Spacehead

2 hours ago, michael8554 said:

In that case Spacehead has come up with the next-best method of displaying the sinusoidal shape of PE. 

Sorry I can't think of a way to I prove his mount. 

Michael 

It isnt a PE error - that occurs periodically and measurably - this is all over the shop and pretty much constant no matter the position of the gears.

Hi All,

I have an EQ5 motorized on RA with a 200p.

For 2 years I did fine with tracking, gradually it got so the stars started trailing a bit so I decided to look into it.

I'm fine with the PA and focus.

I have replaced the motor, the thrust bearing on the main shaft, the main bearing on the main shaft, swapped the RA worm with the hardly ever used DEC worm, re-greased, I can see no wear at all even on close inspection.
I have experimented with different tensions on the Worm drive to main ring and the motor cog to the worm cog.  Nothing makes a blind bit of difference to the outcome no matter what I try.

The following first two pics show my mount tracking with the mount rotated off PA by about 20 degrees clockwise - but in essence - I am deliberately trailing the stars whilst off-tracking so I can see if there is a pattern.
So the first pic is an 11 min sub - a green line through a star trail shows the straight path the star SHOULD take.  The second image is a zoomed in image of an approx 1 minute section of that long trail.  The third image shows what the stars look like when tracked using this mount with strong PA, basically egg shaped (kind of) in the direction of the "bumps" on the trail - as we would expect.

There is no "drift" over time - (well - about 7 pixels per hour) - what is happening here is the telescope is falling behind so the star moves "forward", then the scope catches up again and the star moves back into position creating a wavy line (mainly) but you'll see on the long line image that even this is not consistent.

I am close to trying guiding now - but having replaced pretty much everything on the mount which moves - I am really confused as to what caused this - and more importantly, will this mount even work with guiding.

Any advice/thoughts appreciated.

Cheers


 

The thing is that I write websites for a living - and nobody pays me - the most i get is £150 for two weeks solid work.
In other words im skint as - so guiding is out of the question.
 

I've stripped it all down now today and am changing all the bearings - will have to wait on delivery.  PE on the RA worms are intermingled with this error on the images - I have seen the extreme errors occasionally and am fairly happy with that.
Yes I am only tracking because I have no money.
This problem has been progressively getting worse (I was browsing my old images).
There is about 1mm or even less play on the main bearing (shown hanging on the shaft) - so I am replacing both bearings - see what happens.  Took me two damn hours to get that sealed ring off the shaft - what a bind!!!

3 minutes ago, pete_l said:

The repetition rate of deviations often provides insight into their origin. Do you have the option of producing longer exposures - say 20 minutes? But not with a 90° offset from the pole, but just a few degrees. That way the position of a star won't move it out of frame during the exposure.
The goal would be to see whether these deviations occur at regular times (and therefore are associated with the drive) or are random and therefore have an external source.

Yes I had thought about doing EXACTLY that tonight!!! Because I thought "if only the star would stay in view longer I could get a repeat pattern!!" - I tried joining multiple exposures to achieve the same thing but it didnt work out very well.

The "error" direction (the angle of the star blips within a frame) - when polar aligned - is equal to the direction of the tracking - so I have to find a nice angle for the North leg which allows trails in long exposures, but also shows the error clearly, as it will - if the angle is too small, overwrite itself if you see what I mean!!
 

(I have even tested the ground stability!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!)

8 hours ago, JamesF said:

My initial guess would be that this is just down to the accuracy of the gearing and the amount of backlash in the gear chain.  The gearbox on the motor contains quite a few gears and there can be a fair bit of movement between them all.

If there's any breeze at all the 200P can be a bit of a sail, too.

What you could try is making the east side of the mount slightly heavier than the west, so it's slightly out of balance and the gears are always fully engaged.  Whether that's the counterweights that need to be heavier or the OTA depends on which side of the meridian they're on.

James

Hi James - I have replaced the motor and its gearbox with new, there is no backlash on the worm at all now - during experiments, I have - if anything - very slightly over tightened everything just to eliminate.  To no avail.
No - there is no breeze - during my testing I ensure dead calm only - if there is even the slightest breeze I do no testing.  Breezes tend to give a more random wobble too in my experience - but this error is consistent over many nights - always the same.
I have overloading the east side to varying amounts over various nights - no effect - the error still occurs.

I am thinking its the large main bearing in the RA head now - that is the only thing I have not managed to gain access to yet.

Hi All - I track with an eq5, RA motor I added, SW 200p, PA = perfect, balance perfect and tried different things.

I get stars deviating over time and then re-locating themselves in the correct position.

So lets say I do a 1 min sub - I will get this when tracking (see small pic with stretchy stars zoomed in).

If I point the north leg of the mount to east, then switch on the RA - I am tracking offset to the actual motion of the planet.  Thus, I can now see the deviation of the stars on the mirror over time.

But not all the stars show the same deviation / bumps!!!!! 

It is important to know that this is NOT drift.  My alignment is perfect and the end of a 1 hour shoot results in only 6 pixels of drift.  Whereas each shot can be 20 pixels out - but over time the stars come back into position - within a minute normally.

I've got two examples below with star trails and ive coloured in a straight line to show how the stars deviate to give the stretched / jumpy appearance in the actual tracked properly image.

I have stripped it (the mount) down - re-greased the worm gear and main ring, replaced the RA motor completely - but to no avail.



Totally at a loss.


 

Guys I cannot thank you enough!!!!!!!!!! THANKYOU - I would never have guessed "lens" spanner or "compass" spanner.

Hi All I am trying to dismantle my EQ5 - but need the tool as shown in the photo.  The thing is - not knowing what its called I cant find one online!!!
I've tried pin spanner - but that doesn't get me the right thing - anyone know by any chance?  Much appreciated.

Hi All.

Disaster has struck tonight.  I track using a fitted RA motor and its been great for about three years.  Then tonight, I noticed that the control knob on the mount for the RA was "thudding" very slightly with each motor pulse - ive never felt this before.
On looking at the photos, I have trails on stars at 1min exposure 

Can anyone advise me what may be wrong?  I changed the batteries but the result was the same.  When moving the RA manually with the control knob it seems ok - smooth etc.  But when the motor clutch is tightened, the thudding starts