[amsat-bb] Optical shaft encoders

[Robert McGwier]

This is an awesome conversation and we are extremely grateful.

Zach is trying to build a robust repeatable super ground station.

Bob
On Mar 18, 2016 6:30 AM, "Daniel Cussen" <zg3410 at gmail.com> wrote:

> >for those with Alfa Radio HR model rotators, maybe you have same/similar
> issues?
>
> I do not have a HR model, but I do have a similar system and we are
> seeing similar problems.
>
> First off there is no end stop safety switches. This means if the
> control box becomes confused it can damage coax cables and move
> elevation to positions to damage antennas etc.
>
> Second, there is no absolute position sent, meaning if it gets
> confused it cannot reset itself as only the amount of movement is
> sent, not the actual current position. Over time this means errors
> accumulate and grow.
>
> The basic Yaesu G5500 has both safety protections meaning it is
> unlikely a confused control box will result in damaged antennas or
> coax.
>
> >So first off, Bob is basically asking if anyone has built a custom
> optical shaft encoder to >replace the magnetic hall effect sensors in the
> High Resolution Big-Ras rotators.  >Machining, circuit design,
> performance.....?
>
> I do not know, however I have nearly added safety switches to a
> similar model to turn off the motor to protect the coax cables. This
> is also very important if the relays stick in the control box.
>
> Others have removed or replaced position sensors with more accurate
> absolute positions sensors. In particular the HH-12 is used by a lot
> of large EME stations as it is both accurate, cheap and absolute
> position. If you connect it using a rubber hose it will protect itself
> from damage if you try turn it too much.
>
> http://www.vk5dj.com/hh-12.html
> Mounting it to the Big-Raz is unknown, but here is a similar project:
> http://e-kutz.eu/seite10.html
> Here is a complete controller with two sensors:
> http://f1frv.free.fr/main3o_AZ_EL_Display.html
>
> >The noise voltage was 1 or 2 volts peak to peak when measuring the lines
> with an o->scope.
>
> This is not good.
>
> > The shields of the cables are connected together at the connector on the
> rotator (8 pin >MIC connector) and at the connector on the MD-01 control
> box.  The shield is also >jumpered to a good station ground at the control
> box.
>
> To reduce noise the recommendation it to only connect the shield AT
> ONE END, and not both ends. Normally only at the shack end. I think
> this prevents ground loops.
>
> >So that's about it in a 'nutshell.'
>
> So in my case we have a similar sensor. All the HAMTV ground stations
> in Europe (6) are using Prosistel Az/El with uses hall magnetic
> sensors with thousands of pulses per second. We too are seeing
> positions change with the motor stop, so much so thousands of pulses
> must be read while stopped.
>
> The solutions we have used so far:
> 1) Multiple screened cables as you suggest grounded at one end
> 2) Adding filters to the motor wiring to reduce motor noise/cross talk
> 3) I experimented with stepping up rotation feedback from 0/5V to 0/20V
> 4) I am working on a replacement control box, where we can modify the code
> 5) I am adding safety switches to protect the coax.
>
> The real solution would be for the manufacturer to use absolute
> position feedback. There is complete controllers available, if you can
> manage to connect their sensors to your existing system using
> belts/gears/cogs etc.
>
> Another option I think you should consider is using your own control
> box. We found that the Prosistel supplied control box was flawed in
> some ways. The open source control box is already designed to take
> pulse inputs, and seems to work with thousands of pulses per second.
> You can even just hook the inputs in parallel to see if the problem is
> the control box or the sensor outputs. All you need is an arduino
> (mega preferably) and the correct version of the code. It will display
> a second opinion of the position, so you can determine if the control
> box has issues too. We found our control box misses some pulses, we
> think it is busy updating the LCD or talking to the computer and
> misses pulses.
>
> Other features of this is a master/slave option, meaning the
> controller can be mounted at the antenna, meaning only short cable
> runs to the position sensor.
>
> http://blog.radioartisan.com/yaesu-rotator-computer-serial-interface/
>
> In the long term absolute position sensors combined with safety
> switches are the only real  solution. For HF even a bog standard
> potentiometer would probably work better. Some suppliers use 3 or 10
> turn potentiometers to allow 360 degrees or 1.5 turns rotation.
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