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Re: Is there any reason for missed steps only at low speed

December 13, 2018, 8:57 am
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Hi MKSA,

I have done a huge range of speeds and protocols and think it unlikely to be the microswitch. At the moment I am trying to set up an encoder to compare exactly what is happening at the stepper compared to what I think I told it to do.

For the moment the problem is solved by not being too fussy, I have replaced the attempt to get a baseline by simply detecting the microswitches: I ramp up the stepper to full speed and run it until it meets the microswitch - then back off a bit and move slowly until the microswitch is contacted.

I have not given up trying to find out what is happening with the original method - I tend to get annoyed when something that is impossible happens anyway and I will worry at it until it yields. The diagrams below show what I am getting - the axes are speed against time. The jiggle at the beginning of each run is to get a precise first microswitch position in case it moved. The problem is that the distance from A to B in the first diagram is the same as the distance from B to A and is repeatable, about 1990 pulses . In the second diagram B to A is the same as the return A to B, both about 2012 pulses.


[attachment 108654 ToggleMotorSpeed.jpg]

The apparent impossibility is that the second half of the first diagram is exactly the same trip as the first half of the second diagram yet the count is different. My present theory is that MplabX has some bugs that I don't know about - or maybe my brain has been leaking away.

Maybe it is time to start believing in the supernatural.

Mike
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Re: Is there any reason for missed steps only at low speed

December 15, 2018, 12:42 am
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22 pulses difference doesn't sound like a binary error ( 8-16-32 pulses would be a hint ), but nevertheless did you try to store the stepcounts in an array instead of using the same register back and forth?

BTW: Is the microswitch debounced in hardware or software manners?
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Re: Is there any reason for missed steps only at low speed

December 15, 2018, 3:44 am
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Quote
o_lampe
22 pulses difference doesn't sound like a binary error ( 8-16-32 pulses would be a hint ), but nevertheless did you try to store the stepcounts in an array instead of using the same register back and forth?

BTW: Is the microswitch debounced in hardware or software manners?

I think I have found it by looking at what is happening on an encoder that I connected to look at the stepper motor.

In each of the two round trips there are several changes of direction, most of which are from a standstill to a low(ish) speed. The speed at which the stepper could pull in was determined by trial and error and the figure used is 2/5 of the reliable pull in speed. The apparent cause of the error is that there is one transition in each round trip where the speed changes from 66.7pps in one direction to 66.7pps in the other direction - a change of 133.3pps. This seems to be reliable if going from clockwise to counterclockwise but misses steps going from counterclockwise to clockwise. Only the end of the "jiggle" is effected as all other transitions have a short delay between stop in one direction and start in the other. Mug-shot of the accused below.

[attachment 108694 Foundit.jpg]

This does not seem to be the whole of the answer as it doesn't account for the non-jiggle halves being equal, but it is possible to see that the direction transition is poor one way and good the other.

On your other point, I use no debounce at all - devilishly avant-garde I know but the only point where this may be a problem is the forward part of the jiggle and the reverse to MS detect which has a long delay due to the number of pulses in the jiggle - a sort of debounce of the serendipidous kind.
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Stepper driver SD6128

December 18, 2018, 10:15 am
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I’m using tmc 2130 with SPI interface in my kossel build the motors have 2.0A peak. I’m using 12v in my power supply. That driver are winey at 12v its goes very hot. I read that is good for a low-current motors.

With that said I'm looking for a good driver, (good resolution, silent). I've found SD6128 that uses the chip THB6128. However I'm not seeing the configuration for that drive/chip in marlin 1.1.9. So I'm investigate how to connect this driver using marlin.

Could anyone give some help were? There is any other good drive for my spefications?
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Stepper motor locks up when going higher than 8mm/s

December 20, 2018, 8:47 am
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Hello everyone. I'm having a problem with my stepper motor,it appears to lock up on speeds higher than 8mm/s. It's only my Y axis motor that does this,my Z axis uses the same motor and stepper drivers and it works fine. In the video I hooked up another motor to the Y axis cable to show that the problem isn't mechanical. I've reinstalled Marlin and checked the wiring. I've replaced the stepper motor,cables and the driver. Nothing changes. I have even tried switching Y and X outputs on the RAMPS board from the original code and the problem still appears on the Y ,even if it has switched places the problem follows it. What could be causing this issue? It's running at 1/16 step. My 3D printer is limited to 8 mm/s printing because of this which is really really slow.
Specs
Arduino Mega,Ramps 1.4,Marlin 1.1.9,Nema 17 motors,A4988 drivers
Video and even more info in my original reddit post
[www.reddit.com]
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Re: Stepper motor locks up when going higher than 8mm/s

December 20, 2018, 11:06 am
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From your video it looks as if your printer does not use pulleys and belts, but uses standard threaded rods (M8?) for the X/Y linear movements...

If so, have you calculated the actual step rates Marlin must generate to reach your desired speed and compared this with the limits of your controller setup?

According to the table on the step rates page of the RapRap Wiki, using an M8 thread with Marlin on Mega/Ramps with 1/8 micro stepping is limited to 12mm/sec - which corresponds to about 6mm/sec with 1/16 micro stepping.

