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Gina's Mini Widefield Imaging Observatory

Gina

By Gina
in DIY Observatories

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Gina

Gina

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Thank  you :)  Makes sense now :)  I'd forgotten about parking contacts.  Return through chassis then two motor connections, slow and fast, and two connections for the parking contacts.  Should be easy enough to sort out which is which :)  Just hoping the motor mechanism will be "happy" going backwards as well as forwards :D

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Gina

Gina

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Hmm...  reading all that it seems they have field windings rather than permanent magnets, in which case reversing the polarity will reverse the field as well as the armature and the motor will still rotate in the same direction, as I recall :(

The motors used in garage roof openers look just the same from the outside and they are reversible.  I wonder if it's just the older wiper motors that have field windings.  With modern rare earth "super" magnets, fields have generally changed to permanent magnets.  Guess I'll find out when I get the wiper motor on power :D

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Tinker1947

Tinker1947

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Thank  you :)  Makes sense now :)  I'd forgotten about parking contacts.  Return through chassis then two motor connections, slow and fast, and two connections for the parking contacts.  Should be easy enough to sort out which is which :)  Just hoping the motor mechanism will be "happy" going backwards as well as forwards :D

Its only going to happen maybe 140 time a year with the way the weather is, you may need to a Sunday morning test run each week just to make sure its used once a week and moves the grease about a bit........ :grin:

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Gina

Gina

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Sorry but that's not reversible :(  Has a release so that you can run the cable out!  I already have one like that which I bought some years ago.  Far too powerful as well.  I also have two 12v reversible winches which are too powerful and hellish noisy to boot! :(  It's only to turn a counterbalanced little roof and douesn't need a multi-horsepower motor :D

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Gina

Gina

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Did a quick test with a steel screwdriver and couldn't detect any external magnetic field so I think it has field windings and won't be reversible. 

Found a window motor on ebay and ordered that - only £13 inc carriage.

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Gina

Gina

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Good news :)  Found one of my DMMs and sorted out the connections to the wiper motor and it IS reversible :)  Draws 1.4A on slow and 2.5A on fast when run off 13.8v.  Runs nicely in both directions :)  Next thing is to sort out the drive system.  The shaft doesn't stick out very far from the mounting plane that's one problem.  I think I shall have to make a dished pulley, gear or sprocket.

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Gina

Gina

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I'm getting towards a decision on the drive system for the roof.  The idea of an axle right through at the roof pivot level would appear to get in the way so I'm thinking of driving both ends separately with the common drive shaft lower down, well clear of the imaging system and mount.  I rather like the simplicity of bicycle chain and sprockets - a solid drive and much cheaper than timing belt and pulleys.  I can 3D print the smaller sprockets and the large sprockets could be either printed or I could use bicycle chain rings such as these. 

The drive from wiper motor to common drive shaft could be either chain drive or printed spur gears.  Sprockets are much stronger than the teeth on spur gears so I think chain drive will win.  With sprockets and the flexibility of ABS plastic all the teeth in contact drive the chain (or vice versa) take the drive force so the loading is much less.  I bought more bicycle chain than I now require for the main observartory roof automation so have some spare :)

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Gina

Gina

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The aluminium sheets have arrived and I've unpacked them :)  They ar quite a bit stiffer than the 0.5mm thickness but I think they will do.  I'll find out later :D  Of course, the thicker sheet may mean it has sufficient rigidity not to need driving from both ends, though it's a third longer.  Time will tell.

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Gina

Gina

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I have now built the outer roof section with one of the new aluminium panels.  I bent an angle on both long edges using the hinged flap of the table :D  It was a bit of a struggle to bend the ali sheet to fit in between the ply and the plastic angles but alright in the end.  With the second bent down edge I had to cut slots in the ply for it to slot into.  Used a little hacksaw for that.  Photo(s) to follow shortly...

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Gina

Gina

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I did a test with the outer roof section and it seems that there will be sufficient rigidity to allow driving from one one only :)  That will simplify things a lot!  I'm currently working on a sprocket to fit the wiper motor.  A 12 tooth one will fit between the mounting posts :)  For the large sprocket I have ordered a bicycle chain ring.

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Gina

Gina

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The bicycle chain wheel came today and looks great :)  Here it is atop one of the roof quadrants.  The hole in it is slightly smaller than the axle I've already made so a bit of reworking will be needed - no problem :D

post-13131-0-66711600-1423076916_thumb.j

I've been thinking about the drive and decided I don't like driving via the 25mm axle, though with good balancing it wouldn't be so bad.  I would much prefer to attach that sprocket directly to the roof quadrant and reduce stresses.  That would mean the sprocket and chain drive would be outside the main carcass.  I think it could be covered though.  I shall investigate :D

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Gina

Gina

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I've also been thinking about controlling everything and how to run cables etc.  I've concluded that having the control computer in the main observatory warm room and running cables along the boundary fence would be much better than a laptop or netbook within the mini observatory with the problem of dew and it would still need a power cable (or power tank).  I could use the same computer to run the mini obsy as the main rig and the same power supplies etc.

I think the mini observatory could be moved a bit nearer the main observatory without losing too much available sky to the NE. 

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  • 8 months later...
Gina

Gina

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I've examined how the latest design of NB triple imaging rig with carrying frame attached to the NEQ6 will fit in the current design of mini observatory and foresee no problem.  In fact the metre long roof is excessive and could be reduced by something like 150mm or maybe more.

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