Input shaping... how?

StevePS3

My D-bot has some fairly bad ghosting so I am hoping that input shaping will be able to help. I have wired up my accelerometer and it is working just fine. Now comes the confusing bit. How do I record any data. Even the official webpage has practically zero detail on how this is done. From the youtube videos that I've watched it looks like I need to do a print. The duet3d documentation simply says "Use command M956 to collect accelerometer data.". Do I add a single M956 at the end of the gcode, after every movement, it doesn't say? Rather than simply relying on trial and error I was hoping that there may actually be a guide showing me exactly what I need to do.

If anyone has setup input shaping then please let me know how I go about collecting data.

thanks

dc42

@steveps3 have you read https://docs.duet3d.com/en/User_manual/Connecting_hardware/Sensors_Accelerometer#using-accelerometers ?

StevePS3

@dc42
Yes, I have read that. It tells me almost nothing. What are all the shapers? Nothing is actually explained.

dc42

@steveps3 the basic process is:

Use the accelerometer to identify the resonant frequencies that are causing ringing.
Choose a shaper that suppresses those frequencies effectively. If there is only one frequency to be suppressed then we suggest a simple shaper such as ZVD, ZVDD or MZV. If there are multiple frequencies then EI2 or EI3 are likely to be more suitable.

You may find the input shaping plugin at https://github.com/Duet3D/DSF-Plugins/releases useful for determining resonances and showing the effect of the various shapers. Further work on this plugin is under way to make it easier to use.

StevePS3

Ahh, yes, the plugin looks to be more like what I was expecting. Everything just seems to vague "Choose a shaper that suppresses those frequencies effectively"? How do I know what the shapers do. Does everything have to be trial and error?

engikeneer

@steveps3 the input shapers are complex beasts designed to cancel out the ringing oscillations you see on your prints. The different types have slightly different characteristics (e.g. targeting a single narrow frequency range, or targeting a wider range but to a lesser extent).

Every printer will have different vibration properties (natural frequencies, damping factors etc) and so there is no sensible way to get a one size fits all solution, and tuning is the only real way of getting the best result.

The suggested approach is to use the accelerometer to identify your printer's resonant frequency(/ies), then use the ringing test print to try the different shapers to see which one gives the best results. Once you've narrowed it down to one or two, you might also want to try varying the frequency a little to see if that improves things further.