Blog 2022/9/30

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# 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](https://www.google.com/search?q=creality+ender+3) 3D printer.

![IMG_1979](https://user-images.githubusercontent.com/223396/193396314-61f2516b-7618-4e77-a031-5b3bfe351d77.jpeg)

![IMG_1978](https://user-images.githubusercontent.com/223396/193396317-fbf733ed-7dc0-4fd6-a3e9-54b111c413df.jpeg)

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](https://www.google.com/search?q=ender+3+vref)) until the gantry could lift the weight
- increasing the weight again, etc.

![IMG_1993](https://user-images.githubusercontent.com/223396/193396305-eb9e4513-4d18-4531-9e95-bc7835e92ed7.jpg)

Here are the results:

![Screen Shot 2022-10-01 at 1 54 03 AM](https://user-images.githubusercontent.com/223396/193397031-96b53ef5-ea30-4cae-abf6-6a65663bd310.png)

A bit of explanation:

If you move the Z-axis by [0.04mm](https://www.google.com/search?q=ender+3+0.04mm+magic+number),
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](https://www.google.com/search?q=dual+z+axis+ender+3) 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](https://www.youmaketech.com/wp-content/uploads/2022/01/Creality-42-34-Motor-Specifications.pdf), 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).


## Epilogue

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](https://www.google.com/search?q=A4988) driver (it only makes one step on startup now).

Fortunately, this is exactly the excuse I needed up upgrade to [silent stepper drivers](https://www.google.com/search?q=ender+3+v4.2.7+board) 😎