Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

Vixen GP Capacity?

pumpkincannon

By pumpkincannon
in Discussions - Mounts

Recommended Posts

pumpkincannon

pumpkincannon

Posted
Posted

Hey Guys - not sure if anyone can help me out...

I have an old (green) Vixen GP mount (which has been fitted with the EQ5 GOTO upgrade) - and I was wondering if anyone knew what the capacity of this mount was (purely for visual observing).

I've got a SW 250PX which i'm pretty certain is WAY too heavy for the mount - and I'm not sure I'm brave enough to see what happens if I connect them both up just incase I kill either.

I haven't managed to find out a definitive weight limit online however - so I'm toying with the ideas of either making (or rather getting a friend to make) a dobsonian base for the 250, or finding someone wiht apeture fever who might like to swap the 250 OTA for either a 200/150 (which I'm hoping the GP mount WOULD be able to cope with).

The other option is of course to have the dobsonian base made anyway, and then buy a smaller OTA to go on the GP mount - that might be somewhat tricky to sneak past the Mrs, however....

:)

Thanks in advance!

Link to comment
Share on other sites
A McEwan

A McEwan

Posted
Posted

Well, my old greenie rests on a Berlebach UNI-18 wood tripod and I have several counterweights. I have mounted a Skywatcher Pro 180 Mak on it with no problems for visual, and currently use it with a 6" f8 refractor, again with no problems. I find the trick is to accurately balance it all up with the counterweights. I routinely use two weights (don't have the actual weights here to identify them) with the 6" 'frac, and did so with the 180 too. For smaller OTA's I used one counterweight and made sure it was in the right position on the shaft.

With the 6" and two weights, I can balance it absolutely perfectly so that I can slew by hand to any point in the sky and let go of the tube - no lock knobs engaged!! - knowing that the tube will stay exactly motionless.

Preparation is key. I also tighten up all the leg-braces and mount-head fixing knobs to quite tight levels and make sure that the accessory tray is FIRMLY attached to the tripod for security. I also tighten the "backup" bolt on the dovetail clamp on the mount head using a screwdriver to make sure that it will, if needed, act as a backup.

I'm afraid I don't know the exact weight of everything I load onto it, but hopefully that will give you some idea of what you can get away with for visual. (Non-jiggly focusing action in the mid-200x's with the heavy 'frac is achievable).

Ant

Link to comment
Share on other sites
pumpkincannon

pumpkincannon

Posted
  • Author
Posted

Assuming the Helios is a "big heavy beastie" - I'm now wondering what the worst case scenario of overloading the mount is going to be. Is it just going to be unstable and wobbly and hard to use, or am I actually likely to damage the motors if I try it and see what happens?

Link to comment
Share on other sites
pete_gamby

pete_gamby

Posted
Posted

Vixen factory specification is indeed 7kg but my friends at Vixen Optics in the US quote 22lbs (10kg) as the maximum loading weight. They have told me in the past that they quote "real world" numbers i.e. figures based on what they have seen over time as to what the mounts are capable of holding reliably.

HTH

Cheers, Pete

Link to comment
Share on other sites
Ludd

Ludd

Posted
Posted

I regularly load my old green GP with a C8 and its associated gubbins that will take it way over the 7kg level. When well balanced, the motors purr very happily (but slowly - the max slew speed on my drives is still at a snail's pace).

I sometimes mount a chunky little 70mm ED scope on a "Telepack" adapter that clamps onto the end of the counterweight bar - this takes the overall weight on the mount even higher but doesn't upset the balance.

How do you find the EQ5 GOTO system works with the GP? I've been thinking about upgrading from my ancient Skysensor 3 controller but it's not a cheap upgrade.

Link to comment
Share on other sites
Kai

Kai

Posted
Posted

How do you find the EQ5 GOTO system works with the GP? I've been thinking about upgrading from my ancient Skysensor 3 controller but it's not a cheap upgrade.

Dont look at the AWR upgrade then :):eek::D

Luckily mine was already fitted when i bought it second hand :D

Link to comment
Share on other sites
Ludd

Ludd

Posted
Posted

Indeed, I did look at AWR but ran away very fast.

Of course, I could just go out and buy the synscan kit but I'd then have a lot of explaining to do about how I thought we'd have enough food to feed the five of us now that the money's all gone. As it is, I'm probably going to be quizzed about the new 2" diagonal that I'm expecting to arrive today or tomorrow!

