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# Synchro motors for wind direction indicator

#### JoeSmith

Sep 22, 2018
6
Hi All
I was here a few years back because I wanted to build a wind direction meter. Various life events outside of my control distracted me but they're all sorted now and I'd like to resume with this...
I want to build a wind direction indicator.
It's got to be analogue rather than digital with LEDs because I want a hand on a dial to physically spin round to the correct compass bearing that indicates the direction of the wind.
My idea is to put a small weather vane on top of my chimney (I'm in a listed house so it has to be pretty much invisible and I'm surrounded by other buildings so the chimney top is pretty much the only location where wind direction isn't blocked).
My plan is to use synchro motors. One attached to the bottom of the wind vane as the "transmitter" and a "receiver" motor that drives a compass needle on the wall in the kitchen at the bottom of the chimney and which will mirror the position of the transmitter motor.

The two motors will be linked with wire so it won't be a remote/radio system because that's beyond my skill level which is very basic.

I've been looking at this motor on Amazon and wondered if this would do the job.

What I'm trying to achieve, somewhat ambitiously, is a similar functioning wind direction indicator to that in the library at the National Trust's Coleton Fishacre. I contacted them about it and they kindly sent me the information that I've attached here.
As I say, my knowledge is basic so please bear with me but if anyone can tell me if I'm barking up the wrong tree or can suggest better methodologies or a different motor to use, I would appreciate friendly input.

Many thanks
Joe

#### Attachments

• wind dial info word.pdf
254.5 KB · Views: 10

#### Bluejets

Oct 5, 2014
5,989
My plan is to use synchro motors.
If by that you mean synchronous motors, I don't think you'll get anything out of that.
Synchronous motors are typically used in AC and spin at near frequency speed , hence synchronous.
Things like washing machine timers, clocks etc.
They do not have any permanent magnet to generate any type of signal.

Think you'll find stepper motors can be used but may require some amplification of the signal to drive your "dial indicator".
That or reed switches.

#### JoeSmith

Sep 22, 2018
6
Thank you ever so much for taking the time to reply to my query. I'll look into stepper motors.
The reason I was looking into Synchro motors (aka Selsyns) was because of this article. I'll keep looking. Thank you again.

#### Alec_t

Jul 7, 2015
3,242
I've been looking at this motor on Amazon and wondered if this would do the job.
I don't see how that, or any synchronous motor, will do what you want. You need a synchronous resolver, which is essentially a rotary transformer.

#### kellys_eye

Jun 25, 2010
5,107
Other than getting the terminology wrong (as above, it's a synchro resolver you want) your idea has merit and would work however it's not just a case of wiring them together as you still have to provide an AC signal (reference) for them to work. This in and of itself isn't difficult either but consider the cost of such synchro resolvers (£100-ish and upwards EACH) plus the reference signal and the connecting cable etc.

Look into marine wind speed/direction indicators as full systems can be found at reasonable prices and many are of the analogue system that you desire.

#### JoeSmith

Sep 22, 2018
6
Other than getting the terminology wrong (as above, it's a synchro resolver you want) your idea has merit and would work however it's not just a case of wiring them together as you still have to provide an AC signal (reference) for them to work. This in and of itself isn't difficult either but consider the cost of such synchro resolvers (£100-ish and upwards EACH) plus the reference signal and the connecting cable etc.

Look into marine wind speed/direction indicators as full systems can be found at reasonable prices and many are of the analogue system that you desire.
Thank you so much for this. I very much appreciate the terminology correction as this helps my searches.
You're absolutely right about the costs of these things. I think that's why I went down the Amazon rabbit hole and was pleasantly surprised to find the components available for an affordable amount...albeit the wrong things!
I've had a look at Marine Wind Direction Indicators in the past. It's a good call. Finding one I can butcher for a reasonable cost is proving tricky.
Maybe I'll have to expand my knowledge and look into methods of doing this.
Thank you for your input though.

