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Author Topic: Z "Home" bug causing me problems  (Read 2548 times)

NoiseReduction

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Z "Home" bug causing me problems
« on: February 19, 2013, 03:03:49 AM »
I'm not sure if there's another forum thread for this problem specifically, but here it goes -

After installing the single-extruder arduino firmware, everything seemed to be working perfectly.
5 minutes later, I noticed that pressing Z's "Home" or "Home All" in Repetier started pulling z up, not down.

I reset the board, power cycled the printer, and even restarted Repetier to no avail.

Update: Z behaves as if the minimum value was 200 or so. As long as I make it go up a little first (Z+), I can then do Z- the same number of steps (i.e., if I click +2, I can then do -2, but then it stops, acting like position ~=200 is somehow the minimum stop position).
« Last Edit: February 20, 2013, 03:01:08 AM by NoiseReduction »

jit

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Re: Z "Home" bug causing me problems
« Reply #1 on: February 19, 2013, 07:28:13 AM »
I'm just guessing here, but..

(1) bug in host software?  Does it happen if you use pronterface instead?

(2) firmware bug on the Azteeg?  (Does reflashing help?)

(3) One motor coil driver not working or not connected?   This last problem is described here: http://bukobot.com/jitsbuild-failure-conditions#thing-not-moving-correctly.  It can cause things to go in the wrong direction, usually randomly, but maybe you're just lucky.

Try this:  Manually move all 3 axes to the middle of their respective ranges.  Don't hit any home buttons during the following.

Remove all driver boards from the Azteeg, then plug the (current) X axis board into the  Z axis socket (maintain correct orientation!).  Unplug all motors, then plug the X axis motor into one of the Z connectors.  Then tell the Z axis to move 10 cm in one direction, then the other direction.  This should cause the X axis to move one direction, then the other.  Does it?
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buildrob

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Re: Z "Home" bug causing me problems
« Reply #2 on: February 19, 2013, 11:38:29 AM »
Isn't the motor moving in the wrong direction normally caused by the motor connector being flipped over? [Not necessarily your fault as they apparently don't always wire up the motors the right way around in the factory.]

Edit: oh no ... you said it was working and then not working.
That is strange. Because its the Z axis it seems unlikely that both motors with be intermittent due to a wiring problem. Jit's advice of swapping the drivers around to try to isolate the problem is a good one.
« Last Edit: February 19, 2013, 11:43:57 AM by buildrob »

NoiseReduction

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Re: Z "Home" bug causing me problems
« Reply #3 on: February 19, 2013, 07:25:13 PM »
I'm just guessing here, but..
(1) bug in host software?  Does it happen if you use pronterface instead?

With Pronterface, the issue is the same. It did help me notice that it goes down, as long as I make it go up a little first (i.e., if I do +2 in Z, I can then do -2 in Z back - but then it stops, acting like position ~=200 is somehow the minimum stop position...

(2) firmware bug on the Azteeg?  (Does reflashing help?)

I can try to reflash and report back soon. Thanks

(3) One motor coil driver not working or not connected?   This last problem is described here: http://bukobot.com/jitsbuild-failure-conditions#thing-not-moving-correctly.  It can cause things to go in the wrong direction, usually randomly, but maybe you're just lucky.

Seems unlikely, but I'll check it out, thanks!

Try this:  Manually move all 3 axes to the middle of their respective ranges.  Don't hit any home buttons during the following.

Remove all driver boards from the Azteeg, then plug the (current) X axis board into the  Z axis socket (maintain correct orientation!).  Unplug all motors, then plug the X axis motor into one of the Z connectors.  Then tell the Z axis to move 10 cm in one direction, then the other direction.  This should cause the X axis to move one direction, then the other.  Does it?

I'll try out that procedure and get you an answer - thanks a lot!

NoiseReduction

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Re: Z "Home" bug causing me problems
« Reply #4 on: February 19, 2013, 07:29:05 PM »
Isn't the motor moving in the wrong direction normally caused by the motor connector being flipped over? [Not necessarily your fault as they apparently don't always wire up the motors the right way around in the factory.]

Edit: oh no ... you said it was working and then not working.
That is strange. Because its the Z axis it seems unlikely that both motors with be intermittent due to a wiring problem. Jit's advice of swapping the drivers around to try to isolate the problem is a good one.

