Why is my GOTO so crappy on HEQ5 Pro?

[Screwdriverone]

Hi Everyone,

I did a field test of the new pier last night and while I was out, I noticed the same thing as I had with my tripod, the goto on my mount rarely gets the target within the inner third of the finderscope and very rarely, if ever, onto the CCD FOV.

I have the EQdirect cable (no synscan handset) and drive the scope using Stellarium Scope and EQAscom. I start the scope and then Stellarium Scope, then Stellarium and the "scope" target appears on the SCP, I click on say Canopus, the scope slews to where Canopus is supposed to be, but then I have to slew manually with the game pad or the computer normally south and west in order to get Canopus centred. Once done, I "sync" on Stellarium using CTRL-3 and this realigns the scope reticle onto Canopus, then I slew off to another target not too far away and find the same problem, even if it is in the same quadrant.

Subsequent repositioning and syncs in Stellarium build up the EQAscom pointing model and I can see where the scope thinks it is pointing, but I rarely do a nearby goto and have the target centred in either the CCD camera or the finderscope.

I have checked the tripod is level, the pier is level and the SCP is in the polar scope, the tube is pointing to the SCP before starting, the scope is off before I start connecting, the GPS coords in EQAscom are spot on, as is the date, time and altitude (confirmed by GPS) and Stellarium Scope is using JNOW coords and the time is set from NTP servers on the PC.

Am I missing something? What could be causing my goto's to be so crap?

Any ideas?

Cheers

Chris

[Peter.M]

Do you have EQmod set as "append on sync" or "direct mode". I have to swap between the two because alignmaster needs direct mode but to build a model you have to have it set to "append on sync" if it isnt it wont record any alignment points. The only other reason I can think of is if you have bad backlash in one or both ra and dec.

EQmod will also need quite a few points before accuracy is good across the whole sky, it should however slew to close stars very well after 3-5 points.

[Screwdriverone]

Hi Peter,

I use append on sync and I have tried removing an alignment set after building up about 10 sync points and then starting again in the same quadrant, but it doesn't seem to help much.

I notice my mount shoots off at almost full speed when I give it a goto and if I have any slop as you say, maybe it is exacerbating the issue? I don't know if you can set the slew speeds in EQAscom too reduce the top speed of the slews?

Most of the time I need to "plate solve" by recognising the star patterns on the CCD view to figure out where I actually am in relation to the intended target, and then slew in the direction I think I need to go. It's starting to annoy me, especially on faint galaxies etc....

Chris

[White Rabbit]

I had the same issue with mine when I had it. I bought a copy of max point and it helped quite a bit. It makes a model of your mounts imperfections and corrects your slews.
What planetarium software are you using? Maxpoint is a stand alone and will work with anything but if you have The Sky x it has the tpoint addon which is much better and much more expensive.

Maxpoint will only do a maximum of a 200 point model but tpoint can do a 600 point model to get a very accurate model.

Both packages can do this automatically with little user input but for tpoint you'll need TSX as well as the camera add on. For maxpoint you'll need maxim Dl 5 for automation. Tpoint is the better of the two but maxim can be used as stand alone but you'll need to slew to every star and centre them manually.

Thanks
Sandy

[Barrykgerdes]

I suspect your polar alignment is the problem. Using the polar scope without a follow up with a drift alignment will give goto errors.

That is why multi star alignment is used as it can provide correction for polar and cone errors.

The first check you should do after the two star alignment is to do a slew to a new star a long way off (don't centre it or move the slew buttons) and then back to the original. If the original is still in the same place polar alignment is the problem. If it is not the problem is mechanical and will need to be corrected first. This sort of problem can be poor balance, overload. excessive backlash or even a faulty mount.

Meridian flip is also a possible source of errors especially if it occurs during the selection of two alignment stars.

Barry

[whzzz28]

My thought would also be polar alignment. A drift align or even just a drift check would confirm if it is. Align the scope to the point that you think it is aligned. Slew to a star, get it dead center (use crosshairs if your imaging program supports it). Turn on sidereal slewing and take a photo.
Wait 5-10mins then take another photo. Star still centered? Then your polar aligned - really well actually.
Star off center? your not polar aligned. Star not visible? Your really not polar aligned.

My other thought is - are you using a side-by-side adapter? They will never center first try no matter how good your polar alignment is but should be good once you manually center it and sync.

[Screwdriverone]

Hmm some good tips there, thanks.

One thing to point out is that I am not using the handset for the HEQ5 Pro, just the EQDirect cable and using Stellarium to drive the scope. I don't do any "alignment" procedures, I simply start the scope up via Stellarium Scope, start stellarium and then click on my first star, adjust, sync, click on one nearby, adjust, sync etc. I have looked at the built up sync points in EQAscom and it looks fine, it is just the fact that most of the time, if I have the Main ATIK CCD camera, the finderscope AND the guidescope all pointing at the same place and then I slew to say Eta Carinae Nebula, I can see in the guidecamera the region is close, but the CCD camera (narrow FOV) is never normally centred and I have to adjust again and again.

I checked the drift the other night on the main CCD camera using the crosshairs while adjusting the mount on the pier for the first time and I had a PIXEL of movement on the star in the N/S direction every 15 secs or so and almost NONE in E/W so I think I got it pretty close. This was at the native 1000mm focal length and a very narrow FOV on the Atik.

If I had left it out, or had something to cover the mount then I would have had a very good base to refine it further, but I do have texta marks on the mount and pier top plate to get me started very close next time.

The weird thing is, that if the STAR map is very accurate and I baseline the object I am centred on by synching in Stellarium on it, then slew to a nearby star (normally Mag4 or brighter) I can see that it isn't correct quite quickly. I will try Nathan's suggestion of slewing straight back again and see how that works, but I am pretty sure I have done this in the past when I get "lost" and cant find the target I am supposed to be pointing at.

