Keeble

Sorry, I've been on travel and only had limited time to work on this. I contacted ASA and they were not concerned about the gap between the saddle and the scope. As long as the screws are tight, the telescope should be fine. The jerking behavior and bad tracking remain. I've made new pointing files but have been doing it using single stars. I got a copy of PinPoint and will try to create a pointing file using their autogrid feature. Maybe I just need more data points.

The weights will balance the telescope, but I think something happened during the balancing process. Before we moved the telescope, we could balance the telescope in both RA and Dec with the camera off, to the point that we could put it in any position and it wouldn't move. Our first attempt to move the telescope was to put it in a horiztonal position and push on it, but we could not get it to move. We then re-tightened the screws holding the telescope to the saddle. After we tightened them, we found the telescope was behaving in this manner. Tilting the telescope North would cause it to swing to the ground. I had hoped this behavior would go away after we did our final balance, but it has remained. I am wondering if we perhaps tightened the screws too much and it is somehow affecting the balance. Perhaps it is unevenly distributing the weight? Is there a specific torque value that these screws should be tightened to? I have also noticed that there is a slight gap between the saddle and the telescope. You can see light coming through this gap in the photo I've attached here. Is this normal? I'm not sure if it has always been like this.

We were able to move the telescope in the mount to re-balance it. However, we still have some issues: The balance is changing depending on the position the telescope is in. I've followed the manual and balanced the telescope in the horizontal position. I can get the red lines to lie on top of each other by adjusting the counterweight. But when I move the telescope to another position, it is no longer in balance, and the lines do not match up. It is about as bad as is seen on the image I uploaded on the 28th. This will happen, for instance, if I move the telescope to a vertical position. It is no longer balanced. If I take the camera off after balancing the telescope, naturally, the telescope is now out of balance because I've just removed weight. But I have found an odd behavior here. The telescope appears to be more unbalanced in the Northern direction than in the Southern direction. What I mean is that if I position the telescope purely vertically, I can tilt the telescope say 15 degrees in the Southern direction (moving in the Dec axis only) and the telescope remains motionless. If I tilt it 15 degrees in the Northern direction, the telescope will begin to rotate and fall. I do not understand why this is, unless the telescope itself does not have a uniform weight distribution. When I am using Autoslew to fine tune the balance, I will often get encoder position errors for the RA/AZ axis, and sometimes the DE/AL axis. The yellow line will start jumping off the screen. I am not sure what is happening. I uploaded a video of this behavior to YouTube to show what is going on: https://youtu.be/wsPovvNkYw4?si=7XTYfh0C8GJGMua3 The Dec motor now appears to be running slower than it was before. I did not adjust any speed settings. When I slew to the home position, for example, the telescope can slew fine in RA, but it takes longer to slew in Dec. A window that pops up with the "Estimated slew time" when slewing to a target, and it takes longer than the estimated time because the telescope is taking longer getting there in Dec. This is a smaller issue. When I open the Balance screen on Autoslew, the telescope is supposed to slew for 5 seconds in a given direction, then stop and slew in the other direction. It will often not do the full 5 second slew, but change direction after only a second or two. You can see this happen at 00:25 in the YouTube video. We also found that we could not move the telescope when it was in a purely horizontal position. There was too much weight pushing down on the saddle. We ended up having to tilt the scope in a similar position as in the diagram you posted on November 30th, and let gravity pull the thing down. It was a bit nerve-wracking but it was able to move.

Is there a way to lock the RA axis to stop it from moving? When I try to move the telescope up the saddle plate, it swings in the RA axis. I'd like to lock that axis of motion if possible. I do not want the telescope to slide around.

Yes, our setup is similar. We will try this and I will post back here if we run into problems. Thanks!

We can definitely look at moving the telescope to balance it. Do you have any manuals or diagrams that would show us a procedure for that, or which screws to adjust?

No worries! Do the log files track manual movement of the telescope? I suspect that the observer was manually slewing the telescope using the NSEW buttons on the Autoslew window, to try and align the telescope with our target. Could that be the cause of the changing Dec mag-angle? I will take a screenshot of the advanced pointing control screen and post it here. When I was tuning the motors and balancing the telescope, I do recall that the motor signal would get very high when passing through these "resonance" positions. I saw this on the balance window - the yellow line would go off the screen, which was set at 7 A. It would also produce an audible hum. I believe in this specific instance the spike in amps would occur when balancing the RA axis. Adjusting the RA counterweight was able to reduce this effect, and I was able to get the telescope balanced in RA. Photos of our setup are attached. The camera is not attached. It is about 1.5 kg, and attaches to the bottom of the telescope. The best balance I could get in Dec is shown in the attached file. Moving the counterweight up the shaft was not able to bring the two red lines closer, but it did push both more to the left (lower amps). I assume this is better, as the motor has to work less. The counterweight is flush against the bottom of the telescope and can't be moved any higher. Should I look at trying to add more weight?

Any thoughts on this? I am losing data and would like to try some solutions.

We have adjusted the servo settings where we've seen these oscillations, and were able to eliminate the ones we saw. But we have continued to see this effect. Perhaps we pushed the oscillations to another location? The servo log for one of our recent lobed star issues is attached. The telescope was also not tracking well and we had to re-slew to the target star, as it was drifting out of frame, in the direction of the lobed shape. The log is attached as 2023_11_8...txt. We started seeing the stars appear as lobes and the telescope drifting at 22:30, then eventually re-slewed to the target around 22:43. The logs don't seem to show anything out of the ordinary during this time period. The tracking was better after we re-slewed. I don't have instances of the oscillating behavior during observations marked, unfortunately. The image I attached of the circles was taken when we were adjusting the PID loop so there is not much information in the log, but I'm including that here too. This log is 2023_7_26...txt. The circles image was taken at 00:31. I don't remember much about the rest of the observing session that day, so I can't say what was going on before or after that. Let me know if I should include anything else! 2023_11_8_17h10m.txt 2023_7_26_20h2m.txt

We have an ASA400 RC telescope, 40 cm F/8, with a DDM85XL-A mount. We have had several issues with tracking with the mount. One issue is a kind of jerking motion with the telescope, where the telescope will seemingly jump positions, resulting in double-lobed stars. Another issue, potentially related, is that in specific positions the telescope will start to rapidly oscillate. This happens when the telescope is looking close to the north celestial pole, oriented over the mount. We've tried rebalancing the telescope and have gotten a good balance in RA, but are limited in the Dec axis. The counterweight wants to be higher up than is allowed before it hits the base of the telescope, so there is a mis-balance there we can't seem to get rid of. The PID loops are below 0.5 arcsec and look ok. Anyone seen anything like this? I found a post here that talks about a similar oscillation problem, and another post here that talked about the jerking motion, but sadly no solutions.