My EQ3-2 DEC axis direct drive mod

[JamesF]

Very much inspired by stan26's direct drive mod for his EQ3-2, I thought I'd have a go at my own (which is the old black model with the "2001 Sky Surfer" logo on). Up to now my experience of the DEC adjustment is that it takes five to ten seconds to take up all the backlash and then the target can shoot off the screen before you can lift your finger off the button.

Before starting on the direct drive mod itself, I took the DEC axis apart, cleaned off all the black goop, regreased it with decent grease and reassembled it to remove as much backlash as possible. I also opened up the DEC motor and gearbox to discover a fair bit of backlash in the gearbox. I've not sorted that yet because I'm waiting for some IPA to arrive to clean the muck off, but at least I know what I'm in for...

As part of a related project I have a motor focuser drive I'm working on. More of that another time. It came with one of those springy "universal joint" couplings and I wasn't going to need it so it got donated to the direct DEC drive project. I removed the gear from the end of the DEC gearbox output shaft and replaced it with said coupling. I also removed all the extra gubbins that goes on the end of the DEC worm shaft when the motor drive is installed. My initial plan was to directly couple the drive to the shaft, but whilst that may be possible it means the motor is at a very awkward angle to mount to anything. In the end I reinstalled the brass extension that comes with the drive kit to give me more room to play with. It meant that the motor could be lined up with the mounting bracket at right angles to the original mounting lug and with enough room not to foul the mount as it turns.

As luck would have it my father-in-law had just used a length of ~5mm thick aluminium with a 90 degree section and left the scrap on his workbench, so I found myself with an ideal piece to make the mounting bracket for the motor. I cut off some of the excess width on what would become the top (I'll use that offcut in the focuser mod, too) and enough of the side to leave easy access to the DEC worm tensioning screws. In one end I drilled a 6mm hole to allow the original mounting screw to be used with the motor mounting bracket (though it needs a couple of washers as spacers) and in the top at the other end I drilled and tapped an M6 thread to allow a second M6 bolt to fix the bracket to the mount.

Final indoor testing has been done this evening and everything seems to work well. Now I just need to give the bracket a coat of Hammerite black to match the mount. Too cold for doing that at the moment though. Outdoor testing will happen as soon as we get clear skies next.

The next step to improve the DEC response is to get the gearbox backlash improved a bit, and then I move on to the motor focuser.

Finally, some photos. first is the bracket itself, with the 6mm hole on the bottom left and the M6 threaded hole at the top right. It would still benefit from the attention of a fine file, I think. Second is the mount with the motor drive attached using the coupling. Third and fourth are "front" and "back" views of everything assembled.

(My DEC power connector is in a different place from normal because at some point in the past the section of PCB has snapped and a repair was required.)

James

[stan26]

Nice one James! better than my attempt really, its more light weight than the hefty bit of steel I used. Hope it improves things for you, It certainly did for me.

Thanks for sharing

Stan

[JamesF]

Well, you work with what you can find, don't you? If I'd not happened to see the offcut of aluminium on the bench I'd have done something very similar to what you did using a piece of steel I had lying about. For my motor drive focuser I've just re-purposed a piece of launcher tube from the fireworks we had last November because I needed a spacer and it was just the right size

All I need now is some clear sky to test it out in...

James

[Gonzo]

From where in the UK can I get my hands on that black flexible coupler thing please, planning to also do this direct drive mod.

[JamesF]

I don't know where they can be bought individually, but perhaps these would do the job?

Shafts & Adaptors :: Shaft Couplings - Technobots - Electronic & Mechanical Components

Do not assume the shafts are the same diameter at each end. It's entirely possible that the motor end is 6mm and the worm end is 5mm. My IPA has arrived so I'll be taking the motor off tonight. I'll check the sizes when I do.

James

[Gonzo]

Thanks for the link.

[JamesF]

Just got the vernier calipers out and I can confirm that the motor output shaft on my mount is 5mm diameter and the brass extension for the DEC worm spindle is 6mm diameter, so it's definitely worth checking yours before you order. I didn't even notice the difference until I attempted to assemble everything with the connector the wrong way around.

James

[Gonzo]

While waiting for the sky to clear up... I've ordered that coupler as I'm doing this direct drive mod.

[JamesF]

I hope it goes well. I think it's definitely been one of the things that has contributed to a big improvement in my imaging this year.

I've just taken my EQ3-2 back out after doing a bit more tweaking on the DEC axis. I decided it really wasn't quite right, so brought it in to play with the end float and meshing adjustments on the worm. Seems better now, but it's very hard to test "on the bench", so I'll try to get out and do a bit of testing under the stars this week.

James

[wrinkly]

Looks a neat job, James.

Just one query from your first post, you mention "waiting for some IPA".

Did Indian Pale Ale do the job?

[JamesF]

Any sort of beer always helps However, in this case it's IsoPropyl Alcohol

James