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tech / sci.astro.amateur / Re: Harmonic drives. Period error. WTF???!

SubjectAuthor
* Harmonic drives. Period error. WTF???!RichA
+- Re: Harmonic drives. Period error. WTF???!fred k. engels®
+* Re: Harmonic drives. Period error. WTF???!StarDust
|`* Re: Harmonic drives. Period error. WTF???!RichA
| `* Re: Harmonic drives. Period error. WTF???!StarDust
|  `* Re: Harmonic drives. Period error. WTF???!RichA
|   `- Re: Harmonic drives. Period error. WTF???!StarDust
+* Re: Harmonic drives. Period error. WTF???!Chris L Peterson
|`- Re: Harmonic drives. Period error. WTF???!fred k. engels®
`* Re: Harmonic drives. Period error. WTF???!Martin Brown
 `* Re: Harmonic drives. Period error. WTF???!Chris L Peterson
  `* Re: Harmonic drives. Period error. WTF???!RichA
   `* Re: Harmonic drives. Period error. WTF???!Chris L Peterson
    `* Re: Harmonic drives. Period error. WTF???!RichA
     `* Re: Harmonic drives. Period error. WTF???!Chris L Peterson
      `* Re: Harmonic drives. Period error. WTF???!RichA
       `- Re: Harmonic drives. Period error. WTF???!Chris L Peterson

1
Harmonic drives. Period error. WTF???!

<4f7a1489-baf2-4fb6-9b2d-41e04902a37en@googlegroups.com>

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Subject: Harmonic drives. Period error. WTF???!
From: rander3...@gmail.com (RichA)
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 by: RichA - Mon, 27 Dec 2021 18:36 UTC

I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??

Re: Harmonic drives. Period error. WTF???!

<sqd74i$cu5$1@gioia.aioe.org>

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From: kengels....@realKeP20vens.house (fred k. engels®)
Newsgroups: sci.astro.amateur
Subject: Re: Harmonic drives. Period error. WTF???!
Date: Mon, 27 Dec 2021 12:19:28 -0800
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 by: fred k. engels® - Mon, 27 Dec 2021 20:19 UTC

Prime Minister Justin Blackface just tweeted
So, How's that pretty picture astro photography horseshit® working out for
ya?
The Ruscoms have just launched another massive satellite into
orbit!!!!!!!!!!!!!!!!!!!

https://www.youtube.com/watch?v=4EoAHdwGBvU

Re: Harmonic drives. Period error. WTF???!

<410f67cf-2b0e-4463-9752-6ff4b72f05een@googlegroups.com>

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Subject: Re: Harmonic drives. Period error. WTF???!
From: csok...@gmail.com (StarDust)
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 by: StarDust - Mon, 27 Dec 2021 22:35 UTC

On Monday, December 27, 2021 at 10:36:51 AM UTC-8, RichA wrote:
> I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??

What were you expecting?
Zero?
🤔

Re: Harmonic drives. Period error. WTF???!

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Subject: Re: Harmonic drives. Period error. WTF???!
From: rander3...@gmail.com (RichA)
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 by: RichA - Tue, 28 Dec 2021 03:23 UTC

On Monday, 27 December 2021 at 17:35:39 UTC-5, StarDust wrote:
> On Monday, December 27, 2021 at 10:36:51 AM UTC-8, RichA wrote:
> > I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??
> What were you expecting?
> Zero?
> 🤔

More like 5 or less.

Re: Harmonic drives. Period error. WTF???!

<441a66f1-a574-4cdd-a865-a161c3d156d9n@googlegroups.com>

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Subject: Re: Harmonic drives. Period error. WTF???!
From: csok...@gmail.com (StarDust)
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 by: StarDust - Tue, 28 Dec 2021 03:39 UTC

On Monday, December 27, 2021 at 7:23:28 PM UTC-8, RichA wrote:
> On Monday, 27 December 2021 at 17:35:39 UTC-5, StarDust wrote:
> > On Monday, December 27, 2021 at 10:36:51 AM UTC-8, RichA wrote:
> > > I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??
> > What were you expecting?
> > Zero?
> > 🤔
> More like 5 or less.

Vixen GPDX mount gets less than 5!

Re: Harmonic drives. Period error. WTF???!

