Control Unit for Home Built Rotator from Pitch-Prop Motor
 

Hi All,

I acquired a Pitch-Prop motor a number of years ago, with the intention of
building a antenna rotator.
I still have the intention of doing this, and have checked the motor for
operation. This works out very nice, and was able to control it to different
speeds with different voltage.
I have a construction design for the mounting of the motor and gearbox to
the tower, and antenna.

The problem I have now, is I wish to construct a suitable control unit, with
digital readout, and the possibility of controlling via a mini PIC control,
or via PC.

I have searched the internet without much success, so my next course of
action was to see if anyone on these groups might be of help.
So I put my hands up for HELP! :)

Any help would be gratefully received.

Thanks in Advance.

Kevin, ZL1KFM.

Control Unit for Home Built Rotator from Pitch-Prop Motor
 

Kevin & Natalia wrote:

Hi All,

I acquired a Pitch-Prop motor a number of years ago, with the intention of
building a antenna rotator.
I still have the intention of doing this, and have checked the motor for
operation. This works out very nice, and was able to control it to different
speeds with different voltage.
I have a construction design for the mounting of the motor and gearbox to
the tower, and antenna.

The problem I have now, is I wish to construct a suitable control unit, with
digital readout, and the possibility of controlling via a mini PIC control,
or via PC.

I have searched the internet without much success, so my next course of
action was to see if anyone on these groups might be of help.
So I put my hands up for HELP! :)

Any help would be gratefully received.

Thanks in Advance.

Kevin, ZL1KFM.


Excepting the readout, this should be a fairly routine motor control
problem. Depending on what you want to do your control box could be as
simple as a current-limited power supply and a couple of switches or as
complex as a fully fed-back motion control system.

How's your electronics skills, and how fancy do you want it to be?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html

Control Unit for Home Built Rotator from Pitch-Prop Motor
 

I'm going to recommend against electronic feedback unless you are a
control systems hobbyist... I did PID
(proportional-integral-derivative) servo on a homebrew rotating mast so
I didn't need a readout and eventually decided to go with a rotation
sensing pot, a voltage-to-current converter, and a surplus meter.

This was after I tweaked the PID to get rid of the oscillations but
still had some average position errors...

I guess with a digital system it would be easier to optimize. Mine was
all analog... and only one op amp, so the settings interacted :-)

Making the motor go and watching the meter is a more sensitive and
intelligent form of feedback, as long as you've got a system you can't
break by turning too far.

A simple pulse-width-modulator for speed control might be in the cards
though. That way you send a variable duty cycle full-on full-off pulse
train to the motor. Good torque and you don't need a variable power
supply just to run the rotor.

I'm going to add one to my rotator soon... I've got that on manual
right now... pulsing the switch makes a nice slow smooth rotation!

If you do like electronics projects for the sake of electronics
projects, feedback control is an interesting way to go, though.

73,
Dan
N3OX

Control Unit for Home Built Rotator from Pitch-Prop Motor
 

On 23 May 2006 08:31:29 -0700, "
wrote:

This was after I tweaked the PID to get rid of the oscillations but
still had some average position errors...

I guess with a digital system it would be easier to optimize. Mine was
all analog... and only one op amp, so the settings interacted :-)

Hi Dan,

If anything, going digital has all the prospects of thrashing the
antenna into shreds. The oscillations you speak of are eminently
suited for an analog solution - you simply have to understand the
nature of resonance, coupling (over, critical, and under), and attack.
If you don't, translating them into binary code will be impossible.

For instance, your average position errors were probably due to
under/overshoot and a too heavily dampened system with too much gain.
No computer program is going to improve that.

73's
Richard Clark, KB7QHC

Control Unit for Home Built Rotator from Pitch-Prop Motor
 

Kevin & Natalia wrote:
Hi All,

I acquired a Pitch-Prop motor a number of years ago, with the intention of
building a antenna rotator.
I still have the intention of doing this, and have checked the motor for
operation. This works out very nice, and was able to control it to different
speeds with different voltage.
I have a construction design for the mounting of the motor and gearbox to
the tower, and antenna.

The problem I have now, is I wish to construct a suitable control unit, with
digital readout, and the possibility of controlling via a mini PIC control,
or via PC.

