Does M906 set RMS or peak current?

wilriker

One question that came to my mind: will any one or a combination of the factors rated current, resistance and inductance have an effect on the noise level of a motor?

My final goal is to modify my printer to be the most silent as possible at a given speed. The TMC2660 already do a great job in reducing noise level (I know that TMC2130/2208 would have been even more silent using stealthChop but I could not resist adding the very best board out there to one of the most low-end printers available ) but can a specific selection of motor specs also reduce the noise level even further?

dc42

@wilriker said in Does M906 set RMS or peak current?:

One question that came to my mind: will any one or a combination of the factors rated current, resistance and inductance have an effect on the noise level of a motor?

The answer is yes, but I don't yet know what the best choice is. Also we may be able to reduce the noise level for particular motors by adjusting the chopper configuration register settings.

wilriker

@dc42 said in Does M906 set RMS or peak current?:

Also we may be able to reduce the noise level for particular motors by adjusting the chopper configuration register settings.

Is there something I can do to help testing this out?

dc42

@wilriker said in Does M906 set RMS or peak current?:

@dc42 said in Does M906 set RMS or peak current?:

Also we may be able to reduce the noise level for particular motors by adjusting the chopper configuration register settings.

Is there something I can do to help testing this out?

Yes! See section 2 of https://www.trinamic.com/fileadmin/assets/Support/Appnotes/AN001-spreadCycle.pdf for guidance on tuning the chopper configuration register settings. You can change the value of the chopper configuration register in firmware 2.0RC5 using the C parameter of the M569 command.

PS - the default chopper configuration register value is:

// Chopper control register defaults

// 0x901B4 as per datasheet example

// CHM bit not set, so uses spread cycle mode

const uint32_t defaultChopConfReg =
TMC_REG_CHOPCONF
| TMC_CHOPCONF_TBL(2) // blanking time 36 clocks which is about 2.4us typical (should maybe use 16 or 24 instead?)
| TMC_CHOPCONF_HDEC(0) // no hysteresis decrement
| TMC_CHOPCONF_HEND(3) // HEND = 0
| TMC_CHOPCONF_HSTRT(3) // HSTRT = 4
| TMC_CHOPCONF_TOFF(4); // TOFF = 9.2us

Only the lowest 17 bits of the value you give in the M569 command are used.

wilriker

@dc42 I will look at the documentation and see what I can do. My biggest problem here might be that the real inductance of the motors I currently still have is unknown (stock Anet A8 motors - you already researched a bit about them and guessed they would be aroun 8-10mH). Should I wait until I replaced the motors with something where all specs are known for sure or can I already go with the estimated inductance?

Also, is there any simple way to measure the inductance? I guess not, but still want to ask.

wilriker

@dc42 said in Does M906 set RMS or peak current?:

PS - the default chopper configuration register value is:

// Chopper control register defaults

// 0x901B4 as per datasheet example

// CHM bit not set, so uses spread cycle mode

const uint32_t defaultChopConfReg =
TMC_REG_CHOPCONF
| TMC_CHOPCONF_TBL(2) // blanking time 36 clocks which is about 2.4us typical (should maybe use 16 or 24 instead?)
| TMC_CHOPCONF_HDEC(0) // no hysteresis decrement
| TMC_CHOPCONF_HEND(3) // HEND = 0
| TMC_CHOPCONF_HSTRT(3) // HSTRT = 4
| TMC_CHOPCONF_TOFF(4); // TOFF = 9.2us

Do the drivers use their internal clock at 15Mhz or is an external clock used as recommended in section 13 of the datasheet for TMC2660? And if the latter is the case what frequency does it have?

dc42

The drivers use the internal clock. We were originally going to use an external clock, however the drivers would be likely to blow up if the clock failed for any reason (e.g. because you flashed bad firmware to the Duet); so we reverted to internal clock.

wilriker

@dc42 Yeah, I just read the big fat warning about external clocking being turned off (out of whatever reason) without taking the necessary precautions... They say on the one hand, if you need the most precise chopper, using external clock - but that makes it prone to blow up also...

wilriker

@dc42 Section 2.2 of the Parameterization of spreadCycle document says

Use highest possible microstep resolution for your tests.

Should I use native 256 microstepping or would this also work with 16+interpolation?

dc42

@wilriker said in Does M906 set RMS or peak current?:

@dc42 Section 2.2 of the Parameterization of spreadCycle document says

Use highest possible microstep resolution for your tests.

Should I use native 256 microstepping or would this also work with 16+interpolation?

I suggest you work with x16 with interpolation, because that is what most people use.

