Using Input Shaping. Any suggestions or advice??

tfjield

I'm starting to look at input shaping (for the first time!), and I could use some guidance...

I've attached the accelerometer (LIS3DH from adafruit) to the Duet2 WiFi, and it appears to be working properly. I configured it with M955 P0 C"spi.cs4+spi.cs3" I01 and I mounted it to my hot end with a zip tie (and some tape to avoid shorting the back).

I'm able to collect data using the Input Shaping Plugin, v4.3.1-b1:

This is with XY maximum speeds set to 16000 mm/min and acceleration set to 3000 mm/sec^2.

This is on a Modix Big-60, and the accelerometer is connected to the printhead, so there is no z-motion. But the big printhead bracket has a decent amount of movement around the y-axis, so I would expect to see some significant ringing along x, and I see see one peak around 27 Hz.

Do these curves look right? (Why all the z-axis data? Is this just a byproduct of the FFT without any strong frequency components?)

Turning on ZVDD at a 27 Hz center frequency (arbitrary choice, and the white checkmark next to the center frequency entry is fun!) gets me this:

So it seems like it's working, right? Any advise or suggestions? I haven't tried printing any ringing tests, yet.

oliof

I'd try to add strain relief to the wires as close to the board as possible. Also make sure that you've configured the right orientation of the sensor.

On a CoreXY system, divergent graphs for X and Y are an indicator that the belts aren't equally tensioned. You could try loosening Y tension or increasing X tension a bit to see if it helps.

oliof

oh also, use two zip ties to fasten the board, one is effectively a lever.

tfjield

@oliof Thank you! Great idea about the wires; I didn't think of that. I'll add some strain relief to minimize any artifact they might be introducing.

I don't think the x and y being different on this machine means much. In my first photos you can see 4 silver screw heads. Those are the only attachments to the y-axis rail, so that whole head can twist around the y-axis forward and backwards (so the hot end oscillates in the x-direction). There's a bit less play rotating around the x-axis.

But the belts could be contributing. There is one y-axis belt and two x-axis belts, and I know the y tension is higher than the two x's.

oliof

Some variance in the vibration peaks don't matter much due to the damping factor of the IS algorithms. You should measure your second head too to make sure that two X belts have about the same tension as well.

chickenwoman

@tfjield this is off topic but what wire did you use on your Modix and what length? I have a Big 60 and have tried several different types of wire and cant get it to work.

tfjield

@chickenwoman said in Using Input Shaping. Any suggestions or advice??:

@tfjield this is off topic but what wire did you use on your Modix and what length? I have a Big 60 and have tried several different types of wire and cant get it to work.

The first time I tried I used an old, unshielded network cable and it wouldn't recognize the accelerometer. Then I went with a USB cable.

I followed this guide:
https://forum.duet3d.com/topic/22878/software-package-3-3beta3-released/68?_=1624809172098

I purchased this USB cable from Amazon:
https://smile.amazon.com/dp/B014RWATK2

I left the cable at about 5 feet / 1.5 meters. There are two shields inside wrapped around two different pairs, and a shield around the whole thing. I attached all three shields together, and connected it to one of the ground points on the Duet boards. (I have the DueX5, so I used one of the grounds on one of the 5 endstop connectors.)

I use a PT100 daughterboard, and the daughterboard moves CS3 and CS4 from pins 7 and 9 to pins 3 and 1, respectively. So my CS connects to pin 1 and INT connects to pin 3.

EDIT: Here are some pics of my connection. I didn't have a dual inline plug that took crimp connections for the Duet side so I made one with the connectors that I had.