steppers with lots of Amp... + M906 command
-
@wilriker
Thanks!To be honest all that is so new to me, that I do not know if it is what I am looking for - that said - I am realizing, what I am looking for is how to convert what is given in most datasheets for steppers to what I need to put into the "inertia-match"/"inertia-ratio" formulas, so if I take your formula I have a few questions:
- rotorMass? -> In gramm (you divide by 1000 in the end)
- motorCount? -> rpm or rps? Or what else?
- pulleyRadius? -> Of which pulley, the "main" pulley?
At least a first thread I can maybe follow down the road...
-
@lb said in steppers with lots of Amp... + M906 command:
To be honest all that is so new to me, that I do not know if it is what I am looking for
Don't worry, so it is to me. I am learning as I go - and usually I create online calculators along the way and learn more by the feedback I get for these.
- that said - I am realizing, what I am looking for is how to convert what is given in most datasheets for steppers
Can you be a bit more specific on that? Stepper data sheets contain a lot of values.
- rotorMass? -> In gramm (you divide by 1000 in the end)
The result is of course in kg. Relevant here is rotor inertia which is given in the datasheet of stepper motors as g.cm².
- motorCount? -> rpm or rps? Or what else?
This is for the case where you have multiple motors driving the same axis as in CoreXY machines. This really is the count of motors.
- pulleyRadius? -> Of which pulley, the "main" pulley?
The pulley fixed to the motor shaft.
Manuel
Duet 3 6HC (v0.6) with RPi 4B on a custom Cartesian
with probably always latest firmware/DWC (incl. betas or self-compiled)
My Tool Collection -
@wilriker said in steppers with lots of Amp... + M906 command:
Can you give me a formula how to calculate the inertia of a drive pulley? I know how to do it for the rotor inertia based on the value given in the datasheet. If this is based on the pulley's diameter this could even be added easily without another input field.
Rotational mass would be diameter x "length" correct? Some people run 6mm belts and some run 9mm belts. Maybe others as well.
Maybe too trivial to worry about...
-
@danal From what the OP added as resources via links this was actually the inertia added by the mass of the pulley and belts themselves. Those 10 to 50 grams.
Manuel
Duet 3 6HC (v0.6) with RPi 4B on a custom Cartesian
with probably always latest firmware/DWC (incl. betas or self-compiled)
My Tool Collection -
@wilriker said in steppers with lots of Amp... + M906 command:
@lb said in steppers with lots of Amp... + M906 command:
To be honest all that is so new to me, that I do not know if it is what I am looking for
Don't worry, so it is to me. I am learning as I go - and usually I create online calculators along the way and learn more by the feedback I get for these.
- that said - I am realizing, what I am looking for is how to convert what is given in most datasheets for steppers
Can you be a bit more specific on that? Stepper data sheets contain a lot of values.
rotor-inertia given in g cm^2 -> "J" for ratio
- rotorMass? -> In gramm (you divide by 1000 in the end)
The result is of course in kg. Relevant here is rotor inertia which is given in the datasheet of stepper motors as g.cm².
sounds good with g cm^2
- motorCount? -> rpm or rps? Or what else?
This is for the case where you have multiple motors driving the same axis as in CoreXY machines. This really is the count of motors.
Oops sorry for that question
- pulleyRadius? -> Of which pulley, the "main" pulley?
The pulley fixed to the motor shaft.
But what if there is a small pulley going from the motor to a "main"-shaft that has a ratio? -> What pulley then? Say 25,465mm r(-motor) to 14,006 r(-mainshaft) (gear-ratio of 1,818) -> Pick the one where the load is driven from?
-
@wilriker
do not make the same mistake as I did: If there is a reduction/adduction (gear-ratio) of the motor involved the NM of the Motor is (de-)amped by the amount also... -
@lb said in steppers with lots of Amp... + M906 command:
rotor-inertia given in g cm^2 -> "J" for ratio
To calculate that you need the radius of whatever is attached to the motor shaft and then in insert it into the formula a bit further above (and I think it also is on that page you linked with all these formulas).
