Chriske

My friend Henri made me a PCB to drive a Nema17 stepper (Nano + stepper driver) and it worked just fine.

A few months ago I could vary the speed of that stepper over the complete range of the potentiometer.
Yesterday I started the stepper again to see if all was still ok and it didn't work at all. Turning the pot it did it's job but turning even further to speed things up the stepper stopped and started to make noises....😟
Problem is I do not know what is wrong with that PCB

So I need to change the main body of that planetary reduction unit to install another motor(dc most probably)

Together with a Nema17 stepper I will use this planetary gear system to drive my platform.

To make it more printable I changed a few things.
On the left is the original unit, and right is my modified PGU.

Next time I'll be posting this planetary gear system in my 'Equatorial platform' thread.
Planning to integrate this unit in that EQU-platform.

The main body was not printable at all, especially in the lower part. It needed lots of support, so I change a few things there.
Stronger main body.
New holes for a Nema17 stepper.
Widening the foot. Holes were hidden under the main body. No way to reach the screws or bolts to fasten the unit.

Depending on the weight I make my own connection. I usually print a few holes If it's a larger part. But in a case like the one I'm printing right now they're already there.
These 'special' inserts I do not use them. They have to be applied correctly to be save.
Very often I use these wood inserts. I have different sizes, I do insert them at the back of the printed part so the inserts can not be accidentally pulled out because you'd be pulling toward the part instead of pulling away from the part like these special (hot insertable) inserts.
These inserts I use, you need to screw them in with an Allen key. When done you're left with a metric thread inside. In my case I have M6, M8 and M10 inserts. Very strong, but most of all very handy, and safe, I very often use these inserts in wood, for which they were intended to be used for. But I also use them very frequently in printed parts. When applying I warm them up first a little bit first.

3 hours ago, vlaiv said:

What will be reduction of that assembly, and what sort of backlash and precision do you expect from it?

I'll tell you all about when finished and assembled. Should be very soon...;-)
Planning to use it on my equat. platform. Observing visually will not be a problem, nor taking pictures with a widefield lens on a tripod on top of that platform.

Busy printing this one this very moment...
Its a three stage drive.

The holes on which the 'planets' rotate, I'll fill them with brass rods instead of printed versions.
I also will redraw the part on the right, to allow a stepper instead of a round DC motor.
The outer diameter of that thing is about 95mm, small enough for me.

Thanks Stu, picture just sent..👍

Nice, very nice indeed...! Going to make me one, a strain wave gear...👍

It's not a good idea to give different opinions while searching for solutions in a case like this. It's most confusing for kbrown.
So Nigel please you continue helping to solve this problem.
To be clear : no hard feelings here.

And one more thing. Maybe you already removed the alu sheet. If not, While cutting, leave the silicone blobs on the SM.

Before you re-glue the mirror to that sheet of alu, do one more test please.

Remove that sheet of alu.

You can now continue without that heating system.
If you hold on to that heater you need to soften the aluminium to get rid of that strain.
I'll explain later how, it is not the same as softening metal...!!
The silicone blobs should be much smaller and very near the edge, almost peeking out of the perimeter of that SM.

Oops ...!  looking bad that heating system. How hot does that thing get...?  (about)

Carefully place the flat agianst the SM and see what result you got.
See that there are no dust particles between SM and reference flat...! do  not remove the alu-sheet at this point.
take a picture of that result.
Next remove that aul-sheet, and do exactly the same.
Compare these two pictures and post them both here please.

This way you can eliminate possible problems of that alu-sheet.

Ok, some issues can be eliminated after that last post.

You need to concentrate on that SM or it"s holder.
a few possibilities there.

Before we go to removing strain out of that sheet of alu...this is most important not to do that yet.
You need to rule out some possibilities first.

- Do you have a reference flat..?
-Do you have a Foucaulttestes and know to use it..?

32 minutes ago, Astrobits said:

I suspect that the "hot" backing plate is simply heating the back of the secondary causing it to warp. If there are only three small blobs of silicone, with decent ( 3mm is fine) gaps to the secondary, then any warping of the backing plate should have no effect on the shape of the mirror.

Personally, I am against any heating anywhere near a telescope. Thermals of only 1 or 2 degrees will spoil a perfect image.

Nigel

If the backing plate is warping then it should not distort the shape of the mirror, as you said Nigel. That is correct. But what about the size of the blobs..? I'm afraid (tell me If Im wrong here kbrown) that the blobs are not to big. That's why I asked before to make an estimate drawing about that.
Heating a mirror, be it Pyrex, Duran or any other decent glass it should not deform at all, by the heating it that is. That's what all these types of glass are suppose to do, hold its shape when cooled or heated.
And btw 1 or 2 degrees should not warp any mirror at all.

Let's first find out what kbrown has to say about the quality of his mirrors.

First : Make a picture, same as above, turn he primary mirror 90° around it's optical axis in it's holder and make a second picture holding the same position of camera and scope. What happened with the pattern.? Did it hold it's position or not...?

The very first error has nothing to do with this new astigmatic pattern, as you can see.
Twee different causes.

You need to adjust the heat to just one, or two degrees above ambient. Just enough to keep the dew away from that SM.

But as your SM has already astig, when cold, there's another problem. Looking at the surface of the aluminium I think that sheet of alu is most probably hardened alu.
Meaning that sheet of alu is full of strain. That has to be removed first. Now as it is heating that sheet of alu the tension in the alu get worse and pulls on that mirror. You need to remove that strain by softening the alu. Sadly enough you need to remove the mirror first from that sheet of aluminium.
If you do not know how let me know.

BUT what I do not understand is why the ast has a perfectly elliptical shape. Maybe just maybe it has nothing to do with that hardened sheet of alu. at all.
First this :
Are you ab-so-lu-tel-y sure that both these mirrors are free of astigmatism...!!!  Maybe in the past you didn't notice..?
Can the primary mirror move freely in it's holder. Just a fraction of a millimetre is enough. The clamps/hooks (to hold the mirror down), are they not to tight.

Make drawing please, were are the silicone blobs located..? It's not a major issue, but it could reinforce the error you're dealing with right now.

Hold on,  you're saying(if I understand it correctly) : no heating and there's practically no astigmatic error at all ..

?

Al done. Also adapter for another scope(blue)

Stu,

Can I please use one or two of your pictures to show on a Dutch forum.
There are a few non-believers here about pictures taken with a smartphone. That'll convince them that it actually can be done.
Yours are far better then mine, but I think that will change in time. I hope to reach the same level as yours and that of others here on this forum.
It's almost mind boggling what can be done with these small lenses in a smartphone. I fact it tells something about the quality of these little lenses...😳

Chris

I'm drooling all over the place....😱

6 minutes ago, Stu said:

The distance will depend on the eye relief of the eyepiece.

 Of course....! ... Why didn't I think of it myself, silly me...  I thought only the FL would change position of the SP.

Btw...estimate cost for this printed  holder is 6.5€ + a few nuts and bolts M3