Payload question - SW EQM-35 Pro GoTo mount

BadWolf (Stewart) · #1 18-10-2021, 03:36 PM

I acquired a new SW EQM35 (payload said to be 10kg) mount a few months ago, and it is paired with a SW80ED scope (weight about 2.5kg and length no more than around 600mm). The setup works very smoothly and efficiently.

GoTo has been very good once I finally found a way to find the Celestial South Pole (time lapse star trail photo, and reference that image to a couple of trees). Not a chance in hell of finding Sigma Octanis through the inbulit polar alignment scope under Brisbane skies!! On a good night, if I have aligned it properly, the EQM35 GoTo can put the object within the FOV of my Baader 21mm eyepiece, or at least in the 8 x 50 finderscope FOV on a bad alignment night. I use the Skyscan 3 star alignment, then the Polar Alignment process.Happy enough with that.

My question to this forum relates to payload capacity and more so the payload physical size. I purchased an inexpensive Skywatcher 120mm Achromat - f/8.3 (1000mm FL). Reason being a larger aperture for viewing double stars and planetary observing. It is about 4kg and 1 metre long.

(As an aside, I know that chromatic aberration can be an issue, however I placed a 2 inch Baader Fringe Killer filter as a "permanent" fixture screwed into the star diagonal box, and any blue/violet is now gone - even with the lunar limb and shadows inside craters.)

I digress - on to the question. The 120mm seems to work on the mount quite well with no apparent extra effort needed by the mount, however there seems to be a bit of "play" or wobble in the Dec axis when the scope is at rest. The ED80 does not seem to have that slackness. I think that possibly a scope of that length is not really suited to the EQM35 - not too heavy, but maybe too long which could introduce a shift in the weight distribution causing the slight wobble. The wobble could also be something loose in the Dec axis assembly, that becomes more apparent with the extra size of the 120mm?? Any information or comment from those who experience it these matters would be appreciated.

LewisM · #2 18-10-2021, 04:16 PM

I have an EQM-35, well adjusted.

Imaging, I wouldn't even dare put more than 6kg on it - more like 5. Visual, I'd go 8kg, and not a long scope (inertial moments and wind)

Seeing these have only surface tube bearings (no actual bearings or even babbitt), weight affects one side different to the other more so than with regular bearings - hence why these tend to not balance easily or bind in certain spots.

It's a SIMPLE mount to disassemble - takes about 10min tops. Adjusting the dec nut and RA nut don't do much because of the lack of bearings.

BadWolf (Stewart) · #3 18-10-2021, 07:24 PM

Appreciate the the comments. Good points, thanks.

Drac0 (Mark) · #4 19-10-2021, 10:24 PM

I've been using the EQM-35 with lighter (shorter) scopes without a problem. This evening I put a fully equipped C8 on it, just over 9kg in total and it seemed quite stable, no noticeable 'wobble' on either axis - though I doubt I would even bother to try running it at that weight...so maybe it is the length effecting it.

I've got a heavy 102mm refractor coming in the next couple of days (I hope), 714mm focal length, so I'll load that up when it arrives a check if the extra length makes a difference.

Cheers,
Mark

BadWolf (Stewart) · #5 21-10-2021, 10:41 PM

Thanks for that. I would be interested to hear how the EQM35 performs with the new large refractor. I think my issue is length rather than weight related. Your new 714mm FL may be ok, whereas my 1000mm FL might be pushing the envelope a bit.

Stewart

DeWynter (ILYA) · #6 22-10-2021, 06:52 AM

I'm using EQM35 with ED100 f9 and fully loaded binoviewer (prism, BV, two eyepieces) for the last three years and have no issues at all. Wind is certainly not an issue. Touching refractor by hand - yes.

BadWolf (Stewart) · #7 23-10-2021, 12:56 PM

Thanks Ilya. Your 100Ed F/9 plus binoviewer would be close to the 120mm in length and weight. The wobble is really only when I bump it with my hand, so I may be overreacting a little.

Stewart

Drac0 (Mark) · #8 24-10-2021, 12:02 PM

Been checking mine out over the last couple of days & there does appear to be a little play in the DEC, the RA is fine. It did give me a little trouble with guiding the other night. I've found out there is adjustment available so going to give it a try once I work up the courage to pull the DEC motor off...don't want to make things worse if I get it wrong.

Cheers,
Mark

Drac0 (Mark) · #9 24-10-2021, 02:16 PM

OK, got it done. Was nice & easy. Just waiting for night & an hour or two of no clouds to test it out properly but the slight movement is gone & everything appears to move just fine.

The Process:
(This is what I did - I take no responsibility if you destroy your mount but will accept all credit if it works!)
1. Remove the two small screws holding on the gear cover & remove the cover.
2. Undo the top bolt (3mm allen key) holding the motor in place & remove the motor.
3. Under the motor location you will see two silver bolts (3mm) with a grub screw between them (2.5mm). Tightening the silver bolts move the worm drive closer to the worm gear while the grub screw pushes it away. Adjust these in small steps until the movement is acceptable to you without being overly tight. If you use the gear to turn the DEC it should still move easily & smoothly. It is a bit of a juggling act to get this just right.
4. Reinstall the motor & cover, ensuring that the motor gear meshes with the DEC gear correctly.
5. Test movement of the mount is correct with no binding or strange noises.

That's it. I can post some images later if anyone requires them - didn't think to take any while doing it. Will update after I've had a chance to test it fully & check tracking/guiding performance.

Cheers,
Mark

BadWolf (Stewart) · #10 24-10-2021, 09:57 PM

Many thanks Mark. Much appreciated. I am expecting several days of cloudy weather here in Brisbane, so I will tackle the task and pass on results in a week or two. Thanks again,

Stewart

LewisM · #11 25-10-2021, 05:24 PM

I'm currently deciding whether to sell my new EQM35 or not. I finally found a mint old Vixen GPD with SkySensor2000 GOTO, and of course it is magnificent.

EQM makes a good source for some spare for the GPD, seeing Skywatcher ripped off the GPD with their EQ5 (almost direct copy), and used some parts on the EQ3/EQM35.