<70de25b1-c310-4dff-bd6e-393fb84a12ecn@googlegroups.com>

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Subject: Re: Harmonic drives. Period error. WTF???!
From: rander3...@gmail.com (RichA)
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 by: RichA - Tue, 28 Dec 2021 12:39 UTC

On Monday, 27 December 2021 at 22:39:06 UTC-5, StarDust wrote:
> On Monday, December 27, 2021 at 7:23:28 PM UTC-8, RichA wrote:
> > On Monday, 27 December 2021 at 17:35:39 UTC-5, StarDust wrote:
> > > On Monday, December 27, 2021 at 10:36:51 AM UTC-8, RichA wrote:
> > > > I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??
> > > What were you expecting?
> > > Zero?
> > > 🤔
> > More like 5 or less.
> Vixen GPDX mount gets less than 5

Pretty good given the gear size.

Re: Harmonic drives. Period error. WTF???!

<rr7msgh61n5banmpv4nejo56lumnm32rm0@4ax.com>

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From: clp...@alumni.caltech.edu (Chris L Peterson)
Newsgroups: sci.astro.amateur
Subject: Re: Harmonic drives. Period error. WTF???!
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 by: Chris L Peterson - Tue, 28 Dec 2021 14:31 UTC

On Mon, 27 Dec 2021 10:36:50 -0800 (PST), RichA <rander3128@gmail.com>
wrote:

>I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??

Why not? Modern drives don't need to eliminate PE, they need to ensure
that it's consistent and definable. Modern drives have ZERO periodic
error because it is removed by the control system.

Uncorrected PE isn't a terribly useful concept.

Re: Harmonic drives. Period error. WTF???!

<sqfvn0$suo$1@gioia.aioe.org>

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From: '''newsp...@nonad.co.uk (Martin Brown)
Newsgroups: sci.astro.amateur
Subject: Re: Harmonic drives. Period error. WTF???!
Date: Tue, 28 Dec 2021 21:31:11 +0000
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 by: Martin Brown - Tue, 28 Dec 2021 21:31 UTC

On 27/12/2021 18:36, RichA wrote:

> I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??

Most are operated on closed loop guiding so provided that it is regular
and systematic the periodic error can be corrected out. The main PEC
component can be trained out by lookup table in some circumstances.

Why make the mechanical precision so much more difficult and expensive
to manufacture when CCD autoguiders are cheap and getting cheaper?

--
Regards,
Martin Brown

Re: Harmonic drives. Period error. WTF???!

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Subject: Re: Harmonic drives. Period error. WTF???!
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 by: Chris L Peterson - Tue, 28 Dec 2021 22:07 UTC

On Tue, 28 Dec 2021 21:31:11 +0000, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:

>On 27/12/2021 18:36, RichA wrote:
>
>> I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??
>
>Most are operated on closed loop guiding so provided that it is regular
>and systematic the periodic error can be corrected out. The main PEC
>component can be trained out by lookup table in some circumstances.
>
>Why make the mechanical precision so much more difficult and expensive
>to manufacture when CCD autoguiders are cheap and getting cheaper?

Lately, the best mounts have included absolute encoders with
sub-arcsecond precision, so mechanical errors in the drive system
don't even need to be regular or systematic!

Re: Harmonic drives. Period error. WTF???!

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Subject: Re: Harmonic drives. Period error. WTF???!
From: csok...@gmail.com (StarDust)
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 by: StarDust - Tue, 28 Dec 2021 23:18 UTC

On Tuesday, December 28, 2021 at 4:39:07 AM UTC-8, RichA wrote:
> On Monday, 27 December 2021 at 22:39:06 UTC-5, StarDust wrote:
> > On Monday, December 27, 2021 at 7:23:28 PM UTC-8, RichA wrote:
> > > On Monday, 27 December 2021 at 17:35:39 UTC-5, StarDust wrote:
> > > > On Monday, December 27, 2021 at 10:36:51 AM UTC-8, RichA wrote:
> > > > > I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??
> > > > What were you expecting?
> > > > Zero?
> > > > 🤔
> > > More like 5 or less.
> > Vixen GPDX mount gets less than 5
> Pretty good given the gear size.

Precision ground!
Not machined!

Re: Harmonic drives. Period error. WTF???!

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From: kengels....@realKeP20vens.house (fred k. engels®)
Newsgroups: sci.astro.amateur
Subject: Re: Harmonic drives. Period error. WTF???!
Date: Thu, 30 Dec 2021 15:49:14 -0800
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 by: fred k. engels® - Thu, 30 Dec 2021 23:49 UTC

WONDERFUL NEWS!!!!!!!!!!!
Prime Minister Justin Blackface just tweeted condolences that

The Iranian Hostage Makers have just has suffered another Hostage Making
failure.

