Tracking..., and GoTo....
The scope had been built on a tight schedule, having first-light just one night before my friends flight arrived for the OSP party, so the mods needed for ServoCAT were not all implemented initially. So now I must router grooves for the steel cable which will eventually drive the altitude direction, but first I have to lift the scope up on one side. A 2 ton scissor jack was used to lift one side of the mirror box up 1/2".
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The pads are out! Now it's time to set up the router.
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Deep and wide enough.....
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The pads are reinstalled and the cable slides smooth....
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...But, next is to lift a 1500 pound telescope to get the 100 pound ground board out to make it round for use as the azumuth gear. ServoCAT will engage the perimeter....
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Where's the center pin? It got destroyed.... Look, no trick mirrors!
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I've not seen this part in quite some time....
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Barely fits for the ride home....
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Ready to become round....
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My new pin....
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The new pin was modofied to reduce the threading qaps by coating with hot glue. In effect making a smooth surface....
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The new pin was then wrapped in aluminum tape as a bearing surface inside the bronze bushings....
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The previous system of lifting the scope at the center pin used three 3/8-16 bolts tipped with 2" diameter teflon disks. They surrounded the center pin and pressed against a 6" square of FRP. In five years the scope was operational the system worked but needing replacing if I was removing the ground board. The three bolts will now press on a 3/16" thick steel plate atop a 4" lazy susan greased bearings....
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The gap between the rocker box and ground board is 3/8", so to allow for the extra thickness of the lazy suan and steel plate I routered out a pocket removing much FRP....
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Routering FRP "Fiberglass Reinforced Plastic" is nasty and every precaution should be taken not to expose oneself to flying fiberglass particles....
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With the pin installed, and an extension plate made to accomodate the 55" square turning into a 55" circle, the distance was set....
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Teflon pieces were put under the jig to keep the screw heads from scratching the urethane, and a teflon plate was made to lift the router up 3/8" so the jig could pass over the three wood dowel pins used for the large teflon pads the scope rides on....
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Fearless.... It takes nerves of steel to do major surgery on scope parts....
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Eventually, it looked round. The 1/4" router bit had 1.125" long cutting length and a single pass was done to remove the corners at a speed of about 1/10" per second....
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All that is not ground board....
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Next the fine grinding had to be set up. Using the same 3" diameter by 4" long sanding drum used for making the altitude bearings perfectly round all that was needed was a new plate, again with teflon pads to keep the ground board up to miss those dowel pins, pivot clamp and another to lock the pivot angle....
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The plate was pivoted inward as the ground board became more round. Eventually there was uniform sound from the sanding drum and little sawdust made....
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Sometimes you just gotta stand back and look at the tools modified to get the job done....
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Once round and de-dusted, the parts were reattached. This is the center bronze support so the center lift system can transfer the weight to the ground. The center pin is jam-nutted to a 6" steel plate....
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The 50 amp circuit breaker and quick-diconnect had to be relocated to the now-circular edge....
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Yes, 50 amp circuit breaker 4-gage cable.... The power source is remote and voltage drop negligable in this system....
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Side view of the finished center pin area....
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Top view of the finished center pin area....
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Almost finished ....
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The seal, composed of foam rubber topped with expanded teflon tape for a smooth seal against FRP....
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The finished ground board, ready for install back under the scope....
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Next..., drilling the hole in the floor of the rocker box for the spline shaft of the azimuth motor..., but first I have to get the now-round ground board to the telescope without damaging the nice perimeter.
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It got loaded in the truck during dusk and unloaded in the dark...
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Now to unpack all the tools again...
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With parts in-hand...
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I first scribed an arc of the ground board radius on the rocker box floor in that one corner where ServoCAT will be mounted. I made a paper template of the Az motor mount to see how things lined up, new and existing to see the problems I'd have to work around.... This helped...
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Using a 2" Forstner bit and a steady hand the hole for the motor shaft and gear was created. The plan was to have a 2" hole, 1/8" of ground board protruding into the 2" hole and have 1/8" extra for disengagingv the 1.75" gear... alignment was perfect!
