Chriske

Oh...! Nooooo.....!   PINK...!!😳

Following the building instructions from Dave Trott I drew this very basic version.
It is basically nothing more then three parts(in the drawing) Hinges are not included in the drawing. But the constraints(to simulate these hinges) are in place.
The driven part is the brown one, the bleu surface is where the camera(s) go.
Pushing the brown part upward, the blue part has to go with it. Notice that  both moving parts do not have the same speed. The difference is very little. But just enough to correct the error that is produced by a 'single arm Barndoor tracker'.

In fact the error is no more then 1 arc second (max) during a one hour tracking session, according to this list.
After two hours tracking the error gets smaller again.

Fully opened the angle between the two moving parts is a little bit wider. Not much but apparently just enough to eliminate tracking errors completely.

How did you guess...😁

52 minutes ago, happy-kat said:

When I built my barn door (modified type 1) the size of the boards was driven by the size of the bolt which governed the distance to the hinge, I had used an M10.

This was the site for the calculation what I don't know is if the same applies for type 3 or 4, but I imagine it does as the aim is the same.

https://blarg.co.uk/astronomy/barn-door-tracker-calculator

If you are after reducing tangent error (the point I think of type 3 and 4 designs) then on my build thread, there is a link in my signature, is a contribution from a member on how to print a 3d part to use on a type 1 design to reduce tangent error.

Hey thanks for replying so quickly ..!

I'm planing to build a type 4, I found a PDF and need to recalculate the distances and speed of the threaded rod.
Not planning to build it this way, I'll be printing lots of parts(of course..😁), only a larger version.
Point is, looking at the drawing, How do I recalculate distances r, b and c when I want to make it twice as large.

heavy-duty-double-arm-barndoor-building-plans.pdf

I'd like to make a type 4 barn-door tracker, only I want it to be a bit larger.
How do I proceed, can I simply enlarge all the figures linearly, lets say size x2. And also speed x2..?

We use float and never wait to measure mirrors on the optical bench.
How..? We always rinse with water at ambient temp and dry immediately afterward..

8 minutes ago, markse68 said:

I was thinking of making a shallow alt az platform with computer control to create a virtual polar axis. You could enter your latitude and use it anywhere in the world. At the pole it would just use the azimuth turntable and at the equator it’d use only the altitude rocker, side on, and in between a combination of the 2. I think it could work but a bit more complicated than a simple rocker platform...

As a matter of fact, you've re-invented a fork mount...😉

1 hour ago, Stub Mandrel said:

TLDR: I found that arrangement very critical in term,s of positioning and worried that the PLA might 'creep' so I lost drive. Instead I've come up with an arrangement more tolerant of my woodwork skills!

 

 

I've had a rethink!

The problem with the angled sectors is that although they have a simple, circular cross section is it makes the positioning of the support/driving rollers critical. I found that this made getting a good drive to the sectors difficult, and a slight twist (just a couple of mm) in the board was enough to make a difference.

I'm also wary that the PLA could 'creep' under a sustained angular load despite the hefty design.

The elliptical design avoids this by having a vertical load but needs long rollers as the contact point moves in and out.

An ideal design MIGHT be to make the sectors part of the surface of the 52-degree cone so they track across the same point like my original angled sectors, but can use almost horizontal rollers angled in line with the pivot point.

Hard to do in wood without a 3D jig but easy in CAD. The front curve of this new runner follows the same curve as my MK 1, but instead of havinga steeply angle rolling surface it has an almost horizontal one. It also means the upper surface can be supported by the upper board, even though the fixings will be set back. Importantly, as the load will all be acting vertically that small twist in the board effectively becomes irrelevant as the position of the rollers is no longer critical. Instead of having to set them so the sector falls at the right place on the roller, the roller can be made over-length without any criticality in positioning. Finally, almost all the weight of the scope will be keeping the roller in contact with the sector instead of about 60%:

The downside is that it means the aluminium strips may not be feasible. I can get a decent surface finish without steps using careful orientation and support material (on a non-working surface). Any residual irregularities will, hopefully, be too small to cause problems and partly compensated by give in the rollers.