Try reducing the micro stepping. If that allows you to get to higher speeds, that might indeed be an indication that you are hitting the step rate limit of your controller...
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Re: Stepper motor locks up when going higher than 8mm/s

December 20, 2018, 12:07 pm
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Interesting,I'll try reducing the microstepping. But why does the motor lock up even without it being hooked to the screw?
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Re: Stepper motor locks up when going higher than 8mm/s

December 20, 2018, 12:08 pm
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The problem also occurs if I connect the X axis to the Y axis output so I doubt it's a mechanical issue
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Re: Stepper motor locks up when going higher than 8mm/s

December 20, 2018, 1:32 pm
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Please explain us the mechanical setup of your axis.
What belts/pulleys resp threaded rods are you using on which axes?
How is your setting of STEPS/mm for the axes in Marlin's Configuration.h?
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Re: Stepper motor locks up when going higher than 8mm/s

December 20, 2018, 2:56 pm
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X has a belt I have no info on and Z and Y run on M8 threaded rods. I have calculated the steps/mm by sending commands to move 10 mm and then adjusting accordingly. Here are my current settings
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Re: Stepper motor locks up when going higher than 8mm/s

December 20, 2018, 3:13 pm
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The problem is your very high value of 2048 steps/mm on the Y axis. To achieve a good movement speed with that steps/mm, you will need a combination of fast electronics and firmware to generate the step pulses fast enough, and a low inductance stepper motor and at least 24V power to provide sufficient torque at high motor RPM.

Reducing microstepping will mitigate the limitation of your electronics, but not the reduction of torque at high rpm. Your best bet may be to change to either a belt drive or a leadscrew with a course pitch.
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Re: Stepper motor locks up when going higher than 8mm/s

December 20, 2018, 10:00 pm
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But why does my motor lock up even while not hooked to the rod as seen in my video?
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Re: Stepper motor locks up when going higher than 8mm/s

December 20, 2018, 11:27 pm
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Quote
hermanelfino
But why does my motor lock up even while not hooked to the rod as seen in my video?

Probably because there is not enough supply voltage to run the motor that fast. Reducing the Y acceleration may allow it to go a little faster. Changing to 24V power (assuming you are using 12V) would be likely to more than double the achievable speed.
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Re: Stepper driver SD6128

December 21, 2018, 9:31 am
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You treat any driver that comes without SPI, like a standard Pololu driver:
You set the Vref via potmeter and calculate steps/mm according to the jumper settings inside the driver socket.
Then change this line in Marlins configuration.h:
// X Y Z E steps/mm
#define DEFAULT_AXIS_STEPS_PER_UNIT   {200, 200, 200, 140.6}  //  steps per mm for Kossel (GT2, 16 tooth @1/32 and e-steps @1/16)
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Re: Stepper motor locks up when going higher than 8mm/s

December 21, 2018, 10:18 pm
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But if I connect an even smaller motor to the Y axis driver it locks up as well. I'm really confused as to why this is happening
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Re: Stepper motor locks up when going higher than 8mm/s

December 21, 2018, 11:28 pm
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If the smaller stepper motor has high inductance, the same considerations will apply. There is a calculator at reprapfirmware.org to calculate the speed at which torque starts to drop.

Have you tried reducing Y acceleration?
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Re: Stepper motor locks up when going higher than 8mm/s

December 22, 2018, 12:53 am
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Hermanelfino, have you checked the Wiki page about maximum step rates?

IMHO you are simply trying to operate the M8 Y-axis at a step rate which is way to high for the Marlin/Mega setup you have.
With 2048 steps/mm you will reach the safe limit of 10000steps/sec at about 5mm/sec - so I wouldn't even trust the 8mm/sec you are using.
This has nothing to do with the stepper motors you use, it's the Marlin software on the 16Mhz Mega that reaches its limit.
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New Pololu-Style driver ST820

December 22, 2018, 2:06 am
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Hi,
on some aliexpress stores a new Pololu-Style driver with ST´s ST820 chip has popped up.
It supports driving your motors with up to 45V which is kind of massive (would be cool for Nema23 in CNC use)
and supports REAL 1/256th microsteping which is IMHO the only Pololu-Style driver whith this feature.
not even the TMC2xxx drivers have real 256 microsteps, they take 16 Microsteps and interpolate them internally and
drive the Motors with 256 Microsteps.
To be honest 256 Microsteps is also kind of overkill and our Nema17s won´t be able to resolve them repeatably
but the feature is there, and I bet they will be as silent as the Trinamic drivers.
The driver is also quite cheap, 3.29$USD and keep in mind that the price will surely drop with time.
So, I think the chip will surely be a competitor to at least the TMC2208 since I bet it will be quite silent,
it does not support the back-EMF sensing StallGuard(TM) feature which the fancier Trinamics have
but then again, 3.29$ is quite cheap.

What do you guys think about the driver chips? Has anyone actually used one?

Aliexpress store link
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Re: New Pololu-Style driver ST820

December 22, 2018, 4:16 am
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Re: New Pololu-Style driver ST820

December 22, 2018, 5:56 am
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The biggest problem with any of those modules is that they can't dissipate enough heat to let you run any but small motors at rated torque. Add an easily broken current setting pot (and who knows how much current you'll actually get when you twist it?) to it and you have a perfect recipe for an unrelaiable printer.

45V NEMA-23 motors? Sure, if they'll deliver any torque at the very low current that thermal dissipation allows in this module. Take a look at a DM860 driver module for CNC machines. See that heatsink? It's not there because it looks nice.

"real" 256:1 ustepping offers the "advantage" of requiring a 16x greater pulse rate to drive the motor at the same speed as a motor being driven at 16:1 ustepping (or using interpolated 256:1 ustepping). Calculate the maximum speed your controller can deliver at 16:1 ustepping and divide it by 16 if you use this module at 256:1. ooops.

At 256:1 this thing can't go fast enough for a 3D printer (OK, it would be fine in the Z axis) and it can't supply enough current for a CNC router or mill.
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