Adapting a mount to work on an unstable platform

[scott_hurst]

In a few years, I'll be giving up the terrestrial life to live aboard a sailing yacht.  I had always planned to get a large Pelican case (or several) and pack a rig to take with me.  I'd then haul it ashore and it use it there in the conventional manner.  This has enormous appeal, as I intend to be a "world citizen" and live along the shores of every continent.  I'll get spend as much time as I like living at any reasonable latitude, North or South.  I've never spent much time with access to the Southern skies, and so far I've never brought a telescope along.

It occurs to me that the way a direct drive mount functions, with just a bit of modification and the additional of a high quality 3-axis gyro, other options might exist.  So, I hope to find out how hackable the DDM60 might be, or plant an idea in ASA's mind so that by the time I'm ready for it, such a product might exist.
 

Anyway, looking at the specs and design, it appears that the DDM 60 mount would be capable of AltAz operation with nothing more than a software update.  (Has this been done by anyone?  I've searched but so far failed to find it)  If the mount can be made to operate that way, it seems relatively straight forward to have the tracking computer subtract out the motion of a slow and gently rolling platform (the deck of a 60 foot sailboat sitting at anchor in a quiet harbor) fed to from a high quality solid-state gyro system.

The speed and strength of the direct drive design, coupled with the servo-like operation from the motor/computer/encoder system working in concert make this type of mount the ideal starting place for my dream... at least on paper.  The deck of a large boat at anchor is often so steady that it's impossible to perceive that is moving.  But no matter how steady it seems to be, it isn't steady enough to use a telescope on.

I don't image, even with a 3-axis gyro in the loop that it would be suitable for AP.  But if it could be made to work even for visual observing it would be an amazing thing.  It would be quite easy to have a deck plate mounted that would provide an easy, rapid, and very secure way to erect a sturdy observing pier.  And I imagine I would get a great deal more observing done without being required to haul it all ashore and find a suitable location each time.  This is especially true when the darkest harbors will frequently be completely unimproved.
 
It might be a silly dream, but there you have it.

 

Edited August 3, 2015 by scott_hurst

[scott_hurst]

Ideally, I'd be able to flip back into equatorial mode if I decide to go ashore and do something more serious.

[MarkS]

Apart from the rolling platform, a boat at anchor will also swing, so you would have to address the PA problem....

 

Mark

[scott_hurst]

That was the whole point of running it in AltAz mode, so that PA wouldn't be an issue.

[MarkS]

Clearly I'm too new at this game to know enough about AltAz!!!

 

Assuming the AltAz operation can be organised, it may come down to the response rate capabilities of the DDM 60 with whatever the mass loading is. In normal operation, I allow >5sec settling time after a slew, but I've never chased tight tuning parameters for slewing..... Clearly, though, there'd be a limit on roll rate of the boat.

 

Interesting proposition!

 

Mark

[scott_hurst]

The mass would want to stay still, naturally.  So, it should actually help the drive motors.
 
I've never seen or played with one of these mounts, so I'm super curious.  But reading things like this in their literature, "Software compensation of telescope hysteresis" and "Actually the normal tracking operations disrupted by a momentary gust of wind will be quickly and easily compensated with this technology." it sounds as if they can react very quickly.

As I mentioned above, "The deck of a large boat at anchor is often so steady that it's impossible to perceive that is moving."  It wouldn't have to work terribly hard.
 
Another option is to use a conventional mount on a gyro stabilized platform.  That could be technically simple, but mechanically bulky/heavy/impractical for the space I expect to have available.  I know that can be done beautifully, I've played pool/billiards on a gryo stabilized table on a significantly rocking cruise ship.  It was perfect. 

Here is a clip on youtube clip of even worse conditions than I experienced.  (presuming they allow this link to post)  https://www.youtube.com/watch?v=hieWwnWrzCw

Doing it via a the mount and solid-state gyro feedback seem much more practical given the weight and space limitations I'll have.  I mean, this will not be able to be left in place on the deck, but taken down after each use.  A gyro stabilized platform large enough to carry a mount and scope would probably be pretty challenging to do this with.

I was a RADAR tech in former life and currently a software developer.  I'd be a prime candidate to do this kind of modification, if the schematics and source code are available.  But I'd much rather buy it already tested and working. 

 

[MarkS]

The drive motors will still have to move the scope relative to the base. I have no idea what the dynamics of that situation would be. Provided the system is very well balanced ( the DDM 60 is VERY particular about that!) maybe the load will be low.

 

The DDM 60 is pretty good coping with a gusty breeze - I've relied on this fact often.

 

As to the software - that's a question for ASA.

 

Mark

[scott_hurst]

"The drive motors will still have to move the scope relative to the base."
 
Imagine a scope sitting on an inert mount with no power and completely freewheeling axes.  With perfect (impossible) frictionless bearings on each axis, the mount could be moved all around and the scope would not move at all.  The inertia of the scope would take care of it.
 

The forces involved for the motors would be very close to zero.  They would merely be allowing  the scope to stay in its orientation relative to the Earth.  They would actually be "relaxing" to allow the mount to move without moving the scope.  This is basic physics.  Newton's first law of motion.  Inertia would/could do all the work, so long as the mount can be "prevented from interfering".

And the published slew rate is many fold faster than would be required to track the gentle movements of a large (ish) sailboat at anchor.


 

Edited August 5, 2015 by scott_hurst

[scott_hurst]

"As to the software - that's a question for ASA."

I was rather hoping that ASA took a look in here on occasion and might chime in.  If that doesn't happen, I'll role this all up into a message and figure out who to send it to within the company.

 

[admin]

Hello,

 

Dietmar is currently on holidays, but I'm sure he will give feedback when he's back

 

BR,

Michael