Here's a couple of pictures of the scope collapsed for transport. Click on the pictures to enlarge. Not shown are the four 40" long 1" diameter aluminum tubes. The total weight of the scope is about 40 pounds. The weight of the original was 50 pounds for the OTA and 50 pounds for the base.
The ground board consists of three hockey pucks attached to a triangle made of 3/4" square aluminum tubing. On top of that is a 21" diameter circle of 1/4" plywood, which serves to keep dirt off of the azimuth bearings as well as to hold the azimuth center baering in place. Speaking of which, in the center is a bolt with ball bearings and a split lock washer to adjust the pressure on the teflon pads. The teflon pads are glued directly above each hockey puck.
The rocker box consists of a 21" diameter disk of 1/4" plywood, with a
3" wide x 1" thick ring of plywood to stiffen it around the edges.
The bottom of the plywood is covered in ebony star formica.
Mounted on the ring are two altitude trunions, 1 1/2" thick laminated
plywood, with cutouts for weight and to serve as handles. The altitude
bearings are teflon coated furniture glides.
The mirror box (shown on its side here) is a 15" x 15" x 12" high box of 1/2" plywood with 1x2
braces at the corners, and a 1/2" plywood bottom with a ventilation hole
cut out of it. The bottom was made to receive my existing mirror cell.
On one side of the mirror box is a 4" fan for cooling.
In the center of each side is a hole with a tee nut to accept a
truss tube connector. At each corner is an eye bolt that accepts a
caribiner, connected to a turnbuckle connected to a wire that runs up to
the top ring.
In use, the ring sits atop the four truss poles, and is held in place by
six wires leading to the four corners of the mirror box.
The top ring consists of a ring of 3/4" foam insulation between two
sheets of 1/4" plywood, covered inside and out with birch edge banding to
match. The ring is 15" inner diameter and 18" outer diameter. descending
from the ring is a baffled box on which the focuser is mounted. angle
brackets stick up from the top of the ring to hold the 4 vane spider and
secondary holder, produced by Gary Wolanski. The
focuser is a 2" crayford made by MoonLite Telescope Accessories.
The blue tape in the picture is a temporary measure to protect the wood from being scratched by the eye bolt until I work out a more permanent solution.
The ring is held down by small toggles on the ends of the wires.
Click on the images to see more detail.
The altitude bearings consist of a ring identical to the top ring (I was going to make a conventional top with the two rings, but decided to use one and cut the other one in half for the bearings), fastened to an 18" diameter 3/4" plywood circle, also cut in half. The 3/4" plywood is overkill for the bearings, but I wanted them to be the top of the scope when it was packed up, so I wanted them to be able to protect the rest of the scoep if something heavy was put on top. The bearings are not identical. One has a "nub" at the hub to mount an encoder on, the other has an "innie" that matches it.
The rest of the photos show the steps in setting up the scope. Refer to them as you read the rest of the description.
As the scope is shown, the mirror box rests on the base, with the top ring on top, followed by a foam spacer, followed by the bearings, followed by the mirror box cover. The top is bungeed on using the four eye hooks. The plastic bag on top contains the wires and all associated hardware (all screws have 1" knobs so the scope is assembled without tools.
Set up is a little harder than a conventional truss scope. I take apart the pieces, connect the altitude bearings to the mirror box, velcro the battery to the side of the mirror box (where it acts as a counterweight), and set the mirror box on the base. I then screw the truss poles to the four sides and set the top ring on top of the four poles. I then attach the six wire supports, and twist the ring until the truss poles are all parallel (visually, by looking past the edge of one at another). I then tighten down the wires using the turnbuckles until they all vibrate at the same pitch when plucked. Only a little tension is needed to keep everything stiff.
I then insert my laser collimator, adjust the secondary to put the beam on the center of the mirror box cover. Then I remove the mirror box cover and adjust the primary to return the beam to itself. The laser collimator I use is by APM Telescopes.
The scope moves well, holds collimation all night, and holds collimation from horizon to zenith. There are some things I'd likt o improve (aren't there always), but for now I'm very pleased with it.
All packed up and ready to travel. This is all that's needed. Total weight is 35 pounds for the packed up scope, 13 pounds for the (18 Ah) battery, and 10 for the tubes, telrad, baffle, and counterweight. |
Here's the view from the "front", showing how the focuser nests above the fan. |
...and a shot from the side. The cutouts in the altitude trunions serve as handles. |
with the cover removed you can see how the altitude bearings fit together. |
Under the altitude bearings is a foam spacer that protects the optics from anything dropped on the scope as well as keeping the altitude bearings (and their eventual encoder) from knocking against the spider. |
With the foam removed you can see the upper ring. The "White Castle" cup covers the secondary, and is held on by friction plus a small velcro strap (just in case). |
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Everything attaches with 1/4-20 screws with 1" knobs on them. I'd like to make the screws captive, but haven't figured out a good way to do this yet. In the meantime, they sit in a little ziploc bag hwne not in use. |
The poles attach the same way. The angle brackets are screwed into tubing connectors pushed into the ends of each tube. The tubes are loosely filled with foam packing "peanuts", and the top of each tube is stiffened by a small wooden plug epoxied into it. |
The poles stay in place nicely, but can be knocked down if pushed. Since the Telrad is attached to one of them, I have to be a little careful not to bump into the scope until the top ring is seated. |
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The tops of the tubes sit in 1" hoes drilled 1/4" deep into the bottom of the top ring. The only thing holding it in place are the wires pulling it downward. This sounds scary, but once it's in place, the tubs are held nicely upright. |
The wires attach to turnbuckles which are in turn attached to the eye bolts by caribiners. |
The top of each wire has a little toggle, which is a piece of aluminum, 1/4" x 1/4" x 1" with a hole drilled through the center. These are flipped parallel to the wire and threaded through 3/8" holes drilled next to each truss attachement point. |
Then the toggle is flipped perpendicular to the wire and the wire is tightened by the turnbuckle. Each wire is left slack until all six are attached (I originally planned for eight, but six is more than stiff enough). |
When all six wires are attached, the top ring is twisted by hand until the truss tubes all appear parallel. Then the tunrbuckles are tightened until each wire produces the same note when plucked, indicating that the tension is about equal in all of them. This produces a nearly collimated scope. |
If needed, I have a baffle made out of foam board that attaches to the top ring with velcro. I planned on making a shroud, but ths was quick and dirty, and it works very well. |
As you can see, looking through the focuser at an angle, the only stray light is that reflected off of the inside edge of the top ring. I plan to cover that with black velvet, but haven't gotten around to procuring it yet. |
Here's the scope all set up, as seen from the front. |
...and from the back. Note the battery velcro'd on (I forgot to take closeups of this). |
All ready to observe. |