Pillars vs Tripods

[James]

Hi,

A similar query to beamer3.6m's question here really but like him I'm pushed for time so can't afford a really long setup time. I've been forbidden a roll off/pier etc etc but have a small 6ft x 6ft paved and sheltered area I can use. The hope is to leave things largely set up but a tripod really takes up too much of that space so I'm considering a pillar.

I'm interested in people's opinions as to whether a pillar will be 'good enough' as I can't help but think a tripod must be steadier? I'm not worried about which pillar, more about whether it'll work or not.

It'll have an EQ6, Megrez 72 and ED100 on it.

Any thoughts, please

James

[tinvek]

if your going to use a tripod, get one of these, very easy to move about, very stable and good at keeping any light fingered types at bay

[adamsp123]

I would think a pillar mount of good quality to be less flexible ie "sturdier".

The tripod legs are thinner than a single pillar and any one of the 3 could flex due to loading changes and remember the loading on an angled tripod leg is trying to bend it, on a pillar mount the loading is mainly straight down the pillar tube to the base and base legs, and those legs should be very inflexible.

Wish I could draw a loading diagram to better explain!

Pizza Pete

[barkis]

Are you forbidden to concrete in a pier James?. An 8" length of plastic drain pipe in two foot of below ground concrete, and the pipe filled with same, and surmounted with an EQ6 pier head would be Ideal. Easily camouflaged as a Bird Bath or Sun Dial when not in use.

Ron.

[RobH]

Much easier to shoot at the zenith with a pier too....tripod legs tend to get in the way when using refractors.

Cheers

Rob

[Psychobilly]

Leave a 2" diameter hole in the center of the pier , but a De Longhi rotary washing line , chop a few feet off the "pole" and then the whole family can enjoy it

[James]

Wish I could draw a loading diagram to better explain!

Pizza Pete

No need to, I can see what you mean. Thanks!

Are you forbidden to concrete in a pier James?.

Absolutely I have been given permission to lop the top foot or so off a rapidly growing tree to the south and a big tree we have in the north end of the garden is getting cut back drastically so all is not lost.

I'm off to consider which pillar...

James

[The Warthog]

I would think a pillar mount of good quality to be less flexible ie "sturdier".

The tripod legs are thinner than a single pillar and any one of the 3 could flex due to loading changes and remember the loading on an angled tripod leg is trying to bend it, on a pillar mount the loading is mainly straight down the pillar tube to the base and base legs, and those legs should be very inflexible.

Wish I could draw a loading diagram to better explain!

Pizza Pete

Actually, the forces on a loaded tripod are along the legs, not aside them. If a leg flexes it is because it is overloaded. A pier would also flex if overloaded. Furthermore, the base of a pier needs to be very strong, as any off centre loading creates a lateral movement that is magnified by the length of the pier to exact a force at the base of the pier. Loading changes on a tripod act at the top of the tripod legs, and are converted into a compressive force along the leg in the direction of the strain. For this reason, a tripod needs less bulk in its construction.

[James]

Ahhh... hence pillars and the like usually being great big lumps of metal?

Any idea how thick a pillar would need to be to handle a Megrez 72 and an ED100 on a side by side bar on an EQ6?

James

[barkis]

It does not need to be metal James. There are plastic pipes that have fairly thick walls. A length of that, with a 1/2" wall, buried in, and filled with concrete, and metal capped, suitable to attach your EQ6, will suffice. A local builders yard might turn a length up.

My lx90 12" is mounted on a superwedge attached to a 12" dia. pipe which has a inch thick wall. It is encased in concrete below ground, and filled with it almost to the top. A 2" dia. conduit is inside prior to pouring in the crete, to carry any cables I need to service the setup.

Ron.

[James]

Problem I have Ron is that I'm not allowed any alterations to the paved area so I can't concrete in a pier. I'm considering options such as the Skywatcher Pillar Mount support (as an example).

A real concreted in pier would be nice but just isn't going to happen

[Whippy]

I know how you feel mate, I don't have the space for an obs, nor will L'missus allow a big metal pole protruding out of the floor into the middle of the garden. Before the midsummer lull, I had the mount just sitting out in the garden underneath a cover (it was a bit close to the bottom of the kids slide though!) as it was pretty well polar aligned and that's what I find the most time consuming part of the imaging setup. I'm trying to think of another way of having the mount in the same place over a period of time without making any real permanent marks to the garden. Best one I've come up with so far is to make a weatherproof 'box' that can just be taken off the mount as and when. As it'll be already polar aligned, all I need to do is add all the rest of the kit and off I go.

Tony..

[adamsp123]

Ahhh... hence pillars and the like usually being great big lumps of metal?

