I saw a video for that an add-on board that adds closed loop control to NEMA stepper motors called the S423B by BigTreeTech, the company that does the SKR series mainboards. I went ahead and ordered myself a set as from time to time I’m known to have terrible feeds and speeds that result in skipped steps and ruined projects, so hopefully this will help prevent some of that. Has anyone already tried the S42B? At $16USD each they are very reasonably priced. Closed loop control looks like it would be pretty revolutionary (pun intended) if it works as intended.
It looks like you can either add it to existing stepper motors or buy it with stepper motor attached. Personally, my preferred option is to attach it to my current motors as it looks like the ones they sell are 42 oz/in instead of the 76 oz/in I got from Ryan.
It’s coming on the slow boat from China so it may be a little bit before I have an update as to if and how well they work.
You might be exchanging skipped steps for broken endmills.
These are an amazing addition, that should not be needed, but could help with random issues like knots and things. If you are getting skipped steps though you really need to do some more test cuts in each type of material, endmills are not free.
Had the same thought just now watching this video - made for 3D printers but CNC router seems like a better use case considering how much more physical strain the machine is under. Though I see Ryan’s point, any quick movements due to loop closing could possibly break bits.
If you end up trying it, definitely let us know how it goes.
I found your project and ordered the BIGTREETECH S42B V2.0 Closed Loop Driver too and wait for their delivery including the PRO board and the 4.2" Display which should be done within the next weeks.
Are there anyone which already use this kind of closed loop steppers for the MPCNC?
Which issues beside the bit break should I expect?
Skipping steps is a very rare occurrence. These are just going to be a backup plan, and an easy one since you don’t really need to change anything to use them. I would say you will never notice a difference. It could possibly allow for faster rapids, but cutting is limited by rigidity not stepper power.
I now do have the MPCNC Primo build with SKR Pro 1.2 and five S42B V2.0 closed loop stepper and RepRap Firmware with dual end stops.
Currently I do have some strange issues with the S42B with the stock Firmware:
six out of ten times after startup the home fails because one of the two steppers of X or / and Y moves in the other direction → to fix it I need to move the axes three times 1mm in one and then in the other direction. Then the axes getting squared with the dual end stops on home again.
the do not move smooth at all, even with just 10mm/s the pen starts shaking and if I go faster the whole table starts to vibrate.
Yes @vicious1 you are right there is no need for closed loop stepper, but I like to test it and if it will not work I can use the Stepper with TMC2209 anyhow
Btw. the design ob the MPCNC Primo is genius, it was a pleasure to build it, all fits together very smoothly!
That’s my biggest worry. Getting the controls tuned for closed loop is going to be tricky, and it isn’t anything that gets you a bullet on a product page, so I am not sure the vendor is going to put the time in that it takes to make that work well. Besides, the amount of mass we are moving is significantly more than most printers, so I wouldn’t expect the same PID values to work the same for our purposes. But, no one can work on a solution until there is hardware to work on, so I’m glad we have that now.
Closed loop control for the steppers can work really well if the controller is also looking at position feedback, as this driver is doing locally. The whole idea is to never have skipped steps because it’s critical to always know the position of the tool. But, this means that the motion control should slow down when reaching a potential stall condition, and I don’t believe that flexibility is built in to existing firmware (Marlin). If the closed loop drivers are buffering commands then it could work until or unless the buffer overflows, but this is a local driver solution to correct for upset, not degraded performance due to misprogramming.
We ran into the same issues when designing an emergency ventilator last year. The decision to run closed loop steppers changed everything in the control setup. It resulted in much better performance but at that cost of a higher level feedback which no printer or DIY CNC I’ve seen has. (We did get FDA approval for the ventilator, though)
That said, I’m a fan of closed loop control and I would definitely build a system with it if I could. I’ve had more than one instance of steppers skipping; all correctable by different CAM, but I’d love for the machine to adapt to conditions (wood hardness, etc.) by itself. A complete implementation would require significant changes to Marlin, though.
you are right, currently only a red led on the stepper driver shows that the stepper could not move to the position which is requested.
The driver V2 on the S42B or V1 on the S57 (nema 23) do also have a can bus interface. So maybe we see here in the future some improve beside that the firmware of the boards even also needs to handle this news situation.
Anyhow I belive that closed loop will be used more often in the future so we can expect a better integration because the price difference beetween normal and closed loop drivers are not relevant anymore.
