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AC selsyns — Parallax Forums

AC selsyns

johnbsaxonjohnbsaxon Posts: 2
edited 2005-09-22 02:53 in BASIC Stamp
Hi to all:

My name is John Saxon and this is my first post - I hope I don't do anything wrong :-)

I am an embedded software developer, but·new to the Basic Stamp world.· So far, I have been very impressed with what I have seen.

I have an interest in WWII aviation and have written 2 programs that simulate flying WWII B-29 missions (www.b-29softworks.com).· I have hooked up with a guy who has a B-29 flight deck and we are making a B-29 sim using *actual WWII instruments*.

I have purchased the professional development board, the 2p40 stamp and have been breadboarding some D/A, A/D, etc.· I have lotsa documentation, including schematics, and have noted that a lot of the B-29 instruments are AC selsyns.

I searched this forum and didn't find any reference to selsyns.· Does anyone have any experience interfacing Basic Stamps to a selsyn device?· I think I could take two instruments, connect and power up, and rotate the shaft of one (the transmitter) and the indicator (receiver) would track.· But I would like to investigate simulating the output of a selsyn transmitter with a Stamp, or Stamps.

Thanks,
John

·

Comments

  • steve_bsteve_b Posts: 1,563
    edited 2005-09-20 19:14
    Welcome to the wonderful world of Stamping John!
    Just to note, I'm just a fellow hobbyist and am in no way affiliated with Parallax, except that I'm a purchaser of quality items (does it sound like I'm kissing butt...I am! haha)

    You'll find that the quickest response you can get from most posts here, is to include as much information as is relavent.
    How about a website for these AC selsyns (sure I can google....but it's easier -- i'm lazy!)?
    What kind of signals are we looking at!?

    I'm assuming (from the sounds of "rotate the shaft of one (the transmitter) and the indicator (receiver) would track") this is a synchro type of setup?
    We use something similar to this on some of our dated weather direction sensors.
    You have a shaft w/magnet rotating through 3coils....you impose an AC voltage on the rotor and the coils pick up the voltage....each coil will have a differnet amount depending on where the shaft is oriented. -- call this the transmitter.
    On the other end you basically have another one of these paralleled (slaved) and the voltage on the transmitters' coils will energize the rcvrs coils and cause the rcvr shaft to orient just like the transmitter.

    You can buy synchro to digital converters....but I imagine they're pricey!!

    What we've done to interface these types of devices to dataloggers (which want analog signals) was to attach a shaft enoder to one of the shafts and read that.
    It made for a slightly bulkier package, but was an easy field mod.

    Then you could use either an A/D converter (if you bought an analog shaft encoder) or the RCtime command....or buy the digital encoder!

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    ·

    Steve

    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
  • SPENCESPENCE Posts: 204
    edited 2005-09-20 19:26
    I am not shouting. I have been able to read and type all caps much easier for over 50 years.

    A digital shaft endoder is the only way i would consider. Electronic conversion cost are rocket sky high.(astrinomical).

    Btw i have flown in a t-29. (a trainer version) that was equiped for training navigators in drift meter and radio manual df
    vlf. 190-550 khz. Operated the rdf from waco to granada ms and return. The students were running drifmeter final exam. I had worked on the rdfs before but never live in a aircraft. Had a lot of fun ploting course out and back and whiping the heck out of the nav students according to the chief nav instructor.

    73
    spence
    k4kep
  • johnbsaxonjohnbsaxon Posts: 2
    edited 2005-09-20 20:56
    Thanks, guys:

    Yes, Steve, you assume correctly, you have described exactly these devices. Apparently the thinking from you folks is that to attempt to simulate the waveform output from the transmitter is not practical. Of course I just want the instrument panel indicator to rotate to a value that my program has calculated (flap position, for example). Perhaps the best way is to get a second flap indicator and hook it up as a selsyn transmsitter. I think I should be able to couple the shaft to something like a stepping motor and rotate the shaft from the Stamp. It's just that this would take two instruments, and there's not that many around.

    Thanks, Spence for your comments as well.

    Does it sound like I might be on the right track?

    --
    John
    K5ENQ
  • steve_bsteve_b Posts: 1,563
    edited 2005-09-20 23:58
    If you can still use the bezzel/housing....you might try getting an old RPM guage out of a car. Someone can correct me....but some of these needle indicators were actuated by a voltage.
    So if you could hack your housings, then you could slip in one of these things and get them to move with the appropriate voltage.

    I still haven't searched for the particular device you're after....but the ones we have use 3 synchro measurement lines. And each carries a voltage different from the others....or relative to the position of the transmitters rotor. So, measuring one line wouldn't be sufficient. The relationship is something to the affect of a cosine/sine or something (trying to remember the module we use to decode it)....anyhow, I'd think you would be better off using a shaft encoder.

    Again, you only have to simulate the original signals if you plan to use the original synchro....otherwise...attach a stepper motor to the needle the connects to the synchro and just drive the stepper and have it do the needle indicating!
    (hope I didn't ramble too much...just ate some pizza and it's sitting kinda funny-like!)

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    ·

    Steve

    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
  • T!T! Posts: 17
    edited 2005-09-22 02:53
    Yes, a Selsyn is indeed a Synchro.· Sometime about mid WW II the term Selsyn was dropped in favor of the term Synchro.

    To drive a selsyn, or synchro, RX from a Stamp you will need to produce three sine waves and control the·amplitude of these sine waves to control the poisition of the indicators.· Alternately you can use a single Digital to Synchro converter and drive it via a digital word from the Stamp.· This will be quite expensive unless you can find the converters surplus.· I was lucky enough to buy a lot of them for scrap value several years ago and have used them on many projects.

    Less sexy, but much cheaper if you absolutely want to use the original indicators, would be to use a synchro TX and RX pair.· Have the RX (the indicator) mounted where you want it.· Have the TX mounted 'below decks' out of the way, and the two connected as any synchro pair would be in normal operation.· Then use a standard hobby servo to move the TX, this will cause the RX to respond and your indicator can be made to read whatever you want.· All using one pin and a standard pulseout approach with the Stamp.· Brute force, I must admit, but it should be fairly straight forward and cheap using surplus parts.

    If you have never worked with synchros before keep in mind that the TX and RX must be for the same ref freq (R1 and R2) and voltage.· A good primer for synchros can be found here http://www.earth2.net/parts/basics/14187.pdf

    T!
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