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IEQ45 flexure


E621Keith
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My GPDX is at its limit with some of my larger scopes, so I went to IAS yesterday to see whether there are any special offer at the show. Widescreen Centre had an AZ-EQ6 on offer. It was tempting but I ended up buying the used IEQ45 from Astronomia/Telescope Outlet.

After I got home I tested the mobile pier in my garden which had a slight incline. I was happy to find the pier had enough adjustment to level the mount. Then I brought it back into the house and assembled the mount. When I put my scope on it, I found two problems.

1. I don't have enough counterweights to balance my scope and that was before I put on any accessories. This should be easy to fix, I will have to buy the weight extension bar or more weights.

2. There seems to be a lot of movement in the RA and Dec axis after the clutches were tighten and the RA motor box seems to flex when I shake the OTA by the focuser. The flexure in the IEQ45 seems worse than my GPDX which is only rated to carry half as much. The IEQ45 is rated to carry 20kg and the GPDX is rated 10kg. The OTA in the video weights 14kg, so the GPDX was already overloaded.

Is this flex caused by the mount being off balance or am I looking at a more serious problem?

Here is a video of the problem

Thanks

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I suspect that what you are seeing there is simply the engineering "clearances" being taken up as you "waggle" the mount/scope. Every junction between the parts of a mount has a clearance and as you waggle the scope these are "adding and subtracting" to give the movement. If you are waggling the scope by the focusser you are putting a huge leverage onto the mount. This will act to amplify any tiny movement that you are applying.

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Just tried mine and can't detect any movement, though I've only got ST80 guide scope and tube rings for the main scope on it at the moment.

On the balance point I made myself a longer dovetail and moved the scope etc forward to get balance without resorting to more weight.

I have 100mm f/6 refractor, ST80 and DSLR balanced using the supplied weights and bar.

Dave

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Yes, as Jesper says the iEQ45 relies on spring loading the worm into mesh with the wheel. This is a worthy idea for reducing the backlash Roger mentions but I've seen it misbehave systematically and I'm not convinced by the design, which seems to develop a greater lack of spring tension over time. One thing that can happen is that the plastic covers which cover (inadequately) the worm can foul and prevent the worm from springing into mesh with sufficient force.

I found with the iEQ45 that it was not much good with long OTAs which have a high moment. This moment works against the spring loading and overwhelms it. It is a far better mount with physically short OTAs which don't work as hard against Dec. Our longish TEC140 is fine for AP on an NEQ6. The iEQ45 could never carry it satisfactorily, even for visual. The TEC is actually quite light and well within the claimed payload but it is long and defeats the design of the mount.

Olly

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I suspect that what you are seeing there is simply the engineering "clearances" being taken up as you "waggle" the mount/scope. Every junction between the parts of a mount has a clearance and as you waggle the scope these are "adding and subtracting" to give the movement. If you are waggling the scope by the focusser you are putting a huge leverage onto the mount. This will act to amplify any tiny movement that you are applying.

What you said about clearance makes sense.

The huge leverage on the mount was the main reason I decided to get something stronger than the GPDX. I'd expect a higher capacity mount to cope with this better than the smaller mount, not the other way round.

The worm is spring loaded and I guess that's what you're seeing. Try and adjust the tension on the worm.

It's in the design so not a fault per se.

/Jesper

Thanks, I will have a look at the worm. Is the RA drive box part of the spring loading mechanism and is it suppose to flex? The flex in the RA drive box is what worries me the most.

I can't really test this the mount in action until I get another counter weight and have a clear night, but I have to decide whether to go ahead and order another counter weight or return this to Telescope Outlet under the 14 days return policy.

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Yes, as Jesper says the iEQ45 relies on spring loading the worm into mesh with the wheel. This is a worthy idea for reducing the backlash Roger mentions but I've seen it misbehave systematically and I'm not convinced by the design, which seems to develop a greater lack of spring tension over time. One thing that can happen is that the plastic covers which cover (inadequately) the worm can foul and prevent the worm from springing into mesh with sufficient force.

I found with the iEQ45 that it was not much good with long OTAs which have a high moment. This moment works against the spring loading and overwhelms it. It is a far better mount with physically short OTAs which don't work as hard against Dec. Our longish TEC140 is fine for AP on an NEQ6. The iEQ45 could never carry it satisfactorily, even for visual. The TEC is actually quite light and well within the claimed payload but it is long and defeats the design of the mount.

Olly

Thanks, the plastic cover fouling the worm would explain the movement I see in the RA drive box. The fact that the 125 is both long and heavy probably didn't help.

I was just worried if I bought a faulty mount. If this flex is normal, as caused by the spring loading, then I will live with it. I will be using this mount mostly for visual.

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Well, I wouldn't feel obliged to live with it. For a longer refractor I'm certain that an NEQ6 would be a better choice. The flexure against the springs, which seems to get worse, is a defect more than a feature.

Olly

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I think you would be much better served by an EQ6 or AZ EQ6 GT but if you do decide to keep this mount, don't use an extension bar to achieve balance. You would be better off with another counterweight IMHO as I don't like these long moment arms - better to have greater weight closer to the centre of gravity.

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I think I will get some weights for it and see how I get on. If the flex was part of the 'design' and not a 'fault', then in the worst case I will just sell the mount and get an EQ6.

Thanks for the advice on the extension bar. I suppose if 'flexure' was caused by a long scope, then using extension bar will probably make it even worse.

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Paul's mods are something I'll look into doing myself one rainy day. The results speak for themselves.

It's a great mount for ap too, just stay clear of long FL or big OTA's if wind is a factor. It will buckle well before an HEQ5...

/Jesper

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  • 2 weeks later...

Finally had first light with the mount. Fortunately, the amount of flexure seems to be acceptable visual use.

Thanks for the link, I will look into various mods, but I think I will upgrade the mount if I decide I want to start imaging with the 125.

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