I’ve built the lowrider v4 and completed a few basic projects on it. As I learn (and make mistakes), I occasionally have missed steps when I my passes are too aggresive. These missed steps ruin the workpiece when the CNC loses position and continues trying to cut in the wrong position.
Has anyone tried using the stallguard feature associated with the Jackpot drivers as a sensor to detect missed steps? My thought is to write a macro that’s triggered when the stallguard hits a threshold that suggests the machine is facing more resistance than it can handle. The macro would then lift the gantry off the workpiece and throw an alarm.
This wouldn’t correct the position of the machine after a missed step, but it could prevent the machine from carving a chunk out of a workpiece when I’ve set my feeds and speeds incorrectly.
Any thoughts on whether this would work or better ways to detect and respond to missed steps?
The stallguard has been talked about a few times around here. I am not the best to explain it but I will try
The load varies so much on the motors going through a cut that it makes it extremely hard to tune. Also I am not sure that we can even use that feature in fluidnc, but I could be wrong.
Yes, I’ve done this. In my experience, it works in theory but not in practice. The issue is the value is speed, material, and depth dependent. So, you can get it to work, but not reliably.
The best takeaway here is if you skipped steps your CAM is drastically wrong. Stall guard might help a little but test cuts and more correct CAM are a better option here.
I just did tests at 10lbs force and there is zero missed steps at the lower holding torque. If you are exceeding 10lbs on a cut, you need to cut your material removal rate by about half, or make sure you are using the right end mill.
Thanks Ryan, I’m getting good success at 850mm/min and 1.5mm depth on a 1/8” upcut.
My thought is on implementing this to mitigate mistakes in my CAM programming. I know I will continue to forget to set the depth of pass on one of my parts or tool changes in fusion. I’ve had a couple times where a piece is running well for a couple hours, and then transitions to the next section of code where I forgot a setting and I end up with a black scorch across the piece before I can stop the machine and router.
I’m an electrical engineering student and I’m looking for final projects this term that can improve my CNC. Adding some level of error/fault feedback seems like a good place to explore.
Do you think it has potential to work in extreme cases - throwing a fault at very high levels of resistance? Are you willing to pass along the code you used to implement the test?
In what material? In anything other than metal that is very very slow so I would assume a bad endmill or maybe your spindle is running backwards. We need more details, on your build, steppers endmill, router, material.
That is just it. In anything other than metal 2mm/s-50mm/s should work 1mm doc to 12mm doc should work. If you skipped steps something is drastically wrong. The machine is already built with a huge range of acceptable so when I hear skipped steps I know something else is wrong.
If you wanted to see that I would suggest trying to add some load cells to watch real time load on the XY axis, that will tell you way more than adding power and not knowing it. Plus I would love to see this!
If you really want to go this route, you need encoders on the motor and closed loop control.
That’s already available in the FluidNC ecosystem if you use a board like a Doberman and external closed loop stepper drivers.
Note- this won’t “Fix” bad CAM, so your lesson to learn is exactly what was shared above- understand your machine and material, and stay within the capabiliteis therein.
