Re: Soldering resistor onto A4988's ROSC pin April 24, 2019 04:58AM |
Admin Registered: 13 years ago Posts: 6,995 |
Re: Soldering resistor onto A4988's ROSC pin April 24, 2019 04:42PM |
Admin Registered: 11 years ago Posts: 3,096 |
Re: Soldering resistor onto A4988's ROSC pin April 24, 2019 06:30PM |
Registered: 4 years ago Posts: 2 |
Re: Soldering resistor onto A4988's ROSC pin April 25, 2019 04:24AM |
Admin Registered: 11 years ago Posts: 3,096 |
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azbest_hu
Thanks for the comparison
I tried this on my tevo mks base 1.4 8 bit board that has integrated a4982 drivers. Later I read about this mod is changing pwm in a way that is not optimal for 8bit boards. [hackaday.io]
I tried it out beacause my setup had really bad salmon skin effect and this can improve quality.
Did you see any difference in quality? Maybe the sensing resistors are also affecting the behavior of the steppere.
For me, it was similarly noisy after the mod. Also i heard more motor whining.
I have all metal frame, so that higly amplifies noises.
When I added noise dampers to the motors It made a much bigger difference. That is basicly two metal plate with scew holes and has rubber in between them.
I have this type, like this image shows [ae01.alicdn.com]
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Back to the HR4988. I need to do some more active probing of this chip while driving a motor, particularly because my current probe has a bandwidth of 20 kHz and the PWM current control has a clock rate of ~32 kHz when RSOC is shorted to ground. When dealing with the current control, the HR4988/A4988 doesn't have the ability for a straight up fast decay mode. This is partially why in prior captures, the current fails to escape the windings and we begin missing microsteps when we try and go faster than ~50 mm/s. However, if you put a pull-down resistor between RSOC & ground, you can change the frequency of the PWM current control, but this is caused by adjusting the off time of the logic. With reduced off time, faster speeds can only be achieved through hardware means: "braking diodes". These are factors 3 & 4 that affect speed and resolution.
Re: Soldering resistor onto A4988's ROSC pin April 25, 2019 09:18AM |
Registered: 9 years ago Posts: 752 |
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Ohmarinus
Phase Resistance: 1.7 Ohm ± 10% (20º C)
So in theory, that should be close to 1.65 Ohms.
Oh, and they're 1.2A stepper motors. Properly running, not getting hot. I think CoreXY needs way less power to move the carriage, since the movements are always coordinated by two motors simultaneously.
Re: Soldering resistor onto A4988's ROSC pin April 25, 2019 09:24AM |
Registered: 9 years ago Posts: 752 |
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Ohmarinus
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obelisk79
I'd love to see(hear) the before and after
Okay, so I have made a video with before and after. Sadly somehow my video editing software cannot use the video files from my phone (Pocophone F1) so I have uploaded two videos with before and afters.
Before (part 1):
[youtu.be]
After (part 2):
[youtu.be]
In video #2 I show the specific mod at the end.
I hope it's clear any comments are welcome as I'd like to hear your reactions.
Re: Soldering resistor onto A4988's ROSC pin April 25, 2019 09:52AM |
Registered: 4 years ago Posts: 2 |
Re: Soldering resistor onto A4988's ROSC pin April 26, 2019 04:39PM |
Admin Registered: 11 years ago Posts: 3,096 |
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azbest_hu
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Ohmarinus
However, I do not see the relation that the mod is changing the pwm in a way that is not optimal for 8bit boards, could you explain it further? Maybe I am missing the point.
No, I just misunderstood something. I got confused by the different numbers and things. Sorry
Re: Soldering resistor onto A4988's ROSC pin July 20, 2019 06:07AM |
Registered: 6 years ago Posts: 5 |
Re: Soldering resistor onto A4988's ROSC pin July 20, 2019 06:15AM |
Admin Registered: 11 years ago Posts: 3,096 |