Re: 900GTO Cold Weather Support (long)


Dec 9, 2002

 


----------------------------

#6219 Dec 9, 2002

I have encountered strange behaviour from my 900GTO mount and would like to

know if I can get some information to try and remedy the problem.



Last Night:



I set up the mount (the first clear night in a over a month). I levelled

the mount and sighted along the bore hole at Polaris. Placed my OTA on the

mount and turned it on. I use the Pyramid AC/DC 12V power source plugged

into an external outlet. I also have my ST-7 and Robofocus plugged into

the same extension cord. On a second extension cord I am running a desktop

computer and monitor. The keypad requested the normal information (Site

and Resume from Park). I sent the mount to Park position One to level the

counter weight shaft and OTA, levels were slightly off since I use the

portable pier. Once levelled, I then instructed the mount to goto Park

2. The mount started moving in the wrong direction. The counter weight

shaft moved higher, instead of lower, while the Dec motion was erratic. I

had the slew rate set at 600X, since the outside temperature was

approximately -20C. I pulled power from the mount and tried again and the

same pattern repeated itself.



The buttons on the keypad also were not responding correctly. The mount

would jump or continue to move even though the buttons were not being held

down. Also the mount did not seem to be tracking at all, I had my CCD in

focus mode and was recording trailing stars in the RA direction.



I brought the mount in to try and diagnose the problem in a warmer

environment and the problem had disappeared. I had checked the time, DST

and location setting outside, but all were correct. I also performed the

mount test and the keypad reported back no problems. At no point did the

mount's or the power supply's LEDs turn yellow or the keypad report motor

stalls.



Tonight:

I set up the mount again as unusual. This time though I set up before the

sun had gone done and was therefore a little warmer than yesterday. The

daytime alignment routine went as usual, no problems. I set even had the

mount slew to the Moon and it was only slightly off in azimuth only. I

allowed the sun to set while my camera was taking dark frames. When I

returned to the mount I experienced the same behaviour as last night. Odd

motion of the mount, the buttons causing continuous motion even though the

buttons were not being held down, mount slewing in odd directions With the

camera in focus mode, there was drift in the RA direction. I don't know if

the mount was even tracking in RA. Could not discern that

information. Clutches are tight. The mount has not been transported

anywhere. I only carry it from inside to outside.



Setup During Problems:

I have the latest version of the firmware for the keypad installed and have

never had this sort of problem occur. The OTA I had on the mount was a TV

Genesis with an ST-7, the combination of which is well under the weight

limit for the mount. All cables are frozen solid. I do suspect that the

cold is the problem but am not sure what to do.



I would really appreciate any input or suggestions as tomorrow night is

also forecasted to be clear and I am suffering from a bad case of imaging

withdrawl. ;)



Thank you for your time,



Bill Gardner







members.rogers.com/gardner.w/



----------------------------

#6221 Dec 10, 2002

Bill-

Those are the exact problems I had with my 1200 GTO last week at 6F

here in MI. I called Wally and he said something about perhaps a

bad controller box. I was out last weekend and I tried

disconnecting the power via the power cabe to the mount-couldn't get

it to point or track. I disconnected the mount & power supply, then

just plugged everything back in and then it worked.



What was most concerning was my mount would continue to slew even

after I let off the slew buttons @ 600 rate. The only was to stop

the mount was to use the stop button. The good news is my mount is

working correctly now, but I don't know what I did.



Carl Burton



--- In ap-gto@yahoogroups.com, Bill Gardner gardner.w@r...> wrote:

>

> I have encountered strange behaviour from my 900GTO mount and

would like to

> know if I can get some information to try and remedy the problem.

>

> Last Night:

>

> I set up the mount (the first clear night in a over a month). I

levelled

> the mount and sighted along the bore hole at Polaris. Placed my

OTA on the

> mount and turned it on. I use the Pyramid AC/DC 12V power source

plugged

> into an external outlet. I also have my ST-7 and Robofocus

plugged into

> the same extension cord. On a second extension cord I am running

a desktop

> computer and monitor. The keypad requested the normal information

(Site

> and Resume from Park). I sent the mount to Park position One to

level the

> counter weight shaft and OTA, levels were slightly off since I use

the

> portable pier. Once levelled, I then instructed the mount to goto

Park

> 2. The mount started moving in the wrong direction. The counter

weight

> shaft moved higher, instead of lower, while the Dec motion was

erratic. I

> had the slew rate set at 600X, since the outside temperature was

> approximately -20C. I pulled power from the mount and tried again

and the

> same pattern repeated itself.

>

> The buttons on the keypad also were not responding correctly. The

mount

> would jump or continue to move even though the buttons were not

being held

> down. Also the mount did not seem to be tracking at all, I had my

CCD in

> focus mode and was recording trailing stars in the RA direction.

