[amsat-bb] Optical shaft encoders
tosca005 at umn.edu
Wed Mar 23 21:58:24 UTC 2016
Bob et. al.:
Would something like this:
...be useful for the purpose of determining absolute position without
relying on mechanical linkages of gears, belts, pulses, potentiometers,
etc.? It uses 3-axis magnetometers, 3-axis gyros, and 3-axis
accelerometers, and a Cortex M0 ARM to do all the hard computations that
combine the three types of data into a viable position indication. It is
inexpensive enough that I will probably install one when I finally get
around to raising a tower at my new QTH, and using it only for readouts at
first. I have been using and will resume using Yaesu rotators when the
tower goes up, so no urgent need to add safety limit switches etc. In many
years of operation at my prior QTH, the rotator never got "confused" about
its position except when somebody put tension on the cable plugged into the
back of the control box and loosened some of the connections between plug
and socket. I do realize that even the G1000SDX model I was/will be using
is not hefty enough for some applications, but again it served me well for
many years in spite of temperature swings from -40F to +105F. (Yeah, it
turned a bit slower at the begining of a contest when the temp was -40F and
the wind chill was -60F. OK, wind chill doesn't apply to inanimate objects,
but -40F actual is pretty darned cold. Plus the ice and snow added on
didn't help.) :-)
73 de W0JT/5
EN34js -> EL09vu
On Tue, Mar 22, 2016 at 8:53 PM, Robert McGwier <rwmcgwier at gmail.com> wrote:
> This is an awesome conversation and we are extremely grateful.
> Zach is trying to build a robust repeatable super ground station.
> 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
> > 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
> > 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
> > 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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