Maximum Acceleration Calculator
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@3doeste It should do. The way to treat it is to use the mass to be moved in the Y direction, which is the worse case. That is to say, the mass will be the X carriage plus the X rails and Y carriages. As you rightly say, pure X or pure Y moves will use both motors but 45 degree infill will use only one. So spec the motors as you would for moving Y on a Cartesian.
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@3doeste I have 2 Hypercube Evolutions and have been doing some testing before the calculator was available. My next Step is to weigh my X and Y moving masses. But the calculator is just a starting point. For example one of my machines is very light so I have also been wondering about jerk that the calculator doesn’t address and which smaller CoreXY s should perform quite well. When I get home from holidays I will see how high I can push jerk.
Another factor is the overall flexibility of the machine, including the belt stretch and associated resonances, X rod flex, hotend mount etc. I have no feel yet for how the belts affect performance - others might be able to comment.I suspect the best acceleration is much lower than the calculator provides, depending on your machine construction and quality preferences.
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@garis The calculator is for stepper motors only. It is an attempt to calculate the maximum acceleration that a given stepper motor can produce for a given mass.
Whether the rest of the machine is capable of attaining those acceleration values without problems, is of course an entirely different thing.
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I have a fully machine aluminum CoreXY, I weigh my Y axis and it's around 1500gr of moving mass and my motors have 65n.cm of torque.
The calculator give an aceleration of around 4000, I tried 6000 without problems but used 4000. And with jerk I was using 1800 until I had to do a print with sharp corners and they got wavy in Z (only on corners), so I put the jerk at 600 and it came out perfect, but otherwise, 1800 works great.
I can't get more than 200 mm/s of speed though without losing steps. Perhaps that will improve with 24v and / or 20T pulleys. I have 16T currently. -
CoreXY is complicated.
X axis moves divide the force to accelerate the X carriage by two, split between the motors. Likewise Y axis moves divide the force to accelerate the entire bridge by two. That’s straightforward enough.
Diagonal moves are weeeiiiird. The CoreXY belt path is effectively a sqrt(2):1 compound pulley. IE each 1 mm of diagonal XY travel requires 1.41mm of belt travel, and you get a corresponding force multiplication effect because of that travel ratio. That’s one little-appreciated reason why CoreXY tends to produce nicer prints than an equivalent Cartesian — you’ve effectively geared down the motors.
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@rcarlyle " That’s one little-appreciated reason why CoreXY tends to produce nicer prints than an equivalent Cartesian — you’ve effectively geared down the motors. "
So is it worth it running at .9deg motor?
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@og3d depends on your PSU voltage and desired speeds. 0.9 degree motors can only spin half as fast, all else being equal, and CoreXY can only move on diagonals 71% as fast as Cartesian, all else being equal. But the typical 24v Cartesian printer with 1.8 degree steppers can do like 300mm/s without any issues as far as the motors are concerned and people seldom ever go that fast.
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Well on average the printers usual do not get close to 300mm/s, so on CoreXY using a .9 deg I wont see much improvement vs a 1.8deg motor, since by design CoreXY is geared down. Just making sure I understood it correctly.
I have a delta but at speeds 100mm/s quality is not good and seeing Rail Core II print results at 100mm/s got me inspired to build a CoreXY for my second printer.
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Hi! Thanks for making this tool, it is very handy.
I'm currently trying to grasp the limitation of accelleration on stepper motor drives. I've used your calculator on a few motors, and i noticed that generally people report running 2-4 times higher accelleration on their printers before running into issues than your calculator says is possible.
I am not sure these printers actually run at the requested speed, but certainly there is some difference between running at the speed your calculator produces and a vastly higher speed, i can see that on my own printer which accellerates more violently.
So i am wondering, what gives? Shouldn't the stepper skip steps if you ask it to go TOO fast? The stepper driver has no feedback loop to tell. I can't notice lost steps below 20.000 mm/s² accelleration using really small NEMA 17 motors with only 1.68 A capability and a rated torque of only 36Ncm, inertia of 54 g/cm² driving a rather heavy gantry at 800gr.
I would really apprechiate if someone could explain this discrepancy to me, i am not very familiar with stepper drives.
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@genewild said in Maximum Acceleration Calculator:
Hi! Thanks for making this tool, it is very handy.
I'm currently trying to grasp the limitation of accelleration on stepper motor drives. I've used your calculator on a few motors, and i noticed that generally people report running 2-4 times higher accelleration on their printers before running into issues than your calculator says is possible.
I am not sure these printers actually run at the requested speed, but certainly there is some difference between running at the speed your calculator produces and a vastly higher speed, i can see that on my own printer which accellerates more violently.
So i am wondering, what gives? Shouldn't the stepper skip steps if you ask it to go TOO fast? The stepper driver has no feedback loop to tell. I can't notice lost steps below 20.000 mm/s² accelleration using really small NEMA 17 motors with only 1.68 A capability and a rated torque of only 36Ncm, inertia of 54 g/cm² driving a rather heavy gantry at 800gr.
I would really apprechiate if someone could explain this discrepancy to me, i am not very familiar with stepper drives.
You raise some good questions - and unfortunately I'm not the one that can appropriately answer them.
I too see a lot of discussions of folks using acceleration values ~10x what I would expect. A related reason why this and the inverse is true (why the calculator is 10% of what some other folks are using) is because of the below fact:
https://forum.duet3d.com/topic/6/stepper-motors-for-corexy
From: @dc42If you want the motion lag to be no more than one 1/16 microstep during acceleration, then you need to multiply by 9.8%. So the available torque is 65 * 0,85 * 0.71 * 0.098 = 3.8Ncm.
In the past the general consensus was to multiply by the available torque for a given stepper by 9.8% as a sort of factor-of-safety. I follow this factor-of-safety approach.
I recently came across this super cool spreadsheet - however the equations/macros omits the factor-of-safety for available torque, while using it when calculating what the required torque is - the opposite of what I would expect. Here is an example screen grab of a few motors using the equations (without the factor-of-safety):
The chart shows the expected speeds at which motor torque begins to drop off - which match the Duet calculations for max speeds here:
https://duet3d.dozuki.com/Wiki/Choosing_and_connecting_stepper_motorsThe issue, to me, is that the red dashed line for torque required is of an extraordinarily low value relative to the stepper curve maximums. A (in my eyes, appropriately allocating the factor-of-safety) corrected chart is below - note the Y-axis changes:
Anyways, more to dig in there. Perhaps @dc42 can go into more detail regarding the motion lag considerations at 1/16th of a microstep. Maybe nowadays that consideration isn't too big of a deal.Side note - but most folks I see using more than, say, 20,000 mm/s^2 acceleration values (on motor/machine setups I would calculate having issues) typically run Klipper. Perhaps issues they may see at such accelerations are reduced by that input-shaping implementation.