>

> I brought the mount in to try and diagnose the problem in a warmer

> environment and the problem had disappeared. I had checked the

time, DST

> and location setting outside, but all were correct. I also

performed the

> mount test and the keypad reported back no problems. At no point

did the

> mount's or the power supply's LEDs turn yellow or the keypad

report motor

> stalls.

>

> Tonight:

> I set up the mount again as unusual. This time though I set up

before the

> sun had gone done and was therefore a little warmer than

yesterday. The

> daytime alignment routine went as usual, no problems. I set even

had the

> mount slew to the Moon and it was only slightly off in azimuth

only. I

> allowed the sun to set while my camera was taking dark frames.

When I

> returned to the mount I experienced the same behaviour as last

night. Odd

> motion of the mount, the buttons causing continuous motion even

though the

> buttons were not being held down, mount slewing in odd directions

With the

> camera in focus mode, there was drift in the RA direction. I

don't know if

> the mount was even tracking in RA. Could not discern that

> information. Clutches are tight. The mount has not been

transported

> anywhere. I only carry it from inside to outside.

>

> Setup During Problems:

> I have the latest version of the firmware for the keypad installed

and have

> never had this sort of problem occur. The OTA I had on the mount

was a TV

> Genesis with an ST-7, the combination of which is well under the

weight

> limit for the mount. All cables are frozen solid. I do suspect

that the

> cold is the problem but am not sure what to do.

>

> I would really appreciate any input or suggestions as tomorrow

night is

> also forecasted to be clear and I am suffering from a bad case of

imaging

> withdrawl. ;)

>

> Thank you for your time,

>

> Bill Gardner

>

>

>

> members.rogers.com/gardner.w/







----------------------------

#6225 Dec 12, 2002

Hi Folks,



I have not been able to respond to thsi post until today since Yahoo

had shut my access to thsi group off while I was away on vacation. It

took until today to get back in the group. For 3 days I was not able

to post or get into the group, and it took some jumping thru hoops to

get back on. It happened because they got a bounceback and treated me

as a spammer. Now I know better to deactivate my account if I'm gone

on vacation.



I'll try to answer this question about the strange behavior of the

mount for anyone who might have experienced similar conditions. Marj

already responded with a private Email, and I hope that this may have

been of help.



First, I doubt that there is anyone on the newsgroup that knows what

is happening except perhaps myself. Therefore it would have been more

advantageous to get in touch with me either through our ap web site

or by telephone. I can usually diagnose a problem pretty accurately

over the phone.



As far as the symptoms:



1. slewing the wrong way. The use of resume from park was intended

solely for the case where the scope was parked, power turned off, and

the operator walks away without touching the scope or mount. If,

however, the scope and mount were disassembled, and then reassembled

some other day, there is no guarantee that the original parked

position has been recreated accurately. In fact, the axes could have

been flipped 180 degrees during setup. It is very easy then for the

mount to slew to China when asked to go to the pole. In the case of a

mount set up in the filed, resume from park should not be used unless

you really know how it works. A safer bet is to start by aligning on

a known star and syncing on it. The 2 star alignment makes that

outomatic. You don't even need to go to the second star if you think

you have pretty good polar alignment. Just exit after calibrating on

the first star.



2. symptom: The buttons on the keypad also were not responding

correctly. The mount would jump or continue to move even though the

buttons were not being held down. In this case, I can say with good

confidence that the servos were being starved for power. What happens

in any slew command is that the motors try to accelerate and run at a

predetermined rate set by the microprocessor. The micro gets a

command from the keypad buttons, for instance, to run at 1200x for 10

seconds (because you held the button down for 10 seconds). However,

in the case where the mount is ice cold, the bearings and gears are

very stiff, in order for the servos to attain that speed, they have

to draw large amounts of power form the supply. They can easily draw

3 to 4 times normal current (normal 1 to 2 amps max) at 1200x. This

high current demand can cause the power supply voltage to sag below

12 volts. The motors will then slow down, and if they run at less

than 1200 x commanded speed, they will continue to run the extra time

it takes to get to the commanded final position. For instance, if

they run at 600x, then it will take 20 seconds to get to where the

motors will finally stop. And they will stop with a bang because the

commanded slow down in speed happened 10 seconds ago and is long

gone.



If the power supply collapses below about 11 volts in an erratic

manner, the microprocessor and motor drivers may indeed do some

strange things as they try to reset (undervoltage spikes on the power

supply line will reset the micro in some cases). For this reason I

always recommend that you go to the main menu on the keypad and set

the max slew rate to 900x or even 600x when the temperature is below

freezing, or the mount is heavily loaded or both.



We are working on some new hardware that will solve this one

shortcoming of this servodrive, but for now, there is a workaround.

Limit the max slew rate. The motors will love you for it, and your

power supply will not have cardiac arrest.



