On 11/16/18 4:16 AM, Steve Lott wrote:
On the unit I had years ago,
The selsyn on the tower
was driven by a small chain from a gear sprocket
on the rotor assembly
That selsyn drove another selsyn that is in the shack on the control box
basically the selsyn are dc motors
the one in the shack has a pointer on it
that is on a dial face showing headings (bearings of the compass)
The unit on the tower drives the one in the shack
(the unit on the tower becomes a small generator)
The down side was chain slippage
Selsyn, or synchro, are actually AC motors, either 2 phase or three
phase, with a excitation winding. You put AC power on the excitation
winding and the voltages and phases on the other windings correspond to
the angle of the shaft. at the receiving end, those voltages cause the
rotor of the receiving synchro to turn to match.
https://en.wikipedia.org/wiki/Synchro
They're pretty cool to play with.
They're also potentially very high precision and very long life
(compared to a potentiometer) and have no issues with wrap around.
There are commercial synchro to digital converters with 16 bit accuracy
(0.005 deg, about 1/3 arc minute) so a synchro and converter is WAY more
accurate than a pot and an adc. The system is also insensitive to things
like dc biases and resistive losses, so it works well with long wires.
See below...
I would recommend a more modern approach
either a wireless GPS Compass module around an Ardunio or Rasperry Pi box
with wifi transmitter/receiver
Which is available off the shelf from a place called Ham Station if my
memory on it is any good
I once built a ring of very small relays
and placed a very small but powerful button magnet on the mast
when the magnet was perpendicular to the relay it closed the normally open
contacts
and the relay contacts were wired to the shack panel to illuminate a small
LED
on a rose Compass diagram showing my present beam heading
It was visually appealing in the shack
Cheers!
Steve
KG5VK
http://sdxa.blogspot.com/
KG5VK Blog
http://www.KG5VK.com
My Ham Radio Friends
On Thu, Nov 15, 2018 at 11:04 PM Martin Sole <hs0zed@gmail.com> wrote:
Hi,
I'm restoring a Telrex A3695RISX rotator. It's quite a monster but if I
can figure out a way to use it I think it's unlikely I would ever need
anything bigger, 1/3hp reversible AC motor, dual worm reduction gearbox,
chain drive to 3" output shaft and it weighs about 125 lbs, around 57kg.
I have no control box which poses a small problem. Wiring to the motor
is straightforward enough though I think the limit switch arrangement
could be handled better.
It uses a selsyn for position indicating. In this case actually a
General Electric Selsyn Control Transformer 2J161. This is marked
57.5-57.5 V 400CY. The device is working in that I can get the three
outputs from the stator winding when I excite the rotor winding, all
three stator outputs rise and fall with rotation so I'm pretty sure its
good.
The problem is what to do at the other end. Without a matching selsyn,
not something I expect to ever turn up around here, I am wondering how I
might be able to take the selsyn outputs and interpret them by some
other means. My understanding is the 3 stator outputs are AC voltages
varying in amplitude and with a fixed phase relationship in order to
produce an unambiguous value related to absolute position. I'm not 100%
on this yet though. They are in a delta configuration though so I'm
thinking anything I do first needs to make them Y configured
You can probably use almost any other synchro as a readout, Although
yours is a 400 Hz part, a lot of folks use them with 50 or 60 Hz
excitation (at *lower* voltage. if it's rated at 100V 400Hz, you want to
use 12.5 V at 50Hz). I've run a lot of synchros off a 6.3 V filament
transformer. You don't get as much torque out, but in this kind of
application it works.
Or there's a variety of synchro to digital converters. The DDC parts
are kind of expensive.
Ultimately, what you need is a 3 (or more) channel ADC. Then it's a
matter of calculating position from the 3 numbers. I'd hunt around and
someone has probably done a synchro readout using an Arduino or similar
microcontroller.
Here's someone doing the opposite (generating synchro signals)
https://www.eevblog.com/forum/projects/trying-to-emulate-three-synchros-using-arduino/
Here's an article on Reddit about reading a synchro
https://www.reddit.com/r/AskElectronics/comments/2lq0pn/measuring_angle_of_synchro_on_an_arduino/
Here's someone who built a 3 channel resolver to number converter using
a Arduino
http://wiki.linuxcnc.org/cgi-bin/wiki.pl?ResolverToQuadratureConverter
What are my options?
I had thought about an I2C compass module but that will entail placing
some other conversion hardware at the rotator to convert to something
like RS422. Any other thoughts. Just looking for ideas to think of what
might work well enough. Ideally keeping the selsyn as it's all purpose
built around that.
The synchro is rugged, reliable, and accurate.
Martin, HS0ZED
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