Michele Scotti

20 hours ago, Peter Drew said:

@Rusted.  Yes, I must have made hundreds of worm and wheel gear sets during my career.  They were all hobbed on a 4.5" lathe.  I always took great care to make sure gear blanks were turned with all details perfectly concentric, not difficult just needs care.  How big players such as Meade can often get this wrong escapes me!  My worms were turned from solid in one operation which ensured complete concentricity of bearing journals, drive shafts and worm teeth.  I still wince when I see composite designs.

Getting the correct number of teeth was a mixture of always using the same tap, same blank diameter, a few tricks of the trade plus a bit of luck.  On expensive large diameters it was prudent to pre gash the blank with a dividing head to guarantee the correct number of teeth.

I've no idea how good my gear sets were but I never had any complaints, users got good imaging results and some owners brought their mounts back for minimal adjustment after "donkey's years" of reliable use.   🙂

Next time make sure you shot a video - worm gear hobbing is fascianting.

Would you reckon you had a similar set-up to any of these? 

https://www.youtube.com/watch?v=19jKlq8Ofd4&list=PLJtiP4DlrmJROzFYnk0rYQ9fnJPO9KyCn&index=16&t=0s

https://www.youtube.com/watch?v=eKJe1JnvRc0

Hope not to detour the thread here....

On 08/02/2020 at 10:10, MarcusH said:

No rush, but please do, or a video. Seeing sub 100u movements sounds intriguing...😮

Rather than a video let's see some maths behind this - it applies to any modern smartphone with Mpixels.

At the minimum focus distance - usually 50mm or something- this is a clear picture of a caliper.

A crop-up shows that 5mm takes 77pixels. This equals to 65um/pxl

By the way in a video you wold appreciate sub pixel movement for sure. 

Out of curiosity this is what happens using the zoom (digital in this case)

Reoslution here is 14um/pxl

Not maybe the most accurate tool but it detects tiny movements very efficiently - it might be handy when checking mounts for slack

3 hours ago, MarcusH said:

Could an angular contact bearing be an option ? Much easier to find with a 10 mm bore, if that's the only critical measurement.

Can take both axial and radial load, but don't know if it's much inferior to tapered roller bearings. I think I've read somewhere that the tapered rollers were preferred in slow rotating assemblies whereas the angular contact was preferred in fast rotating ones (think it was on some CNC-forum....)

https://simplybearings.co.uk/shop/p88001/Budget-7000-Single-Row-Angular-Contact-Open-Ball-Bearing-10x26x8mm/product_info.html?backstep=1

2tons of axial load - i guess its enough

2 hours ago, MarcusH said:

Perhaps the test could be reversed to find out. I.e. clamping the laser to the bottom of the tube and apply pressure to the jig. If the bottom is immovable the laser dot shouldn't move. If it moves any added rigidity to the pipe itself would be a moot point.

I've check most of jig elements -and specifically the upper and lower bearings- is in a pretty funny and maybe novel way.
I pointed the smatphone at the area where movements would manifest and shoot a video while applying load. 
As funny as it sounds you can detect way finer movment than naked eye.
I was trying to put some maths behind it...maybe later.- you can see sub 0.1mm for sure. I have few videos where the check is OK but can't find the one that was clearly showing a minimal movement in a different area of the jig that was later fixed.

Bottomline - to my surprise- bearings are ok.

Anyway if they moved the laser pointer wouldn't move as the pipe would not bend but rather tilt.

The quest for a stiff and reliable platform

I've used some counterweights at the end of the board to evaluate the stiffness of the system. Not a good starting point... 0.9mm with something like 6Kg placed some 30cm outboard, just to exacerbate the flexure.

I've then tighten all screws and added M6 bolts with inserts to cement the position of the wooden blocks. Better but still 0.6/0.7mm.

Where's the flexing coming from?? Maybe from the element assumed to be the most rigid? Let's check the pipe...

A cheap laser was clamped on the top of the pipe -see pic- pointing down. Some paper tape on the bottom to act as a 'screen' for the phone to record just under it.

And there you go – the pipe flexes big time!

Movement -subtle-is caused by pushing on the board and releaseing - laser dot moves 1 or 2mm. Smoking gun!

So the pipe that fits perfectly in the bearings and we made all the wooden blocks around is not up to the task. Shall we throw it away? Nah!

