[amsat-bb] Re: U-110 Rotor Setup

Greg D ko6th.greg at gmail.com
Tue Jul 3 20:49:23 PDT 2012

Joel Black wrote:
> @KO6TH: I like your approach. Let me see if I got my head wrapped 
> around your design - serial interface to the FODtrack board which then 
> controlled your controller? That's pretty cool.

Hi Joel,

Well, sort of. FODTrack has two different Az/EL rotor interfaces which 
you can choose from. One uses a parallel port, and talks to a bit of 
custom analog hardware to directly sense the rotor position and turn 
on/off the motors. The other uses the serial port, and was intended to 
be used with the Yaesu controller of the day. What I did was to build my 
own controller that emulated enough of the Yaesu serial protocol for the 
FODTrack software to talk to it via the serial port. So, I wasn't using 
the analog FODTrack controller board hardware at all.

A fundamental decision that needs to be made early on is what type of 
feedback your rotors give. There are two kinds - analog (potentiometer), 
and digital (index switch). The analog type can be controlled much more 
precisely, but the interface is more complicated. The digital types 
(which are what I have), have a resolution of around 5-10 degrees. 
Fortunately, 10 degrees is plenty accurate for most uses, so I went with 
what I had. Others have added Pots to their digital rotors, and I 
suppose one could add an index switch to an otherwise analog rotor too. 
Just decide which way you want to go up front, then work out the rest 
from there.

By the way, I've long ago retired the FODTrack software, and now use 
Predict on my Linux box. I had to tweak the code a little (yea Open 
Source!), to output the same Yaesu commands as what FODTrack spit out. 
Alternatively I could have modified the controller. Either way, it's 
still working great.

Good luck,

Greg KO6TH

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