Remember that the pictures are clickable to bring up larger, bandwidth-eating versions.
To view the AVI clips on this page, you'll need to install one of the Intel CODECs below. Sorry they're not Mac compatible.
Early in 1999, I started thinking of ways to miniatuize the DARTS base station. I was patently delusional, anyway, and reeling from the backlash against the monstrous pedestal. I started experimenting with using model-airplane servo motors, augmented with external encoders to feed back position. There was no way this was actually going to work, but I learned a little bit about servos in the process.
At this point, I was completely disconnected from reality. No radar hardware was actually being field-tested, as it was in the Sooner-Boomer days.
What was I thinking? A small two-axis, servo-driven, low-cost pedestal for the phased-array antenna. In all the pictures, the silver-colored square plate is the baseplate for the phased array. The baseplate is made of FR-4 PC board material, as are the flanges that connect the antenna baseplate to the servo/bearings.
All the servos are the model airplane variety, obtained from Tower
Hobbies. The azimuth servo is a 1/4 scale Futaba clone, and the
elevation servos are the standard-sized Futaba clones. The motor
and electronics have been removed from the right-hand elevation servo;
one drives, one reads back the position to the controller. The azimuth
servo does not feed back its position to the controller; however, there
is a limit switch so that it can find the "home" position.
Above is a shot of the pedestal, looking edge-on of the baseplate. The "lazy-susan" type bearing with the servo in the middle can readily be seen. This structure is actually quite sturdy and very stable.
Underneath the aluminum box are the controller and batteries to run both the electronics and the servos. Surprisingly, the servos take very little current -- less than 0.5 amp total, even when slewing.
Here's another shot, with the azimuth servos in rest position.
The azimuth servo can slew the antenna from 0 degrees to 90 degrees
(pointing straight up) in less than two seconds, although it wouldn't have
to be that fast for actual rocket tracking. The azimuth servo is just as
fast -- plus or minus 90 degrees in under two seconds. The fast rates
are due in part to the low mass of the gimbal assembly. There will be electronics
mounted on the antenna baseplate, but they are very low mass and will be
mounted close to the centerlines of the azimuth and elevation axes..
The first movie shows the pedestal moving in slow motion. The second shows fast motion, followed by a maximum-speed retract. The third movie shows the pedestal moving at near-maximum speed, in both axes. I'm almost ashamed to show these.
Thanks to Gregg Wonderly for capturing the video.
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Generation IV: 2001
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This document copyright Steve Bragg, KA9MVA. Updated:
June 22, 1999