Re: Stepper motor mount for Losmandy GM-8

Khalid Baheyeldin

On Thu, Dec 19, 2019 at 01:00 PM, Howard Dutton wrote:
On Wed, Dec 18, 2019 at 05:39 PM, Khalid Baheyeldin wrote:
19,200 steps per degree is above the minimum threshold of 12,800 which translates to 0.28 arc second per step.
0.28 arc seconds is between the 0.15 and 1.25 specified as limits in the spreadsheet.
So it is adequate, specially if it is for a short focal length optical tube.

That 0.28" is the calculated step angle the estimated resolution is 0.58".

~1.2" res - Some of the Instein OnStep kit users run the GM8 at 180:1 driven by a 400 step motor so evidently that works though I wouldn't recommend it except perhaps for visual only use.

~1.0" res - The original Losmandy Digital Drive on GM8's.

~0.6" res - My G11 w/400 step motors (32x microstep mode) into 360:1 lots of folks use this with good results.  Maybe there is room for improvement maybe not.

~0.5" res - The original Losmandy "Digital Drive" on G11's.

~0.3" res - Your proposed GM8 w/timing belt 4:1 driving the 180:1 worm/wheels would come in at 25600 steps per degree.
Add to the above this fact:

Atmospheric turbulence (seeing) limits resolution to 0.4" - 1".
The former being the best there is on earth, i.e. Hawaii, Atacama, Canaries ...

So, 0.3" should be more than adequate.

~0.2" res - This brings me to another project I'm working on... over the next few months I will swap out the bipolar 400 step motors on my G11 with 5-phase 1000 step motors.  Will they really track at 2.5x higher resolution?  According to the datasheets slew speeds should be much higher than with my 0.9A bipolar motors; a couple of times higher?  I'd guess these would work a treat on the GM8 too since resolution is so high and torque is up there too and the usual G11 mounting plate/etc would be all that's needed from what I understand.  Not the cheapest option though...  ;)

I'm trying these (the oriental drivers were just too much $$$):
Very interesting. I have seen these 1000 step 5-phase motors on eBay, used. Seems that Oriental Motors are the only one that makes them (for now). But the lack of a suitable driver was an obstacle.
Good to offer support for them, for those who need the extra resolution.

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