Little troubles with GRBL - overheating and configuration

[newnoise]

Hello!

First of all: thanks for the cool Shield! I think mine is a cheap China-Board

I finished a ShapeOKO like build yesterday and ran the first test. My setup is the following:

• 3 axis, 4 motors (23LM-C355-34V motors) -> Y-axis is cloned to A
• it's moves on threaded bars
• CNC Shield V3.00 with 4 x DRV8825 and GRBL 0.9j
• Microstepping is set to 1/8
• 24V Switching Power Supply (10A)

I ran some test yesterday and most of it works, some things happend and some things I just don't really understand, so I would be more than happy, if you could help me with some of them! I will give you a short description of what I did and than shoot the questions.

• the first run was a bit "adventerous", since I did not configure the DRV8825-drivers. This gave me some stink (they got really hot)
• I then configured them to a Vref of 0.5V which made them stay cool (for quite a while)
• it worked quite ok but the movement was way too slow (fixed this by adjusting the step/mm setting)
• running the ShapeOKO "Hello World" G-Code would still have way too small movements (only about 1cm)
• running another GCode (just a square grid) worked well, but the stepper-driver got very hot again

Now to my questions:

• first of all: how do I figure out which microstepping option is the right one for me?
• I had to set the step/mm to 3125 to make the CNC move the correct distance, this seems extremely high, compared to other settings I've seen
• the cloned axis stops from time to time. I already replaced the stepper driver, but same issue. It might be mechanical problem too.
• after I ran the last job the drivers still got really hot (although Vref is set to 0.5V now), I attached the GCode

So far so good, thanks for reading all this. Best,
Tom

## GCode (sorry could not attach it as file)

Code: Select all

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( File created using Intuwiz Software Service )
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( File created:  2016-06-18  22:27:20  )

G00 Z0.5 F70
G00 X0 Y0 F70
G01 Z-1 F50
G01 X0 Y50 F50

G00 Z0.5 F70
G00 X10 Y50 F70
G01 Z-1 F50
G01 X10 Y0 F50

G00 Z0.5 F70
G00 X20 Y0 F70
G01 Z-1 F50
G01 X20 Y50 F50

G00 Z0.5 F70
G00 X30 Y50 F70
G01 Z-1 F50
G01 X30 Y0 F50

G00 Z0.5 F70
G00 X40 Y0 F70
G01 Z-1 F50
G01 X40 Y50 F50

(do horizontal lines)
G00 Z0.5 F70
G00 X40 Y50 F70
G01 Z-1 F50
G01 X0 Y50 F50

G00 Z0.5 F70
G00 X0 Y40 F70
G01 Z-1 F50
G01 X40 Y40 F50

G00 Z0.5 F70
G00 X40 Y30 F70
G01 Z-1 F50
G01 X0 Y30 F50

G00 Z0.5 F70
G00 X0 Y20 F70
G01 Z-1 F50
G01 X40 Y20 F50

G00 Z0.5 F70
G00 X40 Y10 F70
G01 Z-1 F50
G01 X0 Y10 F50

G00 Z0.5 F70
G00 X0 Y0 F70
G01 Z-1 F50
G01 X40 Y0 F50


G00 Z0.5 F70
G00 X0 Y0 F70
M30
%

[DRobs86]

If your build is driven by threaded rod then you do not need much microstepping.

Let us say for simplicity that you had a rod with a 1mm pitch. Most steppers are 200 steps per rotation. You therefore, in this example, would have 200 steps per mm with no microstepping. I would use no microstepping or at most 1/2. In this example 1/2 microstepping would require you set 400 steps/mm. That is much more precision than your machine will ever achieve anyway.

Dont try to change steps per mm to change speed. Max rate settings do that. Things will come out the right size once you have this set correctly.

I havent addressed your other issues much, but I will say that extremely hot isn't a useful description. Absent a way to objectively measure, it might be useful to share about how long you could touch the driver with a finger. Too hot to even get your finger near communicates something different than "dont want to touch for more than 3 seconds." Even though though they claim these things are rated for 2 plus amps per phase they really aren't that useful in that range. It looks like you are only running at about 1 amp, but even at that point heat sinks and even a fan is helpful. For instance, I run some on that same shield at a vref of 0.6V with heat sinks and about a 40cfm fan blowing on them and they are probably 95 deg F at most.