1910 replies to this topic

[dhines32]

Hi, Mike.

 

It can survive failure of one or two wire loops, but if the shock dislodges the secondary glue, it would be game over. If I can't fix the vibration at 0.008", I will go back to 0.010". It was very durable.

[N-1]

There is a certain coolness factor to the wire spider and kudos for trying it out - but it would make me nervous too. Also, guitar strings being designed to vibrate being used in an application that seeks to minimise vibration is not without irony

 

Anyway, if this turns out to be too difficult, a 3-vane spider mod using more conventional materials may be a good alternative if improved contrast is the aim. 

[Kuba_81]

 I had never problems with moisture on the primary mirror, but the secondary sometimes get foggy. I don't believe in electric heaters, so recently I made a cap for the secondary to deal with the dew. It was made of pipe insulation, black duct tape and black velvet. Yesterday I put the scope outside to cool it down before session. The cap was on. The forecast said it was 5degC  (41F) and 90% r.h. After an hour outside, the tube was soaking wet. But the secondary was dry & clean. Then it stayed clean for 3 hour session. Good enough for me.

 

As you can notice, there is a flocking on the secondary's side wall. I can share a template of the flocking wrap for the secondary mirror of GSO 10" F/5 dob. It has a minor diameter D=62mm and thickness equal 12mm. I plotted it in a cad software. Just print it on A4 sheet while keeping the 100% zoom level to match the exact dimensions.

Attached Files

•  LW gso 10.pdf   13.41KB   9 downloads

[dhines32]

There is a certain coolness factor to the wire spider and kudos for trying it out - but it would make me nervous too. Also, guitar strings being designed to vibrate being used in an application that seeks to minimise vibration is not without irony

 

Anyway, if this turns out to be too difficult, a 3-vane spider mod using more conventional materials may be a good alternative if improved contrast is the aim. 

Update: I continued to add guitar tuners, adding one for each wire, thinking that the tension was the issue. I even offset the position of the wires on the hub and widened the distance between the guitar tuners, but it turned out to be the tuner and bracket combo that I made.

I discovered this when I decided to go back to bolts for the wire mounts to the OTA, using eye-bolts this time. I didn't get a pic of the eye bolts, but it was similar to my original attempt pictured here:

This attenuated the vibration a great deal, even with the 0.008" wire. Collimation shift was still there, but it was also small.

 

I didn't get a great session in because of high clouds, but I suspect the results would be similar to what I experienced before incorporating the guitar tuners into the mix.

 

I will try thin vanes in >o< fashion to see if I can do any better. I cut them out of 0.005" steel shim stock. Hopefully, I can try them soon. I don't expect the views to be much better, but if I can tension them well, the collimation shift will reduce.

[kfiscus]

Bump.

[HenkSB]

For transportability I converted my Z12 to a collapsible Dob.  This changed the center of gravity, so I was able to take 4" off the base panels.  It now fits in my Chevy Cruze Eco on one seat (except for the top assembly that goes in the trunk).  The truss tubes have 2 sets of holes, one set for visual and another one for binoviewers and astrophotography.

 

 

Note that I also added setting circles for Az, and stick-in carboard Alt setting circles (not shown).  I use a magnet and sheet metal pointer for Alt calibration, and a sheet metal clamp pointer for Az.

 

To be able to do EAA and have somewhat decent tracking I got the mechanical part of the Romer EZ-goto kit.  I added an OnStep controller along with Ekos for the high-level control with plate solving / goto and KStars planetarium.  KStars/Ekos runs on an RPi4b with a 4-port USB3 powered hub and 12 to 5V DCDC.  It runs on a small Li-ion battery.  The plate solving is done with a guide scope and an ASI120mm autoguider.  The guide scope was made from a RACI finder and a ring that I glued on.  I can also just use the OnStep controller by itself without the Pi.

 

[N-1]

Update: I continued to add guitar tuners, adding one for each wire, thinking that the tension was the issue. I even offset the position of the wires on the hub and widened the distance between the guitar tuners, but it turned out to be the tuner and bracket combo that I made.

8tuners.jpg

I discovered this when I decided to go back to bolts for the wire mounts to the OTA, using eye-bolts this time. I didn't get a pic of the eye bolts, but it was similar to my original attempt pictured here:

bolts.jpg

This attenuated the vibration a great deal, even with the 0.008" wire. Collimation shift was still there, but it was also small.

