.

I suggest, that each coil should be operated with a maximum of 60% of duty cycle to avoid overheating of the small coil wires. 100% duty cycle would mean DC current that could lead to overheating and burning of the coil wires. The 490 Hz PWM frequency seems to be fine compared to the specified 400 Hz (AC) frequency of the synchros.

As far, my theory.

UNFORTIONATELY I HAVE NO EXPERIENCE TO WRITE AN ARDUINO SKETCH THAT COULD BE APPLIED TO MY PROBLEM.

HELP NEEDED, PLEASE.

Even a simple test sketch only for testing one sector with varying duty cycles for 2 coils and 2 H-Bridges will be appreciated.

 

Many thanks.

Peter


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Peter Elsler
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CORRECTION:

Read: "Rotor" in spite of "Stator"

60° Position:      Applying PWM signals (always via two H-Bridges) from S2 to S1 and S3 to S1, the Stator Rotor should go to the 60° position.

180° Position:    Applying PWM signals from S1 to S2 and S3 to S2, the Stator Rotor should go to the 180° position. Important that in this case, S2 should be negativ (-) and S1 and S3 should be positiv (+).

300° Position:    Applying PWM signals from S1 to S3 and S2 to S3, the Stator  Rotor should go to the 300° position. Important that in this case, S3 should be negativ (-) and S1 and S2 should be positiv (+).


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robotBuilder
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@peter-elsler

I put in a poti in the MODE SELECTOR to the PITCH CMD. But a poti has some disadvantages: smaller lifetime, less precision and, of cause, it occupies a lot of space that I often don´t have.

Looking at the images those appear more like 6 positional rotary switches?

Instead of a pot maybe a rotary encoder no physical wear and tear?

I remember having seen the article with the scheme and equations you mention in your selsyn9 picture. But I confess, I don´t have the experience and expertise to create the right Arduino sketch for it.

Essentially the equations produce sine wave outputs as shown below which shows the voltages required for any angle. You write a simple subroutine to compute the voltages for any particular angle. The voltage range is determined by v. You then need to convert the digital numbers to analog values. The pwm outputs are not really analog and limited to a range of 0 to 255 so maybe external digital to analog circuits would be required to handle a wider range of values (as determined by the value of v). The actual arduino pins only produce two voltage outputs 0 or 5volt as the "analog" mode (pwm) isn't real analog. A pwm is just a pin being turned on and off. Also the pin values are 0 to +v not -v to +v generated by the equations this means inverting the direction pin value for negative numbers and converting them to positive numbers to drive the h-bridge.

float v;
float v1;
float v2;
float v3;
float angle;
v = 255; // range of pwm values
v1 = v * sin(angle);
v2 = v * sin(angle+120);
v3 = v * sin(angle+240);

So I could write a sketch to produce the required outputs for any angle but the range is 0 to 255 pwm not 360 analog levels.

Still think it would be simpler if you could have the 400Hz power supply for the selsyns and just convert the resulting rotation to digits or convert the voltages to digital numbers using analog to digital converters and computing the rotation.

I have no suitable 400 Hz sinus generator. Considering that I have a lot of indicators, I would need a lot of such generators.

But isn't this just a 400Hz power supply? One should power all the instruments?
https://www.keysight.com/us/en/assets/7018-01321/technical-overviews/5989-3700.pdf

This seems to be about the type of project you are working on?

One post has a utube video and some links that might be of interest.
https://www.element14.com/community/thread/21494/l/i-need-help-designing-a-400hz-115vac-3phase-power-supply-help

Ideally if you could find others working on similar projects 🙂

waveOutputs

 

 

 

 

 

 

 

This post was modified 3 months ago by robotBuilder

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Peter Elsler
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Posts: 19
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Many thanks for your quick answer.

There are a lot of informations. I need some time to understand all the details you mentioned.

We will keep in contact.

Many thanks.

Peter


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robotBuilder
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@peter-elsler

An interesting problem but apparently no electronics expert to give a definitive answer to your problem.  It would be nice to have a gif animations of  rx/tx selsyns showing the changing voltages and currents along with the expanding and contracting magnetic fields as the tx rotor is turned.

I am still interested enough to see if I can arrange 3 electromagnets around a magnetic compass to see if I can write the code needed to point the needle in any direction.

Some further thoughts: The selsyns require AC voltages so when you are using DC voltages they will not actually work as selsyns. Turning the tx selsyn rotor to another angle will not produce any voltage in the stator coils for an Arduino to read. You may as well just have an encoder or high precision POT attached somehow to the shaft. The connections between the tx and rx would also have to be disconnected if you are to apply voltages to the stator coils of the rx selsyn to turn the rx rotor.

An Arduino driving the rx selsyn I would assume would need to duplicate the behavior of the left side of this circuit.
http://www.industrial-electronics.com/aircraft_10b.html

slide 27

http://www.austin-champ.co.uk/mech/fgjacksn.htm

unnamed (2)

I still think the easiest way would be to replace the rx with an encoder to the Arduino and replace the tx with a stepper motor (or servo motor) controlled by the Arduino. The actual physical panel would look the same.

 

This post was modified 3 months ago 3 times by robotBuilder

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Peter Elsler
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Hi, robotBuilder.

Many thanks for your post and your continued interest.

„You may as well just have an encoder or high precision POT attached somehow to the shaft.“

„I still think the easiest way would be to replace the rx with an encoder to the Arduino and replace the tx with a stepper motor (or servo motor) controlled by the Arduino. The actual physical panel would look the same.“

Unfortuanately, I have no space inside the housing of these instruments to attach anything else. And, of cause, I really don´t want to scrap these beautiful fine mechanical instruments. I want to keep them as original, as possible. Trying to dismantle some smaller instruments, they broke up.

