AP900 Dec backlash - more help required


John Winfield
 

Hi all,

Thanks to the guidance here, I've removed the motor box cover and
inspected the gear train underneath.

I've discovered that when driving the Dec motor at 1x sidereal speed,
it 'jumps', once or twice per revolution.
This seems to predominantly happen after changing direction - if I
keep running in the same direction the jumps seem to stop after a few
revolutions.
I'm guessing this is indeed due to a loose locking screw on one of the
gears.

I put a pencil mark on the end of the motor shaft and after a few
jumps it still seemed to be in the same orientation wrt to the locking
grub screw, so I'm assuming it's not that one.

I can't get to the locking screw on the motor shaft through this side
cover to check it's tightness and can't even see the locking screws on
the other gear shafts.

Am I on the right lines - and are there any guidelines on how best to
adjust the locking screws on these other hard-to-reach gear shafts?

I'm not a mechanical whizz, but I'm reasonably competent.

Regards,

John


--- In ap-gto@..., chris1011@... wrote:

In a message dated 4/23/2007 2:08:04 PM Central Daylight Time,
winfij@... writes:


Thanks for clarifying that - this is a circa 2003 mount, purchased
used as you say.
In a lot of cases, when a mount has been purchased used, the person
who ships
it will not package it correctly, and the result is that stress is
put on the
motor box/worm gear. This then results in poor worm mesh, so the
first thing
a new user must do when he/she recaives a used mount is to do a
re-mesh on
both axes. Probably the biggest mistake is to take such a mount out
of the box,
set it up outside and expect it to work perfectly. It probably will
not work
quite right until the gear mesh has been checked. Also, many times a
mount can
have other minor things out of adjustment which the previous owner
never
realized, but which the new owner will see right away. Therefore do
not hesitate to
check all things in the daylight before trying it out in the dark.


Are there any instructions/pictures as to how to remove the motor box
cover, just to make sure I get the correct screws?
The motor box cover is located on the opposite end of the worm shaft
cover.
Remove the 6 small Allen head screws and the cover will slip off.
You will then
see the spur reduction gears. Once you see them, you will understand
how it
all works.

Rolando


**************************************
See what's free at
http://www.aol.com.




Roland Christen
 

In a message dated 4/24/2007 10:10:02 PM Central Daylight Time,
winfij@... writes:


I can't get to the locking screw on the motor shaft through this side
cover to check it's tightness and can't even see the locking screws on
the other gear shafts.
There is only one locking screw, and that is on the last spur gear on the
worm itself. The other gears all run free on their pinions. You can remove the
largest gear in the train (use a normal srew driver to unscrew the shoulder
screw). Once you remove this gear, you can see the underlying pinion gear which is
attached to the worm. This gear has a small set screw on the side, and this
set screw must be tightened - it also must be centered on the flat, otherwise
it will probably loosen on you. If you cannot follow this, please call AP and
talk to Wally. He will guide you step by step in this procedure.

By the way, I do not know what you mean by "jumping", but it could be that
you have dialed in some backlash compensation on your keypad. Go into the setup
procedure and put 0 for backlash in both RA and Dec axes. This will eliminate
any motions that you may not be familiar with, and will aid in your
visualization of what needs to happen when reversing the RA and Dec axis.

Rolando


**************************************
See what's free at
http://www.aol.com.


Jeff Young <jey@...>
 

John --

It's quite unlikely to be the motor shaft -- that gear is glued on as
well as being set-screwed.

The gears in the middle are just transfer gears, so they rotate freely
on the shoulder-bolts which hold them to the motor housing. The gear on
the worm shaft (that closest to the mount) is the most likely culprit.
You might try your pencil line trick with it and see if that shows
anything up. You should also be able to get to the setscrew in that one
more easily.

-- Jeff.


________________________________

From: ap-gto@... [mailto:ap-gto@...] On
Behalf Of John Winfield
Sent: Wednesday, April 25, 2007 4:07 AM
To: ap-gto@...
Subject: [ap-gto] Re: AP900 Dec backlash - more help required



Hi all,

Thanks to the guidance here, I've removed the motor box cover
and
inspected the gear train underneath.

I've discovered that when driving the Dec motor at 1x sidereal
speed,
it 'jumps', once or twice per revolution.
This seems to predominantly happen after changing direction - if
I
keep running in the same direction the jumps seem to stop after
a few
revolutions.
I'm guessing this is indeed due to a loose locking screw on one
of the
gears.

I put a pencil mark on the end of the motor shaft and after a
few
jumps it still seemed to be in the same orientation wrt to the
locking
grub screw, so I'm assuming it's not that one.

I can't get to the locking screw on the motor shaft through this
side
cover to check it's tightness and can't even see the locking
screws on
the other gear shafts.

Am I on the right lines - and are there any guidelines on how
best to
adjust the locking screws on these other hard-to-reach gear
shafts?

I'm not a mechanical whizz, but I'm reasonably competent.

Regards,

John

--- In ap-gto@... <mailto:ap-gto%40yahoogroups.com>
, chris1011@... wrote:
>
> In a message dated 4/23/2007 2:08:04 PM Central Daylight Time,

> winfij@... writes:
>
>
> > Thanks for clarifying that - this is a circa 2003 mount,
purchased
> > used as you say.
>
> In a lot of cases, when a mount has been purchased used, the
person
who ships
> it will not package it correctly, and the result is that
stress is
put on the
> motor box/worm gear. This then results in poor worm mesh, so
the
first thing
> a new user must do when he/she recaives a used mount is to do
a
re-mesh on
> both axes. Probably the biggest mistake is to take such a
mount out
of the box,
> set it up outside and expect it to work perfectly. It probably
will
not work
> quite right until the gear mesh has been checked. Also, many
times a
mount can
> have other minor things out of adjustment which the previous
owner
never
> realized, but which the new owner will see right away.
Therefore do
not hesitate to
> check all things in the daylight before trying it out in the
dark.
>
> >
> > Are there any instructions/pictures as to how to remove the
motor box
> > cover, just to make sure I get the correct screws?
> >
>
> The motor box cover is located on the opposite end of the worm
shaft
cover.
> Remove the 6 small Allen head screws and the cover will slip
off.
You will then
> see the spur reduction gears. Once you see them, you will
understand
how it
> all works.
>
> Rolando
>
>
> **************************************
> See what's free at
> http://www.aol.com. <http://www.aol.com.>
>
>
>
>