PHD2 PPEC on Low end mounts

[Startrek (Martin)]

Other than improving the mechanical efficiency of my HEQ5 mount with Rowen Belt mods, replacement of bearings etc... is there any advantage using the PPEC algorithm in PHD2 over hysteresis to improve guiding. I’ve read a few posts on CN where people have only improved their error by 0.1 or 0.2 arc sec using PPEC whereas other didn’t see any improvement at all. I guess each mount is different and each night is different but being a predictive algorithm it should improve guiding slightly one would think. My guiding has been ok considering I have a newt on board with 67% payload capacity but I would like to get it a bit tighter. I use the guiding assistant sometimes but most times I can read my mount fairly well and tweak the settings according to conditions and performance
I like to get some feedback from members who use PHD2 PPEC on low end mounts

Thanks in advance

[peter_4059 (Peter)]

I'm using it and I think it works well. There is no downside.

[ChrisV (Chris)]

I tried it for a while and then went back to hysteresis. And I don't remember why. I can't see that anyone has done a comparison of the different algorithms. Be nice to see ...

[Startrek (Martin)]

Thanks Peter and Chris
Next time I’m out I’ll try it on my HEQ5
From memory the worm cycle period on my HEQ5 is around 638sec so I’ll use that in the Period Length
If I find no improvement after a few nights out using PHD2 , I might try PEC training through EQASCOM and EQMOD
For my other mount , the EQ6-R , does anyone know the worm cycle period ( sec ) ? as I might try PHD2 PPEC on it too.

[billdan (Bill)]

The older EQ6-Pro worm cycle is approx' 478.7 secs. Not sure if the R version has a different gear in it though.

[doppler (Rick)]

Another thing that can cause issues is drive motor speed, I have a suspicion that mine runs a smidge fast, this was noticeable when I was only tracking, not guiding.

[Jasp05 (Aaron)]

What kind or RMS Error are you getting on an average night with your Heq5?

I've got mine down to around 0.6-0.8 on a good night and no more than 1.2 on bad seeing. I've also got the belt mod and replaced the bearings etc.

But I haven't applied PPEC to my mount as yet. Been meaning to try it out also.


I'm not convinced that PPEC will get the guiding that much lower than it currently is with the HEQ5 internals.

[Startrek (Martin)]

Rick,
I run my mount tracking unguided on Sidereal for a minute or 2 and can still get decent star shape
After 30 minutes it’s only drifted off the bullseye at 2 x zoom on BYEOS a small amount
So I think sidereal tracking is sort of ok , but polar alignment plays a big part too

Aaron
My guiding error on most nights with the HEQ5 is 1.20 to 1.40 arc sec
I’m finding that dithering is knocking the DEC around a lot and recovery / settle is taking up to a minute even on a low Dither
I’ve never got it down to 1 arc sec or below
Most posts I’ve read where members have done the Rowan belt mod and / or bearings etc are guiding below 1 arc sec error
Your balance and payload is a big factor as well, I’m carrying a 6” f6 newt , DSLR, guide scope , finder scope , dew heater bands etc.....so roughly about 9kg , so my payload is up there ( it should really be no more than 7.5kg on these mounts )

[doppler (Rick)]

My rms is usually around 0.4 arc sec’s on the dec and 0.8 on the ra and averages at 0.7 total. It rarely goes over 1. I think you need a pretty regular wave in the ra drive for pec to work. My ra errors are mostly a bit random so pec training hasn’t done much good on my setup. Having the mount on a pier makes good polar alignment easy, as well as increasing payload capacity.
Rick

[RobF (Rob)]

+1 what Rick said

You'll get most benefit if you PEC curve for RA isn't too wild. Remember there can be signficant inter-mount variability for chinese mounts.

My HEQ5Pro seems to have reasonable and predictable peak to peak PE and I feel PPEC helps, especially if you image a few nights in a row.

My belt modded EQ6 has some steeping PE moves in its RA worm, so still benefits, but little harder to predict exactly when the worm is approaching that steeper period.


For large gear mounts like EQ8 you would think there would definitely be benefit, as Peter has said.

[Startrek (Martin)]

Thanks Rob
Next clear night in Sydney I’ll try it on my HEQ5 and when I’m down at my dark site next I’ll try it on the EQ6-R mount too

In regard to doing a future belt mod to my HEQ5, do most people buy direct from Rowan Engineering in the UK or through a vendor in Australia ?

[RobF (Rob)]

I got mine from Rowan astro UK without issues some years ago.
Be curious if others have bought from Aus ok.

Should have also mentioned, arcsec tracking is ultimately all relative around your imaging scale of course. I'm often tracking around 1.2" RME but very happy on nights it settles around 0.6-0.9" on the HEQ5Pro.

I'm normally imaging at 2.1 arcsec/px though.....

[Startrek (Martin)]

My image scale is oversampled on both rigs
The 6” f6 newt with HEQ5 is 0.98 arc sec / pixel
The 8” f5 newt with EQ6-R is 0.88 arc sec / pixel
I’m imaging with a canon 600D with pixel size of 4.3um

One thing I forgot to mention, when I’m away down the coast at my dark site using the 8” f5 newt and EQ6-R mount I’m usually guiding on good nights between 0.75 and 1.20 arc sec error which is a huge improvement on the HEQ5 in Sydney where I can’t get below 1.20 arc sec error
The belt driven DEC on the EQ6-R must make all the difference plus better bearings and worm drive etc...on the bigger more expensive mount

[RobF (Rob)]

Yes, people seem to generally comment that the average Skywatcher mount performance has continued to improve in recent years, particularly the later belt driven mounts.

[doppler (Rick)]

I also got mine direct from the UK, took a bit over a week.