Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: marky68 on August 29, 2019, 05:44:29 PM
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Hi could I have some advice on my new to me but used CNC router.
I'm very new to Mach3 but have been programming woodworking Cnc's for about 10 years.
Here's the spec and the question,
My machine is approximately 1mtr x 1mtr cutting area with 150mm Z clearence, 3 Axis
2.2kw Chinese water cooled spindle
4 x Nema 34 stepper motor 878 oz.in bipolar Model 34HST9805-37B2 Step Angle 1.8, Rate Voltage 6.4, Rate Current 2A, Phase resistance 3.2,Phase Inductance 15mH
4 x Stepper motor drivers DM860A, PEAK 7.8A , Set to 3.0 RMS Peak 4.2A and 2000 microstep resolution
4x Power Supply 200W-60VDC
Cheap chinese HY-JK02-M 5-axis interface board. ( I'm not enthused with the board now I understand a little bit more about them and at £10 cost it seems penny pinching to run an expensive machine with one)
16mm dia 16mm pitch 4 start thread lead screws on all axis
My Mach3 motor settings are the same for for all three motors
Steps per = 125
Velocity = 2000 mm/min
Acceleration =650 mm/sec
Step Pulse =2
Dir Pulse =2
Kernal speed at 25000 Hz
All that sounds like I know what I'm talking about but I don't :)
My issue is the axis speed only been at 2000mm, I would like to get to at least 5000 or slightly higher if possible.
I've been informed that it should be possible with the current setup but when I increased just the velocity I got some stalling on the X axis when jogging around.
I've watched many videos and read all sorts of info and it seems motor tuning is an art as well as a science and becuase it's a reflection of the sum of the parts it can differ for everyone.
From what I've gleaned I maybe able to increase the steps per to 200 as that is what my motors are rated at and also that my stepper motor drivers could have been much bigger voltage which would also improve things but I don't how this works, oh and less microsteps?
If anyone can advise with explanations so i can get my head around how it is worked out that would be great thank you.. ;D
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Hi,
I suspect with those steppers that 2000 mm/min is about as good as you are going to get.
All steppers lose torque the faster they go. The principle determinant in how badly they fare at speed is
the winding inductance, the higher the inductance the quicker the torque degrades with speed.
For 34 size motors you should be looking at units of 2-4mH, such motors will have about 30% of their holding
torque at 1000 rpm.
Your 15mH units are likely to have less than 5% of its holding torque at 1000 rpm. That describes why you
cannot increase the axis speed without loosing steps.
Craig
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Hi,
to flesh out the answer I have taken these published torque/speed curves from the Leadshine website for two of their
34 size steppers.
The smaller of the two (86CM35) has a rated torque of 496 oz.in with a very respectable inductance of 2.67mH. Note also the
low resistance of 0.42 Ohm. The time constant, a figure of merit, is 0.42 X 2.67=1.12ms.
The slighter longer(86CM45) motor has a rated torque of 638 oz.in and a still respectable 2.95mH inductance with a resistance
of 0.43 Ohm for a time constant of 1.27ms.
On the face of it you would say the bigger motor is better....right......but the smaller motor does very well at speed. The somewhat
smaller inductance, and therefore time constant, means that it retains 50% of its torque at 1000 rpm whereas its bigger
sibling retains 30%. In fact at 1000 rpm both motors produce the same torque (1.6Nm).
This illustrates the point that sometimes smaller motors but with low inductance can outperform larger motors but with
commensurately higher inductance.
Leadshine is one of the few companies to publish torque/speed curves but they are very useful. Both of these motors are
'low inductance designs' and are both good but note how even a small reduction in inductance can have a large bearing on the
motors performance at speed.
Your 15mH units will fall well WELL short of these, and note Longs Motors don't publish curves. I think you should
consider replacement.
Your 16mm pitch leadscrews are aggressive and you will require high torque to have reasonable acceleration and thrust to
accommodate cutting forces but really only modest speeds.
For instance at 2000 mm/min with a 16mm pitch the motor rpm need only be 125 rpm.
To get 5000 mm/min with the same leadscrew the motor rpm is 5000/16=312.5 rpm.
In both cases the required rpms are not high. Would you consider putting a belt or gear reduction or 2:1 in place?
That would effectively make your steppers twice the torque and yet still not require high rpms, 625rpm at 5000mm/min.
For example the 86CN35 of 496 oz.in rated will have nearly 1000 oz.in with a 2:1 reduction, even more than your existing
motors and yet according to the torque/speed curve still have 2.2Nm at 625 rpm or 2.2/3.1=71% of its rated torque.
