I'm moving on to installing the dome rotation motor system. I was just looking carefully at the parts in preparation for its installation and I have a question. The motor shaft has a slot and a key as I would expect to see. The mounting hub for the gear does not have a slot. Instead, there is a set screw and the set screw is slightly bigger than the slot. This setup doesn't look right to me. Has anyone dealt with this and if so, what did you do? In case it's not clear, the gear will not fit on the shaft at all if the key is in the slot. The key must be removed and set aside.
I could just tighten down the screw in the slot to secure the gear on the motor shaft. To me, this seems like something that will fail, perhaps even over and over again. The easiest thing I can think of doing is to slightly grind down the tip of the set screw so that it will reach down into the slot. I think this will work but wanted to see if anyone came up with a better idea.
can you post some pictures ?
My magnet is dead center with my dome slit. My sensor is a 0º (due north, as I don't use the NexDome wall but built my own small structure for it). My park position is 321.5 degree (charging pads).
in my application (TheSkyX) I do enter these 2 values. The home azimuth is the most important as it defines the absolute position. The Park position is also important to make sure the battery can be charged. but can only be set after the home azimuth is set.
Once the home azimuth is known and set, hone the dome, then use the buton to move the dome back to the charging pad and use the displayed position in TSX to set my park position :
This is true for any dome controller (I've written over a dozen dome X2 plugin so I kind of know ;) and I also wrote my own firmware for my own dome controller).
And this is on my own dome controller , same principle (which is what I now use in my observatory with my NexDome dome, but as said, all are using the exact same way, set home azimuth, all move are in relation to that position) :
The magnet defines the home position. So if it's at 12º that's all you care about for position (aka dome goto done when the mount move the OTA to an object).
Saying the dome slit center is at 0º has no meaning because it rotates.. The magnet is centered in the dome slit.. and that's how it should be.
You do not need to move the controller to make the sensor be at 0º, you only need to know its position (12º here) and enter this as the home.
if your charger is at 0º, that's the park position
The magnet is ON the rotating part of the dome, not on the controller, the SENSOR is on the controller. And this is the azimuth we care about.. the SENSOR azimuth.
Where is your dome controller located with the SENSOR ?
In the picture bellow I circled the home sensor.. this is what defines the home azimuth... this is what I labelled "NexDome Home Sensor" in my diagram above.
So, where is yours in relation to due north. This is what you need to set as the dome home azimuth.
I think we're getting lost somewhere.
If your SENSOR is due north, then the home azimuth is 0º.
But you did say the NexDome controller was on a post at an azimuth of 12º from North, and as the sensor is on the NexDome controller box, then the home Azimuth would be at 12º... or did you relocate the sensor (the magnet is just a point marking the middle of the slit... it is not the home azimuth)
Also, Home position and park position can be different.
Home position/Azimuth = position/azimuth in relation to due north of the SENSOR.
Park position/azimuth = position /azimuth in relation to due north of the charging pads.
So in the diagram bellow, The home azimuth is not a 0º because the SENSOR is not due north.
So all you need to figure out is what is the position of the home SENSOR in relation to due north
When the magnet, place centered to the slit opening, is on top of the sensor then the slit is a the home position. All other dome move are in relation to the home position.
Using the telescope to asses the location of the origin (the sensor) is also not correct as it doesn't take in account a lot of the OTA offsets from the axis of the mount (aka what is needed in application and often call "dome geometry").
The sensor is the 0 point for the internal step counter.
The controller knows how many steps it needs for a full rotation, and of course it knows how many steps it needs to move per degree.
This 0 position for the step counter can be anywhere, BUT as this is the 0 for step, the controller need to know what this azimuth is.
So if you put the sensor 12 degree east of north, the 0 step is at 12 degree.
Let's say (not a real value) that you have 10 steps per degree. if you are at home (so at 12 degrees) and tell the dome to go to 180 degrees. The controller calculate that it needs to move (180-12) * 10 steps clockwise to land on 180 degrees.
So 180 - 12 is 168. It will move 1680 steps. That new position in steps is 1680 , or 168 degrees .... plus 12 ... so it is indeed at 180 degrees.
So what is REALY important for accurate pointing of the dome is :
1 - Proper value for the home azimuth (aka the position of the magnet)
2 - Proper value for the steps per degrees (of proper number of steps for a full rotation).
#2 is set by default for a 2.2m NexDome but can be refine via calibration.
#1 is really what you have to figure out. I set mine (I have a structure with the dome on it, not the original NexDome round wall) to 0 degree using sun noon when I was building my observatory. You can also use sun noon to figure out actual north (absolute 0 degree position in space) and then measure how far the sensor is from north. This distance can then be converted to degree which is your home azimuth.
now if that value is already known (looks like 12 degrees for all of you), then this is your home azimuth. And of course the magnet itself need to be centered on the slit, not anywhere else.
