Does M906 set RMS or peak current?

wilriker

@whosrdaddy Thanks for your input. I was struggling a bit to use such a "weak" stepper because according to https://duet3d.dozuki.com/Wiki/Choosing_an_extruder_drive one should aim for at least 10N and with a 3:1 gearing it would require at least 17Ncm.

Speaking of which: I commented on that page that I assume the formula for 0.9° steppers is missing another zero to be correct. Am I right in that assumption?

whosrdaddy

@wilriker : You are aware that E3D sells a 0.9deg pancake stepper that only has 12Ncm? I have one on my P3Steel and is a bit weaker than the OMC's on my CoreXY....

wilriker

@whosrdaddy Yeah, I know but at least it is not the one they sell in the bundle (anymore?!) and say something like "hey, look here, we have a stepper that has a lot of power but still is lighter than the regular ones without beeing a total weak-o".

I am not long enough into 3D printing to have an educated meaning on E3D but I know (and probably everyone does) that sometimes sellers just sell things out of customer's demand and not because it is the best product/combination, so I have trusted the wiki here a little more than the wide product range of E3D.

Is a 0.9° stepper on a geared extruder really an additional improvement, I am wondering?

dc42

The minimum extrusion force that I give in the wiki page is set at a value that makes it unlikely that you will be short of extruder force. I am not saying that you can't extrude with lower force but it depends on your hot end, filament, print speed and print temperature (including how much the extruder temperature drops when the print cooling fan turns on). For a directly coupled extruder such as the Titan Aero it would certainly be worth trying a lighter pancake motor that provides less than 10N force in order to reduce weight, but preferably make sure your print head design will accommodate a slightly longer motor too in case it proves inadequate.

wilriker

@dc42 Thanks for clarifying. I now ordered a Titan (actually I have to admit it is a clone) and the included motor has 12 Ncm with slightly better values for resistance and inductance than the short pancake that @whosrdaddy has. This will through the gearing already give me about 2N more force than my current extruder which is ungeared.

My extruder carriage is not restricting motor size, so I could upgrade to a larger/stronger one later.

Oh, and thanks for fixing the formula on the wiki page.

AlexLin

I found the e3d pancake getting very hot, so I switched to the e3d compact one which works better for me. Direct drive normally printing at 70mm/s and .4 nozzle, .2 layer height

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.