Could explain this a bit more in an assembly drawing please, not sure I understand, sorry...

I might have come up with a completely 'new' EQ-platform, First need to do some more brainstorming...🤔

Waiting to be finished and installed.

On 02/06/2020 at 15:01, Gina said:

Is the astronaut to scale?  I thought the HST was bigger than that.

Mind-boggling isn't it..😳
In this case I made the astronaut juuuust a little bit taller, my size actually...😁

Forgot to blacken the inside of HST, sorry...

These rods, I suppose there for strengthening/stabilizing the tube, 4 of them have been added. They run under the grips
Also a secondary secondary mirror holder. As a telescopebuilder I (of course...😁) added 4 collimation screws. Wonder if somebody will notice.

Today a few last/minor parts to be mounted on HST before it is 'shipped' to Urania(local observatory) tomorrow.
It'll not be hung tomorrow. Scaffold will be delivered only in a fortnight. So meanwhile it'll be parked there on the floor. If I had the room to store it, I'd rather keep it here. But now it's hanging in my van, and I need my van from time to time...😁

I hope all goes well during transport...fingers crossed..!

Nope... Facebook, not for me either, and I don't even sorry for it...😬

16 minutes ago, Glasspusher said:

Gluing is definitely not the way to go.

I know  ...😟

Did exactly the same 35(or so) years ago.
In my case I glued the 'sandwich' together with silicone.
Resulting in very weird star patterns.
That scope was nothing more then a 'light bucket'.

Using very low magn. it was doable, but high magnification revealed the true problem. Six fat spikes were visible, and no, not spider diffraction. I had glued  6 thick glass-blocks between two 19mm thick sheets of glass. Strangely enough after a few our the image got better.

One of my earlier experiments...😏

One minor issue about our HST project is that I had to built it all on my own.
It was suppose to be a two man job. Michel and I did lots of planning, research, lots of drawing together.  In the past he never drew, after a CAD-crash-course he's now drawing like the best...
Planning to gather, building that thing in my workshop, and then  'C19' comes along and 'kept us all at home'...😳

Pity... dam...!😡
 

Looking good Marcopolo...
You still need to test that focusing knob using gloves...😉

And now you can start thinking on drawing V2 : adding a dual speed focusing knob to the unit...😁

Just determined the COG. All components needed to be attached. Even a few astronauts were dumped in HST to find the correct spot.

Thanks JOC..!
This HST is to be hung in our local observatory. Transport will be done in my van.
The device I use to work on HST, I will screw it in the bottom of my van. A friend will sit beside it during the ride. It's only 3 (long) streets away from my home and workshop. Next Sunday D-day as a matter of fact. Total weight is about 30/35gkg. Parts sticking out of the hull will be removed before transport of course.

Now busy making/printing the very last smaller things, front-cover, astronauts brackets, Maybe we will put some tools in the astronauts hands. Hammer, nails, saw...🤭
Need to make a bracket to attach the WideFieldCamera3. That camera is floating outside HST while astronauts are working/installing it.

We also have to find proper names to put on each of the astronauts arm patch.

We also have to think WideFieldCamera3

Thank you for the kind words..

Prin

1 hour ago, Stub Mandrel said:

The good news is the 3D printed pivots appear to be strong enough.
Restrict the tilt to around 15 degrees by fitting stop switches.

PLA is strong enough indeed to do this kind of job. You did a good job there making it thick enough...
And yes 15° is about the max you should aim for.
A knurled axis will help you improve grip on the sectors.

I always build to track no more then 15°. After a session I return to my starting point every time again. But in my case it's a bit a different story. It's not a regular eq-platform. I have my own version( a Box-mount).  Still, no more the 15° of tracking is my 'rule'.

I thought so too as a matter of fact.
Yep, it is.

Astronaut is 25 cm x 7 = 175 cm.  That is a small astronaut imo. If I would make it my size it would be 28cm
Diameter HST is 60cm x 7 = 4.2 meter.

These smartphones have all wide angle lenses. So it is all a bit deformed, out of proportion.

One of the astronauts started his first EVA.
Probably repairing a few of my mistakes...🤭

Opened it with Gimp(Linux), far better, moire is gone.