Craig
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Hi Joe,
Thanks for the reply and information,
I'm a little lost with what your saying here, your first paragraph says to get 5000 rpmmy motor would spin at 312.5 rpm which your implying i will have next to no torque with these motors at that speed. The next paragraph says with gearing i would be at 625rpm to get the same speed surely there would be no torque left at all then?
"For instance at 2000 mm/min with a 16mm pitch the motor rpm need only be 125 rpm.
To get 5000 mm/min with the same leadscrew the motor rpm is 5000/16=312.5 rpm.
In both cases the required rpms are not high. Would you consider putting a belt or gear reduction or 2:1 in place?
That would effectively make your steppers twice the torque and yet still not require high rpms, 625rpm at 5000mm/min."
What I'm planing to do in the morning is change the stepping to 1/8th 1600 on the drivers and reduce the acceleration from 650 to 250 and see what happens.
What effects will increasing the supply voltage make as it's been mentioned my motors could take 120v rather than the 60v from the current supplies?
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Hi,
the next step is genuine-honest-to God AC servos like:
https://store.dmm-tech.com/products/dst-0-4kw-ac-servo-motor?variant=23270271046 (https://store.dmm-tech.com/products/dst-0-4kw-ac-servo-motor?variant=23270271046)
Its rated torque is 1.27Nm and short term overload rated at 3.82Nm. With a 3:1 reduction that equates to
3.81/11.46 Nm at the leadscrew or 500/1500 oz.in at 1/3 of rated rpm or 1000rpm. On 16mm pitch
leadscrews that is 16000mm/min....it that fast enough???
Craig
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Looking at both of those motor graphs the torque is very good at rpm's below 500, so surely running at 312rpm will be fine or am I missing something obvious?
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Hi,
I'm a little lost with what your saying here, your first paragraph says to get 5000 rpmmy motor would spin at 312.5 rpm which your implying i will have next to no torque with these motors at that speed. The next paragraph says with gearing i would be at 625rpm to get the same speed surely there would be no torque left at all then?
I understand you confusion.....you are right..... I believe your existing motors have vanishingly small torque at even low speeds.
No amount of gear reduction or change in mirostepping or increase in driving voltage is going to materially improve that.
What I'm planing to do in the morning is change the stepping to 1/8th 1600 on the drivers and reduce the acceleration from 650 to 250 and see what happens.
Try it and see. I suspect changing the microstepping from 2000 to 1600 will be scarcely noticeable, in fact changing microstepping
to any setting will have no effect on the motors torque at speed.
Reducing acceleration may help. High acceleration promotes stalling. However you want the highest acceleration you can for
accurate toolplath following and acceleration is vital to fast cycle times.
What effects will increasing the supply voltage make as it's been mentioned my motors could take 120v rather than the 60v from the current supplies?
Increasing the voltage is the classic means of overcoming high inductance steppers. The highest voltage drivers I have seen
(Leadshine and Gecko) are 80V, so a 25% increase on what you have already. Higher voltage drivers are always an advantage
but I think you will get much MUCH more benefit from replacing those high inductance steppers.
Craig
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Hi,
Looking at both of those motor graphs the torque is very good at rpm's below 500, so surely running at 312rpm will be fine or am I missing something obvious
Yes, you are correct, they both have excellent torque at 312.5 rpm, but even the larger of the two motors still has only
2/3 the torque of your existing motors. You will probably require q belt/gear reduction to have either of these motors match
the low speed torque of your existing motors.
You could of course go for higher torque motors and not need a belt reduction. The only trouble with that approach is that
higher torque motors also have higher inductance.
The 86CM80 motor by Leadshine has a rated torque of 1133 oz.in and an inductance of 4mH with a time constant of 2.5ms.
This would be a superb replacement for your existing motors, no reduction required and 1/4 the inductance.....a huge step
in the right direction.
Craig
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So you you believe 312.5 rpm is far to fast for these motors and at that speed there will be no torque?
[/quote]
Try it and see. I suspect changing the microstepping from 2000 to 1600 will be scarcely noticeable, in fact changing microstepping
to any setting will have no effect on the motors torque at speed.
Craig
[/quote]
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Hi,
So you you believe 312.5 rpm is far to fast for these motors and at that speed there will be no torque?
Without some published data from the manufacturer I cannot tell for sure.
You stated that you tried to increase the max velocity and they started stalling......doesn't that tell you exactly that?
