Well to answer this a little better...these direct drive units use harmonic drive mechanism that virtually eliminate backlash (they drive the axis directly ...no gear train) and also have very accurate encoders that can drive a scope so accurately that you probably don't need guiding.
Well that's the principle. I guess they should work but they haven't yet reached mainstream ..yet. Probably due to high costs. More here.
My original comment was referencing the original article,
not direct drives in general.
As others have posted, direct drives suitable for mounts are still
a tad expensive at present.
Again, the biggest step forwards here is in having encoders on
the output shaft, not the motor.
Having a good feedback loop tied to this is where the gains come from,
and even a std worm drive could probably achieve the specified positioning/driving tolerances with this sort of feedback.
What it needs is some young smarty-brains to design and develop a home-made direct drive mount from bits in his shed, then post pics and info in Forums like this.
Then we all say "Build me one too please"
Actually the Belt-drive system available for the EQ6 mount is probably good enough and would cost a whole lot less!
It works well, with zero backlash.
But if they can get mount drives to 8.38 million steps within a reasonable price it would be lovely.
What it needs is some young smarty-brains to design and develop a home-made direct drive mount from bits in his shed
One ( at least ) already did, ( tho i dont know how good it really is ) http://www.mda-telescoop.com/index.p...tpage&Itemid=1
IIRC there was a thread on this gizmo about a year back.
There was also a mob called NORTEK who did encoder mods
for Meades ( 14" and 16" ) to put absolute encoders on the output shafts.
Once you can get a true reading of the output shaft,
the drive mechanism,
ie direct drive, worm drive or water wheel powered clepsydra becomes irrelevant.
The clepsydra would probably have a prohibitively slow max slew speed tho
One ( at least ) already did, ( tho i dont know how good it really is ) http://www.mda-telescoop.com/index.p...tpage&Itemid=1
IIRC there was a thread on this gizmo about a year back.
There was also a mob called NORTEK who did encoder mods
for Meades ( 14" and 16" ) to put absolute encoders on the output shafts.
Once you can get a true reading of the output shaft,
the drive mechanism,
ie direct drive, worm drive or water wheel powered clepsydra becomes irrelevant.
The clepsydra would probably have a prohibitively slow max slew speed tho
Andrew
Absolutely amazing!
I have never heard of this product before!
Thanks for the link.
With the new Gemini II coming out for Losmandy mounts I will keep an eye out for an older well loved Titan Mount.
I would then replace the servos and gearboxes with harmonic drives. These have encoded servos and with a 100:1 harmonic drive the number of encoder pulses or resolution is 800,000 per rev of the output shaft. This corresponds to 800,000 per single worm turn which is 1.333r degrees of mount movement. This is 21.6 million for a full 360 degrees of mount movement.
Of course a stepper motor could be used with a harmonic drive or 'gearbox' and with a ratio of 100:1 a 200step motor would have 20,000 steps per worm rev before microstepping.
Harmonic drives have no backlash. They do have a small PE but that would disappear when divided by the worm ratio.
There is no 'correct' solution for drives and mounts. It is only the best that is affordable to us amateurs. Advances in drive technology and computers puts previously undreamt of precision within reach.
I looked into harmonic drive and direct drive when upgrading last year. In the end a Paramount ME was hard to beat. If I could have afford it, I would have brought this http://www.astelco.com/products/ntm/ntm.htm - NMT-500 direct drive. But it was a BIG unknown.
Fact is, for astroimaging and 95% of the other work I do, a rock solid GEM with "wheels and worms" was the way to go. Also, the majority of high end images out there use a bisque or AP mount and support from Daniel Bisque wonderful.
I looked into harmonic drive and direct drive when upgrading last year. In the end a Paramount ME was hard to beat. If I could have afford it, I would have brought this http://www.astelco.com/products/ntm/ntm.htm - NMT-500 direct drive. But it was a BIG unknown.
Fact is, for astroimaging and 95% of the other work I do, a rock solid GEM with "wheels and worms" was the way to go. Also, the majority of high end images out there use a bisque or AP mount and support from Daniel Bisque wonderful.
cheers
Terry
That's just going with what you know is the tried and true method (despite the flaws). Fact is the professionals use this type of drive and it's proven to be more accurate than worm geared systems. The stock standard EQ system is so widespread because it is fairly accurate and it's easy to produce and (relatively) cheap. Harmonic and direct drive systems are dear at present, so aren't as widespread.
The big unknown comes from the fact of its price and not having any confidence in if it'll work (for you). The manufacturers have to bring the prices down to allow for these drives to become more popular.
The Sitech Goto system can do pretty much the same thing, all you need is a Hi-res encoder on the RA Shaft. This Hi-res encoder is the expensive part, the cheaper version is about 400USD. But the beauty is that the Goto system already has the brains to use this encoder to improve perforamce. You dont need to buy a secondary controller to achieve it.
But here is what you can achive with it on a typical G-11
1.41 arc seconds p-p (almost the Seeing conditions of the night).
I think for the near future the above type of systems using Hi-res encoder feedback can improve exisiting system performance. While we wait for Direct Drive motors to be realized in a more ecconomical package.
That being said, DIY Direct Drive is live and kicking. And it was done in shed by a braniac.
The Sitech is a also the system used by the Planewave mounts, and has been tested (with modifcation) to run Direct Drive motors. This particular motor in the bellow link is a "Home made" direct drive made by Davd Rowe (more well known for the design of the CDK optics).
Yikes!
