Micro obsy advice please

[Skipper Billy]

I am planning my micro - obsy and would appreciate your views on the foundations I am planning.

The concrete pad is shown in the attached (amateur!) drawing - the mount will be holding a HEQ5 mount, ED80, CCD, filter wheel etc and a custom built fold down shed will be on the edges of the concrete pad.

The pier is a 5" diameter 10mm thick walled tube with flanges welded on top and bottom and will be fastened to the concrete pad by 6 x 13mm bolts set in construction epoxy.

Do you think its sufficient ??? It will not be stood on for observing it will be remotely controlled from a separate warm room purely for imaging. The edges of the pad around the pier block will be about 4 - 6" thick.

I prefer over-engineered to borderline.

Thanks in advance.

[laser_jock99]

Do you think its sufficient ???

Definately solid enough for the rig you are proposing. My widefield rig sits on a much smaller concerete mass and carries bigger payloads sucessfully. Your PA should not change if you are not de-mounting the scope each session?

[Skipper Billy]

Thanks laser_jock99

I am hoping that I wont need to polar align every session - the idea is to build a wee fold down shed around it and leave it set up. (That's the big attraction !!)

It will be remotely controlled from a warm room 15 metres away so no-one will be standing on the pad when its in action.

[Kropster]

I think the PA will only change if you remove the mount.... removing the scope wouldn't affect it.... I think.

Could be wrong!

[Scott]

The pad will be more than up to it (its about the same as mine). the only "possible" problem I can see is flex it the pier from wind. 5ft is quite long for a 5" pier. if this happens it can be easily negated by putting in wire cables tentioned with turn buckles. as a "skipper" I'm sure yuo can handle this .

Mine is a 4'x4' shed that rolls off. pretty much the same as yours and pa hasn't shifted since I last had the mount off at sgl X. just do a drift align every few mths to check it:)

good luck with the build

[Zakalwe]

The pad will be more than up to it (its about the same as mine). the only "possible" problem I can see is flex it the pier from wind. 5ft is quite long for a 5" pier. if this happens it can be easily negated by putting in wire cables tentioned with turn buckles. as a "skipper" I'm sure yuo can handle this

If the wind is strong enough to cause a 125x10mmCHS cantilever beam to bend by any significant amount, then you can guarantee that the flex will be the least of the OP's problems. He'll be more concerned about his house being blown away.

[Scott]

If the wind is strong enough to cause a 125x10mmCHS cantilever beam to bend by any significant amount, then you can guarantee that the flex will be the least of the OP's problems. He'll be more concerned about his house being blown away.

Not like you to have an opinion differing from mine...much. Sorry, but you are wrong. I have the same size pier and with a 200p it movesif the wind is strong enough

oh and my house is still standing. the 10mm wall means very little, its the diameter that gives it the strength

[Zakalwe]

Easy, Scott. It wasn't a personal attack.

There's a lot of things to take into account- how the pier is attached to the pier base, the size of the base plate (thickness and diameter), the size of any fillets connecting the CHS to the upper and lower plates, for example. 

An 8" Newt on an EQ6 is a big old sail and I would expect something in  the mount to be moving before the CHS section deflected (happy to be corrected though).  Assuming I've calculated this correctly (always dangerous to assume!)  a rough calculation for the deflection of a 127mm RHS cantilever beam, with a 100Newton point load at the tip gives a deflection of 0.07mm. RHS has a bit more meat in it than CHS, to be fair.

Weld a few decent fillets to the base and top plate or, as you suggested, arrange some stringers.

[Psychobilly]

I went overboard with mine.. both the foundations and the pier...

I drove 3  lengths of 3"x1/4" angle iron  at angles into the soil base of the "hole" before casting the concrete block around it...

Peter...

[D4N]

Be sure to consider soil type and what effect water and freezing will have.

Not sure where you are but I get seriously frozen ground in the winter and then in the Spring a lot of surface water as everything melts. It goes down cracks then re-freezes causing subsidence.

The concrete base for my pier is surrounded by insulating foam boards which are in turn surrounded by gravel and soil. This gives the water somewhere to go and prevents subsidence. My pier actually goes all the way down to the bedrock but here that isn't very deep!

The lower part of my pier has good protection from lower half of my obsy, very little protrudes above this.

/Dan

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