The particular issue that some users have is that the drives are noisy at standstill. Section 2.4 of the app note suggests reducing TOFF in this situation.

wilriker

@dc42 OK, I will further read the document and will test over the next couple of days and then report my findings.

The particular issue that some users have is that the drives are noisy at standstill.

Should I set the standstill current via M917 to a specific value for this?

An interesting note in Table 1 says that current in standby could even be reduced to 0 depending on the setup. I saw that M906 allows a range of 0..100 for the I parameter. Will using 0 really set idle current to 0mA? That would be basically the same as using M18/M84 just without requirement to rehome (given enough trust in the positions not having changed out of any reason).

dc42

Setting standstill current with M917 doesn't yet work on the Duet 2. But you might want to temporarily increase the idle current to 100% in M906 so that the motor current doesn't get reduced after 230 seconds of inactivity, making the standstill noise easier to hear.

Setting M906 I parameter to zero will reduce the current to 100mA.

wilriker

@dc42 said in Does M906 set RMS or peak current?:

Setting standstill current with M917 doesn't yet work on the Duet 2. But you might want to temporarily increase the idle current to 100% in M906 so that the motor current doesn't get reduced after 230 seconds of inactivity, making the standstill noise easier to hear.

I have my timeout even reduced to 15s. Which reminds me of another question that came to my mind: is idle current reduction also applied while printing (from SD card)? I ask because that might mean that with this rather short timeout I have set it would reduce the Z motors to idle current for any layer above 10mm height (mesh level taper) that takes longer then my timeout.

Setting M906 I parameter to zero will reduce the current to 100mA.

OK, I will add this to GCode description so it will be known when reading documentation about M906

dc42

@wilriker, the idle timeout only takes effect when all enabled motors are idle for 30 seconds, or whatever you have the timeout period set to. So the only time it should happen during an SD card print is while heating up.

wilriker

@dc42 I just wrote a little tool in Go to create me the integer required for M569 Cnnnn based on a more human-friendly input. I used the macros in TMC2660.cpp as a basis but decided to allow only exactly the values as specified in Trinamic's documentation, e.g. 16, 24, 36 and 54 for TBL which should make it a little less brain-twisting when working with their guide.

I have to check an issue with motor stall detection on low Y positions first that my today's print spit out a lot but after that I can start looking into CHOPCONF register.

EDIT: can this value be set live or do I need to set them in config.g and restart?

dc42

You can set the value live.

wilriker

@dc42 OK, my results so far: we are already at the more or less best values.

Test Setup

Motor: 42SHDC3025-24B

Axis: X
Step Angle: 1.8°
Rated current: 900mA
Resistance: 4.4Ohm
Inductance: unknown - estimated to 8-10mH
Rated torque: 40Ncm

Motor current set to 400mA with idle current reduction disabled (by setting it to I100)

Standstill noise is clearly audible and a high pitched sound.

Results invalid, see post(s) below.

Results

Moves

HSTRT/HEND
I could get a little bit quieter moves on some circumstances and listening angles/distances when setting HSTRT=5 and HEND=0 (for clarification these are the values that will be put into the macros of the C++ code). But the difference is very faint.

Standstill

TOFF
Regarding standstill noise, I could not find any combination that was quieter. TOFF starting from 8 or 9 up to 15 gets worse with every step but below that they are all about the same, so reducing this from 4 to 2 does not make any audible difference.

rndtf
I also tried enabling rndtf but that makes it very minimally worse or equal at best but definitely not better.

TBL
Also tried all values of tbl but the current value of 2 already gives best results regarding noise level.

Any idea what else to test?

wilriker

@dc42 I only now realized that my X motor nearly does not give off any standstill noise. It were my Z motors I was hearing all the time because I did not disable them while testing. I will need to retest and come back with new results.

wilriker

So, this was a rather quick one because currently I have some mechanical squeaking on my Z axis, so I cannot really test movement noises.

TOFF
For standstill noise setting TOFF=3 makes a noticable difference towards being more silent and a less annoying frequency. All other values are either equal to a value of 4 or are definitely worse.

TBL
TBL=2 is already the best value.

rndtf
Enabling rndtf this time makes it noticeably worse.

Conclusion

Reducing TOFF to a value of 3 will definitely go into my configuration for Z axis.

wilriker

I now also tested all other axes.

Best values for TOFF per axis:

X: 6 (makes it inaudible in standstill)
Y: 3 (large improvement)
Z: 3 (large improvement)
E0: 4 (current default) even though 9 also gives a quite good result

So it might be interesting to provide a dedicated parameter for TOFF to either M569 or M906 (or maybe M917?) so everyone could work out the perfect values for themselves without having to fiddle around with bitmasks.

I will have to retest values fo HSTRT/HEND for all axes again tomorrow.