future of mount tech

[Somnium (Aidan)]

While researching what to spend my money on, turning grey and generally ageing considerably over my choices, i have been thinking about the future of mount technology. systems like autoguiding, goto, computer operation etc, have made their way to relatively inexpensive mounts. i can't help but thinking that the next big step will be a move to direct drive. it seems like a no brainer, you eliminate any mechanical PE, have complete knowledge of the mount location at all times etc. what does everyone think? 5 years down the track will there be an eq10 with direct drive?

[AndrewJ]

Gday Aidan

i can't help but thinking that the next big step will be a move to direct drive.

Direct drive is essentially just a big stepper, and will have a minimal gain ( at arcsec resolution ) without high quality encoders as well.

The big advances will be gained as absolute encoder technology matures and becomes cheaper/simpler to setup and use.

you eliminate any mechanical PE

Again, at the arcsec level, you can reduce, but not eliminate errors ( both periodoc and non periodic ), as all mechanical devices are built to tolerances.
Errors in fabrication of the poles of the motor, will affect its use without encoders and errors in the etching of the encoders themselves will result in errors in the final position.
Just do the math to see what 1 arcsecond of error is on say
a 5" dia encoder disk, and then factor in thermal stability,
eccentricity in mounting, flexure etc etc. Its not trivial.
There sure are ways to get the errors down low, but in the end, it gets down to a cost benefit equation as the tolerances drop and the costs skyrocket.

Andrew

[gregbradley]

I am not sure of the difference between Direct Drive and Encoders. I assumed they were the same thing.

AP's absolute encoders are promoted as removing PE completely (I think down to .2 of arc sec or less) and they have examples of 10 minute unguided perfectly round stars on their site.

They don't exaggerate their claims.

Cost would be an inhibiting factor as these cost about AUD$6000 on one axis and less on the other. So something like AUD$10,000 to $12,000 at the moment.

Its one reason why I chose an AP1600 as it is user upgradable in the field to install these encoders. At some point in the future I'll probably go for that.

It seems inevitable that these will be cheaper for all mounts as Chinese manufacturers make their products more sophisticated.
Just like RC scopes used to be multi thousand dollar scopes until just a few years ago.
Greg.

[AndrewJ]

Gday Greg

I am not sure of the difference between Direct Drive and Encoders. I assumed they were the same thing.

Nope
Direct drive is essentially a type of motor design, where the output axle of the motor IS the RA ( or DEC ) axle, ie no gears, no worms etc, but it still needs to be driven accurately, and hence still needs a feedback loop for very precise positioning.
The encoder is part of the feedback mechanism that tells the motor drive system where the motor is currently pointing, and it is the accuracy of the encoder, ( and its integration into the mounts drive system ), that makes the difference in overall system accuracy.

AP's absolute encoders are promoted as removing PE completely (I think down to .2 of arc sec or less)

I would want to see some real raw data on that first.
Ie look at the new IOPTron CEM60EC mounts that touted something similar.
These still use a stepper driving a timing belt reduction then worm/wormwheel, but have an encoder on the output axle. The encoder is what controls the systems "basic" accuracy.
Lots of threads on CN have looked at how well this works, and show up some of the difficulties in getting it all to work together.
ie it tracks very well from a "normal" PE perspective ( with a very low rms ), but it has a very high freq 2-3arcsec ripple ( that is an artifact of the encoder reading code ), superimposed on its generally very "flat" playback , so doesnt get the absolute best out of its feedback system ( yet ).
That said, no amount of accuracy in the encoders etc can account for variable refraction and flexure, so its again a tradeoff of accuracy vs cost for unguided vs lower accuracy/cost and guiding.

Andrew

[LewisM]

""Future" has been around a few years now: http://www.astrosysteme.at/eng/mount_ddm60.html

Also available as the 85 and 160 - will handle large weights. Been available in Australia through Astronomy Alive in Melbourne for almost as long as they have been available.

[gregbradley]

Thanks Andrew for explaining how direct drive works.

Interesting about the new mount. Software Bisque mounts also use a drive belt that runs other gears. The PME 11 can be fitted with encoders but it has to be at the time of ordering.

Here is the link for the Astrophysics encoders with sample images:

http://www.astro-physics.com/index.h...ducts/products

From what little I have heard about it they work. Unguided works on most parts of the sky so I guess that implies you may need to autoguide on the other parts.

I believe it. My AP1600 when going along with an autoguider with PEC at around half an arc sec some of the time ( almost half the time) and at about 1.5 arc seconds briefly. The bulk of the guide graph is around 1 arc sec. Average last time I used it was 1.2 arc secs of error. Without PEC it was about 3.5 arc secs. Much like a good PME.

Greg.

[Somnium (Aidan)]

Originally Posted by LewisM

""Future" has been around a few years now: http://www.astrosysteme.at/eng/mount_ddm60.html

Also available as the 85 and 160 - will handle large weights. Been available in Australia through Astronomy Alive in Melbourne for almost as long as they have been available.

Hi Lewis, i am familiar with ASA and their technology, just wondering if more manufacturers are going to get into this game. planewave have done a bit with their fork mount. the question really was are we likely to see this as the next move for some of the cheaper mounts, the skywatchers/Orion's of the world rather than being upwards of 20k

[uwahl (Ulrich)]

What I would like to see is a portable mount that, once placed on the ground reads an internal GPS, levels itself and points its RA axis to the pole while I do other things.

[Somnium (Aidan)]

Originally Posted by uwahl

What I would like to see is a portable mount that, once placed on the ground reads an internal GPS, levels itself and points its RA axis to the pole while I do other things.

You would think that sort of thing wouldn't be too difficult in a mount like the azeq6. You would need an inbuilt compas, gps and accelerometer then it is just a software issue, although you would probably want to incorporate plate solving to make it really accurate .

[el_draco (Rom)]

The no brainer is adaptive optics. The stuff out there now is pretty basic. I suspect we'll be be getting super dooper clarity eventually. Mounts are already capable of very precise tracking. M2CW

[Somnium (Aidan)]

Originally Posted by el_draco

The no brainer is adaptive optics. The stuff out there now is pretty basic. I suspect we'll be be getting super dooper clarity eventually. Mounts are already capable of very precise tracking. M2CW

you talking about full frame adaptive optics ? or just AO for guiding. because AO for a large field would require complicated mirror flexing i would imagine.