Link to comment
Share on other sites
michael.h.f.wilkinson

michael.h.f.wilkinson

Posted
Posted

My GP carries the C8 with added 70mm finder scope with no issues, but I did have to add an extra counterweight. For visual and planetary photography it is it is fine. Vixen suggests a max of 6" for a Newtonian, 8" for an SCT/Mak, or 4" for a refractor. The differences stem from both weight and length of the scope. A longer scope needs to be lighter, because it exerts more torque on the mount. A very short (F/4) 8" Newtonian might work well, whereas an 8" F/6 might be more problematic. The C8 is of course one of the shortest and lightest 8" OTAs around (4.7 kg).

Much depends on how much you are annoyed by vibration: The scope will not fall over and the mount will not just break if you go over the limit slightly, but it will show more vibration, and they will not be damped out as well.

Link to comment
Share on other sites
661-pete

661-pete

Posted
Posted

I've been loading my Europa 250 onto the trusty GP for years now: complete with the finder and 350D I reckon that makes a good 10Kg-plus of payload - well over the GP's stated capacity.

So far it's been going quite smoothly without my ever having stripped down the mount (over a span of some 7 years). Of course I can't add any more load, so auto-guiding is out for the present. And the mount does show a fair amount of backlash in RA - more than a degree I reckon. This isn't usually a problem just so long as I take care to avoid the meridian. There's no noticeable backlash in declination.

So it seems the GP can cope with a fair amount of 'excess baggage' - yes. But you might invalidate its warranty.

Without any guiding I reckon I can, some of the time, achieve under 10 arcseconds of trailing in RA, in a 3-minute sub. Other times its as bad as 20". It all depends what part of the worm I'm currently at: straightforward PE. I use FocusMagic to try to iron out some of the more obvious trailing: no substitute for guiding of course, but it does get you a result!

One thing I really like about the GP is the excellent polar scope - easy to get it spot-on for Polaris. It even has a graticule with separate markings for each 5-year period - compensation for precession. I don't know if there's any other mount with similar. Of course, without guiding, pretty precise polar alignment is a must. I've always used the polar scope - never tried drift alignment.

Hope this is of some help.

PS: I should have added I use 2 x 5Kg counterweights. To balance, they have to be positioned about 1cm from the end of the counterweight arm. That tells you something about the load I'm supporting.

Link to comment
Share on other sites
Ludd

Ludd

Posted
Posted

Yes, I've wondered about relying on the excellent polar scope for alignment. I've never had a go at drift alignment, and it doesn't look too difficult, but it involves spending precious time setting up, and my observing time is already very limited. If I could get my head round setting the polar scope properly (so I can enter the date and time) I might have more chance of untrailed unguided shots.

Link to comment
Share on other sites
pumpkincannon

pumpkincannon

Posted
  • Author
Posted

Well I just threw caution to the wind and mounted the 250px onto the GP. Well, I say I threw caution to the wind, I spent a good while getting the balance perfect (took 12.5Kg's of weight in total) - and then I had the Mrs hovering over the power switch ready to kill the juice at the first sign of an abnormal noise from the motors, and myself poised to catch just in case of a topple......

.... and everything went fine. No abnormal sounds from the motors, sounded exactly the same as it does when my little NexStar 102 is mounted.

Did everything in the lounge as it's somewhat foggy here, but I'm assuming that I might just be able to get away with this?

Link to comment
Share on other sites
  • 2 years later...
davkt

davkt

Posted
Posted

Can't find it now but I read somewhere from what seemed a trustworthy source the stated capacities of Vixen mounts (at least the ones of the GP vintage) were for imaging whereas most of the competition give visual use capacity, hence why they seem a bit conservative.

Link to comment
Share on other sites
pete_gamby

pete_gamby

Posted
Posted

There's an explanation of how Vixen calculates its so-called torque load capacities on page 19 of the company's new catalogue - http://www.vixenoptics.com/PDF/Vixen%20Catalog%202014.pdf

To illustrate how "under-rated" the mounts are, the SXD2 has a maximum torque load of 370kg-cm so can carry an 8" scope of up to 15kg (370 divided by (10cm + 4cm + 10cm)) - this is the stated photographic loading weight. But when you calculate for a 4" scope, the load becomes 18.5kg (370 divided by (6cm + 4cm + 10cm)).

The same basic calculation would apply to the GP series mounts.

HTH

Cheers, Pete

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.