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Once the gear hole and 0.5" pivot hole were in I found the shaft wasn't long enough for the set-screws to reach, so I'll have to drop in new tapped holes for set-screws. With large scopes come custom made parts. Future versions of "Large Scope" parts will have a slightly longer motor shaft. I fortunately had drilled a 2" hole. If I had drilled the stated smaller hole I would not be able to get at the new set-screw locations to tighten them and the hold would have been large enough to attach the gear and drop the whole assembly in, but 2" was perfect...
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So, the Az motor assembly went in rather well, every hole getting stained and urethaned...
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And now, to complete the ground board installation.... The spring-loaded pins that ride on copper rings were reinstalled and aligned.
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The copper rings got a fresh coat of conductive silver grease that the pins will ride on, and then, my wife Lori and I, with Kuiper (pictured) and Sagan (not pictured) watching, manuvered the ground board into position and lifted.
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The ground board was lifted and supported so I could work on the center pin.....
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With deep twilight setting in the center pin retaining nut was installed....
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With deep twilight setting in the scope was lowered onto the modified ground board and once again spun...!
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On Sunday the 29th of January the ServoCAT control box location was determined....
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And the Alt motor was installed.... Using 1/4" spacers between the spool and the Alt bearing and rocker box, the holed were transfer punched.
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I put the assembly up to the scope several times.... I don't mind drilling holes in my nice looking scope as long as they are in the right spots.
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Just about level....
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Az motor installed....
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A view looking at the teflon routered slot....
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With motor and encoders.... I just gotta remember not to hit it with my knee or the ladder....
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The computer plate would need upgrading to accomodate the newer laptop but instead I decided to build a new, thicker plate but use the same mounting hardware....
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5/16th plywood with walnut veneer....
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Ready for mounting....
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Wiring Diagram for ServoCAT. When Argo Navis and ServoCAT arrived and the shipping box was loaded with cables, I had to lay it out for my own understanding.... All the cabling was laid out and must still be routed securely.
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The altitude cable anchor was installed and included a copper corner protector as the cable wraps over the edge....
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Another view of the cable anchor....
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The other end of the cable will terminate at the clamp. Because of the thickness of the bearing, 3" thick Oak, and the gap between the mirror box and rocker box, three 0.5" aluminum blocks were cut and stacked onto which the clamp is attached. Each block is identical so that one could get the hole pattern needed for the clamp and if I ever replace the manual clamp with a motorized disengage I can bring the second block forward to the top and it can have its special hole pattern....
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The Alt cable was terminated, though I did replace the spring that came with it with another, increasing the spring tension from 30 to 45 pounds force....
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And, I did go with three wraps of the cable on the Alt spool, not two.... Any extra drag was not noticable and it increased the friction on the spool by 50% since the force to move the scope in altitude is 50 pounds at the Alt bearing location.
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The motor power and encoder cable were clamped in place thereby keeping their seperation.
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The wireless hand controller base unit was attached at the upper rocker box corner. This unit had been sent back to have its 30-foot transmitting radius increased to 100 feet because it's 25 feet just to the location of the future control room. With no other ServoCAT units at this location there'll be no interferance.
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The hand controller unit was attached to the upper cage. The small junction pass-through board was installed in a small enclosure. This same enclosure also had a momentary normally open switch installed. The Remote Status Unit is also accessible when on the ladder.
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This switch, when pressed then activates a relay which cuts power to ServoCAT. The reason behind it is that once the scope is pointed at the North Celestial Pole ServoCAT must be powered down and in speed position #2 when it powers up. I have the speed switch and a kill switch right there when NCP is in the crosshairs. After this the system is tracking making the two-star alignment much easier since the stars aren't flying by....
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The wiring inside the rocker box is considerable, the kill switch relay box is above and left of the blue cat5 cable coil. The wiring harness has enough travel for the scope to move in altitude. All of this is to the left of the removeable step plate that I use when I have to step into the rocker box to remove or replace the mirror cover.
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Another view of the wiring arrangement.
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