When I first saw the articles with the pictures of th D.C. Selsyn System you mentioned, I was very interested, but thinking further, I would not like to risk burning the fine coils with 100% DC current. I prefer a maximum of 50 to 60% duty cycle of  a PWM input.

„Some further thoughts: The selsyns require AC voltages so when you are using DC voltages they will not actually work as selsyns.“

In the end, I don´t need that they work as „Synchros“, transmitting from one „TX-synchro“ to another „RX-synchro“. I want that the Arduino takes the principal part. The TX-synchro sends it´s signals to the Arduino and the Arduino sends the codes to the X-Plane FS. This I want to discuss in the other topic that I opened in the subforum: „SYNCHROS "SELSYNS" as Input Devices“. I want to treat this in the future, because I think, understanding how to drive a synchro as output device (indicator needle), will help to get a solution easier for the other problem. Therefore, I prefer getting a deeper inside look to the topic of this subforum, „SYNCHROS "SELSYNS" as Output Devices”.

As output device, the X-Plane FS sends it´s codes to the Arduino, which commands the RX synchro.

My point of view is, that in this case, the synchro doesn´t need to work in the way, that a selsyn normally works with the 3 sine wave inputs. I see the 3 coils of the synchro as 3 ampermeter coils.  The Arduino should drive always two coils simultanuesly with PWM inputs.

Synchro H Bridges

60° Position:      Applying PWM signals (always via two H-Bridges) from S2 to S1 and S3 to S1, the Rotor should go to the 60° position.

180° Position:    Applying PWM signals from S1 to S2 and S3 to S2, the Rotor should go to the 180° position. Important that in this case, S2 should be negativ (-) and S1 and S3 should be positiv (+).

300° Position:    Applying PWM signals from S1 to S3 and S2 to S3, the Rotor should go to the 300° position. Important that in this case, S3 should be negativ (-) and S1 and S2 should be positiv (+).

ALWAYS THE COMMON WIRE BETWEEN TWO ACTIV COILS MUST HAVE THE SAME POLARITY.

 

 

I have found a very simple indicator in my stock, that has only two synchros and two needles:

Boeing 707 Pressure Ratio Indicator

CLIFTON (Litton Company) SYNCHRO TRANSRECEIVER– Type No.  URH-10-JS-1/B606

  Rotor:      1 Phase       26 V       400 Hz  -  2 wires   black/white – red/white

  Stator:     3 Phases  11.8 V       400 Hz  -  3 wires   green– yellow – orange

 

US Gauge – Type No.  AB-1162

  Rotor:      1 Phase       26 V       400 Hz  -  2 wires   red - black

  Stator:     3 Phases  11.8 V       400 Hz  -  3 wires   black – yellow - blue

 

B707 Pressure Ratio Indicator
B707 Pressure Ratio Ind

I will hook it up to an Arduino and see, what happens.

But I need a little bit of time. As soon, as I have some results, I will tell you.

 

Many thanks,

 

Peter

 


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robotBuilder
(@robotbuilder)
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@peter-elsler

I will hook it up to an Arduino and see, what happens.

Poof, a cloud of smoke 🙂

So you have Arduino code and circuitry to generate the desired voltages?

You actually don't need to use an Arduino for testing. You may remember Bill showing the logic of using an L298N without an Arduino.

BillsMotorControlTest

I would love to have a synchro to play with 🙂 I think this is an interesting problem to solve but without the hardware it is hard to test circuit and/or code ideas. I hope my posts aren't too annoying.

Like I wrote, I hope to build a crude synchro using some electromagnets. A long long time ago I used to make them myself using cotton bobbins (see image) but winding them with copper wire instead of cotton. A simple synchro would be easy to make yourself to test how to read the position of a rotor in the rx synchro set by the physical input or to apply the voltages to the stator coils in the tx synchro to turn the rotor with attached dials in the desired direction. The center rotor in the tx could just be a compass for testing purposes and a fixed magnet in the tx.

bobbinCoils

Yesterday I wired up some POTS to see if I could control a synchro with them. Until I get coils I simply used two LEDs one wired one way and the other wired the other way to show the direction of the current. I need to measure the actual voltages for various POT positions but in the short term I just rotated them to their opposite extreme positions (on/off like a switch) to see what would happen.

testImage
circuit2

This shows the directions the current would take through the coils when the POTS are fully on/off.

There are eight possible combinations.

circuit1
This post was modified 3 months ago 2 times by robotBuilder

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Peter Elsler
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Hi, robotBuilder.

Many thanks for your post. Very interesting approach that you present.

I will do some measurments on my synchros. The coils are very fine and have extreme low resistance. In the rotor it´s about 40 ohm and in the stator coils 17 ohm. Some years ago, I did some pre-tests with PWM, but only on one stator coil each, and simultanuasly on the rotor coil. Even with far lower voltages than indicated on the synchros, I obtained needle movements. If I remember right, I used PWM signals from the arduino and transistors to apply a separate 5.0 V to max. 7.5 V to the coils. The needle moved into the specific sectors. Current flow was extremely low.

I will repeat the tests on the RMI, where I have the 360° scale, which gives me a better precision to read the exact position of the synchro.

With this data basis, I believe, it will be easier to discuss further details.

Many thanks for your help!

Please give me some time, because it took about more than 3 years that I worked a little bit with the arduino. I have to remember some basics.

Until soon.

Peter


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robotBuilder
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@peter-elsler

The coils are very fine and have extreme low resistance.

Sure you don't want to lose energy as heat in the wires, the lower the resistance the better.  Did you measure the resistance to a dc current or an ac current?  How does the amount of current change through the coil when you apply ac voltages of the same value but of different frequencies?

Please give me some time,

Ok enough of the posting already 🙂

 


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