Tuning the EQ3-Pro - or, I need to scratch a tinker itch

[wimvb]

I have never really been satisfied how the EQ3 mount is designed. For example, the mount lacks proper bearings that support the RA and DEC worm gears. Instead it relies on a few plastic and paper washers for smooth tracking.

Last week I saw a youtube clip from a Swedish amateur astronomer who had removed these washers and replaced them with 2 mm needle bearings and cover rings. Today I received the bearings that I will need to make this upgrade, and since the forecast for next weekend doesn't look that good anyway, I might as well scratch that tinker itch and disassemble my EQ3-Pro.

[Dr_Ju_ju]

What's the Youtube link ??

[wimvb]

4 hours ago, Dr_Ju_ju said:

What's the Youtube link ??

 

[Dr_Ju_ju]

Thank you !!  I was looking to do something similar, but I'm also thinking about updating the drives from gears to belt....

Edited February 2, 2022 by Dr_Ju_ju

[ONIKKINEN]

Very interested in seeing the results in the end.

Doesn't seem that difficult to do either, might have to look into doing this to my EQM35 whenever i have the time for it.

[wimvb]

On 02/02/2022 at 17:49, Dr_Ju_ju said:

Thank you !!  I was looking to do something similar, but I'm also thinking about updating the drives from gears to belt....

Thought about that too. The mount has a gear reduction ratio of 66:12, or 11:2, ie 12 cogs on the motor side and 66 cogs on the worm side of the gear box (there's also a 35:35 translational gear). I found some 55 tooth pulleys online, so could do a 55:10 reduction.

Any belt would need tensioning, which would be another challenge. 

Edited February 3, 2022 by wimvb

[wimvb]

Just for future reference: the worm shaft has a 6 mm diameter, while the motor shaft is 5 mm. The tiny motor gear is pressed on the motor shaft. Where the gear sits, the shaft is narrower (2 - 3 mm).

[malc-c]

The problem with belt drive conversions is maintaining the same reduction ratio so the handset can be used.  A decade ago I was experimenting with a belt mod for an HEQ5 way before Rowan Engineering came up with their kit.  There was no off the shelf pulleys that worked, so I had to opt for a 5:1 or 4:1 ratio and then use EQMOD with a custom offset (curtesy of Chris).  The smaller 5:1 ratio motor pulley gave out but I ended up with a 4:1 ratio using a 15t and 60t pulley which was machined down to fit the shafts and the casing.  Rowan came along later and machined a motor pulley  from a solid piece of ali and a worm pulley that kept the stock ratio... the rest is history.

Given the popularity of the EQ3 and EQ5 I would have thought that Rowan Engineering would have also developed a kit to upgrade them to belt drive...  

[wimvb]

I agree, if you can't keep the proper reduction ratio, you're in for trouble. But as I wrote, the motor gear has 12 cogs/teeth, and the next gear wheel has 66 cogs/teeth. The reduction ratio 11:2. This can be maintained with a 55 teeth pulley on the worm shaft, and a 10 teeth pulley on the motor shaft. The problems that remain are how to keep the belt tensioned, and how to remove the small gear that is pressed onto the motor shaft. My guess is that this mod costs more (labour) than what it's worth (in terms of improved tracking). For the time being I'll stick with replacing the washers inside the RA and DEC assemblies with bearings.

But a belt drive EQ3-PRO would be a cool thing to have. 

[dazzystar]

On 01/02/2022 at 23:49, wimvb said:

I have never really been satisfied how the EQ3 mount is designed. For example, the mount lacks proper bearings that support the RA and DEC worm gears. Instead it relies on a few plastic and paper washers for smooth tracking.

Last week I saw a youtube clip from a Swedish amateur astronomer who had removed these washers and replaced them with 2 mm needle bearings and cover rings. Today I received the bearings that I will need to make this upgrade, and since the forecast for next weekend doesn't look that good anyway, I might as well scratch that tinker itch and disassemble my EQ3-Pro.

Think I may do the same. Are you going to post a video or a review / before and after?

[BCN_Sean]

Just watched some, and bookmarked that video for later to finish watching, got about 20 minutes in and I realised that I was twirling a hex wrench between the fingers.  I've discounted the EQ3 in the past for the balcony mount as with hearing about the friction and bearings every so often it put me off.  Just wondering if that red felt one in the dec would be better served with a PTFE bearing instead of a ground shim ring.

[wimvb]

6 hours ago, dazzystar said:

Think I may do the same. Are you going to post a video or a review / before and after?

No video, didn't even take pcitures. I did most of the modification yesterday. It went mostly well, but I also learned that some of the issues that this mount has are not related to the red shims or the lack of smoothness because of them. If you closely examine the video, you'll notice that Petter Åström (who made the video) did a lot of small adjustments to both decrease backlash and to get DEC and RA to run smooth. For example, the central rod with the two bolts that hold the DEC axis in place, needs fine adjustment (besides adding any bearings). You can't just tighten the bolts. I found this to be the case for the DEC bolts (one on either side) and for the RA lock nut. Furthermore, the bearings take up space and push some other parts further out. Petter added washers to the DEC worm block, but this creates gaps where moisture and dirt can get into the mount.

After I put in the bearings, there was a definite improvement in how some parts moved, but I also found several places that needed careful adjustment. Unfortunately, I didn't have time to finish the work, and will have to continue next weekend.

As final notes (so far), some of the bearings that Petter used where too large, and anyone planning to do the modification, should spend some time looking for bearings that fit better. The RA worm wheel (part where the clutch acts on) has a diameter of 34 mm, so a 34 - 35 mm (inner diameter) bearing is ok. The RA shaft has a diameter of 25.5 mm (1" ?), and should have a bearing with this or 26 mm inner diameter. The DEC shaft has a 20 mm diameter and M10 threads on either side. For this you would need bearings with inner diameter 10 mm and outer diameter 20 mm. The DEC worm wheel has a diameter of 32 mm where the clutch acts, and a 20 mm bore for the DEC shaft. This needs a bearing with 20mm inner diameter and 32 mm outer diameter. A bearing under the RA lock nut (the one with 3 grub screws to lock it in place), will push the lock nut out to the point where it interferes with the Right Ascension ring. If you keep this, the scale on the polar scope will push against it.

Some of the bearings will press against the aluminium housing, so they will need steel rings. Petter used 1 mm rings, but they should ideally be thinner.

I thought that the worm end bearings in my EQ3 where quite smooth, but I replaced them anyway. The worm gear runs smoother now. This was the easiest fix.

The plastic cover of at least the RA motor is a poor design, and there is a risk that the RA transmission gear scapes against the plastic. I still need to address that.

All in all, if you, like me, have an EQ3 lying around and like tinkering, then by all means, enjoy yourself. But if you have little or no experience with this kind of work, then stay away from it. Adjust backlash, and enjoy the mount as it is.

[dazzystar]

Thanks @wim for the reply. I'll leave well alone then. I have ordered the parts for a OnStep upgrade so hopefully this will improve things a little.