Motorising WO Field Rotator?

[kbrown]

There is a manual field rotator on the focuser of my William Optics FLT91 (Unlocked with the rightmost thumbscrew in the image below).I'm wondering if anyone has attempted to motorise something like this for remote use?

Might be able to wrap a timing belt around it but mounting a stepper motor in this section would be tricky as the rotator is on the moving part of the focuser. Any ideas?

Edited August 30, 2022 by kbrown

[Dr_Ju_ju]

If there are some mounting holes at the top of the handle ??   Then a piece of 3/4mm aluminium bar could be screwed to it, with a stepper motor mounted at the end, above the rotating section, which if its' possible ? a belt could achieve enough grip to rotate the equipment....  It may even be possible to combine the mounting with an another stepper motor mounting for the focuser.. 

[kbrown]

10 hours ago, Dr_Ju_ju said:

If there are some mounting holes at the top of the handle ??   Then a piece of 3/4mm aluminium bar could be screwed to it, with a stepper motor mounted at the end, above the rotating section, which if its' possible ? a belt could achieve enough grip to rotate the equipment....  It may even be possible to combine the mounting with an another stepper motor mounting for the focuser.. 

I'm not entirely sure if I understand you correctly. The trouble is that the rotating section moves (quite a bit) in and out with the focuser. I think I need to come up with a method to "clamp" the motor to the non-rotating part of the moving focuser somehow...

[Dr_Ju_ju]

The same idea could still work, it's just that the mounting for the rotator stepper motor, instead of being stationary, could be mounted to a Linear Rail system, where the bearing would be fixed and the stepper motor mounted to the rail....

This method is commonly used for 3D printer e.g. Voron2 & CNC machines etc.  https://www.ebay.co.uk/itm/283590463865

 

Edited August 31, 2022 by Dr_Ju_ju

[kbrown]

1 hour ago, Dr_Ju_ju said:

The same idea could still work, it's just that the mounting for the rotator stepper motor, instead of being stationary, could be mounted to a Linear Rail system, where the bearing would be fixed and the stepper motor mounted to the rail....

This method is commonly used for 3D printer e.g. Voron2 & CNC machines etc.  https://www.ebay.co.uk/itm/283590463865

 

Gotcha... Might work but it also could be a source of backlash that could translate to a couple of degrees of error in the rotation... Probably wouldn't matter that much... My existing electronic focuser is in the way anyway so I'd have to something about that too...

Edited August 31, 2022 by kbrown

[Dr_Ju_ju]

I build my own focusers, based on Robert Brown's design i.e. https://sourceforge.net/projects/arduinofocuscontrollerpro/  and although I've not looked at it, but he's also designed a rotator https://sourceforge.net/projects/arduino-myrotator/

 

 

[kbrown]

Here's my current idea:

Basically a clamp that would go around the non-rotating part of the rotator section which would take a NEMA17 stepper motor with a GT2 pulley plus a another GT2 pulley that would be a tight fit on the rotating part of the rotator. This would basically allow me to use a repurposed version of the BullsEye Focuser I designed a while back. Think I'll print these out and see what happens...

[Chriske]

I'd you use a smaller stepper like a Nema11 or even a Nema8 with reduction.
For such a small task I think a Nema17 as way to big.

[kbrown]

4 hours ago, Chriske said:

I'd you use a smaller stepper like a Nema11 or even a Nema8 with reduction.
For such a small task I think a Nema17 as way to big.

I did consider that but there actually is quite a lot of resistance to rotate it. I might try smaller stepper later but since I already have a spare NEMA17 and a design I can quickly put together I think I'll give it a go and see what happens. Might be a bit bulky, I know...

EDIT: Actually as a first test I'll just use the focuser I've already put together to get a feeling how it would work...

Edited September 28, 2022 by kbrown

[kbrown]

Managed to make a bit of progress with this. I redesigned the clamp so that it takes a NEMA11 stepper motor. I first tried with a smaller 6Ncm motor but that turned out to be too weak even with a bit of over current. I then decided to steal the focuser I've made for my other scope which has a 12Ncm NEMA11 stepper inside. That seems to be a perfect match. Just need to rewrite the software to be a proper rotator device instead of a focuser.

 

[Alien 13]

I have found that "follow focus" gears and accessories for cine or DSLR lenses a useful source of parts..

Alan