But what if there is a small pulley going from the motor to a "main"-shaft that has a ratio? -> What pulley then? Say 25,465mm r(-motor) to 14,006 r(-mainshaft) (gear-ratio of 1,818) -> Pick the one where the load is driven from?
Something doesn't add up here. First you say a small pulley in to motor and then in your example the small pulley is the larger one. Anyway, radius or diameter is not the base of gear-ratio (even though in most cases it comes close) but interacting number of teeth of the different gears. Then again the gear ratio on my calculator expects rotation on the motor : rotation on the load. I will fix this later.
In your example this would mean your gear ratio is 1:1.818 since one rotation of the motor shaft leads to 1.818 rotations of the load shaft as far as I can tell from your description.@lb said in steppers with lots of Amp... + M906 command:
do not make the same mistake as I did: If there is a reduction/adduction (gear-ratio) of the motor involved the NM of the Motor is (de-)amped by the amount also...
I don't think I can follow you here. Why would adding gearing reduce or increase the motor torque? It will of course affect the torque that is applied on the load but the motor does not change. What am I missing?
Manuel
Duet 3 6HC (v0.6) with RPi 4B on a custom Cartesian
with probably always latest firmware/DWC (incl. betas or self-compiled)
My Tool Collection -
@wilriker said in steppers with lots of Amp... + M906 command:
First: Thanks for coming back on this!
@lb said in steppers with lots of Amp... + M906 command:
rotor-inertia given in g cm^2 -> "J" for ratio
To calculate that you need the radius of whatever is attached to the motor shaft and then in insert it into the formula a bit further above (and I think it also is on that page you linked with all these formulas).
-> Thanks! So this is exactly that point where we "add" the wheel attached to the motor to the rotor inertia? Can´t we just sum up the motor-inertia + the attached wheel-inertia for that? For what do we need the rotor-mass in Kg?
But what if there is a small pulley going from the motor to a "main"-shaft that has a ratio? -> What pulley then? Say 25,465mm r(-motor) to 14,006 r(-mainshaft) (gear-ratio of 1,818) -> Pick the one where the load is driven from?
Something doesn't add up here. First you say a small pulley in to motor and then in your example the small pulley is the larger one. Anyway, radius or diameter is not the base of gear-ratio (even though in most cases it comes close) but interacting number of teeth of the different gears. Then again the gear ratio on my calculator expects rotation on the motor : rotation on the load. I will fix this later.
In your example this would mean your gear ratio is 1:1.818 since one rotation of the motor shaft leads to 1.818 rotations of the load shaft as far as I can tell from your description.-> These were just examples, will pick one example for this post to ease communication...
You understood the "last" example perfect, will stick to it@lb said in steppers with lots of Amp... + M906 command:
do not make the same mistake as I did: If there is a reduction/adduction (gear-ratio) of the motor involved the NM of the Motor is (de-)amped by the amount also...
I don't think I can follow you here. Why would adding gearing reduce or increase the motor torque? It will of course affect the torque that is applied on the load but the motor does not change. What am I missing?
-> Exactly! Of course the motor-torque is not magically de-/increasing, but the applied torque AFTER the drive-ratio is scaling with the drive-ratio, sorry for my "wald & wiesen denglish" here
Just wanted to point out that I forgot to include this trade of speed<-to->applied-torque in my calc. Anyway was just going through my mind... -
@lb said in steppers with lots of Amp... + M906 command:
-> Thanks! So this is exactly that point where we "add" the wheel attached to the motor to the rotor inertia? Can´t we just sum up the motor-inertia + the attached wheel-inertia for that? For what do we need the rotor-mass in Kg?
