I’ve been running an MPCNC primo with dual endstops for the last 7 months, mostly successfully but electrical issues keep cropping up. Board is an MKSGen L board with A4988 steppers and 84 oz.in nema 27 steppers. I’ve switched the steppers for TMC2209 but similar results occur.
My initial wires were flexible, but not able to take cable movement (despite being in a cable chain guide) and I’ve subsequently rewired my motors with thicker wire.
Current issue is that one y motor often skips steps mid-cut and all motors lose some torque on direction change. Not sure if the latter is normal.
The y motor is the one closest to the cable chain. It also skipped steps prior to rewiring.
I’ve tested the friction and my gantries move smoothly with some, but not excessive friction on all trucks. My belts are not very tight, but are tight enough to prevent slippage.
Ive also checked my gears for slippage and they’re fine.
Applying manual resistance to the motors and it doesn’t take much force to force a skipped step, but the force seems about the same for all motors.
Thinking it may be electrical interference on the end-stops I rewired those with telephone cable, but it’s made no difference to the missed steps.
The motor cable wire in the cable drag chain is a bit stiff, but the cable drag chain is able to move easily and freely. I don’t know if this has much impact.
The other issue is that when I apply a light force to the motor (way less than what’s required to cause step skipping) and reverse the motor’s direction, the motor loses torque and skips steps in the direction of the force.
I had an MKS Gen L V1.0 board. I was using the DRV8825 drivers. Note that the A4988s (And DRV8825s) come with different amounts ov available current, depending on the manufacturer, and many cheap A4988s barely support 1A. The TMC2209s ought to be capable enough, but did you check manufacturer’s recommendations for setting current?
The 84oz-in motors ought to be good enough, I’ve got 3 of those, and 2 others that came from an old printer. I think I looked them up as 76oz-in at some point, but don’t remember. They’re good enough, anyway.
I found the MKS board to work fine, but the processor was a little slow and it would pause doing G02/G03 arc movements, which could cause some jerkiness in the movement of the machine, so I upgraded to 32bit electronics, rather than change the CAM to split arcs into short line segments.
Thanks both for your quick replies.
A4988’s work fine with the MPCNC, but I prefer the TMC2209s.
I forgot to mention that I did check the stepper vref settings. I have a fan blowing over the heat sinks so tried increasing the voltage in case it was not high enough, but the problem persisted.
I have an Skr 2.0 board in the mail so will be upgrading to 32-bit soon.
I run my 2209s at a current setting of 1200 as the stock setting of 900 was having issues with skipped steps. The steppers get warm but not hot to the touch.
You may want to do a diagnostic though and confirm that the 2209s aren’t going into protection mode due to overheating. I think they drop to 50% power if they hit a temp threshold.
Another piece to look at is the rating on your power supply to make sure you have the power to run all your steppers at higher currents.
Ah, thanks! You’re right as always. I was just looking at driver prices earlier, and thinking that the a4988 was on the lower scale considering the pricing. But I know for sure that the Rambo is a great board!
Not all A4988s are created equal, and I have at least 2 different ways to set VRef based on the manufacturers for the 4988s that I have.
In general, as I understand it, stepper motors lose torque at high speeds way before low speeds, given a specific available power supply, so losing torque at low speeds is… kind of weird.
You should be able to apply some force to the gantry when the motors are energized and it should hold position. If holding position is weak, and can be easily overcome, then your current isn’t high enough, or the motors are not the spec you think you bought.
For the record, I used a 24V PSU for my Gen L (And am still using that PSU for my Duet2) which allows higher speed operation without losing torque. At lower speeds, 12V should be more than adequate.
I think Michael hit it on the head. Unsurprisingly it’s something small but important: my power supply is grossly underpowered: 3A!
Casting back to when I first powered up, I only had one 12-24v power adapter readily available and I was in a rush to ‘see if everything worked’ so just went ahead without even looking at the power delivery. It worked and my test cuts had no issues so just I forgot all about and moved on to the next thing to do.
Bloody amazing that my MPCNC has able to cut anything as well as it has.
Thanks all. I’ll leave feedback on how I go once I get another power supply.
I found an old 4.65A 12v laptop charger and it has made a difference already.
The motors still skip when I apply a manual force, but it’s hard to tell without scientific measurement if this differed to what I did before so I tested some cuts that had repeated skipping issues. Result: success! Thanks all for your input and feedback.