Iran's Hostage rocket lifted off from the Khomeini Hostage Makers Space
Centre and no Iranian Hostage Making objects have been detected in orbit.

https://www.youtube.com/watch?v=A8bC1DEYbI4

Re: Harmonic drives. Period error. WTF???!

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Subject: Re: Harmonic drives. Period error. WTF???!
From: rander3...@gmail.com (RichA)
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 by: RichA - Fri, 31 Dec 2021 17:37 UTC

On Tuesday, 28 December 2021 at 17:07:57 UTC-5, Chris L Peterson wrote:
> On Tue, 28 Dec 2021 21:31:11 +0000, Martin Brown
> <'''newspam'''@nonad.co.uk> wrote:
>
> >On 27/12/2021 18:36, RichA wrote:
> >
> >> I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??
> >
> >Most are operated on closed loop guiding so provided that it is regular
> >and systematic the periodic error can be corrected out. The main PEC
> >component can be trained out by lookup table in some circumstances.
> >
> >Why make the mechanical precision so much more difficult and expensive
> >to manufacture when CCD autoguiders are cheap and getting cheaper?
> Lately, the best mounts have included absolute encoders with
> sub-arcsecond precision, so mechanical errors in the drive system
> don't even need to be regular or systematic!

Yes, it increases the price of mount by at least a 1/3 to have those encoders.

Re: Harmonic drives. Period error. WTF???!

<57jusg93dg4268fn7tni5f2g2phcb9m4o3@4ax.com>

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From: clp...@alumni.caltech.edu (Chris L Peterson)
Newsgroups: sci.astro.amateur
Subject: Re: Harmonic drives. Period error. WTF???!
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 by: Chris L Peterson - Fri, 31 Dec 2021 18:34 UTC

On Fri, 31 Dec 2021 09:37:51 -0800 (PST), RichA <rander3128@gmail.com>
wrote:

>On Tuesday, 28 December 2021 at 17:07:57 UTC-5, Chris L Peterson wrote:
>> On Tue, 28 Dec 2021 21:31:11 +0000, Martin Brown
>> <'''newspam'''@nonad.co.uk> wrote:
>>
>> >On 27/12/2021 18:36, RichA wrote:
>> >
>> >> I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??
>> >
>> >Most are operated on closed loop guiding so provided that it is regular
>> >and systematic the periodic error can be corrected out. The main PEC
>> >component can be trained out by lookup table in some circumstances.
>> >
>> >Why make the mechanical precision so much more difficult and expensive
>> >to manufacture when CCD autoguiders are cheap and getting cheaper?
>> Lately, the best mounts have included absolute encoders with
>> sub-arcsecond precision, so mechanical errors in the drive system
>> don't even need to be regular or systematic!
>
>Yes, it increases the price of mount by at least a 1/3 to have those encoders.

The price is dropping. In ten years such control systems will be
routine on most decent mounts. It's the obvious way to go.

Re: Harmonic drives. Period error. WTF???!

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Subject: Re: Harmonic drives. Period error. WTF???!
From: rander3...@gmail.com (RichA)
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 by: RichA - Sun, 2 Jan 2022 07:20 UTC

On Friday, 31 December 2021 at 13:34:13 UTC-5, Chris L Peterson wrote:
> On Fri, 31 Dec 2021 09:37:51 -0800 (PST), RichA <rande...@gmail.com>
> wrote:
> >On Tuesday, 28 December 2021 at 17:07:57 UTC-5, Chris L Peterson wrote:
> >> On Tue, 28 Dec 2021 21:31:11 +0000, Martin Brown
> >> <'''newspam'''@nonad.co.uk> wrote:
> >>
> >> >On 27/12/2021 18:36, RichA wrote:
> >> >
> >> >> I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??
> >> >
> >> >Most are operated on closed loop guiding so provided that it is regular
> >> >and systematic the periodic error can be corrected out. The main PEC
> >> >component can be trained out by lookup table in some circumstances.
> >> >
> >> >Why make the mechanical precision so much more difficult and expensive
> >> >to manufacture when CCD autoguiders are cheap and getting cheaper?
> >> Lately, the best mounts have included absolute encoders with
> >> sub-arcsecond precision, so mechanical errors in the drive system
> >> don't even need to be regular or systematic!
> >
> >Yes, it increases the price of mount by at least a 1/3 to have those encoders.
> The price is dropping. In ten years such control systems will be
> routine on most decent mounts. It's the obvious way to go.

Telescope ones must be quite high-end as you can buy absolute encoders for small robots for $10.00, which technically is
cheaper than the old HP rotary encoders.

Re: Harmonic drives. Period error. WTF???!

