Duet Maesto Stepper Driver Expansion Schematic

[Wurstkarton]

@dc42 from what I could tell, yes. But that really does not mean much.

The layout of output 1 (which is the output that generates the problem) looks a bit different, but I am not sure if this really would be a problem. Would be easier to see with the actual layout in a design tool.

[BotLawson]

I do see some differences in the expansion board schematic. The 470pF ESD capacitors on the motor outputs have different voltage ratings. If the Duet 2 has NPO caps while the Expansion has Y5V (or even X7R) this might cause some noise as the higher capacitance capacitor dialectics are non-linear and piezoelectric while the NPO dialectic is nearly ideal.

I'd also look closely at the grounding and parasitics of the current sense resistors on P5. That current wave-form sure looks like the current loop has started to go unstable. Might not need much series inductance to drive it over the edge. (the TMC2224 data sheet even warns about stray inductance on this circuit) Also check the supply decoupling for stray inductance or capacitor dialectic differences as these could can easily couple back into the loop.

[dc42]

@BotLawson said in Duet Maesto Stepper Driver Expansion Schematic:

I'd also look closely at the grounding and parasitics of the current sense resistors on P5.

I suspect that's where the problem lies.

[dc42]

I've managed to obtain the Gerber files for the expansion daughter board, and I think the difference between P5 and P6 can indeed be explained by layout differences - in particular, differences in the ground plane. Here is the top copper layer of the PCB.

The most significant difference I can see is that in the upper driver, the top (ground) end of sense resistor R3 has to go around a very long path to reach the decoupling capacitors and the ground pad of the chip. You could try adding a wire link as shown between the top end of R3 and either the ground end of the electrolytic capacitor C4 as shown (taking care not to short it against C6) or alternatively looping over the edge of the board to the bottom copper ground plane underneath the ground end of C4.

[Wurstkarton]

@dc42 Thank you for this analysis. At the moment, I do not have the need to try it out (as I have two P6). But I am sure that others may find it useful!

[BotLawson]

![I've been Printing PPE on my IDEX 3d printer recently. This ends up being a bit of torture test for the Meastro and expansion as I have all 7 steppers going constantly for 2 hours.

The last couple of prints I had "P5 short circuit" errors that would trigger about 30min into a print after the controller and motors warmed up. But the prints would complete with almost no change to the motion of the extruder on P5. The extruder did stop for 5-10 seconds 2-3 times during the later prints, but re-started and completed the prints with no other issues.

I assume that poor current loop stability can trigger a short circuit flag, so I went ahead and did a similar fix to what you suggested DC42. Only had a chance to do one test print with P5 in spread-cycle mode, but the short circuit errors are gone. I'll do more test prints in stealth-chop mode tonight to confirm.

Attached are the front and back of my modified expansion.

Looking at the layout render, it looks like the culprit is the Vin trace to C6. It cuts off the direct path to ground and forces current from R3 to loop around the outside of the pcb. Personally, I'd put R3 and R2 between the TMC chip and stepper connector and give them 2-4 vias to the ground plane and the thermal die pad of the TMC. The motor phase connections can then sneak under or around the 805 resistor.

[Wurstkarton]

@BotLawson said in Duet Maesto Stepper Driver Expansion Schematic:

Looking at the layout render, it looks like the culprit is the Vin trace to C6. It cuts off the direct path to ground and forces current from R3 to loop around the outside of the pcb. Personally, I'd put R3 and R2 between the TMC chip and stepper connector and give them 2-4 vias to the ground plane and the thermal die pad of the TMC. The motor phase connections can then sneak under or around the 805 resistor.

Exactly. There is this "unconnected" peninsula to the right of R3/C2. Great job to both of you guys. I guess this fixes it.