OnStep for Losmandy GM8


STEPHEN COLLIE <52scollie@...>
 

I plan to upgrade my 11 year old GM8 from its Digital Drive system to GoTo functionality. I am a visual-only user, having no plans for imaging.
Obsiously, I’ve considered the Losmandy Gemini 2 Retrofit Kit but it is very expensive, especially importing into Canada.

Some forums posted an issue with the OnStep system’s coupler to worm gear and as the motor is direcly driven to the coupler (no gear reduction)
there are some issues with the smaller worm gear (180 tooth) of the GM8?

Does anyone have experience with the OnStep installation and operation on a GM8 mount?

Thank you,

Stephen Collie


"Guilherme Vênere
 

Hi Stephen

I own a GM8 with OnStep and direct coupled motors. They work fine for Astrophotography. I believe you won't have issues with visual observing. Check the showcase for some pictures


Guilherme


On Mon, Oct 11, 2021 at 9:36 AM STEPHEN COLLIE <52scollie@...> wrote:
I plan to upgrade my 11 year old GM8 from its Digital Drive system to GoTo functionality. I am a visual-only user, having no plans for imaging.
Obsiously, I’ve considered the Losmandy Gemini 2 Retrofit Kit but it is very expensive, especially importing into Canada. 

Some forums posted an issue with the OnStep system’s coupler to worm gear and as the motor is direcly driven to the coupler (no gear reduction)
there are some issues with the smaller worm gear (180 tooth) of the GM8?

Does anyone have experience with the OnStep installation and operation on a GM8 mount?

Thank you,

Stephen Collie








John Petterson
 

I installed OnStep onto a formerly Digital Drive GM8.  It was my first OnStep system. I used a 3:1 toothed pulley system (48:16) to mount the motors offset using 3D printed brackets on the same screw holes that the DD motors mounted to.  With the 3:1 and 24V power the slew speed is pretty quick.  Tracking is great for visual.

John


George Cushing
 

As can be seen from the calculator direct drive falls within the acceptable resolution range for AP. 



The demands of visual use are quite a bit less. The Vixen GP with the Sky Sensor and 120:1 GR-1 reduction tracked at 2304 steps/deg. and produced noticeable jumps in tracking at higher magnifications. The Vixen SP using 300:1 GR1 reduction tracked at 5760 steps per/deg. and had no such issues.

Not to say adding GR1 reduction won't improve things even 2:1 increases tracking resolution 200% (0.58). It up to the user to decide whether the improvement is worth the effort.