Yeah - I'll be trying it out, once I get home. Thanks guys!  :)

jit

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Re: Z "Home" bug causing me problems
« Reply #5 on: February 19, 2013, 10:25:59 PM »
If a motor goes one direction for a bit and then backs up a bit, check your endstops.  This is the normal behavior that happens when the carriage hits an endstop.
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NoiseReduction

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Re: Z "Home" bug causing me problems
« Reply #6 on: February 19, 2013, 10:35:22 PM »
If a motor goes one direction for a bit and then backs up a bit, check your endstops.  This is the normal behavior that happens when the carriage hits an endstop.

Totally. It keeps stopping approx. 8 inches before hitting the endstop though... :) And I already tested them, they're all working.

NoiseReduction

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Re: Z "Home" bug causing me problems
« Reply #7 on: February 20, 2013, 03:26:28 AM »
Try this:  Manually move all 3 axes to the middle of their respective ranges.  Don't hit any home buttons during the following.

Remove all driver boards from the Azteeg, then plug the (current) X axis board into the  Z axis socket (maintain correct orientation!).  Unplug all motors, then plug the X axis motor into one of the Z connectors.  Then tell the Z axis to move 10 cm in one direction, then the other direction.  This should cause the X axis to move one direction, then the other.  Does it?

I did as instructed.
Then I pressed Z -1. Nothing.
Then I pressed Z +1. X moved.
Then I pressed Z -1, X moved back again.
Then I pressed Z -1 again. Nothing.

Same behavior I was getting from the Z axis. It only moves in negative after moving in positive - then it stops. As if there's an invisible wall at "0". What can this mean?  :'(

jit

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Re: Z "Home" bug causing me problems
« Reply #8 on: February 20, 2013, 04:00:35 AM »
I'm not an expert on the inner workings of the firmware, but it sounds to me like it thinks it's already sitting at the endstop.  (Somebody who knows the firmware better should jump in on this...)

In other words, when you power up the Azteeg, it apparently thinks it's already sitting at zero.  You press Z -1, but it won't go negative, so it sits there.  You press +1, it goes to 1.  You hit -1, it goes back to zero.  You hit -1, it won't go negative so it sits there.  Consistent with what you see.

But why is it convinced it's at zero when you power up?  It's not supposed to believe it's at zero until it hits an endstop.  Is that endstop switch stuck closed?  Or the leads shorted out somehow?
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NoiseReduction

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Re: Z "Home" bug causing me problems
« Reply #9 on: February 20, 2013, 04:16:01 AM »
I'm not an expert on the inner workings of the firmware, but it sounds to me like it thinks it's already sitting at the endstop.  (Somebody who knows the firmware better should jump in on this...)

In other words, when you power up the Azteeg, it apparently thinks it's already sitting at zero.  You press Z -1, but it won't go negative, so it sits there.  You press +1, it goes to 1.  You hit -1, it goes back to zero.  You hit -1, it won't go negative so it sits there.  Consistent with what you see.

But why is it convinced it's at zero when you power up?  It's not supposed to believe it's at zero until it hits an endstop.  Is that endstop switch stuck closed?  Or the leads shorted out somehow?

Yeah I think Diego mentioned a firmware bug that could be related to this.

Isn't there a way to just recalibrate the damn machine?
What if I had hit the endstop by accident with something else white it was moving? Would it change the print area numbers in the software and get confused later? That would explain how Z homed to +200, hitting the top aluminum bar and then remaining stubborn and refusing to go down...

Seriously, there isn't any kind of "reset" for these situations?  ??? I guess I'll reflash the firmware or something.

Thanks for your help jit!

PS: I reflashed the firmware, and now Z doesn't move at all again. I'd really like to figure out if this is a hardware-originated problem, but for the time being, it seems purely like software. 
Hard to believe no one else ever had this problem... Anyone? Erratically behaving z axis? Maybe the reprap kit route wasn't such a good idea after all :/


PPS: Any alternative x3 firmwares or code tweaks I should be aware of? Should I try the hammer? Dip the azteeg in hot lava? Dry ice?
« Last Edit: February 20, 2013, 05:49:36 AM by NoiseReduction »

jit

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Re: Z "Home" bug causing me problems
« Reply #10 on: February 20, 2013, 07:24:36 AM »
If you have an endstop problem, no amount of reflashing or recalibration will do you any good.  The system absolutely depends on having a properly working endstop on each axis.

Refer to this image from the Wires page:  http://bukobot.com/_media/wiki:jitsbuild:wiring-tamed5c.png (this shows the X3)  and also the Azteeg diagram linked here:  http://bukobot.com/bukobot-assembly-documentation

In the picture, the endstop connectors are at the upper left.  The connectors are keyed, and should go on in only one orientation.  Each has three pins, but only two are wired.