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,761
The article you referenced has a pretty good explanation of how a self-synchronous motor, a selsyn (or more specifically, a pair of them), works. These rotary shaft devices have three stator-wire connections common to both selsyns and a pair of rotor-wire connections, also common to both selsyns. Neither of the pair of "motors" has any torque as a response to the electrical excitation that must be applied to the rotors.

With the rotors excited with ac, if rotary motion is applied to one shaft of the pair, the three stator wires will cause the other shaft to also experience rotation. If there is a reaction torque at the "receiver" sylsyn, that reaction torque will be transmitted back to the "transmitter" sylsyn. This is best experienced in person when two sylsyns are side-by-side on a workbench and both hands are placed on knobs attached to the selsyn. Turning one of the two knobs will result in the other knob turning in the same direction through the same angle. The torque that is transmitted can be easily felt in your two hands.

A resolver was suggested, but this device does not transmit torque. It is used to measure (in analog fashion) the rotary position of the resolver shaft. Two analog signals are produced, ninety degrees out of phase with each other. These signals can be used to derive angular rotation information and direction of rotation, which can then be used to drive a servo amplifier that in turn drives a servo motor.

Selsyns and resolvers were initially created to remotely aim large guns on warships. They have also been used with cannons to control barrel elevation. Electronics technology progressed rapidly after World War II, and selsyns fell out a favor because of their limited torque, accuracy, and relatively large size. Rotary absolute optical encoders have mostly replaced the transmitter selsyns, and powerful, amplified, servo motors (with rotary absolute optical encoders) have replaced the receiver selsyns, although a resolver is often used to provide position feedback for the servo motor.

The difficult part of your project could very well be the inside display. This should be well-constructed to blend with the decor of whatever room in which the display is mounted, especially if you want to make, and perhaps sell, several of these wind-direction displays. The chimney-mounted transmitter is out of sight, and hopefully protected from the elements, but it is complicated (read on, below).

Rotary absolute optical encoders are not inexpensive, but then neither are selsyns. By their nature optical encoders produce digital rather than analog outputs. You will need two of them at about sixty bux a piece: one for the transmitter at the chimney and one for the inside display.

An alternative to the rotary absolute optical encoder is a potentiometer with continuous rotation, to be used as the "transmitter," but these devices almost always have a "dead spot" that must somehow be ignored. Recommended only if a truly analog solution must be implemented. I will not discuss this further in this thread.

Transmitting a digital rotary position signal from the chimney to the display would benefit from converting the parallel digital outputs of the "transmitter" into a serial ASCII data stream. That requires some electronics, perhaps a Microchip PIC microprocessor or an Arduino or a PICAXE processor. Nothing complicated or high-end. You will only need three low-voltage wires between the display and the transmitter, two for power and common and one wire for the serial ASCII data stream.

You don't have to convert the wind direction into ASCII character digits, but it definitely would aid troubleshooting and allow you to also display wind direction on a personal computer with a serial data input. In fact, I would get that part of the wind direction display working FIRST since you will need a personal computer (desktop or laptop) to program the microprocessor in the transmitter.

Another benefit of having a serial data stream is the option and ability to simultaneously drive two or more displays, which can be either an "analog appearing" display with a dial and a compass rose, or a digital display of whatever complexity you want to add... temperature, humidity, rain-gauge/snow load, wind speed, time-of-day, etc. Such "bells and whistles" will certainly add complexity, but with serial data encoded as ASCII character strings, you should be able to "upgrade" your weather station incrementally and monitor it from your personal computer or cell phone (if you add WiFi or Bluetooth capability).

OTOH... if you have deep pockets, you might want to consider a commercial product and have something by the time the holidays arrive, assuming you might want to gift this puppy to someone...

#### Minder

Apr 24, 2015
3,318
Hi All

My plan is to use synchro motors. One attached to the bottom of the wind vane as the "transmitter" and a "receiver" motor that drives a compass needle on the wall in the kitchen at the bottom of the chimney and which will mirror the position of the transmitter motor.

The two motors will be linked with wire so it won't be a remote/radio system because that's beyond my skill level which is very basic.

Joe
Have you thought of using two stepper motors?
One for transmitter, the other receiver.
No other electrics/electronics needed.

