ASTRO: Question on STL filter wheel

"Jonathan Silverlight"
wrote in message ...
In message , Richard Crisp
writes

using those goofy friction drives is just being cheap
when you can use a toothed drive that never slips in my opinion as a
long
time design engineer.


Weird coincidence department - I'm having exactly the same problem in my
day job with a microplate reader (used in medical research).
They allegedly went from a gear system to friction drive because
customers complained about the noise, but why they didn't use a stepper
motor or an encoder to make sure the wheel is in the right place escapes
me.
Yes.
It is wrong to 'fault' the drive as such. The friction drive system, is
'good', in not introducing vibration, and giving a potentially smooth
transport. Some very upmarket equipment uses them for exactly this reason.
Where the units being discussed 'fail', is in not detecting that slippage
is occurring. I did a system a while ago, with such drives. The 'best'
were friction drives, followed by toothed belt drives, with gears in last
place, for the particular requirement of a 'cogging free' drive system.
However we elected to use magnetic sensors for each 'stop' location
(double detector for the 'home'), with detection of the exact stop
location, and error reporting, if the drive was failing to position as
required. This has been trouble free.
The fault in both the system you describe, and the SBIG system, is in not
adding position detection for the intermediate locations, with enough
inteligence to tweak the movement, and give a report if more than a small
error occurs.

Best Wishes

"Roger Hamlett" wrote in message
...

"Jonathan Silverlight"
wrote in message ...
In message , Richard Crisp
writes

using those goofy friction drives is just being cheap
when you can use a toothed drive that never slips in my opinion as a long
time design engineer.


Weird coincidence department - I'm having exactly the same problem in my
day job with a microplate reader (used in medical research).
They allegedly went from a gear system to friction drive because
customers complained about the noise, but why they didn't use a stepper
motor or an encoder to make sure the wheel is in the right place escapes
me.
Yes.
It is wrong to 'fault' the drive as such. The friction drive system, is
'good', in not introducing vibration, and giving a potentially smooth
transport. Some very upmarket equipment uses them for exactly this reason.
Where the units being discussed 'fail', is in not detecting that slippage
is occurring. I did a system a while ago, with such drives. The 'best'
were friction drives, followed by toothed belt drives, with gears in last
place, for the particular requirement of a 'cogging free' drive system.
However we elected to use magnetic sensors for each 'stop' location
(double detector for the 'home'), with detection of the exact stop
location, and error reporting, if the drive was failing to position as
required. This has been trouble free.
The fault in both the system you describe, and the SBIG system, is in not
adding position detection for the intermediate locations, with enough
inteligence to tweak the movement, and give a report if more than a small
error occurs.


it seems whenever you look closely at anything they have designed in the
past few years that it is really easy to find fault and it really isn't that
hard to do it right

regarding vibration it isn't much of an issue for the filter wheel since you
don't have the shutter open at the time of the wheel rotating and you can
always wait a few seconds for any motion to damp out once the carousel has
indexed properly



Best Wishes

"Rick Johnson" wrote
...
The filter wheel in my STL camera has suddenly decided to position the lum
filter at random.........

Any ideas?


Rick,

One time while packing for vacation I was too lazy to take the nose piece
off the STL-1301 and just jammed the case down hard on the camera. I had had
no problem with doing that before, but this time the filter wheel would not
properly position at all. After I took the cover off and put it back on and
then shook the camera the wheel went back to acting normally. So, perhaps
something with your cold weather has got the wheel jammed up a little. Try
taking it out and putting it back in.

The filter wheel with my ST-9 leaves the IR LED on after some moves so I
have to unplug the filter wheel after each move before taking an image. The
camera is too old to bother fixing. SBIG has no idea why it does this.

George N

"Richard Crisp" wrote in message
. net...

"Roger Hamlett" wrote in message
...

"Jonathan Silverlight"
wrote in message ...
In message , Richard
Crisp writes

using those goofy friction drives is just being cheap
when you can use a toothed drive that never slips in my opinion as a
long
time design engineer.