The pipe needs stiffening on the vertical plane where it meets the angle grinder – so next step is to insert a 5mm flat bar that is as wide as the ID of the pipe. Possibly a few welding points at the ends. For a structural application this would be gruesome borderline criminal – in this case it really needs to work under small stress.

7 hours ago, Rusted said:

I still plan to spring load the worms on sturdy hinges.  Presently I am using a pin to provide spring loaded rotation into the worm wheel. I believe a suitably tight, brass door hinge would be far superior. The worm bearing, profile housings are weak and need considerable reinforcement over and above my present arrangements. I need to add considerable cross sections to properly support the bearings against end loading.

I’d suggest a different approach: fixed bearing housing after lapping. The way I see it, is that you have a run-out from the shaft to tollok, tollok to sleeve, sleeve to worm gear I and finally ID to the generated teeth. Actually it’s not all –  your shaft has a nice press-fit brass thread. All of the mentioed interfaces might be very precise but they all come with few hundreths mm of run-out or clearance.

Lapping will take care of all of them. I have to be honest – never did it myself  just because I’ve recently stayed away from worm gears in my telescopes. Also I reckon it is only mandatory for Dec axis. It’s maybe a lengthy process (and messy?) but not that complicated. Let me know what you think about.

7 hours ago, Rusted said:

Taper roller, thrust bearings, or even axial thrust, ball bearings, on the worm shafts would be better. Sadly, the worm shaft extensions are miserably mean. I am trying to avoid couplers just to hang the belt drive pulleys onto something more solid. The shoulders on the worm shafts cannot be brought inwards, to make room for better bearings, because of clearance problems on the large, wormwheel rims.

I suppose the shaft material is not treated/hardened. You could tap an M5 and add an extension – belt&pulleys are pretty forgiving to run-out errors. I would never suggest that for a gear coupling. What is the ID/OD of the bearing and the width of housing? 12x30x8?

3 hours ago, Rusted said:

The BH worm housings are terribly flimsy and poorly designed. 
Needing lots of mods even to make them work as intended.
Very poor bearing retention and no real stiffness to the skinny, channel profile.

The worms moved sideways out of their housings almost on the first slew! Unbelievable!
The worm shafts are almost worthlessly short for timing belt drive sprockets.
I shall make some massive worm housings with far better and bigger bearings... one day

my 2 cents - from previous picture the housing and bearing general dimension doens't look bad - I'd suggest to switch to tapered bearings with a (simple) system to pre-load one of the bearing. That will kill any lateral movement. 

Is the BH fixed or does it have a system to cope witht he inevitalbe run-out of the wormgear? 

22 hours ago, Rusted said:

The weakest factor of any tripod is the radius out to the tilt line [hinge] between any two feet.
Which is why tripods are so unstable relative to any increased number of points of contact.
A four legged [quadruped] is far more stable and the reason there are no tripodal animals.
A tripodal mountain goat is basically a non-starter in Darwinian terms.

The Martians wouldn't stand a chance in a real War of The Worlds.
It would only have taken a car and a brave chap with a rope to pull one over.

For the same reason a tricycle is hideously unstable compared to a quadricycle of the same track and wheelbase.
And a three legged stool, only has value on a rudimentary, brick or paving slab floor.

Every additional leg provides greater stability because it better equates to the full radius of a circle.
Which is why executive, swivel chairs [and my own computer chair] have five feet or castors. 

I trust you realized that all the examples you brought are 'dynamic' at a certain extent - even your swivel chair.

It totally makes sense to have more 'legs' to achieve a more stable set-up simply  by increasing the area on which the CoG can fall on.

One of the perks of a AltAz mount is that all loads are pretty well centered. The CoG of the 'OTA' rotates around on a 124mm circle - well within the 'triangle' set by the 3 rollers. I do not foresee any stability issue.

To me one of the design aspect that I tried to optimized is related to the load transfer from the Alt bars thru the Az table then Az track to the rollers on the tripod and from there to the feet on the ground - which incidentally I haven't designed yet so they are not shown in any CAD so far.

As a matter of fact the FEA we ran was on the worst case where one of the Alt bearing is placed half-way over 2 bearings

15 hours ago, MarcusH said:

And secondly, why a tripod to support your azimuth table and not for example a hexapod ? Would that just be form over function with no added benefits ?

