My Z has jitter and overheats
Posted by uMinded
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My Z has jitter and overheats August 10, 2012 12:31PM |
Registered: 12 years ago Posts: 71 |
I am running Marlin 1.0.0 RC2 () on a Mega 1280 with Ramps 1.4 board.
I have a major problem with my Z axis stuttering around and the driver is overheating! I command the Z to move and it will freak out and wiggle back and forth and after stopping the idle current through the pololu will cause it to get really hot. I am testing this with the stepper not connected to anything at all. The motor is from a known good axis and the problem happens the same when I swap drivers so I figure it must be in the firmware.
Just to eliminate a mis-config what are the common Z settings for a Mendel?
I'm using 1/4" rod and 1/16 microstepping with the Pololu at about 30% current. Steps/mm is 50, feedrate is 5, acceleration is 100
Any ideas whats wrong here??
I have a major problem with my Z axis stuttering around and the driver is overheating! I command the Z to move and it will freak out and wiggle back and forth and after stopping the idle current through the pololu will cause it to get really hot. I am testing this with the stepper not connected to anything at all. The motor is from a known good axis and the problem happens the same when I swap drivers so I figure it must be in the firmware.
Just to eliminate a mis-config what are the common Z settings for a Mendel?
I'm using 1/4" rod and 1/16 microstepping with the Pololu at about 30% current. Steps/mm is 50, feedrate is 5, acceleration is 100
Any ideas whats wrong here??
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Re: My Z has jitter and overheats August 10, 2012 02:20PM |
Admin Registered: 17 years ago Posts: 7,879 |
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Re: My Z has jitter and overheats August 10, 2012 08:20PM |
Registered: 12 years ago Posts: 71 |
The current is set at 30% (so 333mA) and the motors are running off 12V. The Pololu has a heatsink on it.
I tried to scope the signals but their to intermittent to get a clear capture.
I took the Pololu off my X and put it on the Z and did the same with the motor connector. When I command the Z to move I get the jittery behavior still. I lowered the current to almost zero and it still give the same problems with overheating when the motor stops moving.
The steppers are unlabeled but look exactly the same, can you run two different steppers on the same Pololu? And equally can I send the Z step/dir signals to E1's Pololu so each motor has its on driver via firmware?
I tried to scope the signals but their to intermittent to get a clear capture.
I took the Pololu off my X and put it on the Z and did the same with the motor connector. When I command the Z to move I get the jittery behavior still. I lowered the current to almost zero and it still give the same problems with overheating when the motor stops moving.
The steppers are unlabeled but look exactly the same, can you run two different steppers on the same Pololu? And equally can I send the Z step/dir signals to E1's Pololu so each motor has its on driver via firmware?
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Re: My Z has jitter and overheats August 11, 2012 02:32AM |
Admin Registered: 17 years ago Posts: 7,879 |
To set the current accurately you measure the voltage on the vref pin and divide by 8 times the sense resistance.
To look at the waveforms it is best to look at the voltage on the sense resistors on a scope.
Yes you can drive two motors from one Pololu. In series for most torque but in parallel can be faster and stays in sync better.
Yes you could hack the firmware to echo the Z steps to E1.
[www.hydraraptor.blogspot.com]
To look at the waveforms it is best to look at the voltage on the sense resistors on a scope.
Yes you can drive two motors from one Pololu. In series for most torque but in parallel can be faster and stays in sync better.
Yes you could hack the firmware to echo the Z steps to E1.
[www.hydraraptor.blogspot.com]
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Re: My Z has jitter and overheats August 11, 2012 10:15AM |
Registered: 12 years ago Posts: 71 |
My jitter problem occurs at any current level. If my motors are unmarked how am I to calculate what current level to set them at? I just turned the current down to nearly zero and then back up until the axis moves smoothly to set my current levels. I tried running the Z with nothing attached and with a load on it and still the problem occurs.
How would I go about mirroring the Z signals onto the E1 controller? I searched for Z_STEP_PIN and Z_DIR_PIN in stepper.cpp and I copy pasted under each line E1_STEP_PIN or E1_DIR_PIN as appropriate.
I figured this would work as on line 622 of steppers.cpp (#if EXTRUDERS > 1) the extruders do not seem to be on the planning loop and they are just bitbanged as needed. However this does not work and E1 does not mirror my Z.
Any recommendations on where to modify the code?
How would I go about mirroring the Z signals onto the E1 controller? I searched for Z_STEP_PIN and Z_DIR_PIN in stepper.cpp and I copy pasted under each line E1_STEP_PIN or E1_DIR_PIN as appropriate.
I figured this would work as on line 622 of steppers.cpp (#if EXTRUDERS > 1) the extruders do not seem to be on the planning loop and they are just bitbanged as needed. However this does not work and E1 does not mirror my Z.
Any recommendations on where to modify the code?
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Re: My Z has jitter and overheats August 11, 2012 10:31AM |
Admin Registered: 17 years ago Posts: 7,879 |
The current rating of a motor is usually the current that raises the temperature 80C with two coils on. Since this is too hot for plastic brackets we always under run them. The best value to use is the highest current that doesn't overheat the brackets, the motor or the driver, so you can find that out by trial and error. Some people try to use the minimum current that doesn't stall but that is wasting the hardware because you get more accurate microstepping and less backlash with higher currents.
If the motors get too hot without giving enough torque then they are not high enough torque motors. If the drivers get too hot before you get enough torque then the motors are too low resistance. However if you cant get them to spin with no load most likely they are wired incorrectly or you are trying to spin them too fast as hardly any current is needed to make them turn slowly. They might have too much inductance to spin fast.
Perhaps the pins are not being defined as outputs because EXTRUDERS > 1 is false. It might be better to set the E1 pins to -1 and define some Z2 pins to be their old values. Then add extra lines to all the places the Z pins are used. An easy way to find these would to to rename them Z1 pins to create an error everywhere Z pins are referenced which you then fix by changing Z to Z1 and adding another line for Z2.
Edited 1 time(s). Last edit at 08/11/2012 10:34AM by nophead.
[www.hydraraptor.blogspot.com]
If the motors get too hot without giving enough torque then they are not high enough torque motors. If the drivers get too hot before you get enough torque then the motors are too low resistance. However if you cant get them to spin with no load most likely they are wired incorrectly or you are trying to spin them too fast as hardly any current is needed to make them turn slowly. They might have too much inductance to spin fast.
Perhaps the pins are not being defined as outputs because EXTRUDERS > 1 is false. It might be better to set the E1 pins to -1 and define some Z2 pins to be their old values. Then add extra lines to all the places the Z pins are used. An easy way to find these would to to rename them Z1 pins to create an error everywhere Z pins are referenced which you then fix by changing Z to Z1 and adding another line for Z2.
Edited 1 time(s). Last edit at 08/11/2012 10:34AM by nophead.
[www.hydraraptor.blogspot.com]
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