Remote Observatory - Mount Protection

midnight (Darrin) · #1 15-11-2011, 01:36 AM

I hope this is a suitable place for this question I have.

What do you guys and gals do for protection of your mount if you get your observatory up to fully remote status (or even in the field and you're away from the mount)

By this I mean clashes with the mount (and possible damage) due to the mount slewing or whatever beyond its normal operating range.

I know most mounts have electronic limits but I have just experienced my G11 take off 2hrs into a photo shoot and swing in dec to a point where the OTA was pointing nearly 90 deg down and about to do some damage. I have set the limits and tested them. This was just a sudden slew (at slew speed) out of nowhere (under autoguide) and I was lucky to be nearby to kill the power.

Do you really trust the firmware in your controller or is it more like "operator error"

& I'm being a little too worried. I've read many people are more than happy to set and leave the mount go all night.

I would be keen to hear your comments. Esp if you are quite some distance away physically from the mount.

Cheers,
Darrin...

bmitchell82 (Brendan) · #2 15-11-2011, 02:40 AM

My limits I have no issue of walking away, once user error had been worked out of it (which it now has). I had my scope at a recent deep sky trip where i would come back and visit every now and then eg hour to do a refocus check and let it go again while i was roaming around chatting to people.

When I have my scope set up at home I do set and forget runs aka i set it up at about 130 2am (once temp has stabilized and tube isn't shrinking) and go to bed when it goes to do a meridian flip or reaches to within 30 deg of the horizon it parks itself and goes to sleep

If you want ultimate safety have your main power pass though a proximity switch that if the switch is tripped it cuts power to the mount!

midnight (Darrin) · #3 15-11-2011, 08:37 PM

Quote:

Originally Posted by bmitchell82

If you want ultimate safety have your main power pass though a proximity switch that if the switch is tripped it cuts power to the mount!

That's similar to my line of thinking. I have a home made power box with one set of 12V outputs wired through a relay for possible future hook up.

Maybe I am being a bit too over reactive but the G11 Gem 2 firmware gives me a few nervous moments though.

Darrin...

bmitchell82 (Brendan) · #4 16-11-2011, 07:36 PM

Just like a new girlfriend mate. once you two get well aquainted and a few runs on the board everything will be smooooth as glass.!

g__day (Matthew) · #5 26-11-2011, 12:16 PM

Is a proximity switch like a mecury tilt switch?

The other method would be to have a small, purpose built bit of software reading mount position - and if it goes out of bound issue a halt then a goto parked position. If it does it again within 10 minutes - halt and immediate power down.

bmitchell82 (Brendan) · #6 27-11-2011, 01:47 PM

Most astro software already has this inbuilt, I think what darren is worried about is if the software fails.

A proximity switch is mechanical, if it reaches that limit. game over power is off.

midnight (Darrin) · #7 28-11-2011, 09:25 AM

My week off (business and family) is just about finished and now heading home so it'll be good to get back to my setup.

Quote:

Originally Posted by bmitchell82

Most astro software already has this inbuilt, I think what darren is worried about is if the software fails.

A proximity switch is mechanical, if it reaches that limit. game over power is off.

Spot on. The protection referred to here is in software. Ie it is relying on what the mount is reporting back to say the inbuilt controller or a third party software.

Unfortunately, I had a mount crash the day b4 I left for the trip over east. It damaged the RA motor and it did not even report a stall. The G11 limit was set to 95 deg which was well clear. But 30 min into my session at Orion (unguided), it took off again (to the west) at slew speed and I had a crash and the motor overheated. The mount for some unknown reason decided that it no longer thought it was GMT +8hr but suddenly GMT -8hr and for this reason I believe the software limit is calculated on a number of things and you really are at the mercy of the software/firmware. The mount was GPS queried at the start to set everything up and I always disconnect the GPS after its initial update.

Luckily I allowed a trip down to Bintel as part of my biannual excursions and have a chat with the guys down there. And this is apparently not unusual for the Gemini 2 with a few others caught out as well.

BTW, a prox is certainly a good option but I was interested if anyone else put so much faith in modern firmware considering the potential damage.

Cheers,
Darrin...

alistairsam · #8 28-11-2011, 12:39 PM

Reliance on software is one of those things, no matter how reputable they are, there's bound to be glitches or bugs, no matter what application.

For sophisticated remote observatories, they'd have more than one software in the solution, so multiple levels of redundancy.
Even at parkes RT, they have a dead man's switch, that is no movement of the operator for 15 mins, the alarm goes off.
A backup plan or mechanical fallback with a trip switch makes sense for unmanned sessions. critical bit will be placement of the sensor or switch and using the simplest type of switch.

It won't be long before the mount motor controllers come with stall detection so the stepper controller stops the motor if there's a stall like the trinamic ones. that's based on electrical feedback.

higginsdj · #9 29-11-2011, 08:05 AM

Nothing is foolproof so it will come down to a risk analysis - what level of risk are you comfortable with? I leave my Meade 14 on its Meade mount to run all night on it's own slewing between multiple targets and imaging each target is sets (ie Target 1, then 2, then 3, then 4 then back to 1 etc all night). I have been doing this every clear night for a decade (around 8000hrs of operation) and have had 2 mishaps (pointed below the observatory limits) but no hardware damage or even contact.

midnight (Darrin) · #10 29-11-2011, 11:40 PM

Thanks guys for your comments.

I had an LXD55 mount for nearly 9 years and despite some early issues, it has performed exceptionally well for me in the later years in behaving itself and not taking off. I could certainly trust leaving my LXD55 outside unattended all night when I got into AP last year.

In fact I got re-acquainted with my old LXD55 last week over East where my brother in law now has it and I watched it slew and you could tell the firmware has really taken into account mount clashes by watching it sequence the slewing when requiring a large direction change.

The G11 gem 2 is mechanically a giant step above the LXD55 and I am very happy with it but it's these recent hiccups that have me a little on edge. I really do hope it can be put down to the firmware.

I have since hooked up a basic prox switch this evening and my power supply has a relay which can disconnect power to the mount until I am certain what is going on.

Thanks again for your comments.

Darrin...