If you relocate the sensor, then you need to update the home azimuth to the new value so that the positioning calculation can be accurate.
I get exactly the same angles on my system. I started with the fiducial (magnet and sensor) and park position at 0. I did have to peel off the sensor and move it to better align. I'm not sure why this needs to be attached with more than sticky tape. The screws seem overkill. Anyway, move the telescope (with good pointing) to 180 (due south to the meridian). Visually center the dome. The difference between that reading and 180 is the position of the fiducial. For me it was also 12 degrees. I then moved the park location to 12 as well just so it parks on the fiducial. But, the park location can really be where ever you like. I do notice I don't get perfect alignment away from the southern meridian. I have a fork-mount system and it's not perfectly in the center of the dome. I expect I just have to measure the offsets and it will work better.
The dome azimuth AT HOME , aka when the magnet on the dome (middle of the slit) is on top of the sensor, is not 0 in your case, it is 12 degree. All move are then in relation to this position, the home position.
So you home Azimuth MUST be set to 12 degrees or all goto are off by 12 degrees.
I remember way back when I first assembled my dome and that the rotator motor, I'm on my 3rd, would wobble up and down in the track, fall out of the track etc. I ultimately stuck a bolt in the center of the dome floor, loosened every bolt on the walls and kicked and pushed the walls and posts to ensure I had a stable diameter from the center point of the dome. I measured at both the base of the dome and at the top of the wall. Then I tightened everything up, rechecked the roundness of the dome and bolted the dome down into my concrete pavers on the concrete pad. It really helped with the track staying engaged with the rotator motor gear, still had to tighten the motor tension to the track, but the dome moved much better than it had and doesn't disconnect with the track.
I do have a question about the rotator motor magnet position. I have the dome slit center pointed to the CNP, within a degree or two, but the rotator motor is on the closest post about 12 degrees east of the NCP. When I calibrated the dome, I set the azimuth to zero, since the dome slit center is at azimuth 0. My PA of my OTA/Mount are pretty close to the dome slit centerline. Dome to mount tracking is pretty good except on the southwest side of the dome where the mount is off by about half a dome slit opening. Since I'm using a C11 Edge, my view is partially obstructed. I have measured and remeasured the geometry of the dome with a tape measure and laser measure. My numbers are consistent. Should I set the dome azimuth to 12 and the scope to zero?
Yes, I would love to hear about dome circularization!
Well, I hope I don't jinx myself here, but, today was a bit of a breakthrough day. First, I learned that the manual switch is very touchy about working right. The left side of the rocker switch is mostly fine, the right side can be _very_ challenging to find the exact spot to engage the motion. Given that realization, I decided to move on to computer control.
During manual testing, I had noted the magnet sensor didn't ride in a good place to pick up the fiducial magnet. I tried rotating the post to line them up and that adjustment made the dome rotation much, much worse with many disengagements of the gear from the track. I did two things. 1) put the post back where it wanted to be after I learned how to circularize the dome, and 2) detached the sensor and re-attached it further back to where it should be.
Then, I installed all the software per the Lunatico instructions. There was a bit of fumbling there but after a full calibration and setting a proper azimuth on the home position, the motion and tracking now works perfectly under computer control with no other adjustments. I did daytime tracking and dome following and it all seems to work really well. I'm anxious to try it out at night now. I still don't trust the gear and track but, during a 360 rotation, I don't see _any_ variation in gear engagement depth, just a slight vertical wander that stays within the gear. Time will tell if this is robust but things look good for now without any special action like you and others have described. Perhaps I should write up how I circularized the dome. That may be an important consideration.
Oh, one other thing, user Rory Clarke did a presentation on his "Nexdome Experience" on the Astro Imaging Channel on youtube in the latter part of 2021 sometime (September???) and he recommended removing the wheel that is right by the dome motor because it seemed like the dome was riding up on it there due to friction so he just took it off, so I did that too.
It seems like the horizontal 'play' in the dome is larger than the depth of the geartooth/track interface unless you really JAM the motor/gear up against the track so that it's actually PUSHING the dome away just enough that the play can't happen.
Even after doing all this (well haven't tried anything since the wire) but I would have a problem with the gear skipping when the panel with the open shutter would go by. Maybe this was a coincidence but it happened often enough that now I manually move the dome to the approximate location I'm going to need it making sure that the shutter panel 'goes the other way' before engaging 'slave to telescope'.
If during imaging the slit has to go past the motor so be it but until then…
WellI guess that's the"charm" of this particular product; we all get to do our own little bit of engineering to fill in the gaps! KInda fun and kinda not.
I have the same problem with the gear pulling away, had to absolutely CRANK the motor into that coupler to bring it close enough and just yesterday I ran a guy wire to a sunken stake in the earth on the outside of the dome to stabilize the dome wall vertical support bar cause it was moving all over the place when the dome was rotating. I also don't let the dome rate any faster than 1/3 of maximum speed.