PHD2 guide pulses mainly in one direction.

[focaldepth]

PHD2 Guide pulses mainly in one direction

Hi I am just trying to understand why I mainly get guide pulses in one direction.

It is often recommended (in many places and on SGL) that guide pulses in one direction is a good thing. In fact this is what I see on my guiding when it is working well. I do understand backlash and that we don't want the gears chattering.

Lets stick to RA only for now.

This does not sit right with me. If ALL pulses are in one direction, then that implies that the side real time on the mount must be wrong which it is not.

I am moving into narrow band and increasing the sub exposure times and reviewing my guiding.

I have been guiding for a few years now and I am happy enough with the performance.

I have belt drive modded NEQ6.

Goto accuracy is good enough. Confirming belt ratios correct.

I usually go for the east heavy option but find it does not make much (measurable) difference how the mount is balanced.

I do not use any PEC.

I usually image at 1”/pix and guide at 4”/pix (rounded).

Pier mounted and drift aligned. (last polar align several months months ago)

Trying to answer my own question, the only thing I can think of, is that gear irregularities nudge the drive into the backlash area and PHD pulls the gears tight again. Over and over again.

But then again, if PHD is continually slowing down the mount, this can't work, can it, as it must drift out of side real time.

Attached is a trace from last night. The 2 rough patches were 1) I touched the scope and 2) a gust of wind.

Any thoughts welcome.

[Davey-T]

As far as I'm aware PHD doesn't actually reverse the motor in RA just stops and starts it, could be wrong

Dave

[focaldepth]

OK yes. if it stops or slows the RA, it, in my thinking, it reverses in Side real time. I think that was was I meant. So if it stops, slows or reverses I can't see why it does not drift in sidereal time.

Or if I put it another way, how can one directional corrections to the RA mount keep it in synch with the cestial sphere. Surely they must sum to zero or there will be drift ( or sum to zero correction to sidereal).

There is something I am missing in all this.

[chrisshillito]

Perhaps your guide scope and/or guide camera sensor are not truely orthogonal to the mount - so you get a slight drift that phd has to correct for.

Chris

[focaldepth]

Perhaps your guide scope and/or guide camera sensor are not truely orthogonal to the mount - so you get a slight drift that phd has to correct for.

Chris

Wow, I'll have to try and think in 3D geometry. There is, of course, a lot of error in the Losmondy plates and clamps etc. so things will not be at exact right angles.

My first thought is that it must follow the celestial sphere no matter where it points so long as the polar axis is aligned.

I'll have to find my Maths Head. It is in a box somewhere covered in cobwebs from decades of non-use.

I do remember reading the instruction that come with scopes about cone error and completely ignoring it.