Optimum XYZ axis steps/mm in corexy setup February 28, 2017 06:46PM |
Registered: 7 years ago Posts: 26 |
Re: Optimum XYZ axis steps/mm in corexy setup February 28, 2017 07:52PM |
Registered: 11 years ago Posts: 5,780 |
Re: Optimum XYZ axis steps/mm in corexy setup March 01, 2017 07:10AM |
Registered: 7 years ago Posts: 26 |
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the_digital_dentist
There isn't any optimum value, just different steps/mm values. If it can move fast enough for you it's fine.
If you use large pulleys on the XY motors, the machine will theoretically be capable of higher speeds than if you use smaller pulleys, but you'll have reduced torque, so if the moving mass is high, you won't be able to print that fast anyway. In the end, the commonly available 16 or 20 tooth pulleys work fine, with the 16 tooth pulleys providing slightly higher resolution at slightly lower maximum print speed (but probably more than fast enough anyway).
The ultimate print speed will depend on the controller pulse output as well as the pulley teeth, belt pitch, microstepping, and motor steps/rev, available motor torque, acceleration, and the moving mass.
For the Z axis, a high steps/mm value generally means more torque is available to lift a larger load. Speed isn't normally a concern- if the bed can move 10 mm/sec it's probably fast enough.
Re: Optimum XYZ axis steps/mm in corexy setup March 01, 2017 09:47AM |
Registered: 8 years ago Posts: 88 |
Re: Optimum XYZ axis steps/mm in corexy setup March 01, 2017 11:59AM |
Registered: 11 years ago Posts: 5,780 |
Re: Optimum XYZ axis steps/mm in corexy setup March 01, 2017 06:47PM |
Registered: 7 years ago Posts: 26 |
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sigxcpu
On processor is easy: 8 bit - less step pulses per second => less speed. 32 bit more pps => more speed. Get a MKS SBASE, not a MKS GEN.
Revolution = rotation so the M8 has 1.25mm per rotation/revolution.
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the_digital_dentist
200 steps/rev x 16 usteps/step = 3200 usteps/rev of the motor, 3:1 motor:screw, so 9600 usteps to turn the screw one rev which lifts the bed 1.25 mm. So 9600/1.25 = 7680 usteps per mm in Z. Moving the bed at 10 mm/sec will require 76800 pps- OK with 32 bit controllers, but probably not with 8 bit controllers.
I don't think you need the 3:1 step down with the pulleys. Without it you'd still have 2560 usteps per mm of bed lift. More than enough.
Lead screws have two specs- lead and pitch. Pitch is the distance between the ridges on the screw. Lead is the distance that the bed will move in one rotation of the screw. The lead = pitch x starts.
Starts is the number of paths on the screw- it is usually 1, 2, or 4. Check the number of starts or the lead of the screw when making calculations. The calcs above are valid for 1 start (pitch = lead).
Re: Optimum XYZ axis steps/mm in corexy setup March 01, 2017 09:10PM |
Registered: 11 years ago Posts: 5,780 |
Re: Optimum XYZ axis steps/mm in corexy setup March 01, 2017 10:11PM |
Registered: 7 years ago Posts: 26 |
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the_digital_dentist
Expecting a stepper to have any torque left beyond about 6-10 revs per sec is probably wishful thinking.
Arduino/RAMPS running Marlin is limited to 40,000 pps to drive a motor. If you use 2560 usteps/mm your maximum Z axis speed will be just under 16 mm/sec, probably fast enough. But, 40,000 pps / 3200 usteps per rev = 12.5 rev/sec = 750 rpm, probably more than the motor can handle.
A 32 bit controller like the smoothieboard will be able to produce 100,000 pps. 100,000 pps / 3200 ustep/rev > 39 mm/sec, assuming your motor has enough torque to keep lifting the bed at that speed. 3200 usteps/rev @ 100,000 usteps/sec= 31 rev/sec= 1875 rpm which is probably much more than the motor can actually do.
Re: Optimum XYZ axis steps/mm in corexy setup March 02, 2017 02:53AM |
Registered: 8 years ago Posts: 5,232 |
Re: Optimum XYZ axis steps/mm in corexy setup March 02, 2017 08:29AM |
Registered: 7 years ago Posts: 26 |
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o_lampe
40.000 ppm is for all steppers, but it doesn't make a difference for the CPU if it is one stepper or 8 steppers, because the step pulses are all sent simultaneously by an 8bit register.