3. symptom: With the camera in focus mode, there was drift in the RA

direction. I don't know if the mount was even tracking in RA. If

you see that the stars are drifting by in RA, then the servo motor is

not tracking and has been shut down to the standby mode by the servo

software because it has sensed some kind of overload condition, or

the micro has reset by an undervoltage condition. In either case, the

motors will stop tracking to prevent damage in case there is a

mechanical fault that prevents motion. This prevents complete motor

burnout in case there really is a mechanical problem. Motors are very

expensive to replace. If the motor has been placed in standby mode,

it will be reset if any of the 4 buttons are pressed. The servo then

starts sidereal tracking. if another fault occurs, the motors will

again go into standby mode and will stop tracking.



One thing that might cause larger than normal loads on the motor is

if the worms are pressed too tightly into mesh against the worm

wheel. You can tell if that's the problem by grabbing the motor box

and pulling it gently away from the mount while the motor is slewing.

The pressure from your hand is enough to reduce the load on the

motor. If the motor sounds relieved (i.e. less noise or hesitant

motion) then you know you have too tight mesh. Easy to fix.



Lastly, although all these symptoms can be caused by the above, it is

remotely possible that one of the motor drivers, or the

microprocessor somehow fails in the cold and goes beserk. The

components are rated for industrial temperature range and should work

down to -40C, but, these things can fail nonetheless. In that case,

sending the servodrive here to be checked would be the best avenue of

approach.



I hope this has helped to explain some things, and that it allows

people to accurately diagnose their system in the event that things

go wrong. I also hope that Yahoo restores my email priveleges on this

newsgroup soon.



Roland Christen





--- In ap-gto@yahoogroups.com, Bill Gardner gardner.w@r...> wrote:

>

> I have encountered strange behaviour from my 900GTO mount and would

like to

> know if I can get some information to try and remedy the problem.

>

> Last Night:

>

> I set up the mount (the first clear night in a over a month). I

levelled

> the mount and sighted along the bore hole at Polaris. Placed my

OTA on the

> mount and turned it on. I use the Pyramid AC/DC 12V power source

plugged

> into an external outlet. I also have my ST-7 and Robofocus plugged

into

> the same extension cord. On a second extension cord I am running a

desktop

> computer and monitor. The keypad requested the normal information

(Site

> and Resume from Park). I sent the mount to Park position One to

level the

> counter weight shaft and OTA, levels were slightly off since I use

the

> portable pier. Once levelled, I then instructed the mount to goto

Park

> 2. The mount started moving in the wrong direction. The counter

weight

> shaft moved higher, instead of lower, while the Dec motion was

erratic. I

> had the slew rate set at 600X, since the outside temperature was

> approximately -20C. I pulled power from the mount and tried again

and the

> same pattern repeated itself.

>

> The buttons on the keypad also were not responding correctly. The

mount

> would jump or continue to move even though the buttons were not

being held

> down. Also the mount did not seem to be tracking at all, I had my

CCD in

> focus mode and was recording trailing stars in the RA direction.

>

> I brought the mount in to try and diagnose the problem in a warmer

> environment and the problem had disappeared. I had checked the

time, DST

> and location setting outside, but all were correct. I also

performed the

> mount test and the keypad reported back no problems. At no point

did the

> mount's or the power supply's LEDs turn yellow or the keypad report

motor

> stalls.

>

> Tonight:

> I set up the mount again as unusual. This time though I set up

before the

> sun had gone done and was therefore a little warmer than

yesterday. The

> daytime alignment routine went as usual, no problems. I set even

had the

> mount slew to the Moon and it was only slightly off in azimuth

only. I

> allowed the sun to set while my camera was taking dark frames.

When I

> returned to the mount I experienced the same behaviour as last

night. Odd

> motion of the mount, the buttons causing continuous motion even

though the

> buttons were not being held down, mount slewing in odd directions

With the

> camera in focus mode, there was drift in the RA direction. I don't

know if

> the mount was even tracking in RA. Could not discern that

> information. Clutches are tight. The mount has not been

transported

> anywhere. I only carry it from inside to outside.

>

> Setup During Problems:

> I have the latest version of the firmware for the keypad installed

and have

> never had this sort of problem occur. The OTA I had on the mount

was a TV

> Genesis with an ST-7, the combination of which is well under the

weight

> limit for the mount. All cables are frozen solid. I do suspect

that the

> cold is the problem but am not sure what to do.

>

> I would really appreciate any input or suggestions as tomorrow

night is

> also forecasted to be clear and I am suffering from a bad case of

imaging

> withdrawl. ;)

>

> Thank you for your time,

>

> Bill Gardner

>

>

>

> members.rogers.com/gardner.w/







Contact Us
This Site's Privacy Policy
Google's privacy policies

S
e
n
i
o
r
T
u
b
e
.
o
r
g