<ita3tg5bq9fmpsnrcr0it3ng4106qebtjo@4ax.com>

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From: clp...@alumni.caltech.edu (Chris L Peterson)
Newsgroups: sci.astro.amateur
Subject: Re: Harmonic drives. Period error. WTF???!
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 by: Chris L Peterson - Sun, 2 Jan 2022 13:44 UTC

On Sat, 1 Jan 2022 23:20:23 -0800 (PST), RichA <rander3128@gmail.com>
wrote:

>On Friday, 31 December 2021 at 13:34:13 UTC-5, Chris L Peterson wrote:
>> On Fri, 31 Dec 2021 09:37:51 -0800 (PST), RichA <rande...@gmail.com>
>> wrote:
>> >On Tuesday, 28 December 2021 at 17:07:57 UTC-5, Chris L Peterson wrote:
>> >> On Tue, 28 Dec 2021 21:31:11 +0000, Martin Brown
>> >> <'''newspam'''@nonad.co.uk> wrote:
>> >>
>> >> >On 27/12/2021 18:36, RichA wrote:
>> >> >
>> >> >> I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??
>> >> >
>> >> >Most are operated on closed loop guiding so provided that it is regular
>> >> >and systematic the periodic error can be corrected out. The main PEC
>> >> >component can be trained out by lookup table in some circumstances.
>> >> >
>> >> >Why make the mechanical precision so much more difficult and expensive
>> >> >to manufacture when CCD autoguiders are cheap and getting cheaper?
>> >> Lately, the best mounts have included absolute encoders with
>> >> sub-arcsecond precision, so mechanical errors in the drive system
>> >> don't even need to be regular or systematic!
>> >
>> >Yes, it increases the price of mount by at least a 1/3 to have those encoders.
>> The price is dropping. In ten years such control systems will be
>> routine on most decent mounts. It's the obvious way to go.
>
>Telescope ones must be quite high-end as you can buy absolute encoders for small robots for $10.00, which technically is
>cheaper than the old HP rotary encoders.

Absolute encoders with several hundred thousand count resolution still
run hundreds of dollars, which obviously adds a lot to the cost.
There's a workaround using lower resolution encoders with gear systems
to get the high count. This requires precision gears, but they are low
torque and preloaded, which makes them much less expensive than
precision ground drive gears.

Re: Harmonic drives. Period error. WTF???!

<13be2dca-40d6-4f33-b281-048cffc1d9e5n@googlegroups.com>

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Subject: Re: Harmonic drives. Period error. WTF???!
From: rander3...@gmail.com (RichA)
Injection-Date: Sun, 02 Jan 2022 16:07:51 +0000
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 by: RichA - Sun, 2 Jan 2022 16:07 UTC

On Sunday, 2 January 2022 at 08:44:54 UTC-5, Chris L Peterson wrote:
> On Sat, 1 Jan 2022 23:20:23 -0800 (PST), RichA <rande...@gmail.com>
> wrote:
>
> >On Friday, 31 December 2021 at 13:34:13 UTC-5, Chris L Peterson wrote:
> >> On Fri, 31 Dec 2021 09:37:51 -0800 (PST), RichA <rande...@gmail.com>
> >> wrote:
> >> >On Tuesday, 28 December 2021 at 17:07:57 UTC-5, Chris L Peterson wrote:
> >> >> On Tue, 28 Dec 2021 21:31:11 +0000, Martin Brown
> >> >> <'''newspam'''@nonad.co.uk> wrote:
> >> >>
> >> >> >On 27/12/2021 18:36, RichA wrote:
> >> >> >
> >> >> >> I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??
> >> >> >
> >> >> >Most are operated on closed loop guiding so provided that it is regular
> >> >> >and systematic the periodic error can be corrected out. The main PEC
> >> >> >component can be trained out by lookup table in some circumstances.
> >> >> >
> >> >> >Why make the mechanical precision so much more difficult and expensive
> >> >> >to manufacture when CCD autoguiders are cheap and getting cheaper?
> >> >> Lately, the best mounts have included absolute encoders with
> >> >> sub-arcsecond precision, so mechanical errors in the drive system
> >> >> don't even need to be regular or systematic!
> >> >
> >> >Yes, it increases the price of mount by at least a 1/3 to have those encoders.
> >> The price is dropping. In ten years such control systems will be
> >> routine on most decent mounts. It's the obvious way to go.
> >
> >Telescope ones must be quite high-end as you can buy absolute encoders for small robots for $10.00, which technically is
> >cheaper than the old HP rotary encoders.
> Absolute encoders with several hundred thousand count resolution still
> run hundreds of dollars, which obviously adds a lot to the cost.
> There's a workaround using lower resolution encoders with gear systems
> to get the high count. This requires precision gears, but they are low
> torque and preloaded, which makes them much less expensive than
> precision ground drive gears.

