Gina's Mini Widefield Imaging Observatory

[Gina]

Been doing some assembly and found the 12mm marine ply quadrants are rather heavier than I thought.  I checked the weight of the aluminium panels but forgot the weight of the wood when I calculated the drive power requirements.  So I may have to redesign the drive system.  One aspect of this is that the roof sections are not counterbalanced in any way so the drive has to take virtually the whole weight of one roof section from starting the closing operation until well past half closed.  During the last half of the turn the driven section picks up the outer section at around the point that the driven section is balanced in the upright position.  As the turn completes the load decreases as the two roof parts combined approach their balanced position.  I'm not sure yet whether the roof will go past balance in it's closed position.

I have three ideas for the drive system for opening and closing the roof.

1. Timing belt and pulley on the motor.
2. Spur gears.
3. Cord to pull the roof closed with semicircular large pulley with cord attached and winding up on a drum on the motor shaft but only if the balance point is NOT reached before the roof is closed.

I expect to assemble the roof today so will see then just what the situation is.

[Gina]

Found the odd anomaly - something slightly wrong with my calculations   Tried bending the aluminium around the curved quadrants and found it didn't quite reach.  I've probably got the quadrants a bit wide   Easily fixed

Firstly taking the outer section which is 315mm radius.  The ali is 500mm wide and I would like 12mm to bend over to form a seal with the next section giving 488mm.  Circumference of a circle is 2 x Pi x radius = 2 x Pi x 315mm = 1979mm.  So the angle subtended by 488mm is 488 X 360 / 1970 = 89 degrees (within 0.5).

Inner (driven) section is 300mm radius.  Again this wants a bit turned up (in this case) of 12mm leaving 488mm.  Circumference of 300mm circle = 1885mm.  So angle subtended by 488mm is 488 x 360 / 1885 = 91.7 degrees (roughly 92).  Total roof subtended angle is therefore a tad over 180 degrees or a fraction under if I put draught excluder along the central overlap.

Fixed section is 285mm radius and a measurement of the length of the curve gives about 485mm so I will have about 15mm to bend over and seal to the woodwork   Measurement of the fixed end section shows about 15mm overlap from a roof of 180 degrees so that all works out alright in the end

This shows the new scale model.

[Gina]

Outer quadrants trimmed to new size   Also cleaned up bad routing from before   Nice and tidy now   At least along the straight bits

[Gina]

A bit more trimming.

[Gina]

Current state showing the carcass partly assembled temporarily with main bearings.  One driven quadrant can be just seen behind the far end hanging from the bearing on it's mounting flange.  The other with flange and the outer quadrants etc. can be seen on the table. 

[toxic]

hi Gina where did you get the 3d printer it looks brill i would love to have one of those lol sshhhh dont tell the mrs 

[Gina]

hi Gina where did you get the 3d printer it looks brill i would love to have one of those lol sshhhh dont tell the mrs 

I got it second hand from Amazon at just over half price  (£730).  It's an UP! PLus 2, a ready made proprietry printer rather than a kit and is a bit smaller than the more common RepRap open source designs.  Counteracting it's smaller size, it is much higher quality with a price to match   When I bought it this model was £1400 or thereabouts but they've all come down in price since. 

If you are moderately into DIY, a kit might suit or if really experienced you could make one from scratch though I couldn't say if you would save over a kit.  There are also various ready made printers either proprietry or based on the RepRap open source design.  A big advantage of the RepRap designs is that spare parts are readily available.  The downside is that they may need a bit of tweeking to get good results.

You may be interested in this review of 3D Printers from last year   Mine is the last one in the reviews.

[Gina]

The two driven quadrants now trimmed down to the new size   Much less fraying on the end grain this time that the first time.

[Gina]

Holes cut in outer roof quadrants with hole saw.

[Gina]

I've redesigned the bearing system to now accomodate the outer roof section quadrants.  I'm going to try plain bearings for the outer to driven quadrants as these only take the weight of the outer roof part.  I think a ball bearing is unnecessary and I don't like plain steel ball bearings open to the weather even with rubber seals.

I've simplified the way the whole lot is bolted together, including drive pulley/sprocket/whatever, replacing the central M10 bolt and 4 M4 bolts with 3 M5 bolts.

Outer bearing part that goes into hole in outer quadrant and retaining plate.

[toxic]

thanks gina this project is fantastic

[Davey-T]

Hi Gina, could you reduce the weight by drilling some 75mm holes all over it and printing discs to clip in them, make it look really cool.

Don't know the modern term for cool, sure there is one

Dave

[Gina]

Hi Gina, could you reduce the weight by drilling some 75mm holes all over it and printing discs to clip in them, make it look really cool.

Don't know the modern term for cool, sure there is one

Dave

I did think of cutting lots of large holes in them but I didn't think of filling them with printed discs   A spotty observatory ha ha

Could certainly be a way of reducing the weight.

[Gina]

Bearing parts finished and assembled and now attaching the aluminium sheets to the quadrants with the 3D printed curved angles.

[Gina]

Next piece...

[Gina]

Aluminium sheet fixed to quadrants to form the outer roof section.  Now printing the curved angle brackets for the other opening roof section.

[Stu]

Excellent!! [emoji3]

[Gina]

Thank you Stu   It's coming along - gradually

[Davey-T]

Hi Gina, did you seal the end grain on the ply and silicone the quadrant beads on ? even marine ply will delaminate if constantly wet from rain trapped under the bead.

Dave

[Gina]

Not as yet, this is just assembled to check that everything fits together.  I shall be taking it all apart again for sealing and either painting or varnishing the marine ply and probably painting the aluminium.  I'll probably paint it green to match the main observatory and the woodwork of the house.

[saac]

Wow Gina that is looking fantastic, I bet you could even market it.  Are you planning to do a quick functional check to confirm dimensional clearance with your wide field rig installed?  If anything has me convinced of the potential of a 3D printer it is this project.  Good luck with the rest of the build, can't wait to see it finished and working.

Jim

[Gina]

Thank you Jim  

Yes, I shall be doing a test to check that everything fits and clears before finishing off.  Keeping fingers crossed ATM - I shall be none too pleased if I find it doesn't fit   I may make up a stand for the NEQ6 so that I can test it all on the table.

[Singlin]

Cool Gina!

I can't wait to see it finished.

For all of the 3d printers sitting in people's homes I don't believe many would be as productive as yours.

[Gina]

I needed to adjust the length of the side pieces of the carcass to get the roof measurements right.  The length inside the actual roof is 700mm and inside the carcass/body, which is well below the counterbalance weights, is 660mm.  I measured the length required to clear the weights and imaging rig as 650mm so it should be alright in that respect.

Here are a couple of photos of the outer roof section mounted on the bearings and supported by the body.  The nearest inner moving roof quadrant can be seen peeping out from behind the outer section.

[Gina]

Now I have one roof section assembled I can get some idea of the drive requirements.  Firstly, these parts are not stiff enough to drive from one end as I suspected and secondly, the off balance aspect means that a considerable torque will be required to overcome gravity.  So I shall be looking into the possibility of adding some form of counterbalancing.  I think I now need to make up a base for the NEQ6 to use on the table so that I can set up the whole imaging rig indoors.