RoboFocus & FocusMax - Exceeding limits, but not.

[rogerg]

Hi all,

I have a frustrating situation with my long reliable robofocus + focusmax combination I am hoping someone will have suggestions to resolve.

Focus max is intermittently getting a "exceeding limits" error from RoboFocus. For some reason it seems RoboFocus thinks it's limits will be exceeded if it racks the focuser in more, but it's only a software limit (somewhere) because there's plenty of phyiscal room to move. If I hold down the manual buttons of the RoboFocus it will happily rack in past the limit which it is not letting Focus Max travel beyond.

These are example logs:

05:52:38 Best Focus is: -158
05:52:38 Moving to -158
05:52:38 Aborting - move will exceed focuser limits
05:52:38 Moving to previous focus position of 172

Attached is the robofocus config.

I'm not sure where it's getting the max travel from and if that's the problematic number. I have set it to a higher value but it gets reset by something, I'm guessing RoboFocus reads it from somewhere.

Also it seems my problem is with "in focus", and so the RoboFocus not wanting to go below zero position as opposed to the "out focus" direction where I think "max travel" is more relevant?

Really not sure why this has become a problem in recent times and how I can "reset" the robofocus to properly understand it's travel limits :question::shrug:

Roger.

[rogerg]

I've racked the focuser to it's supposed zero point using software, then physically loosened the focuser and slid the drawtube in to physical in-focus stop, and re-tightened. See tonight if that successfully "resets" it.

[Paul Haese]

Roger undo the motor from the focusor and move the motor so it racks out. Make sure you do it for 20 seconds or so. Put the motor back on the focusor and see where the position count is from there. It should give you enough room.

You can also do a reset and power up the robofocus whilst holding down the in button and rack that all the way in and then all the way out to reset the limits. See the manual on that.

[alocky]

Hi Roger - there's a procedure for doing this in the robofocus software - I seem to recall holding down one button when switching the unit on. If you have any slip in the clutch this is bound to end up out if whack. I switch my unit between 3 different motors, so this is an ongoing pain...
Just saw Paul's response - but also seem to recall sometimes during this process the motor stalls...
Cheers,
Andrew.

[rogerg]

Thanks both.

I searched the manual this morning for various terms but didn't find the single button reset, that sounds like exactly what I need.

I am hopeful that having done what I did this morning (read previous comment) that for now the problem is solved, but if it's not this button down while booting up sounds like the ticket :thumbsup: I'll take another look in the manual for that too.

[niharika]

For the focus travel train check the manual http://www.robofocus.com/documents/robofocusins31.pdf

but me being lazy I will do the following
- manually press the in button to move the focuser close to its inward limit
- In get set position reset the number to 0
- manually press out button to move to a approx focus position

That should be it

[rogerg]

I've tried that on 3 separate nights and while it seems to work for that night, some days later the problem has always re-occurred :(

[niharika]

Do you see a change in your focus position inward over time? If yes that's most likely related to slippage somewhere.

[rogerg]

There's an interesting thought!

To answer that I'd need to do some analysis of the logs. I should have logs dating back many years, so generating an excel graph of the focus position should be quite easy.... sounds like fun .. will do that tonight :thumbsup: Perhaps my focuser needs to be tensioned up again.

[MrB]

I was going to suggest slippage but not familiar with the robofocus/focusmax, I decided to keep my trap shut ;)

If the robofocus is a stepper motor and it's an open loop system(no position feedback), it is possible with heavy load or excessive friction etc that the motor is missing steps. It will get the step pulse and will sound like it has moved, but the motor lacks the torque to make the move and springs back to the last step.
This is a common issue with CNC machines that use steppers(and one reason servo's are preferred, at a cost) and pretty easy to test with a dial gauge.

[Octane]

Roger,

See my issue, also: http://www.iceinspace.com.au/forum/showthread.php?t=123824

I've tamed it a little by tightening the absolute crap out of everything.

It's manageable for now until I have the funds for a proper focuser.

It irks me that the STL/FSQ/Robofocus system was ubiquitous for so long and only good things were ever said about them. Mine's been nothing but trouble.

I've got it down to missing 5 position units per focus run now.

H

[rogerg]

How interesting.

See attached.

There certainly is drift in the direction which would suggest slippage. SLow over time except recently which perhaps correlates to after my camera/focuser was yanked out of place by a cable snag.

I can't explain the regular spikes on a monthly basis recently.

I think indications are I have not had it tightened as much recently, it seems it has been slipping more.

Note: The all-time graphs pans many periods of focus calibration and different focal reducers so only sub-sections of it should be considered in their own right.