Part of the reason I believe we pay so much for this stuff is that they are (like most machine parts like bearings) mostly
designed for endurance at high RPM's. Which isn't what telescope drives/mounts are. Pity.

Re: Harmonic drives. Period error. WTF???!

<3ck3tg1rv913tu345tr858e1bmst0ffiob@4ax.com>

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From: clp...@alumni.caltech.edu (Chris L Peterson)
Newsgroups: sci.astro.amateur
Subject: Re: Harmonic drives. Period error. WTF???!
Message-ID: <3ck3tg1rv913tu345tr858e1bmst0ffiob@4ax.com>
References: <4f7a1489-baf2-4fb6-9b2d-41e04902a37en@googlegroups.com> <sqfvn0$suo$1@gioia.aioe.org> <cj2nsgh66altdsoisoj23bk2nurhv9fahq@4ax.com> <6629dd3e-86f9-47a6-bc0c-cabcd10f1504n@googlegroups.com> <57jusg93dg4268fn7tni5f2g2phcb9m4o3@4ax.com> <e49a824c-1b63-4167-a72c-14f843f82d16n@googlegroups.com> <ita3tg5bq9fmpsnrcr0it3ng4106qebtjo@4ax.com> <13be2dca-40d6-4f33-b281-048cffc1d9e5n@googlegroups.com>
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 by: Chris L Peterson - Sun, 2 Jan 2022 16:26 UTC

On Sun, 2 Jan 2022 08:07:51 -0800 (PST), RichA <rander3128@gmail.com>
wrote:

>On Sunday, 2 January 2022 at 08:44:54 UTC-5, Chris L Peterson wrote:
>> On Sat, 1 Jan 2022 23:20:23 -0800 (PST), RichA <rande...@gmail.com>
>> wrote:
>>
>> >On Friday, 31 December 2021 at 13:34:13 UTC-5, Chris L Peterson wrote:
>> >> On Fri, 31 Dec 2021 09:37:51 -0800 (PST), RichA <rande...@gmail.com>
>> >> wrote:
>> >> >On Tuesday, 28 December 2021 at 17:07:57 UTC-5, Chris L Peterson wrote:
>> >> >> On Tue, 28 Dec 2021 21:31:11 +0000, Martin Brown
>> >> >> <'''newspam'''@nonad.co.uk> wrote:
>> >> >>
>> >> >> >On 27/12/2021 18:36, RichA wrote:
>> >> >> >
>> >> >> >> I'm seeing PE of 10 arc seconds, on $4000+ mounts? Is that real??
>> >> >> >
>> >> >> >Most are operated on closed loop guiding so provided that it is regular
>> >> >> >and systematic the periodic error can be corrected out. The main PEC
>> >> >> >component can be trained out by lookup table in some circumstances.
>> >> >> >
>> >> >> >Why make the mechanical precision so much more difficult and expensive
>> >> >> >to manufacture when CCD autoguiders are cheap and getting cheaper?
>> >> >> Lately, the best mounts have included absolute encoders with
>> >> >> sub-arcsecond precision, so mechanical errors in the drive system
>> >> >> don't even need to be regular or systematic!
>> >> >
>> >> >Yes, it increases the price of mount by at least a 1/3 to have those encoders.
>> >> The price is dropping. In ten years such control systems will be
>> >> routine on most decent mounts. It's the obvious way to go.
>> >
>> >Telescope ones must be quite high-end as you can buy absolute encoders for small robots for $10.00, which technically is
>> >cheaper than the old HP rotary encoders.
>> Absolute encoders with several hundred thousand count resolution still
>> run hundreds of dollars, which obviously adds a lot to the cost.
>> There's a workaround using lower resolution encoders with gear systems
>> to get the high count. This requires precision gears, but they are low
>> torque and preloaded, which makes them much less expensive than
>> precision ground drive gears.
>
>Part of the reason I believe we pay so much for this stuff is that they are (like most machine parts like bearings) mostly
>designed for endurance at high RPM's. Which isn't what telescope drives/mounts are. Pity.

Absolute encoders are almost exclusively used in low speed
applications, though. They are expensive because their limited market
can bear it, not because they need to be. They use the same technology
as found in digital calipers, which you can pick up for $20 and
typically deliver 50,000 counts or more over a 6" length of tape.

1
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