To start by stating the obvious: the tripod has 3 legs and at the end of each leg there's a roller. So this set of 3 points defines a plane - adding any additional supporting point will introduce an unwanted constrain. Chairs have 4 legs and they are 'stable' because they deform under load allowing a distribution of weight on 4 points.

So 3 is actually the only choice for such structure.

Class-meter teelscopes uses a different approach - they usually have 2 very accurate flat rings that are part of a hydrostatic bearing where pressurized oil keeps the 2 rings apart.  

Hope this answers your question?

3 hours ago, Rusted said:

Marcus, I agree and it's not silly.

If it were my project I'd just be using long sanding blocks. With various paper grades getting finer over time as needed.
Or even a diametrical, cross board pivoted on the pipe/bearing with an abrasive paper covered block running around the track.
As you say, use the jig only for measuring.
Double check that every single radial measurement is fully repeatable before even trusting the jig at all.
Using maths to analyze "a length of string" is a common fallacy.

EDIT: Can't understand the strike through text! Can't get rid of it either!

I might actually resort to sand blocks, eventually! At least they'll provide smooth transitions although not going to do much for the overall run-out. 

"Using maths to analyze "a length of string" is a common fallacy."          what do you mean with this specifically?

1 hour ago, MarcusH said:

An impressive project and my deepest respect for the courage to start off (and hopefully finish off) such a project while keeping us all informed along the way. You have gotten many well thought out questions and advices from members and you have equally given many thought out replies and you have taken the advise in when needed. So I'm going to feel a little like the odd-ball here when a ask my silly questions, but please bear with me.😄 

Firstly, now that you have invested in a micrometer, have you measured how much vertical run-out you are dealing with ? Is it millimeters, fractions of millimeters or something less ? Why I ask is to find out just how much machining needs to be done to that track. I'm thinking that you have built a great jig, but not for the angle grinder, rather than for the micrometer. You could measure and mark the high spots on the track and then attack them with something with a bit more finesse. Perhaps even a hand tool sufficiently large and stiff with the proper abrasive, just "sanding" or "polishing" off the high spots and not causing any low spots. Now your only worry would be to keep the micrometer at an fixed plane so not to loose the reference point. Quite an easier task for your jig than an angle grinder spinning a 13000 rpm.....

4 hours ago, Rusted said:

You can use your micrometer head to confirm the uprightness of your central tube relative to the ring in its present form.
It should read close enough to an average figure over one complete revolution of your jig before you even consider a run.
Any bias in one particular direction will thin, or thicken, your track in that direction, depending on the slope of the tube.
I still think the angle grinder is a fierce tool for this task. It has no finesse. Nor any pretensions to accuracy.
If it digs in, then it will pull the tube over in that direction as a form of positive, mechanical feedback. Bad!

I just wish I could think of a tool which better suits the task. Your jig just isn't up to using milling tools or even end face, router bits.
There is bound to be far too much flexibility for the accuracy you desire. Or any accuracy at all!
I wouldn't be surprised if it resonates like hell just with the motor free running.
There just isn't enough mass or stiffness. What about an ablation laser? Shouldn't be any vibration.

Don't you have a tech college nearby which could treat your project as a class exercise? 
The machine tool tutors might like oddball projects. Makes a nice change from the usual humdrum.
They might have some useful ideas before you break something important.
A vertical, turntable lathe would do nicely if anyone had one. Try a crane manufacturer?
 

I try to bundle up answers - in first place there's no such thing as a silly question. Only asnwers can be silly.

Also, I totally share with both of you the fact that the likelyhood that all of this is going to be a big mess is very high - I'm not shooting for first time quality. I'll learn by mistakes along the way.

There's a specific reason though why I'm going down this routet. And it's about the spirit of this project - this is a pilot project and an (ambitious) blueprint for a large, attainable imager that should be potentially built around the world without access to expensive/porfessional/dedicated machinery. A go-kart shaft and a couple of bearings are fairly common and inexpensive. Surely we might fail - then I'll reconsider what to do.

Anyway - I took 2 measurements every 15deg - orange and grey lines. I applied a sinusoidal correction to simulate a tilted shaft being straighten-up - in blue.

The result after such correction is the amber line.....which is more than I expected! We are looking at a ca. 1.3mm P-V or run-out. Quite some material to remove....

