Hi John P. Already on it! Following your first post, I saw the logic of your comment and decided to mount each motor between two resilient silicone o rings (about the same diameter as the motor). Luckily the motor mounting design makes this quite straightforward. These will hopefully allow enough torsional 'springiness' to let each motor to twist uniquely dependent on the load it's developing, stopping the ratcheting / lockup happening. I ordered them last week and they are currently on their way from China. Definitely worth a try : ))

 

Ajandco, I'm sorry that you've done a lot of work which so far hasn't rewarded you with a working system. But one thing ocurred to me that might make a multi-stepper drive functional, and that would be to add some kind of resilience to the individual drives. If each motor delivered its output via a spring (essentially) maybe that would allow some mismatch in the motors' rotation versus the dome's movement, and you'd basically see the dome move based on an average of what all the motors were doing. But then again, I can also imagine that at any given moment, maybe some of the motors would be delivering forward torque and some would be holding the overall travel back, and perhaps that would still be a problem. I can't make up my mind what to expect!

A quick follow up as I said I would follow up when I had a solution. Took a while I know, but success at last – the dome turns without stalling.

In addition to all the help and ideas you all gave me I also decided to remake the dome wheel supports which were previously of wooden construction and looked a bit amateurish. So I got a 3D printer, had to learn how to use 3D Autocad, took a while.

Anyway, a summary of things that I think made a difference. I replaced the drivers with 2 drivers per stepper (so much quieter!) and mounted the motors on resilient mountings to prevent possible torsional resonance. I also changed the dome support wheels to nylon as the old ones had developed flat spots that I couldn’t see because of the train tracks they run in and that obviously wouldn’t have helped.

All 8 motors now run together nicely without stalling / chattering. Joy.

Thanks all again. Now I can finally mount the telescope!

 

Pictures would be interesting.
Congratulations!!

 

. I replaced the drivers with 2 drivers per stepper (so much quieter!)

How does that work?

 

How does that work?

Maybe he connected them in parallel? The only difference being twice the current they were previously getting?

OTH, how do they stay synchronized during actuation? ... I too, would like to hear the details of said arrangement.

 

Regardless of the method used, a stepper motor should always be ran at the exact plate rated current.
The bi-polar has slightly more torque for a given frame size.

 

Regardless of the method used, a stepper motor should always be ran at the exact plate rated current.
The bi-polar has slightly more torque for a given frame size.

Oops. I inadvertently wrote2 drivers per stepper - what I should have said was I went from 1 driver per 2 steppers to 1 driver per stepper. Apologies for the confusion there.

 

I went from 1 driver per 2 steppers to 1 driver per stepper.

just the way it oughta be ... congrats!

 

Congratulations! It's good to hear that your project is working out well. Through difficulties, to the stars.

 

Oops. I inadvertently wrote2 drivers per stepper - what I should have said was I went from 1 driver per 2 steppers to 1 driver per stepper. Apologies for the confusion there.

@Ajandco You didn't happen to build a Dobsonian telescope to go with it, did you? I always wanted to build a 24" dia. Dobsonian, and put it in my own observatory like you're doing. If you have a telescope, please show us!

 

@Ajandco You didn't happen to build a Dobsonian telescope to go with it, did you? I always wanted to build a 24" dia. Dobsonian, and put it in my own observatory like you're doing. If you have a telescope, please show us!

I wish it was a 24" telescope : ( The one I have I made over 40 years ago and the mirror is just 6". I hand ground it myself from two ship portholes from a German world war one warship scuppered in Scapa Flow in the Orkney Isles of Scotland. I got them from an old work pal who was a master at grinding mirrors and who started me off on this long adventure.

Unfortunately the telescope perhaps isn't as visually impressive as the mirror's history, but it works well enough. I've never had a decent place to house it so it has been lying around gathering dust and annoying the wife for long enough. Today I finally got it in its home! It has been so long since I've actually used it that I'm having to re-learn the tripod setup procedure, that's tomorrow's task. With the longer days now it will probably be later in the year before I actually get to use it. A picture is attached as requested.

It has been a satisfying journey, a lot of skills learned in the process, so if you get the chance to make your own observatory, go for it!

 

I wish it was a 24" telescope : ( The one I have I made over 40 years ago and the mirror is just 6". I hand ground it myself from two ship portholes from a German world war one warship scuppered in Scapa Flow in the Orkney Isles of Scotland. I got them from an old work pal who was a master at grinding mirrors and who started me off on this long adventure.

Unfortunately the telescope perhaps isn't as visually impressive as the mirror's history, but it works well enough. I've never had a decent place to house it so it has been lying around gathering dust and annoying the wife for long enough. Today I finally got it in its home! It has been so long since I've actually used it that I'm having to re-learn the tripod setup procedure, that's tomorrow's task. With the longer days now it will probably be later in the year before I actually get to use it. A picture is attached as requested.

It has been a satisfying journey, a lot of skills learned in the process, so if you get the chance to make your own observatory, go for it!

I knew a guy who built his own, and did an 8" objective lens himself- I learned how to make lenses from him. One of the reasons I got into electronics a long time ago, was so that I could eventually build the control panel for the telescope so that it could be programmed to adjust azimuth and so forth and track whatever star I wanted to look at. A 24" lens is as big as I think I can go, and it would let me see well beyond Jupiter with enough light-gathering power. I also wanted to control the dome, as you have done, and so forth. But as for now, it sits on the pile due to other concerns in my life

Thank you so much for sharing your project!

 

Oops. I inadvertently wrote2 drivers per stepper - what I should have said was I went from 1 driver per 2 steppers to 1 driver per stepper. Apologies for the confusion there.

Similar system used in the slewing of cranes in ships. Impressive
Congratulations!