This is an artificial mass that is added to the mass of the load to be moved. So if for example the load to be moved of an axis is, say, 1kg and the rotor inertia is 68g.cm² on a 16 tooth GT2 pulley (
r=0.51cm), this will add about 260g of additional mass for the motor to move.
And sinceacceleration = force / masswhere force is given inNand mass inkgthis is converted to kg (although this results inm/s²and I multiply the result by 1,000 to get the more commonmm/s²)-> Exactly! Of course the motor-torque is not magically de-/increasing, but the applied torque AFTER the drive-ratio is scaling with the drive-ratio, sorry for my "wald & wiesen denglish" here
Just wanted to point out that I forgot to include this trade of speed<-to->applied-torque in my clac. Anyway was just going through my mind...Two Germans writing in English about complex mechanical physics... what could possibly go wrong?
Also my calculator ignores speed constraints. It is solely about possible acceleration - if you can achieve high speeds with it is another topic.
Manuel
Duet 3 6HC (v0.6) with RPi 4B on a custom Cartesian
with probably always latest firmware/DWC (incl. betas or self-compiled)
My Tool Collection -
@wilriker said in steppers with lots of Amp... + M906 command:
@lb said in steppers with lots of Amp... + M906 command:
-> Thanks! So this is exactly that point where we "add" the wheel attached to the motor to the rotor inertia? Can´t we just sum up the motor-inertia + the attached wheel-inertia for that? For what do we need the rotor-mass in Kg?
This is an artificial mass that is added to the mass of the load to be moved. So if for example the load to be moved of an axis is, say, 1kg and the rotor inertia is 68g.cm² on a 16 tooth GT2 pulley (
r=0.51cm), this will add about 260g of additional mass for the motor to move.
And sinceacceleration = force / masswhere force is given inNand mass inkgthis is converted to kg (although this results inm/s²and I multiply the result by 1,000 to get the more commonmm/s²)Ah! So but in my case I have 2 synchro-belts per Axis = 4 in total, 2m long, 9mm wide, guess I have to add that mass also
since that will not be neglectable in perspective to the rest mass-> Exactly! Of course the motor-torque is not magically de-/increasing, but the applied torque AFTER the drive-ratio is scaling with the drive-ratio, sorry for my "wald & wiesen denglish" here
Just wanted to point out that I forgot to include this trade of speed<-to->applied-torque in my clac. Anyway was just going through my mind...Two Germans writing in English about complex mechanical physics... what could possibly go wrong?
Also my calculator ignores speed constraints. It is solely about possible acceleration - if you can achieve high speeds with it is another topic.
Yeah but this forum is great & thanks for helping me out anyway in whatever language - "math & physics are some sort of universal language" they told me
-
@lb said in steppers with lots of Amp... + M906 command:
Ah! So but in my case I have 2 synchro-belts per Axis = 4 in total, 2m long, 9mm wide, guess I have to add that mass also
since that will not be neglectable in perspective to the rest massIf you want to use the calculator just add it to the axis mass input field.
But seriously, have you weight them? How much could this be? 50g? These are all very lightweight objects.Yeah but this forum is great
I say that on every occasion. I learn something new every day here.
Manuel
Duet 3 6HC (v0.6) with RPi 4B on a custom Cartesian
with probably always latest firmware/DWC (incl. betas or self-compiled)
My Tool Collection -
@wilriker said in steppers with lots of Amp... + M906 command:
@lb said in steppers with lots of Amp... + M906 command:
Ah! So but in my case I have 2 synchro-belts per Axis = 4 in total, 2m long, 9mm wide, guess I have to add that mass also
since that will not be neglectable in perspective to the rest massIf you want to use the calculator just add it to the axis mass input field.
But seriously, have you weight them? How much could this be? 50g? These are all very lightweight objects....but 4 of them will be already - 200gr? - then, yeah will put some additional mass into that field... (confirmed in this "big" build it will be another ca. 150-200gr)
Yeah but this forum is great
I say that on every occasion. I learn something new every day here.