#### Alec_t

Jul 7, 2015
3,242
A cheap option for direction sensing could be Hall-effect magnetic field sensors. These are available with various outputs, e.g. analogue or PWM, dependent on field strength and polarity.

#### kellys_eye

Jun 25, 2010
5,107
You could take a punt on this:

Looks to me that it only needs an AC signal to get it working (assuming the rest of the system is ok). It's the kind of thing I'd (personally) take a chance on - but I'm an experienced marine electronics engineer so any fault would probably be fixable - YMMV.

<edit> looks like that one requires a DC voltage - the label gives the value but I can't read it. <edit - again!> it's 24V.

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#### JoeSmith

Sep 22, 2018
6
Another benefit of having a serial data stream is the option and ability to simultaneously drive two or more displays, which can be either an "analog appearing" display with a dial and a compass rose, or a digital display of whatever complexity you want to add... temperature, humidity, rain-gauge/snow load, wind speed, time-of-day, etc. Such "bells and whistles" will certainly add complexity, but with serial data encoded as ASCII character strings, you should be able to "upgrade" your weather station incrementally and monitor it from your personal computer or cell phone (if you add WiFi or Bluetooth capability).
Wow. Thank you so much for sharing your knowledge and experience on this. I'm in awe of your skills!

You mention an "analog appearing" display with a dial and a compass rose...can I ask you to elaborate on this? Essentially I'm wondering if it's possible to have a physical needle tracking round on a compass face on the wall which is driven by "IT wizzbangery"? If this is a possibility, I'd be so grateful if you could point me to a few key words I can research to get a foothold on this learning curve.

Your input has pretty much convinced me that following a microprocessor route could be the best way forwards for this and being able to add displays, information and upgrade the system is very appealing. I'm not planning on selling or gifting these at this stage (although I'm currently working on a start up and if that goes belly up, well...never say never!) it's just a project to while away coming winter evenings. Alas, my pockets aren't very deep at all right now hence the self build aspect!

But again, thank you. I'm so grateful for your sharing this information.

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,761
You mention an "analog appearing" display with a dial and a compass rose...can I ask you to elaborate on this? Essentially I'm wondering if it's possible to have a physical needle tracking round on a compass face on the wall which is driven by "IT wizzbangery"? If this is a possibility, I'd be so grateful if you could point me to a few key words I can research to get a foothold on this learning curve.
I see two options for producing an "analog appearing" display: (1) an LCD flat-screen display that simulates (visually) a needle pointer and a compass rose and (2) a mechanical needle pointer that revolves around the center of a printed compass rose. The problem with (1) is writing the software to implement it and the problem with (2) is determining the position of the rotating pointer.

Of course a receiver selsyn (if you could find one) could suffice for (2), but I have no idea what size LCD screen would be available for (1), nor any knowledge of how to program it. Also, without a matching selsyn transmitter, it may be impossible to drive a real selsyn. Be aware that there may be available surplus selsyns that operate at 400 Hz instead of the more readily available 50 Hz and 60 Hz power. Unless you want to build a three-phase 400 Hz power oscillator, I would not use a selsyn whose rated excitation is 400 Hz.

Using option (2) you could use a small stepper motor and provide a means to detect when the pointer is at some cardinal position, north perhaps. You then just count stepper pulses to position the pointer to the proper direction. A small photodiode and an optical slit can be used to define the initial starting position.\

Or you could use an absolute optical encoder at both ends, one connected to the chimney-mounted wind vane and another to which the display pointer is attached. The display pointer could then be driven from a permanent-magnet dc (pmdc) motor, connected by means of two pulleys and an "O"-ring, the motor being part of a servo loop that translates RS-232 serial ASCII characters into binary position information that is compared with the display pointer digital position information. I like this approach because mechanically and electrically it is pretty simple, and because it does not depend on knowing a starting position for the pointer. It does require some sort of microprocessor to read the binary position information and process it to form a serial ASCII character data string and software to implement a positioning servo at the display. None of this is particularly difficult, but the rotary absolute optical encoders are a little pricey, and you need two of them with resolution of 360 "counts" per revolution.