Worst scenario if (likely) the steel left is too thin I'll bond another set of arches like the first time - it probably costs less than 100Euros

2 hours ago, Rusted said:

I agree and questioned my motives [afterwards] for using the ring as its own reference.
So what is your reference and what exactly you are trying to achieve?
Is it your pipe? Is it perpendicular to a fraction of a second of arc?
Is it infinitely rigid? Is it equally rigid in all angles of rotation?

Is the base absolutely rigid when fully loaded? If not, the ring will change form.
It will sag between the feet or be "shaved" over them. Giving you a gentle, roller coaster track.

A lot of good points...
Ref is the shaft and its bearing - the one that will stay on the Az table. I'd like to target a few tenths of microns of total vertical run-out with very smooth transitions - somehow the latter is more importand than the first.

The pipe is a go-kart rear axle with 2mm wall thickness - its rigidity will be scrutinized due course. The idea is that it has to allow the generation of an ideal plane which is the new track surface.

f it is slightly tilted - to a reasonable extent- compared to the table itself is not a big deal. What counts is that the track and the 2 Altitude ground bars are 'parallel' - this can be quite easilty checked and rectified with shimming under the Alitude bearing brackets.

The Az table is fairly rigid - at least by design anf for the purpose- as it's the most critical element for the overall mount performance.

The picture here is for the HUGE investment in a micrometer to test the accuracy of the surface and preliminary the stiffness of the jig.

On 31/01/2020 at 18:21, Rusted said:

That tube is not going to offer much support without some help even if you triangulate. Think of it as merely a center guide pin.
What about adding some counterweights on a horizontal extension to balance the angle grinder and jig materials?
You don't need any pressure for "cutting" and fighting the weight will require too much adjustment to take up unknown levels of backlash.
The triangles can be scrap ply. That board isn't going to offer much resistance to twisting on the axis of the angle grinder.
You could add a roller on the tail end. Your track is the only accurate surface you can trust as a register so you might as well use it.
You could add further rollers at the widest part of the jig. Inline skateboard wheels? The jig will have to be widened to suit.

The track currently is of unknown geometrical quality - hence I can't use it as a reference. Any roller used to help supporting will inevitably act as a "copy-carver" to some extent.

The challange here is to be able to use he tube as a reliable axis to start with. That is the reason why I extended the distance between the 2 bearings in order to better cope with the bending moments. Clearly success in not a given here...

However my way to evaluate how far we are from a solid jig is to check how close to the ideal situation i.e. how insensistive to loading is the distance between the track and the tool.  .

I agree that the grinding forces are not going to be massive but I'd like to start with the most solid set-up.

In the meantime this is the set-up we came up so far. Added quite few reinforcements and a rudimental 'micrometric' adjustment of the head height....still working on that though

19 hours ago, Rusted said:

With respect, I have some recent  experience in trying to "machine" the inside of a 3m diameter plywood ring using a central pivot and a portable router.
The result was extremely violent chatter! I then duplicated the radius arms into a horizontal triangle and this helped to smooth the chatter but not by much.
I used 20x100mm timber arms to form the horizontal triangle.

What was missing from my radius bar system was 3D limitation on the radial cutter. The router could hop up and down despite the sheer weight of the triangle

I see what you are saying and I reckon I have contermeasures in the design of the jig - btw as a flat 2D it didn't provide any hint of the width on the jig itself.

Here are a couple of pics of the early stages of jig build - let me know if it makes sense to you - still I would need to run many checkes before giving it a go on the actual azimuth table

Bottom side with track:

Upper side with the flange to carry the second bearirng:

On to the challenging bits of the build....and the reason why Iwe didn't want to load the strucutre just yet.

Background/assumption: looking at its Periodic Error an ideal mount minimizes the amplitude and it looks smooth – in mathematical terms this means that the higher order content of the Fourier Analysis.
I would add that a desirable element is that the movement is repeatable i.e. it’s ‘smooth’ and without ‘random’ jitters all around the rotation the axis.

To achieve a good tracking capability I’d start from the most precise execution of the components – however soon you realize that even so, errors in the order of few microns will show up in the image given the long focal length.
A bit of math done some time ago showed me that 1 micron error on the azimuth track would generate a 0.22arcsec (arcsin(1/900.000) tilt of the telescope – which is comparable to the sensor pixel resolution.

And of course there is no chance -for me at least!- to produce such an accurate surface. Let alone that all other elements of the system have a tolerance – for instance the roller bearings are specified at around 11microns.