Any idea how thick a pillar would need to be to handle a Megrez 72 and an ED100 on a side by side bar on an EQ6?

James

Vixen pillars are quite light and made of Aluminium, steel ones are the norm because it is a much cheaper material to use and get a suitable quality of finish.

[barkis]

Problem I have Ron is that I'm not allowed any alterations to the paved area so I can't concrete in a pier. I'm considering options such as the Skywatcher Pillar Mount support (as an example).

A real concreted in pier would be nice but just isn't going to happen

Ah!, sorry James, you did make that clear, so I need not have made that last post.

I seem to recall you broaching this same subject not too long ago, or am I getting confused with someone else?

[MartinB]

The thickness of the steel isn't important James, it's the diameter of the pipe. It is easier to firmly bolt a pier in place and like you say they take up less room. You are also likely to be able to go further past the meridian as Rob says.

[steve51450]

Epsilon Telescopes

try these James

these sell a pretty flexible system that you can adjust from a moveable pillar to a fixed pier as you get swmbo to give you more leeway

also it seems a lot stronger than your run of the mill pillar

[MartinB]

I've just ordered a 6" Epsilon pier for my new obs. Rob is very helpful. Not cheap though.

[Marmite]

Pier Design Fundamentals

[coliea]

Problem I have Ron is that I'm not allowed any alterations to the paved area so I can't concrete in a pier.

Rob Gendler does just fine without concrete so a portable pier seems ideal for your circumstances James.

The Epsilon Modular System looks very well engineered, if you can afford to go down that road.

[ollypenrice]

Pier every time. As Rob says, you get tangled in the legs with a tripod. Another thing is that portable tripods have poor resistance to twisting moments (ie East-West.) This doesn't disagree with the principles of Warthog's analysis but arises from the way the legs are, in practice, bolted to the top.

The mighty Astro Physics mounts use a very light-guage pier tube but of considerable diameter like modern racing bicycle frames. This, as has been said, is the way to get complete stability with low weight. If you go down that route you might like to note that AP are also rather clever in triangulating the pier base to the pillar. Instead of using hefty struts intended to work in compression they use light 'spokes' screwded tight to work in tension.

Olly.

PS If you do lots of DIY you could do worse than buy a MIG welder form Machine Mart. With mine I've made 3 roll-off sheds, 2 piers, an observing seat, safety rails and observers benches, a two-scope mounting do-dah and lord knows what else. If I can do it it ain't difficult, believe me!

Olly

[adamsp123]

I don't fully go along with Warthogs analysis although I prepared to be challenged and put right. I agree the force vectors in a static tripod are along the line of the legs but if we imagine a very high load and the bottom of the legs were to be fixed in the ground ie unmovable, the the legs will tend to bend outwards ie the outside of each leg is under tension and the inside is in compression, give "this mechanical system" some form of physical "shove", gust of wind, knocking the scope etc then the legs will tend to oscillate.

Conversly if the bottom of the legs are not fixed then at high loadings I suspect the legs are bending inwards, outside under compression, inside in tension but the same results occur when the loading changes.

With a pier, assuming the thing is nice and vertical, the loading is all compression (assuming no twisting/shear forces) and the whole thing is more stable, ie less energy stored, as there is no opposite stress factors.

OK I only did a little bit of applied maths/ mechanics so I am willing to defer to someone with greater knowledge.

[James]

Thank you for your input but much to my surprise and completely out of nowhere came permission to have a pier

Now we've got to think about piers

James

[RobH]

Go far large diameter and make it so the levelling adjustments are at the top....mine are at the bottom, and although I now have it sorted, the long lever arm did cause resonance problems, even with 16mm steel threaded rods that only projected a short distance from the concrete.

Mine is filled with a sludgy mixture of engine oil and sand, which totally damps any vibration.

If you go down this route, thoroughly dry out the sand first, as the oil will displace the water over time and can cause corrosion of the inside of the pier (learned from bitter experience )

Cheers

Rob

[James]

Thanks for that Rob - it's particularly pertinent as the bottom part of the pier at least is going to be exposed to the elements virtually all the time.

So far it seems I need a wide (fat) pier - ideally I'd like it to be bolted to a concrete plug but perhaps if it's going to be exposed to the elements I should sink the whole thing into concrete?

Regarding the concrete base... I guess as big as possible. Realistically what's the smallest size of concrete plug I can get away with - is the difference that great between an 18 inch square (well, cubed) plug or a 3ft by 3ft that many say is the minimum.

Sorry - I've got about 67 more questions to go

James

[ollypenrice]

Engine oil and sand...mmmm, school dinners!

Olly.