 

I didn't get a great session in because of high clouds, but I suspect the results would be similar to what I experienced before incorporating the guitar tuners into the mix.

 

I will try thin vanes in >o< fashion to see if I can do any better. I cut them out of 0.005" steel shim stock. Hopefully, I can try them soon. I don't expect the views to be much better, but if I can tension them well, the collimation shift will reduce.

Commendable effort. I note that the opposing spider 'vanes' don't look parallel in the 1st photo. If that turns out to be the case, then the reduced visibility of the diffraction spikes may be due to the fact that instead of 4 spikes, there are now 8 half as bright, except where they overlap slightly close to the object image. The thinner material may only play a secondary role here. The stock vanes are pretty thin already.

[dhines32]

Commendable effort. I note that the opposing spider 'vanes' don't look parallel in the 1st photo. If that turns out to be the case, then the reduced visibility of the diffraction spikes may be due to the fact that instead of 4 spikes, there are now 8 half as bright, except where they overlap slightly close to the object image. The thinner material may only play a secondary role here. The stock vanes are pretty thin already.

Thanks N-1. I got a chance to try out the .008" wire build again last night, and it needs a lot of work. The vibration was pretty bad. And, yes, there were more than 4 faint spikes because of wire misalignment. There were four definite spikes, and I could see that two of them split into close pairs. Despite that and the vibration when moving the scope, I really liked the view when things steadied, so I will try to find a more stable wire geometry. I can see a definite difference in the spikes going from 0.010" wire to 0.008". It's amazing. The part I really like is that the peak intensity of the spike seems to be thrown away from the object. 

 

I have been purposely limiting this mod and using the stock secondary hub, secondary holder, and the existing drilled holes just incase I decide to roll back the changes. These parts are probably source of the instability. The examples that produce great results are truss scopes with rigid UTA's and custom secondary holders. The Z12's tube might not be strong enough to pull this off, but I will try a few more changes. The good thing is that there are good discussions on Cloudy Nights that are full of user experiences. 

 

Hopefully, I can nail down a good design before Mars is at opposition. I am hoping to see its moons this time. 

[dhines32]

I tried "wires" again using Jerry Oltion's secondary mount design from here:

http://www.jerryolti...chtrackball.htm

 

I ditched the factory hub, used carbon fiber plate instead of aluminum, and braided 0.007" fishing line instead of wire. The line was just as strong and didn't stretch.

Knots are a little more challenging, but at least I don't get finger poked with 0.007" wire.

 

I also decided to use 8 individual strings unlike before. Things stay put better this way.

 

The 4 thumb screws don't really work well, but I can collimate with the guitar tuners. I probably need to tap the holes better.

 

I only got a brief test in because of the cold, but on a mirror that had only fan cooled for a hour or so and coming from a warm house, I was impressed. I didn't get a great secondary collimation before dark, and my red light wasn't up to the task to use my autocollimator. Despite that, the planetary contrast and contrast overall was very good. The vibration was not as bad as before. It was tolerable even with the wind. It dampened after a second or so when slewing.

 

I only managed to test on Jupiter and Mars. The secondary spikes were very faint, and I could see them thicken where the lines didn't overlap well. The weird thing was that they seemed to disappear after a few seconds. I don't know if it was an optical illusion or what. They would just fade. There was a faint glow around the disks, but great contrast from the planet. Hopefully, I can get to see Phobos and Deimos.

 

I plan on making new mounts for the piano tuners. Right now, I only have 4 tuners in place, but I need all 8 lines to be easily adjustable. I feel like this design is lighter, reasonably stable, and seems to have less collimation drift. I need to tweak a few things, but I am really pleased with the results.

 

[OskiBear]

Does anyone know if the side bearings for these Dobs are interchangeable? I have a 'spare' 10", and enough parts to cobble up a 12" - both Apertura. My original idea was just to hang the 12" onto a wooden ring arrangement, and build a new base. But if I can somehow use the adjustable side bearings I'd be able to add go-to capability. 

 

I realize there'd be some difference in the curvature on the underlying brackets that bolt directly to the tube. And I might be able to take care of that with some stiff backing of some kind. Is anyone aware of an .stl file for these? That would help, a lot.

 

thanks - and I very much appreciate this thread; lots and lots of good ideas here

 

Rich

[kfiscus]

The bearings are interchangeable- the shoulders are not.  I sent you a PM.