As a consequence, for a telescope to be an imager, autoguiding is a necessity. However a smooth repeatable PE is easier to be guided out.

So what’s the plan? A ground track of course! How…?

In the absence of a gigantic lapping machine my choice is going into creating a grinding machine on the table itself.

Here is the sketch which is hopefully self-explaining. Enough to say that it makes use of an angle grinder -with a controlled play- and a controller to limit its speed.

The tool will be a “diamond” cup like the one in the pic.

Sure it will take long time to carry out the machining operation but that’s ok if it yields the result. Also the shaft is rotating into the same bearing that will stay on the azimuth table and that is used to center the "tripod".

On a side note: the use of a central bearing is part of an attempt to reduce the random jitters as the rollers will always be running on a constrained radius with no chance to build slack -on a micro-scale. It’s possibly more difficult for me to explain than for you to guess it.

Well, that's the plan.....

On 27/01/2020 at 07:56, Rusted said:

The more typical DIY habit of fixing pillow block bearings to a flat plate, or even plywood, is fraught with danger.
A flat plate, or even an inverted U-beam, are the weakest forms in twisting.

Can you elaborate on this?

I understand that the flanged bearing and "boxed" approach holds the inherent value of offering solid sides for the fork on the RA axis.

2 hours ago, Rusted said:

Have you tried loading it with the expected weight of the completed structure?
Roller bearings can completely change character when subject to loads.

No loading at all just yet as the SS track still needs to be machined. On top of that I'd like to properly sort out the position of the feet.

I'm going got minimize the distance between the contact point of the bearing and the feet themselves. Ideally they should be just below so that the bending stress and its deformation is minimized.  

Some update on the works on the bottom on the mount.

The 'tripod' is now (almost) completed enough to be tried out on the (almost) completed azimuth table.

The tripod has all bearings in place - at the end of each leg-  to run on a stainless steel track which is placed on the bottom side of the azimuth table.

It was just nice to see the whole thing spinning around....

What's left to do on this sub-assy? 

On the tripod it's the implementation of the drivetrain and sorting out a robust way to place the mount on 3 feet.
The azimuth table just needs the track to be properly prepared to function as a generous bearing - I'll come to that in one of the next post.

However, all of that was good enough for a first 'spin'. I uploaded the video on yt:

(btw does anybody know how to resize the video preview window? If it's even possible...)

Clear skies, Michele

12 hours ago, MarcusH said:

Oh, unlike you who has a finished and working mount, I am very much in early stages, i.e. lots of plans, ideas and parts but nothing finished. The challenge is to piece all together in a DIY friendly way.

Having access to SolidWorks, a 3D-printer, milling machines and lathes at work is a real boon. I quite like the way you did this write-up, first making the mount and then revealing it episode by episode.

But in all fairness, I think you could have kept us in more suspense by posting 1 episode / day. 😉

I hope to be in the same position as you are now by the end of summer / beginning of autumn. I might try to do a similar write-up if all goes well.

Marcus, c'mon show us at lest a sketch! The good part of a forum is that you can 1) collect a lot of ideas that you can consider for your project and 2) gather a bit of that collective feeling of social push to carry out your project.

Either way I'm sure you'll get a positive feedback regardless if you just sharing a sketch on this thread or start a new one

Clear skies, Michele

21 hours ago, Rusted said:

Anyway, I am going seriously off topic for your fascinating build thread.
Perhaps I should explain my design in a fresh DIY thread.

Yup, I think you should start a thread as your approach is fresh and it can easily inspire somebody else.

No worries for the topic - still relevant and  thnaks for the compliment.

Comments slowed down a bit - I wonder if people are waiting to see whether this is 'real' or not.....me too to be honest!

22 hours ago, Rusted said:

Hi,

No mention of my build on FLO. I usually blog and photograph all my projects to death.
The details are all there including my endless discussion of the design as it evolves in my mind.
I rarely bother with drawings and just make it up as I go along. I have a lathe and power tools.

The GEM uses multiple, tensioned, threaded rods [studs] in all three planes, to reinforce each other.
Only the longitudinal and cross studs are shown here. A similar set of studs run towards the camera.