I have searched the internet without much success, so my next course of
action was to see if anyone on these groups might be of help.
So I put my hands up for HELP! :)

Any help would be gratefully received.

Thanks in Advance.

Kevin, ZL1KFM.



It is entirely doable, check here
"http://forums.parallax.com/forums/default.aspx" for ideas on how to implement
your project using a Basic Stamp...
I would do it with digital position sensing, with an lcd display showing
direction of antenna..

Bob N9LVU

Control Unit for Home Built Rotator from Pitch-Prop Motor
 

On 23 May 2006 08:33:09 -0700, "
wrote:

Oh, my bad. you're going to NEED some feedback to control it with a
PC.

OK, so let me retract the advice against it... possibly you could do it
all in software...

Hi Dan,

To underline my last point about software, did software prevent this
error? [Hint, eyes were an analog solution.]

73's
Richard Clark, KB7QHC

Control Unit for Home Built Rotator from Pitch-Prop Motor
 

Richard,
Agreed on the suitability of an analog solution... I certainly made
some steps toward critically damped operation. My circuit design was
bad, though.

I didn't have a very analyzable problem; the rotator rotates one of
those fiberglass surplus military masts with respect to another, so I
get a lot of stick-slip, especially if there's a breeze (there are 12
feet of mast above this thing).

This is not to say a suitable set of P, I and D couldn't be found, and
it would have been pretty slick if I'd set up right for empirical loop
tuning, but I hadn't done that. I got pretty close by soldering
components in and out.

I would have had a better time with a real multiple op amp circuit with
a knob for each of P, I and D.

I think you hit the nail on the head regarding too heavily dampened
with too much gain in the antenna rotator case. I just couldn't really
tune the thing.


In my case, I just decided to throw up my hands and go to the simplest
method so I could get on the air with a rotating antenna. I have a
quite successful analog servo going every day with my remote antenna
tuner (www.n3ox.net/projects/servo). That one is ever-so-slightly
underdamped, proportional only, and works nicely. There's a little bit
of hysteresis and it certainly could be improved, but I stopped at the
good-enough-for-daily-operation level.

I guess what I meant by "going digital" was that depending on whether
you're more comfortable with programming than a soldering iron (not
me!) you might think about having a simple motor drive circuit and
implement the admittedly complex PID loop in software/firmware.

You're absolutely right that you can't do this if you don't know how to
do the analog...

73,
Dan
N3OX

Control Unit for Home Built Rotator from Pitch-Prop Motor
 

hahaha!

Dude, I've got baaaaad software.

Took me a long time to get that.

CU,
Dan

Control Unit for Home Built Rotator from Pitch-Prop Motor
 

On 23 May 2006 09:38:07 -0700, "
wrote:

You're absolutely right that you can't do this if you don't know how to
do the analog...

Hi Dan, All,

The single loudest voice on these matters is Robert Pease at National
Semiconductor. For streaming courses/lectures on this very topic,
visit:
http://www.national.com/nationaltv/index.html

I've been following Bob's no-nonsense contributions for more than 25
years now.

73's
Richard Clark, KB7QHC

Control Unit for Home Built Rotator from Pitch-Prop Motor
 

If you do like electronics projects for the sake of electronics
projects, feedback control is an interesting way to go, though.
============================
Talking rotor position feedback ,instead of the traditional potmeter in
bridge circuit with analogue meter readout ,you could try a low cost
synchro system utilising 2 stepper motors from discarded hard drives ,
dot-matrix printers or flat bed scanners ,with 1 stepper motor
mechanically coupled (either directly or via a reversed rotational
reducer) to the rotor ,the other in the shack as a readout device. The
circuit I found on the web (via Google)needs 5 wires between the stepper
motor coupled to the rotor and the control unit ,located with the other
stepper motor in the shack.
The circuit includes 4 TIP120 NPN transistors 2 LM324 dual Opamps and a
few diodes and resistors. The stepper motor in the shack could either be
provided with a rotating or sliding pointer ( the latter from an old
1950-60s radio) , or be mechanically linked to a counter (for example
from a discarded tape recorder)

A potential 'recycled components' project.

Frank GM0CSZ / KN6WH