The Dish Project

VK3YNV

Moderator
Thanks to Stevo for the 3M C-Band dish which I picked up a few weeks back, the next phase of the project is to sort out a suitable AZ-EL mount, Wayne VK3GMV had some AZ-EL mounts that were originally used as part of the Channel 7 Outside Broadcast system.

They are about 50 kG and look prettty solidly built. 110V DC motors with a gear box, with planetary reduction and worm drive to brass main gear, geared feedback pots, the motors have separate field windings rather than permanent magnets.

There are also some stick on heater pads, I guess for keeping ice and condensation to a minimum for cold environments.

Next task is to trace the circuits, but I was able to drive the AZ motor directly with 30V from a current limited lab supply.


IMG_4082.JPGIMG_4078.JPG
IMG_4077.JPGIMG_4076.JPG
 

Attachments

BillC

Active member
Hi Ray , nice looking motor drives gears and feedback pots. Do you intend to use the drive system for tracking with AZ and EL readout etc, could be a bit of work to get that going . Perhaps you are intending to track the sun?
 

sadarc

Administrator
Staff member
Hi Ray , nice looking motor drives gears and feedback pots. Do you intend to use the drive system for tracking with AZ and EL readout etc, could be a bit of work to get that going . Perhaps you are intending to track the sun?
Hi Bill, I traced the circuit this afternoon, and it's pretty straight forward, 120V DC for the field winding which is always the same polarity, and 120VDC for the armature, which reverses polarity to change direction. There are limit micro switches with diode steering for both axes and of course I'll need to calibrate the feedback pots in degrees AZ-EL.

I'm intending to PWM the armature supply so as to control the slew rate, one of the applications apart from EME is to do a bit of amateur radio astronomy, and getting the slew rate to track the moon's movement as well as the earths rotation would be nice. Being DC motors makes this a bit easier.

The heaters are just controlled by a bi-metallic sensor that switches on at some low temperature. I notice that the heating elements are located near the main AZ-EL bearings, so I'm pretty sure it's an anti-icing measure.

Interesting you mentioned tracking the sun, as that's a standard noise source for checking Rx pre-amp sensitivity. So yes, sun tracking is on the cards. :)
 

BillC

Active member
Good Ray , I am wondering if the heaters on the bearings are to help maintain a constant friction load on the drives , so to reduce lag in the tracking rate. As the tracker is free running and there is no aiming point feedback correction, it could drift . Just a few idle thoughts Ray . Wow i'm getting lots ov typing practis.
 

BillC

Active member
I wonder if it would be possible to make a bore sight tracker with photo cells at the bottom of the bore tube to provide voltages to control the servo motors. If the target moon/sun provided suitable light energy for the photocells and with accurate shading in the boretube perhaps one could hope for accuracy to a few minutes of arc. If that worked it would be a closed loop tracker ???
 

VK3YNV

Moderator
Hi Bill,
Interesting idea, I have been wondering how hard it would be to attach a telescope with a digital camera so as to get a visual feedback on the aiming point.

There are a number of software options for tracking, I haven't decided which one to use just yet.

Just a point of clarification, with the existing feedback pots the system is already closed loop.
 

BillC

Active member
Thanks for the clarification on the loop . I am sure that the tracking geometry would be a bit complex , daresay there would be programs for all sorts of tracking . I suppose it would rely on very accurate timing . Good luck , watching with interest .
 
Top