Altitude Drive Parts on the Way
First, a note on discontinuity in blogs: that happens, at least on my blogs. 🙂
The drive for the altitude controls of the telescope are ordered and on the way. We ended up moving to a center location for the drive unit itself, and we are employing a timing belt arrangement near the center of the drive shaft. The drive wheels, a pair of aluminum hubbed, rubber-tired wheels like the one on the azimuth drive, are mounted near the ends of the shaft and each end of the shaft will be supported by a pillow block bearing.
The pillow block bearings will be mounted on a simple plate and then we’ll pin one end and give the other end an adjustment bolt to push the drive wheel against the altitude bearing surface. We compensate for the motion of the drive shaft by adjusting a similar arrangement on the drive assembly, keeping the tension on the timing belt connecting the drive assembly to the drive shaft assembly. The design calls for no idler – we’ll see how that works!
Our experience with designing and fabrication being a one-directional process is that it’s not so much. Iteration is our by-word and our telescope is getting better and better for it. It turns out that it’s really hard to completely envision all that you will encounter as you put it all together and we are making adjustments as we build. Fabricating the altitude drive will be no different. We already know that the pillow block attachments to the A-frame parts of the base will be improvised around this design theme. I also am looking at the center of the shaft being pulled by the tension of the timing belt. We may want to add a pillow block near the center to keep it supported and in line. It doesn’t seem like a good idea to allow much deflection there.
You can see another change that we made in the azimuth drive design over the last few months in this drawing of the altitude drive. The drive assembly now has a flange bearing on each side of the drive wheel. In the case of the altitude drive, that drive wheel is a timing pulley, unlike the azimuth drive which uses the aluminum-hubbed rubber-tired wheel, which you can see peeking out from under the base platform.
This additional bearing gives that drive assembly shaft complete support independent of the drive shaft from the gear box. While there is a nice bearing on either end of the gear box, we didn’t want to stress that at all. With the flange bearings on both sides of the shaft, the connection to the gear box is stress-free so the gear box can concentrate on rotating and not supporting a side force on the bearing.
Since the azimuth drive assembly was already built, we improvised an L-shaped mounting plate for the second flange bearing. I love that word – improvised. In this case that meant making a drawing of the part; getting it fabricated; finding that I had never revised the drawing as-built for the actual bearing we bought; drilling and tapping new mounting holes for the bearing; finding that I had never revised the drawing as-built for the size of the hinges on the base plate; sending it back to Larry to chop off a piece of the bottom part of the L; and finally, now, incorporating it into the azimuth drive assembly. This is an optimistic statement. I’ll post a picture of the finished product if it all fits this weekend. If it doesn’t fit, we will continue to improvise!