They not only resist each other in compression of the flanged bearing boxes,
but all are carefully placed to contact each other to further resist bending.
These studs are all hidden within the bearing housing's 10mm thick, stressed aluminium plates.
The whole thing weighs "a ton" but was intended for permanent mounting on a solid pier.
I need a chain hoist to lift it as one unit.

It has AWR Goto drives. With multiple drive rates and full planetarium support via ASCOM. 
I am primarily a solar imager, these days, with a fast ZWO camera, so I don't need long exposures.
My long focus refractors 180/12 & 150/10 aren't very suitable for imaging the night sky anyway.
Other than the moon and planets of course.
 

I have to say that it's a very intriguing approach to GEM - I'll dig a bit in your blog.
I like the use of the bearing directly as part of the structure as well as boxing with Aluminium panels and rods.

7 hours ago, Rusted said:

Don't ignore the option of "furniture nuts." I use them all the time in my constructions. A couple of dozen on my big GEM alone.
These are of galvanized steel to avoid rust. A "gold" finish is optional but I wanted to match the aluminium.
The large, flat heads provide a tidy solution without needing load spreading washers and "Nyloc" nuts.
The hex socket doesn't mar easily no matter how often they are driven and removed.
You also have the option of putting a hex driver in a power tool for speedily applied torque.

I like this option when low profile - especially the fact that is low profile apart form the large head.

And I like your GEM too! To you have a thread where you decribe its construction? Can you track consistently for long exposure?

An element of the assembly that I hold dear is the connection of the components. A bad connection of just one of the element will preclude the chance to achieve the modal performance of the mirror box and the telescope itself.

The following is my interpretation of the joints we are extensively using on the pac-men and is works around to 2 main constraints:
  • the Pac-men material is a sandwich of foam and plywood
  • all the connecting element are thin walled Aluminum

Wrt sandwich construction the solution was to we carved out the foam and replaced with solid plywood in the areas where fixings were expected. Here is the picture where you can see few of them - some of these inserts have other function such as the manufacturing and assembly process. They improve the performance of the sandwich too.

Second challenge lays with thin walled profiles - from 1.5 to 2.0 mm. The load from the fixing tightening needs to be distributed to avoid sagging which spoils the ability to reach high bolt loads. Such deformation is obvious for thin Aluminium but it might be subtle yet relevant for steel as well.

So how to deal with that? 2 things: a generous steel washer under the bolt head/nut and a purposely built spacer to transfer the load through the hollow profile. Here is a picture of the rear main bar.

The option to bolt directly on the inner wall in contact with the pacman is far from ideal as it's cutting off some of the material from contributing to the stiffness.

Now to the actual joint – as it works on friction 2 main aspects are taken care of:

  • Contact area treatment
  • Bolt load

As per picture here below we’ve sanded down the surface to flatten it. Or better to secure that the contact pressure will be more evenly distributed.

Bolt load is tricky with a wood sandwich especially when the screw is inserted along the layers plan. As we would have to undo the joint several times even during the assembly tuning, we rules out wooden screws. What we opted for instead are these metric studs for wood. They can accommodate a nice M8 or M10 nut.

They come with an handy torx at the top.

A pilot hole 0.5mm smaller than the screw shank is drilled and some epoxy added in the hole to have a rock solid anchoring.
All of these allows high torque hence high “bolt” load which is transferred evenly through the profile and the pacman.

As always, thnaks for your attention - if you have any comment or if anything is not clear -which is likely!- I'll be please to answer.

Clear skies, Michele

On with the work on the mirror box.

This is just an assembly dry-run to sort out all those details that we've overlooked while producing the single components.

The main piece of work here is to fit some long M10 and M8 studs for wood, preparing the mating surfaces to maximise the contact area and to sort out the right washers.

All of this is to be able to tighten the fixing so that the structure shows its potential and it's not wobbly just because a fixing is not up to the task. With this minimal mirror box concept the structure is as strong as its weakest element or joint.

I attach a pic here and I've just uploaded a video on YT with a bit more details if you're interested:

On 14/01/2020 at 14:34, Gina said:

Errrrr... that's quite a big scope!  🤣

I have to admit that we were quite stunned by the stance of it when we pull it together.

Also, it was less than 10Kg so it felt weirdly light.

When looking at  that as just a sub-assy, the whole scope will look fairly ginormous.

 However my mind goes to the fact that the success of this project is not its size but rather its capability as an remotely controlled, robotizer imager - that's the big challange to me.