Weird coincidence department - I'm having exactly the same problem in
my day job with a microplate reader (used in medical research).
They allegedly went from a gear system to friction drive because
customers complained about the noise, but why they didn't use a
stepper motor or an encoder to make sure the wheel is in the right
place escapes me.
Yes.
It is wrong to 'fault' the drive as such. The friction drive system, is
'good', in not introducing vibration, and giving a potentially smooth
transport. Some very upmarket equipment uses them for exactly this
reason. Where the units being discussed 'fail', is in not detecting
that slippage is occurring. I did a system a while ago, with such
drives. The 'best' were friction drives, followed by toothed belt
drives, with gears in last place, for the particular requirement of a
'cogging free' drive system. However we elected to use magnetic sensors
for each 'stop' location (double detector for the 'home'), with
detection of the exact stop location, and error reporting, if the drive
was failing to position as required. This has been trouble free.
The fault in both the system you describe, and the SBIG system, is in
not adding position detection for the intermediate locations, with
enough inteligence to tweak the movement, and give a report if more
than a small error occurs.


it seems whenever you look closely at anything they have designed in the
past few years that it is really easy to find fault and it really isn't
that hard to do it right

regarding vibration it isn't much of an issue for the filter wheel since
you don't have the shutter open at the time of the wheel rotating and
you can always wait a few seconds for any motion to damp out once the
carousel has indexed properly
However cogging is an issue, as is physically having the wheel locked (a
gear drive potentially allows the wheel to rock fractionally, unless made
rather more expensive), so the soft drive if done right has an advantage.
It rather appears as if the feeling was that the "old drive worked, why
improve on it"...
A pity.

Best Wishes

There's a warning in the manual about that type of problem. But no
mention of cold making it happen, just tightening things up too much.
We've had very light snow since the problem was noted. The roofline is
at 5 foot, my head above that. My back has had too many years on it and
screams loudly if I work hunch backed as I'd have to to work in there
with the roof on. So until it stops and I can roll the roof to stand up
in there it will have to sit. Supposed to stop sometimes today for a
bit. Hasn't amounted to much, just annoying the heck out of me as I
want to see inside.

I wonder at what temp that rubber band goes hard? I paid for my first
scope with a paper route back in about 1950 in Lincoln, Nebraska. I
hated winter as the rubber bands used to hold the rolled paper's
together for throwing from my bike would go brittle. So either you got
snapped by breaking bands like crazy or took the much more time
consuming route of folding them for throwing instead of rolling them.
Never have trusted rubber bands in zero degree weather since those days.

As a side note I still price telescope equipment based on paper route
months. I have had kids then grand kids with paper routes so keep up
with what they earn. Today you can get far more telescope for a paper
route year than you could in my day! It took me two years to get the
money to just afford the materials to build a 6" f/8 reflector with 3
eyepieces and a barlow, a 50 mm finder (nearly unheard of back then)
atlas and cheap binoculars. And I "saved" by using a cardboard mailing
tube with 1/2" walls for my tube. Then it took a year plus to grind the
mirror, get it aluminized and put it all together. I started in 1950
and finished in 1954. Today for just one year's paper route you can get
a 12.5" dob with all those accessories with an assembly time of an hour
and a 2 or three week wait for delivery. It took me another 5 years to
save enough for my Cave 10" on a really lousy mount by today's
standards. Optics though are superb. Nobody could afford a 12.5" not
even the two doctors and one lawyer in our astronomy club.

Rick

George Normandin wrote:
"Rick Johnson" wrote
...

The filter wheel in my STL camera has suddenly decided to position the lum
filter at random.........

Any ideas?



Rick,

One time while packing for vacation I was too lazy to take the nose piece
off the STL-1301 and just jammed the case down hard on the camera. I had had
no problem with doing that before, but this time the filter wheel would not
properly position at all. After I took the cover off and put it back on and
then shook the camera the wheel went back to acting normally. So, perhaps
something with your cold weather has got the wheel jammed up a little. Try
taking it out and putting it back in.

The filter wheel with my ST-9 leaves the IR LED on after some moves so I
have to unplug the filter wheel after each move before taking an image. The
camera is too old to bother fixing. SBIG has no idea why it does this.

George N



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