Asian stepper motors with about 20 steps per revolution could work, especially if geared down to provide several hundred steps per revolution. Your picture showed a rose with 32 cardinal points, so a stepper with, say, 200 steps per revolution could directly drive the pointer, with each step moving it 360/200 degrees or 1.8 degrees per step. You would then need to step the motor 6.25 steps to move the pointer one cardinal position. It is possible to "microstep" a stepper motor to position the motor shaft between full steps, or you can play with a different number of steps per revolution. Whatever you decide, the stepper motor can be mounted on a metal or plastic board to which the compass rose is glued or silk-screen printed. Fascinating hobby, silk screen printing, and the materials are inexpensive. Or, you can get a full-color print made at an office supply store from your artwork that has been saved to a thumb drive.

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#### kellys_eye

Jun 25, 2010
5,107
The key to your success is less about the display and more about the transducer that delivers the signal from the weather vane. These can be synchro transmitters, hall effect, rotary transformer, 360degree potentiometer, slotted opto etc etc so you have to start with the top end, not so much the display (yet!).

Old (or even new) car speedometers (or rev counters) can provide a simple 'analogue' display pointer. Rectangular LEDs glued into a 'ring' can make a nice display too. Going towards a more modern solution I'd mention the paper-white displays (e-ink) as used in Amazon (and similar) make a good 'daylight' display. The suggestion above to use a stepper motor is a reasonable compromise and I'd point you to 'compass repeaters' as used in marine applications. These are commonly stepper motor driven, can be found second hand (not cheaply though) but could be designed and built to practically any scale size using light weight clear plastic sheets - imagine a 1 meter diameter wall-hanging display like that!

Anyway, sounds like a fun project!

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,761
The chimney-mounted transmitting end of the weather vane display is potentially much more complicated than the receiving end, which is why I suggest designing the compass-rose display first. Generating ASCII character strings used to be quite simple when almost all PCs had one or more serial ports. Now you have to use a USB-to-serial adapter cable and try to find a terminal emulator app just to get started on a pointer and compass-rose display. I ran into this problem years ago when working with an Allen-Bradley programmable logic controller: the programming computer was a desktop PC with USB ports, but the A-B needed a DB9 RS-232 connection. The required adapter cable was available from Amazon, but there are also a lot of fake "clones" out there too.

I did some searching with Google and found that round LCD color displays are common, and inexpensively sourced from Asian vendors. Sizes (diameters) range from small (wristwatch size) to humongous (outdoor billboard size). I didn't look for information on how you program them, but once that challenge is met all you need is the microprocessor to convert serial ASCII characters into a pointer display. There is probably enough room outside the compass rose to also display temperature, humidity, wind speed, barometric pressure, accumulated rain or snowfall, and the time of day if the OP wants to add those things later. If so, nailing down the display should be a first priority for a top-down design. That means also defining the ASCII command protocol used to transfer the weather-vane direction data.

#### kellys_eye

Jun 25, 2010
5,107
I'd lean towards a simple (geared) rotary encoder at the top end, connected to a simple CW/CCW detector (and pulse amplification) send the result down a cable to a stepper driver. Some simple calculations to determine any gearing would give a reliable result. Choosing the correct stepper motor for the display would give an 'infinite' number of options as to the final dial size to be used.

#### Sunnysky

Jul 15, 2016
529
- any sync motor including steppers needs datum or home sensor for 0 deg.
- any wind vane needs a damper to prevent "gust inertial overshoot" to be critically or over-damped. It can be small but must be damped.
_ I was on a team in my 1st job to design the world's 1st wind-powered arctic-ice floating weather-station with VLF tracking and GOES 1 custom transmitter.
- now you can get a well-designed Chinese weather station for $100 from Bandgood or your local disti. for more. e.g. a little more$

#### kellys_eye

Jun 25, 2010
5,107
You could take a punt on this:
Yup, quoting myself here!

I took the punt myself and bought that synchro direction indicator. Works perfectly and will be used as an indicator of a rotating loop antenna I plan to install.

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