I think this points me towards something mechanical like Barry suggests, like slop in the gears or too much load or perhaps even gunk in the grease.

My next exercise maybe a visual internal inspection just to see if there is anything obvious (without removing anything) as I may have some sort of defect in the worm or gear wheels which is causing the slippage.

Chris

[Shiraz]

these are pretty tough units and a major mechanical fault would be fairly unlikely - excess play in the worms and/or imbalance in the load would seem to me to be more likely.

I understand that the mounts keep track of where they are using drive pulse counting - if the motor gets a drive pulse, but is under too much load to respond properly, the mount will thereafter think it is at a position different from reality, so balance and slew rate/acceleration are important to keep the motor load manageable. I presume EQMOD slew rate settings apply under Stellarium and that you can try a less strenous goto slew rate to see if that helps.

Also, if using the Newtonian, check to see that the mirrors are not flopping around, that the focuser slop is not too bad and that the OTA is firmly held by the rings - I think that you recently posted that you get inconsistent star trailing, so maybe movement in the scope could be a contribution?

another thing that you might try is to revert to handset control and see if you can get good goto - that might tell you if you have a mount/scope problem or an EQMOD problem.

[Screwdriverone]

Thanks Ray.

I will give the slew rates in EQMOD a look.

The mirror is quite secure so I don't think this is an issue as the finder is off by the same amount as the main mirror.

Likewise I will see if I can take a look inside and check out the worm/gears for any slop.

Good idea about the hand control option, I will give this a try too.

Cheers

Chris

[mithrandir]

Chris, if it behaves anything like a Gemini you need your collection of alignment stars to cover a couple of hours in RA. A bit of variation in Dec doesn't go astray either.
If they aren't spread out they will be accepted, but the small angles make the trigonometry inaccurate.

[tilbrook@rbe.ne]

I Chris,

Just a thought.

Have you checked that the same values are entered for Latitude and Longitude in Stellarium and EQ mod ?.
Also might pay to check your time is right on your laptop.

These two can throw out pointing accuracy.

Cheers,

Justin.

[Screwdriverone]

Hmmm,

I may have found the source of my problem, a few google searches brought up a tutorial about the worm adjustment on my mount and a few quick checks showed there was excessive play on both the DEC and RA axes. I bit the bullet and uncovered the gear wheels on the side and saw the grease condition wasnt too bad so I followed the instructions here http://www.astro-baby.com/heq5-rebuild/heq5-m1.htm and tightened up both worms.

Now I have little if NO play at all and the mount no longer screeches at speed 8 or 9 when slewing and it definitely feels tighter and quieter on full chat.

I thought I had overtightened when I realised the bit about being able to free wheel the gears to make sure they would still move and it bound up during a test, but I just backed it off a bit and kept checking the gears after I tightened each screw, it seems to have all gone back together well and a full 360 degree test in both RA and DEC showed no binding or screeching drives, just the harmonious hum of the motors slewing, even with the ED80 mounted just to make sure.

It's clear out tonight (wouldn't you know it) but I cant be stuffed trying it out and setting up etc, so it will have to wait until next time to see if the goto slop has been eliminated, along with the random backlash issues and ****ty guiding.

Fingers crossed!

Cheers

Chris

[mldee]

I have exactly the same problems. Done all the same checks. Happy to contribute further info, but don't want to hijack the thread.

Mike

[Screwdriverone]

Go for it Mike,

Have you tried adjusting the worms like I did in my previous post?

This is an old thread which I simply updated after last night's testing, so if you want to add anything, feel free.

Cheers

Chris

[mldee]

Thanks, I'll try to keep things relevant. Basically getting back into things after a couple of years break while building/moving house. Small backyard, so decided on just a pier in concrete, no RORO around it, use a $12 tarp for weather protection.

Anyway, bought a new azeq6 for the pier, and am using my trusty old C8 with 6.3fr, plus my DSI II mono guider, as the basic setup to get things lined up. I use EQDIR direct and either PHD2 or Nebulosity 3.2 for camera control. Not yet bothering with guiding.

Results so far mirror yours. I noticed slop in both axes and called Bintel about it. They said to adjust the worms, which I did, and that fixed the slop. Also noticed that I seemed to have some cone error from the azeq6 saddle, and fixed that with some shims. BTW, I use all ADM hardware for the mount. Use the PHD2 drift align wizard, which works well.

It seems OK, but haven't yet been able to get consistent GOTO's. I suspect mount cone error, but clouds presently stopping any further progress. Have some pics of my pier/EQMOD results, but can't attach to a quick reply. Next post maybe.

[mbaddah]

Hi Chris,

Reviving an old thread here... Just wondering how did you go with fixing your alignment issues? Any tips you can share?

[Nortilus]

I was having a similar issue with my EQ6. after discovering some playing in me RA and Dec, i followed the same stuff on Astrobabys site and tightened everything up and adjusted everything to within and inch of its life. now when i do my drift align it is nearly perfect and slews to targets bang on everytime. I guess general maintenance of the mount is a good idea...

[mbaddah]

Hi Josh,

I think I may have the same problem... Did another 3 star alignment yesterday and despite having centred the star in the eyepiece, when I slew away from it and then return to original star its only just inside/outside the finderscope!

Hopefully the astrobaby site can assist.

Thanks.

[Slawomir]

Instructions on astro-baby site are very good; I had no trouble following them and now have very accurate goto; I use my scope exclusively for astrophotography and my cameras FOV is quite small - after accurate alignment I always get the target around the middle of the screen. About six months ago I also changed gears for belts - my HEQ5 has been a joy to use since that upgrade.