ENGR: Motor/Drive for Radio Dish

Fri Oct 10 01:35:52 EDT 2008

==> Automation List post by Mohammed Ahmed...
To view or reply to this thread: http://www.control.com/thread/1223567899

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ENGR:  Motor/Drive for Radio Dish
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Hello everyone,

I have a 5 meter radio dish on a mobile platform that I want to motorize and convert into a computer-controlled radio telescope for amateur radio astronomy. The preexisting dish mount can be manually aimed, but for astronomy use this will not to do. My main aim is to have it track the sky with high precision at low speeds, yet still have the ability to to move at high-speeds when switching to a new target.

The speed and accuracy requirements are a bit of a problem for us; we need to point it with an accuracy of 2 arcminutes (0.03 degrees) in both axis! In addition, the  movement speed needs to go from as slow as 0.1 arcmin/sec (0.0002 RPM) to 60 arcmin/sec (1 degree/sec or 1/6 RPM).

The preexisting mount is altitude-azimuth based. For rotation, the radio dish is mounted on a round swivel base. Right now we're planning to bolt a roller chain around it and drive it with a pinion gear, giving us a 28:1 reduction ratio. Would our setup work if we used a 200:1 planetary gear and a AC servo motor-drive? The combined reduction ratio of 5600 means if we drive the motor at 1100 RPM to we'll get slightly better than 1 deg/sec, and at 50 RPM we can get 3 arcmin/sec.

>From that, is it feasible to use PWM to drive it at lower speed? Should we worry about stiction for these accuracies? What is the proposed solution in this scenario?
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