Azimuth Elevation Tracking Mount
Monday, 25 January 2010 11:42
I purchased this unit a couple of years ago intending to set up a large dish with full azimuth and elevation capability. The intent was to also mount an assembly of 2m, 70cm and 1296 helixes on the same platform from booms extending perpendicular to the beam direction of the dish. Unfortunately time has been extremely limited and I have not progressed with this project.
From what I've been able to determine, this Tracking Mount is a post WWII aircraft / missile tracking assembly which was vehicle (truck) mounted.
It was fitted with a circular rotating waveguide that travelled up through the centre of the unit and the top section had a flexible coupling which fed the radar dish.
A large number of slip rings fitted inside the telescoping shaft allowed synchronous Selsyn motor position sensors to transmit information to electronics in the vehicle whilst the dish was rotating.
The unit rotates fully and continuously through 360 degrees in the horizontal azis and 90 degrees in the vertical axis.
I have not powered up the original drive motors but the previous owner assures me that it is fully operational. I have turned both vertical and horizontal motor shafts by hand and there is very little resistance and the antenna mount moves smoothly in both planes.
Because this assembly is quite heavy, a custom made support platform is required. The previous owner had originally mounted it on a 12' tower made from four vertical lengths of thick galvanised angle iron. These were not braced but relied on their wall thickness and width to provide the strength.
My plan is to make up something a bit more elaborate so that I can raise and lower the assembly inside a frame made from similar angle iron using a winch and pully arrangement integrated into the platform.
There is no noticeable backlash or cogging. The gear ratio must be significant because when I turn the motor shaft and try and hold the antenna mount steady, it continues to move regardless of the pressure I apply to keep it still.
The assembly seems to be predominantly made of both cast steel and aluminium alloy and is very solid. I'd say that the whole thing weighs over 200kg. The motor outer cases are steel and there is a slight amount of surface rust in some places, but there is no pitting. The azimuth and elevation gear assemblies both contain gear transmission oil.
The Selsyn motors are also some type of aluminium alloy and have heavily oxidised, being in the open for many years. I doubt that they would be functional but I have not tried them. All shafts appear to rotate but I'm not sure of the internal electronics.
I do have spare Selsyn motors in excellent condition but I am inclined to use modern hall effect positional sensors and PIC microcontrollers to manage the position of the unit and control the drive motors.
My intial plan was to connect a windscreen wiper motor to the top pulley of the drive motor shaft and use that the rotate the horizontal axis. The vertical axis shaft is not immediately accessible as the unit stands, but the rotor at the rear of the elevation drive motor can be rotated by hand to elevate the unit and it may be possible to remove that and access the shaft at the rear. I have not had a chance to investigate that further. If it is possible, then a windscreen wiper motor there will also suffice to drive the elevation gear assembly.
From what I've been able to determine and have been confirmed by people who have seen these units in action, the original motors rotated the dish at approximately 80 to 90 rpm; maybe faster. I have a folder of technical schematics and info on the unit but have not had time to review it in any detail.