Power down (and unplug from the wall) and wait for a bit, then pull the Z axis endstop connector up a little, not enough to break the connection with the Azteeg, just enough so that you can reach in with ohmmeter leads and touch the two pins that are wired.  (Check that the wires go to the correct pins!  The cable may have been miswired.)  With your third hand, click the Z axis endstop switch on and off.  The meter should go back and forth between zero and many ohms.  It should be many ohms when the switch is open, and zero when the switch is closed.  (It's supposed to be a normally open switch, but they're using SPDT switches, and the wires might be going to the wrong tabs on the switch, or the switch might be malfunctioning, or might be simply the wrong kind of switch.)

If it passes this test, then we might need more help from somebody who understands the system better.
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NoiseReduction

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Re: Z "Home" bug causing me problems
« Reply #11 on: February 20, 2013, 07:36:06 AM »
If you have an endstop problem, no amount of reflashing or recalibration will do you any good.  The system absolutely depends on having a properly working endstop on each axis.

Refer to this image from the Wires page:  http://bukobot.com/_media/wiki:jitsbuild:wiring-tamed5c.png (this shows the X3)  and also the Azteeg diagram linked here:  http://bukobot.com/bukobot-assembly-documentation

In the picture, the endstop connectors are at the upper left.  The connectors are keyed, and should go on in only one orientation.  Each has three pins, but only two are wired.

Power down (and unplug from the wall) and wait for a bit, then pull the Z axis endstop connector up a little, not enough to break the connection with the Azteeg, just enough so that you can reach in with ohmmeter leads and touch the two pins that are wired.  (Check that the wires go to the correct pins!  The cable may have been miswired.)  With your third hand, click the Z axis endstop switch on and off.  The meter should go back and forth between zero and many ohms.  It should be many ohms when the switch is open, and zero when the switch is closed.  (It's supposed to be a normally open switch, but they're using SPDT switches, and the wires might be going to the wrong tabs on the switch, or the switch might be malfunctioning, or might be simply the wrong kind of switch.)

If it passes this test, then we might need more help from somebody who understands the system better.

Thanks.
Yeah I think I need help then. The endstops seem perfectly fine, I really doubt they're the culprit.
Can't be coincidence that the problem started a few minutes after switching from Duo firmware to Vanilla. I played around with the XYZs in the print panel for a couple minutes, Z went insane and has been since then.

Googling for "3d printer axis not moving" returns nothing helpful. I'm really stuck. Giving up until I bring it to Pasadena again.
« Last Edit: February 20, 2013, 07:38:55 AM by NoiseReduction »

whosawhatsis

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Re: Z "Home" bug causing me problems
« Reply #12 on: February 20, 2013, 08:59:35 PM »
The machine starts up thinking that it is at 0,0,0, because there's no other logical place to think that it is. It has soft limits that prevent moves other than homing from moving it in the negative direction beyond 0 (this is a safety feature), so when starting the machine you should always home first so that the machine will have the correct coordinate system. If your Z endstop is not functioning properly, that is an issue, but everything else mentioned here sounds like normal behavior.

NoiseReduction

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Re: Z "Home" bug causing me problems
« Reply #13 on: February 20, 2013, 09:02:43 PM »
The machine starts up thinking that it is at 0,0,0, because there's no other logical place to think that it is. It has soft limits that prevent moves other than homing from moving it in the negative direction beyond 0 (this is a safety feature), so when starting the machine you should always home first so that the machine will have the correct coordinate system. If your Z endstop is not functioning properly, that is an issue, but everything else mentioned here sounds like normal behavior.

Interesting. So if I manually spin the motors so that Z is all the way down, hitting the end stop, and then start the printer up, the problem should be solved?

Thanks!

whosawhatsis

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Re: Z "Home" bug causing me problems
« Reply #14 on: February 20, 2013, 09:22:57 PM »
You still need a properly-functioning endstop. The Z endstop in particular is crucial.

To see if there's an issue with that endstop, you can move the axis up and switch Z endstop with another one. Put one finger on that endstop and the other on the reset button (to prevent the head from crashing if the enstop fails) and tell it to home the Z axis. Press the endstop that is wired to Z and see if it stops. Normal behavior is for it to back off a few mm from the endstop, and then go back toward it more slowly, so you'll want to tap the enstop twice.

 

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