Ender 3 (dual) Z-axis lifting strength vs motor current
I made a small 0.1 Ohm current shunt (from 10 parallel 1 Ohm 1/4 Watt resistors) and used it to measure the Z-axis stepper motor current of my Ender 3 3D printer.
I then entered a cycle of:
- applying increasing weight to the gantry until the Z-axis stalled
- increasing the motor current (by adjusting the Z-axis stepper driver Vref) until the gantry could lift the weight
- increasing the weight again, etc.
Here are the results:
A bit of explanation:
If you move the Z-axis by 0.04mm, that appears to advance the motor by exactly one step of what is a four-step repeating sequence. This is what e.g. "phase 1" refers to. For each weight and Vref setting, I measured all four steps / phases.
Note that this is the current through one coil of both steppers in parallel, as I have added a second Z-axis motor to my Ender 3, and the current shunt is taking the measurement before the split in the cable. This means each stepper only sees about half of the measured current (one stepper will see slightly less because of differences in wiring length).
Considering the Z-axis steppers are rated for 840mA, and apparently it only takes 344mA (per motor) to lift 22.5lb, adding a second motor makes the Z-axis way overpowered.
(Of course, the reason to add a second Z-motor is to increase precision by avoiding cantilevered gantry droop, not to increase lifting power).
Unfortunately my current shunt slipped out of place and shorted against the frame, which took out one of the phases of the Z-axis A4988 driver (it only makes one step on startup now).
Fortunately, this is exactly the excuse I needed up upgrade to silent stepper drivers 😎