If you're in doubt what pulleys to use on the Z-axis: start with 16 tooth ( best torque ) and see, how fast you can move without skipping steps. ( two leadscrews and four linear rails are a challenge to align, so you will need all the torque you can get)
Re: Optimum XYZ axis steps/mm in corexy setup March 02, 2017 10:27AM |
Registered: 11 years ago Posts: 5,780 |
Re: Optimum XYZ axis steps/mm in corexy setup March 02, 2017 12:36PM |
Registered: 10 years ago Posts: 14,672 |
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the_digital_dentist
Higher microstepping gives up a little torque but reduces vibration - i.e. motors run very quietly.
Re: Optimum XYZ axis steps/mm in corexy setup March 02, 2017 02:14PM |
Registered: 7 years ago Posts: 26 |
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the_digital_dentist
All you have to worry about is how many pulses per second the processor/firmware can handle. Each pulse represents one microstep. Marlin/Arduino/RAMPS (MAR) maxs out at 40,000 pps. Smoothieware defaults to 100,000 pps (though I think it can be tweaked upward a little).
The linear speed of the extruder carriage (or Y or Z axis) translates to revs per sec of the motor. revs per sec of the motor translates to usteps per sec which equals pps from the controller.
Almost everyone uses 200 step/rev motors with 16:1 ustepping. That requires 3200 usteps (pulses) per rev. With a common 20 tooth pulley and 2 mm pitch belt, 1 motor rev= 40 mm of linear displacement. You want to print at 200 mm/sec, the motor has to spin at 200 mm/sec / 40 mm/rev = 5 rev/sec. Since 1 rev requires 3200 usteps (pulses), the controller will have to be able to deliver 5 rev/sec x 3200 pulses/rev = 16,000 pulses per sec. So, you can see that the controller is almost never going to be the limiting factor in the speed.
The situation changes if you want to use some of the better drivers that can use finer ustepping- some as high as 256 usteps/step. In that case, the 200 step/rev motor will need 200 steps/rev X 256 pulses/step = 51200 pulses per rev. MAR can only produce 40,000 pps, so you'll be able to go 40,000 pps / 51,200 pprev = 0.78125 revs per sec. If one rev moves 40 mm, that means top print speed will be 0.78125 revs/sec x 40 mm = 31.25 mm/sec.
Smoothie can go faster- 100,000 pps / 51,200 pprev = 1.95 revs/sec which translates to 1.95 revs/sec x 40 mm/rev = 78.125 mm/sec.
Higher microstepping gives up a little torque but reduces vibration - i.e. motors run very quietly.
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dc42
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the_digital_dentist
Higher microstepping gives up a little torque but reduces vibration - i.e. motors run very quietly.
It's a myth that higher microstepping loses torque. The torque for a given lag angle is exactly the same whatever microstepping you use, with the exception that when going from full steps to half steps you lose about 30% of torque if you keep the current the same.Think of it this way: suppose you energise the motor and then clamp the shaft in its current position. If you then send either one 1/16 microstep or 16 1/256 microsteps, the current in the coils will be exactly the same.
What confuses people is that there are tables on the web that show how the torque per additional microstep of lag angle drops with increasing microstepping. That's hardly surprising, because the torque produced by a motor is approximately proportional to the sine of the lag angle - that's the difference between the actual position of the motor shaft and the equilibrium position.
Increasing microstepping from 16x to 256x does make them much quieter, to the extent that the motor noise is typically drowned by the fan noise.
Re: Optimum XYZ axis steps/mm in corexy setup March 02, 2017 05:03PM |
Registered: 9 years ago Posts: 31 |
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renatortb
But this is for one motor only, right? I intend to use four motors, so the processor will not handle. 4x16000 = 64000 pps (Marlin = 40000). I misunderstood something? Going crazy right now! LOL!
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o_lampe
40.000 ppm is for all steppers, but it doesn't make a difference for the CPU if it is one stepper or 8 steppers, because the step pulses are all sent simultaneously by an 8bit register.
Re: Optimum XYZ axis steps/mm in corexy setup March 02, 2017 08:23PM |
Registered: 7 years ago Posts: 26 |
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os3dp
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renatortb
But this is for one motor only, right? I intend to use four motors, so the processor will not handle. 4x16000 = 64000 pps (Marlin = 40000). I misunderstood something? Going crazy right now! LOL!
No, look at the following.
