The end of last week was mostly preparation for the beginning of this week, so I decided to wait until this week for the next post. After getting the first ring bearing and the Azimuth stage installed, we went to work getting the Elevation stage ready to attach. This stage gives us our second axis of rotation, nodding the entire telescope up and down.
The first thing we did was to unpack and attach our second ring bearing. This bearing attaches to the top of the elevation stage and provides the mounting point for the final ring which we simply refer to as “Theta”. As with the first bearing, we inspected the ledges which needed to fit together and did a little grinding away at the paint to make everything match up nicely, then picked the bearing up. Installation was a bit harder since the elevation ring it installed onto was still sitting on it’s shipping support at a 45 degree angle.
Next we needed to prepare a cage-like structure which sits underneath the elevation ring. This frame helps support the elevation ring and keep it from flexing. But because it sits on the bottom side of the elevation ring, we needed to attach it to the ring before we attached the ring to the mount.
Once we had the frame built up, we lifted off the elevation ring, set it down on top of the frame, and bolted the two together. We were then ready to lift this new substructure upwards and attach it to the rest of the assembled mount.
The pictures above show a few different views of the elevation stage. On the left, one of the two gear reducers is visible and the large gear can be seen meshing with the outer half of the second ring bearing. Although the bearing is identical to the first one, this bearing operates slightly differently. Rather than the toothed half being fixed in place, for this bearing it is the free half. In this orientation then, the gears drive the outer half of the bearing and will cause the Theta stage (not pictured) to rotate. The right hand picture shows one of the two bearings that will enable the telescope to rotate in elevation (think “nodding” motions”). These are extremely resilient bearings, supporting over 10 Tons between the two of them.
But one might ask how this addition integrates with the parts we’ve already built up. There are two main interfaces between the elevation stage and the Azimuth stage. You might remember from the previous post that the Azimuth stage has two large triangular sections sticking up off the main ring. The tops of these triangles are flattened and provide an attachment place for the two bearings. The alignment of these bearings needs to be pretty precise because their orientation affects the second interface, the elevation gear (seen at left). This huge toothed gear connects with the two gear reducers mounted on either side of one of the triangular Azimuth sections (at right still in their protective covering). This huge gear is somewhat like the Elevation stage’s counterpart to the toothed half of the ring bearing. As the motors turn the two gear reducers, they will apply torque on the large gear which will then rotate the entire elevation stage by way of the two bearings on either side.
The next step of course, was installation. We lifted the entire Elevation assembly upwards and brought it over to the rest of the assembled mount structure. We had to go quite high in order for the stiffening frame to clear the rest of the structure. With some careful maneuvering, we then moved the stage downwards and inwards in very small steps in order to align it properly with the Azimuth stage. This was a slow process since we needed to be very careful not to smash against any of the gear teeth that were exposed as we tried to get everything to align.
Once we had everything in nearly the right position, we were able to use the bearings on either side to guide us the rest of the way. Then after a slight bit of maneuvering left and right, we had everything aligned correctly and the gear teeth all mated nicely.
With the elevation stage installed, the mount seems even more like a jungle gym. The cross braces provide an easy way to climb up inside the mount where ladders can’t really reach. Although it seems very open right now, much of this space will be taken up by receivers, electronics, and Helium lines when the mount is fully populated. In the meantime though, it’s a nicely accessible space. As long as you watch your step.
With the elevation stage attached we’ve realized we had to adjust the webcam in order to continue capturing our progress. So if you’ve noticed the webcam shift over the past day, that’s the reason. The top-down shot shows a high bay which is significantly less cluttered than when we first unpacked everything. Next up is our final rotation stage “Theta”. Once that’s installed we’re only a short time away from our first motion tests.