I think I will stop posting here and open a new post solely on "inertia" & "inertia-match" and all the calculation involved.
-
@lb By 50g I meant the total weight of all 4 belts...
I have no clue if that is anywhere close to being realistic - I never had the idea of weighing my belts and pulleys. 
-
@wilriker said in steppers with lots of Amp... + M906 command:
@danal From what the OP added as resources via links this was actually the inertia added by the mass of the pulley and belts themselves. Those 10 to 50 grams.
Agreed, highly variable.
My comment was really in response to (paraphrased): "This can be calculated with just pully diameter". 6mm vs 9mm vs ??? comes into it as well.
So the input might need to be pulley weight & radius, belt width and length... maybe more...
-
@dc42
"stupid" (maybe) question, while digging up new motor-alternatives: Those 2,4A, are they "per phase"? Or in total? I assume per phase.Because: Let´s say I pick a motor that has 2,12A (1phase), what would be fine... then this motor will have 2 * 2,12A * 1/sqrt(2) -> = ca. 3A then on every two-phase step in total (with only 1,5A on each single phase of course).
-
Just because I have everything within arms reach (don't ask), here are the weights:
2m of 6mm Width GT2 belt: 16.11g
16T 6mm W, 5mm ID Aluminum Pulley: 2.92g
20T 6mm W, CR10 stock pulley: 6.10g
All of the above measured with an uncalibrated cheap Chinese scale, so just useful to get an idea. -
@lb said in steppers with lots of Amp... + M906 command:
@dc42
"stupid" (maybe) question, while digging up new motor-alternatives: Those 2,4A, are they "per phase"? Or in total? I assume per phase.Because: Let´s say I pick a motor that has 2,12A (1phase), what would be fine... then this motor will have 2 * 2,12A * 1/sqrt(2) -> = ca. 3A then on every two-phase step in total (with only 1,5A on each single phase of course).
The 2.4A is the peak per-phase current. When using microstepping, only one phase gets the peak current at a time. When full stepping is selected, both phases get the peak current all the time.
Duet WiFi hardware designer and firmware engineer
Please do not ask me for Duet support via PM or email, use the forum
http://www.escher3d.com, https://miscsolutions.wordpress.com -
@dc42
Thanks so much! That helps me so much to better understand the whole stepper-stuff!So for learning/understanding:
Even the trinamic-driver in full-step-mode do not scale down to sin(45) = 0,707... * A + cos(45) = 0,707... * A in a two-phase position and have at this time 1.414... times A but with 2 * 1A = 2A in total in a single-phase position
-> That does no user any help because we all have to design our systems for the weakest point then and that is single-phase-on... which means in 2-phase-fullstep with 1*A in each winding I actually have more torque and heat and power consumed then I need because I designed everything in a way it can deal with this less torque in single-phase-on-position that cannot be avoided by any means when using microsteps... (though of course we can think of an always 2-phase full-step-mode)?Another question design-related:
If I have 3,8rps (=225rpm) in my system with 16times micro-stepping I need 3,75 * 16 * 200=12000pulses per second -> Judging on the 300KHz stated here "https://forum.duet3d.com/topic/3493/maximum-stepper-speed/2" I do not run into any problems, even if in total 3 axis-stepper are mounted + 2 printhead-stepper, because that 300KHz is not limited by the amount of steppers connected? -
The 300kHz was measured with just one stepper motor moving; the figure with 3 motors moving simultaneously was 120kHz. When using external drivers, the maximum rate will be less because of the need to lengthen the step pulses.
Duet WiFi hardware designer and firmware engineer
Please do not ask me for Duet support via PM or email, use the forum
http://www.escher3d.com, https://miscsolutions.wordpress.com -
@dc42 Not to hijack the thread, but this makes me curious what the step rate of the Duet 3 will be with a CPU that appears to be about 3x faster. And as a knock on from that, would it be possible to run in native 256x microstepping mode for all axis?