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o_lampe
40.000 ppm is for all steppers, but it doesn't make a difference for the CPU if it is one stepper or 8 steppers, because the step pulses are all sent simultaneously by an 8bit register.
-os3dp
Re: Optimum XYZ axis steps/mm in corexy setup March 03, 2017 01:10AM |
Registered: 8 years ago Posts: 5,232 |
Re: Optimum XYZ axis steps/mm in corexy setup March 03, 2017 04:21AM |
Registered: 10 years ago Posts: 14,672 |
Quote
o_lampe
40.000 ppm is for all steppers, but it doesn't make a difference for the CPU if it is one stepper or 8 steppers, because the step pulses are all sent simultaneously by an 8bit register.
Re: Optimum XYZ axis steps/mm in corexy setup March 03, 2017 08:12AM |
Registered: 7 years ago Posts: 26 |
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dc42
Quote
the_digital_dentist
Higher microstepping gives up a little torque but reduces vibration - i.e. motors run very quietly.
It's a myth that higher microstepping loses torque. The torque for a given lag angle is exactly the same whatever microstepping you use, with the exception that when going from full steps to half steps you lose about 30% of torque if you keep the current the same.Think of it this way: suppose you energise the motor and then clamp the shaft in its current position. If you then send either one 1/16 microstep or 16 1/256 microsteps, the current in the coils will be exactly the same.
What confuses people is that there are tables on the web that show how the torque per additional microstep of lag angle drops with increasing microstepping. That's hardly surprising, because the torque produced by a motor is approximately proportional to the sine of the lag angle - that's the difference between the actual position of the motor shaft and the equilibrium position.
Increasing microstepping from 16x to 256x does make them much quieter, to the extent that the motor noise is typically drowned by the fan noise.
Re: Optimum XYZ axis steps/mm in corexy setup March 03, 2017 01:24PM |
Registered: 10 years ago Posts: 14,672 |
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renatortb
Quote
dc42
Quote
the_digital_dentist
Higher microstepping gives up a little torque but reduces vibration - i.e. motors run very quietly.
It's a myth that higher microstepping loses torque. The torque for a given lag angle is exactly the same whatever microstepping you use, with the exception that when going from full steps to half steps you lose about 30% of torque if you keep the current the same.Think of it this way: suppose you energise the motor and then clamp the shaft in its current position. If you then send either one 1/16 microstep or 16 1/256 microsteps, the current in the coils will be exactly the same.
What confuses people is that there are tables on the web that show how the torque per additional microstep of lag angle drops with increasing microstepping. That's hardly surprising, because the torque produced by a motor is approximately proportional to the sine of the lag angle - that's the difference between the actual position of the motor shaft and the equilibrium position.
Increasing microstepping from 16x to 256x does make them much quieter, to the extent that the motor noise is typically drowned by the fan noise.
What about that? [www.micromo.com]
Quote
The actual expression for incremental torque for a single microstep is:
1. TINC = THFS x sin (90/µPFS)
The incremental torque for N microsteps is:
2. TN = THFS x sin ((90 x N)/µPFS))
Re: Optimum XYZ axis steps/mm in corexy setup March 04, 2017 09:24AM |
Registered: 7 years ago Posts: 26 |
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dc42
Quote
renatortb
Quote
dc42
Quote
the_digital_dentist
Higher microstepping gives up a little torque but reduces vibration - i.e. motors run very quietly.
It's a myth that higher microstepping loses torque. The torque for a given lag angle is exactly the same whatever microstepping you use, with the exception that when going from full steps to half steps you lose about 30% of torque if you keep the current the same.Think of it this way: suppose you energise the motor and then clamp the shaft in its current position. If you then send either one 1/16 microstep or 16 1/256 microsteps, the current in the coils will be exactly the same.
What confuses people is that there are tables on the web that show how the torque per additional microstep of lag angle drops with increasing microstepping. That's hardly surprising, because the torque produced by a motor is approximately proportional to the sine of the lag angle - that's the difference between the actual position of the motor shaft and the equilibrium position.
Increasing microstepping from 16x to 256x does make them much quieter, to the extent that the motor noise is typically drowned by the fan noise.
What about that? [www.micromo.com]
The formulae on that web page say the same as I did in my post:
Quote
The actual expression for incremental torque for a single microstep is:
1. TINC = THFS x sin (90/µPFS)
The incremental torque for N microsteps is:
2. TN = THFS x sin ((90 x N)/µPFS))