In the last few months since we fully assembled the superstructure, we’ve been working on a lot of the smaller and more detailed aspects of the mount. Much of this has been going through the procedures for loading and unloading various components multiple times so that we can figure out if there are any difficult spots we need to watch out for.
Loading and unloading the receivers – for instance – is something we will have to do many times since we can’t open them up or perform much maintenance on them while they are up inside the mount. To that end, we hooked up some eye bolts and shackles to the cryostat and lifted it up into the mount using our gantry crane. While this isn’t the method we’ll use when we’re actually deployed at the South Pole, it did help get a feel for how tight the clearances are and let us practice mounting and un-mounting the cryostat from the four brackets which affix it rigidly to the steel superstructure.
The images above show the cryostat (silver) during the lift. In places, the edge of the cryostat got within one half inch of the blue structure. Though this is partly due to the fact that we didn’t do a perfect job of centering the crane, the whole procedure is very tight. Once it’s up in place, we can attach the so-called receiver harness: a series of 10 adjustable steel arms that connect to the upper and lower flanges of the cryostat via four steel brackets.
When they aren’t attached, these brackets swing out of the lifting path. Once the cryostat is at the right height, all we need to do is swing them in and attach them. It’s a bit difficult to see in these pictures, however the ends of the arms have a right handed and left handed thread on either end, meaning that they can be turned to lengthen or shorten them and adjust the level of the cryostat. They’re designed so that once we adjust them for a single cryostat we can take it in and out again repeatably without having to re-adjust the arms. When it’s all mounted, it looks like this:
These pictures are taken looking across the drum, the central blue bar is not connected to the cryostat, rather it holds the upper half of the Elevation – Deck rotary union.
After loading and unloading it a few times we felt confident enough to sign off on the harness system and start the design of the real loading system we will use when we’re at the South Pole.
One other thing that we just accomplished is the completion and mounting of our drive cabinet. This metal cabinet holds all our amplifiers and controllers for the motors which drive the mount’s three axes of rotation. It’s been progressing steadily over the last few months, however its a slow process. Not only did it need to be built up, laid out, and wired; a lot of manual consultation was required to figure out how exactly everything interacted with everything else.
Once we had successfully tested that we were able to command movement out of the motors and made all of the requisite cords to run up through our rotary union we were ready to mount the drive cabinet and the motors so that we could make the mount move for the first time under motor command.
The drive box mounts to the Azimuth structure. Power and communications route upwards through the first (Stationary to Azimuth) rotary union into the drive box then splits back out to the six motors that run the mount. We hooked up two of these motors (the Azimuth ones) to their respective gear reducers and plugged them in, ready to run from our command station sitting down on the floor. The result is the video below:
This is the first time we’ve moved the mount under computer control! Depending on your reference, it might appear that we’re spinning pretty slowly. However, this is actually about 6 times faster than we rotate during operation. With one axis down, we’re getting ready to install motors on the other three axes and get them up and running. Once that’s complete, it’ll be time for fine-tuning the amp and motor control code to give us the smooth and consistent motion we want.