G11 Astrophotography


Jesse Lichtenberg
 

Good morning everyone,

I am setting up a purchase of a G11 and I was wondering if I could chat with someone on here who has used theirs with OnStep for astrophotography. I know there are several apart from Howard himself who have gone down this road.

I use an Exos-2 with OnStep at the moment, but I'm wanting to size up and the G11 seemed like a great fit. By a happy coincidence, the unit I'm looking at is already outfitted with OnStep via the Blue Pill. However, the gentleman who is selling it has not used it extensively for astrophotography. 

Thank you all!


Henk Aling
 

Hi Jesse.  I bought a G11S (with the 492 non-goto controller) and tried EQStar first then ended up with OnStep.  What I found, working with my 12" Newt of 48 lbs, is that you need stronger motors than the average and/or a timing belt for additional torque and resolution.  The problem is that the incremental torque decreases exponentially with the micro steppping factor.  So consider 24 V motors.  I recommend steppers that support mode switching like the TMC2130 that I use.  Personally I prefer to have a minimal OnStep implementation (motor control and Bluetooth) and leave the higher level stuff to Ekos on the Pi, which can conveniently be placed next to it.  Good luck and let us know how it goes.  You may also sign up for the Losmandy board because there are several OnSteppers there too.


GuitsBoy
 

Hi Jesse -

I use my G11 almost exclusively for AP, and I've had very good luck with it so far.  I'm about 30 miles outside NYC, so not the best skies, but the mount has no troubles guiding all night long in the .5 to .6 range.   With good conditions, and a favorable location in  the sky, Ive seen .3 rms a bunch of times. 

Now to be fair, I have a number of mods done to my G11.  I have 1:3.75 belt drives, tucked motor mounts, homebrew spring loaded worms, new HP brass worm in the RA, bellows couplings, etc.  I'm not sure I would have had as much luck with direct drive steppers.

This was my graph from a couple weeks ago, the last time we had clear skies.  I believe I was shooting the North America nebula at the time, but I'm not positive.  This is with a 240mm focal length guidescope.  I have an OAG, but have been reluctant to try it yet.  The mount was carrying an AT72EDii refractor and DSLR at the time, but I've seen similar guiding numbers carrying 30+ Lb 8" newt.

I also have an EXOS2 PMC8 mount that I almost never use because I don't like the featureset of the ASCOM drivers, most notably the lack of limits.  I do plan on moving the mount over to OnStep when I have a chance.

With a little love and tweaking, I'm sure the G11 will do quite well for you.

Good luck,
-Tony



On 10/19/2021 10:28 AM, Jesse Lichtenberg wrote:
Good morning everyone,

I am setting up a purchase of a G11 and I was wondering if I could chat with someone on here who has used theirs with OnStep for astrophotography. I know there are several apart from Howard himself who have gone down this road.

I use an Exos-2 with OnStep at the moment, but I'm wanting to size up and the G11 seemed like a great fit. By a happy coincidence, the unit I'm looking at is already outfitted with OnStep via the Blue Pill. However, the gentleman who is selling it has not used it extensively for astrophotography. 

Thank you all!


George Cushing
 

Henk, I don't think you mean 24V motors. Rather motors operating at 24V, i.e., 24v VCC/MOTV.

If we take a 1.3A, 4.3V NEMA 17 and drive it with 12V we get 15.6W power. Double the VCC to 24V and we still only need 1.3A, but power goes to 31.2W which means twice the torque.



Howard Dutton
 
Edited

On Wed, Oct 20, 2021 at 06:59 AM, George Cushing wrote:
If we take a 1.3A, 4.3V NEMA 17 and drive it with 12V we get 15.6W power. Double the VCC to 24V and we still only need 1.3A, but power goes to 31.2W which means twice the torque.
From what I've seen the motor's rated current and voltage are as such to yield a certain electrical power, and so how much heat the motor can handle.  Even at the rated current we seem to be well into the realm of diminishing gains since the magnetic field can only couple effectively up to a certain level beyond which there is just more and more waste.  I.e. less and less torque gained for a given amount of power in.

We don't put more current into the motor (beyond its rated spec.) to get more torque.  We put more voltage into the motor to overcome inductance (and so allow the magnetic field to build more quickly) and the driver limits average current delivery to keep the power level within what the motor can handle.  That doesn't give more torque at low speeds but it does make more at "high" speeds.

So the average power delivered stays at the motors spec. (15.6 watts for your example) or below.