Why is my star adventurer not tracking properly?

[Victor Boesen]

A couple of days after Christmas I was out with my star adventurer to capture the pleiades and the mount didn't have any serious problems with 90sec subs with my skywatcher evostar 72, however when I was going to capture the orion nebula the next day the tracking was so slobby it couldn't even manage 60sec exposures and for a minute I questioned the batteries(that I had just changed a month before and only used a couple of times) so I tried changing them with no succes. Then I began to think if it's motor backlash but I really don't know and that's why I post this question. Keep in mind that my polar alignment wasn't the issue cause it was somewhat spot on. I do also have a little imbalance in the declination because of my scopes dovetail.

This image is a 2min sub just to exaggerate the error:

I hope someone can help me here because I really don't know what the problem is. Could it be because of the orion nebula being further away from polaris than M45 and I simply should expect more from the mount?

Victor

Edited January 1, 2020 by Victor Boesen
Typo in title

[Space Bat]

How accurate are you polar aligning?

[Victor Boesen]

10 minutes ago, Space Bat said:

How accurate are you polar aligning?

I was very thorough and tried evaluation polar alignment a couple of times so I'm confident that polar alignment isn't the main issue since you can see the stars' trails are zig-zags.

[david_taurus83]

I'm going to go out on a limb here and say you accidentally set the wrong tracking speed?

[Victor Boesen]

2 minutes ago, david_taurus83 said:

I'm going to go out on a limb here and say you accidentally set the wrong tracking speed?

That was also my thought but I checked and it was set to star-tracking.

[knobby]

Polar align would be a straight line error, tracking rate would also be straight ... I'd say check for balance, cable snags, wind, shutter bounce etc

[Victor Boesen]

1 minute ago, knobby said:

Polar align would be a straight line error, tracking rate would also be straight ... I'd say check for balance, cable snags, wind, shutter bounce etc

My biggest concern of the ones you mention there is balance. I'd have to figure out a way to balance my scope on the declination axis a little more if that could help. Wind wasn't a problem that night and shutter bounce would seem weird to me as the "zig zag" pattern is rather consistent throughout the entire trail.

[knobby]

When I had my star adventurer mini, I'm pretty sure I had a bad area on the drive gear, not sure if you can do this on the non mini but maybe try running the motor for a while with saddle disengaged then tighten up again so you are using a different area of the drive mesh ?

[Victor Boesen]

10 minutes ago, knobby said:

When I had my star adventurer mini, I'm pretty sure I had a bad area on the drive gear, not sure if you can do this on the non mini but maybe try running the motor for a while with saddle disengaged then tighten up again so you are using a different area of the drive mesh ?

I could try this. Thank you for giving every sort of possible advice to help!

[knobby]

6 minutes ago, Victor Boesen said:

I could try this. Thank you for giving every sort of possible advice to help!

No worries and good luck, it could also explain why Pleiades (straight up) was ok but Orion ( low in South) had the issue maybe .

[Victor Boesen]

1 minute ago, knobby said:

No worries and good luck, it could also explain why Pleiades (straight up) was ok but Orion ( low in South) had the issue maybe .

That's exactly what I've also concluded so far... I hope I can solve the problem either by letting the gears run a little or by dealing with the balancing issues.

[joe aguiar]

About your battiers just wondering if u should just get good 3500 ma rechargeable batteries and charger and save money on the long run.not saying that's the issue of tracking tho.

I think it may be the imbalanced. Even a little weight off can put alot stress on the smaller motors.

Joejaguar 

Edited January 2, 2020 by joe aguiar

[Davey-T]

Bear in mind that "normal" batteries are 1.5 volts X 4 = 6 volts and rechargeable are 1.2 volts X 4 = 4.8 volts, shouldn't bother the Star Adventurer and I've used both in mine but think it's designed to run on 5 volts.

Dave

[joe aguiar]

ohh that I didn't know that rechargeable are 1.2v, I just memtioned that so he doesn't throw money out in long run

joejaguar

[Davey-T]

4 minutes ago, joe aguiar said:

ohh that I didn't know that rechargeable are 1.2v, I just memtioned that so he doesn't throw money out in long run

joejaguar

I've used them in my Star Adventurer with no problem but only use light weight stuff on it, suppose it might become an issue with heavy out of balance load.

Dave

[Pompey Monkey]

On 01/01/2020 at 13:57, Victor Boesen said:

A couple of days after Christmas I was out with my star adventurer to capture the pleiades and the mount didn't have any serious problems with 90sec subs with my skywatcher evostar 72, however when I was going to capture the orion nebula the next day the tracking was so slobby it couldn't even manage 60sec exposures and for a minute I questioned the batteries(that I had just changed a month before and only used a couple of times) so I tried changing them with no succes. Then I began to think if it's motor backlash but I really don't know and that's why I post this question. Keep in mind that my polar alignment wasn't the issue cause it was somewhat spot on. I do also have a little imbalance in the declination because of my scopes dovetail.

This image is a 2min sub just to exaggerate the error:

I hope someone can help me here because I really don't know what the problem is. Could it be because of the orion nebula being further away from polaris than M45 and I simply should expect more from the mount?

Victor

East-West is almost Up-Down in you image. As the (very wiggly) star trails in your image are neither vertical or horizontal, I'd say it was a balance/weight/gear slipping/bearing issue. So it is not the RA tracking.

The movement is largely in the East-West direction, so my guess is that the DEC axis was continually slipping in little increments, and then these movements were enough to also upset the RA tracking somewhat. This also fits in with the Pleiades tracking OK, as the more vertical the scope gets, the lower the turning moment it produces on the DEC axis.

Balance again and make sure that the clutch is done up a wee bit tighter next time, and see what happens.

 

[Victor Boesen]

Thank you @joe aguiar, @Davey-T and @Pompey Monkey!! I will be more cautious with my DEC axis balance and maybe get a battery pack in the future.

Victor

[knobby]

How did you get on Victor, I hope it's ok.

[Victor Boesen]

6 hours ago, knobby said:

How did you get on Victor, I hope it's ok.

The weather has unfortunately been very bad and my time has been limited since I started in school again monday so I have yet to try out my star adventurer and try to fix the problem. I will definitely return with a post as soon as I have anything to share:)

[ollypenrice]

On reading down the thread I found myself asking what the RA-Dec alignment was with regard to the the trailing.  Paul (Pompey Monkey) was clearly thinking along the same lines. I think his analysis is excellent (not for the first time!)

Olly

[Fred_76]

This trailing is due to periodic error. The SAM periodic error is big, about +/- 90" (or 180'' peak to peak). This is why you shall perfectly balance your equipment on the mount to reduce it a the minimum, and not use to long focal length or exposures. The SAM is not designed for focal lengths above 150 mm or exposures times above 60 s. Look a the internals here :

https://www.webastro.net/forums/topic/181169-star-adventurer-mini-périodes-des-rouages/