They work OK at 125 rpm but stall out at 312.5 rpm.
Longs Motors make stepper motors with really high torque but also very high inductance. They sell to first time buyers
who think the higher the torque the better but what they don't realize is that high inductance kills a motor at speed.
Savvy buyers want to know both the torque AND the inductance, or to be technically correct, time constant.
Until I mentioned 'time constant' in this thread had you ever heard of it? Would you consider making a buying decision on
the basis of a time constant?
Now that you have heard of it and seen torque/speed curves that illustrate what a 'time constant' means in the real world
what would be your decision today?
May I suggest that if a company/supplier cannot provide either a torque/speed curve, or a time constant or an inductance
then walk away....they are selling to first time buyers.
Craig
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I didn't increase the steps per just the velocity. I bought the machine second hand because the size and build of the structure and its capacity was exactly what I needed, unfortunately finding out that the cutting feed rates are a little low now is a pain yes but if it is an issue I'll have to change the motors.
I have attached a graph for these motors.
Hi,
So you you believe 312.5 rpm is far to fast for these motors and at that speed there will be no torque?
Without some published data from the manufacturer I cannot tell for sure.
You stated that you tried to increase the max velocity and they started stalling......doesn't that tell you exactly that?
They work OK at 125 rpm but stall out at 312.5 rpm.
Longs Motors make stepper motors with really high torque but also very high inductance. They sell to first time buyers
who think the higher the torque the better but what they don't realize is that high inductance kills a motor at speed.
Savvy buyers want to know both the torque AND the inductance, or to be technically correct, time constant.
Until I mentioned 'time constant' in this thread had you ever heard of it? Would you consider making a buying decision on
the basis of a time constant?
Now that you have heard of it and seen torque/speed curves that illustrate what a 'time constant' means in the real world
what would be your decision today?
May I suggest that if a company/supplier cannot provide either a torque/speed curve, or a time constant or an inductance
then walk away....they are selling to first time buyers.
Craig
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Hi,
just as an illustration:
Leadshine 86CM80 (4mH,0.63 Ohm) time constant=2.5ms
Longs 34HST9805 (15mH,3.2 Ohm) time constant= 48ms
Thus for the same input voltage the Leadshine motor would run 19.2 (48/2.5) times faster at the same
percentage torque reduction.
That's nearly 20 times faster!!!!
Craig
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A selection of longs motors attached, the one I've highlighted seems to be a better specification, much lower Phase Inductance , Phase Resistance and slightly more holding torque?
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If these are much more suitable Craig can i use my existing drivers?
This product contains/This item includes: 3 pieces/PC act NEMA34 34HS9456 stepper motor with dual flat shaft (threaded)
Step Angle/Step Angle: 1.8 °
Voltage/Rated Voltage: 2.1 V
Rated Current/Rated current: 5.6 A/phase
RESISTOR, CHIP resistance: 0.39 OHM/phase
Induk Dance/Inductance: 3.76 MH/phase
Securing moment/Holding Torque: 7.5 N.m
Locking Catch moment/Detent Torque: 9.6 N. cm Max
Torque/Rotor torque: 1700 g/cm²
Cable slots/Lead Wires: 4
Thread diameter thread/shaft diameter: 14 mm
Dual flat dimensions: Male thread/Dual Flat Size of shaft: 13 mm (1 mm for flat)
Length/Motor Length: 98 mm
Weight/Motorised, Weight (kg): 3.0
Cable connection/Lead Wires Connection: 4 lines/4 leads: red - a +, Green - A - B + - Yellow Blue - B channel
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Hi,
yes that is a vastly superior motor. In fact so is the model above it.
Compare:
34HS9840 (3.5mH, 0.8 Ohm) time constant=2.8ms
34HS9456 (3.76mH, 0.3 Ohm) time constant=1.128ms
Verses your existing:
34HST9805-37B2 (15mH,3.2 Ohm) time constant=48ms.
The 34HS9456 is the hands down clear winner and the 34HS9840 not an unreasonable second place whereas the
34HST9805-37B2 is really just nowhere for CNC purposes.
Note that while the 34HST9805-37B2 is poor for your machine say for slewing a telescope where it might turn 1 or 2 rpm
through a reduction box it would be perfect.
CNC demands high torque at high speed.....a performance requirement that does not favor stepper motors.
Craig
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Hi,
If these are much more suitable Craig can i use my existing drivers?
Provided they can handle the much increased current (5.6A vs 2A) then yes. Note it maybe you don't even require full current,
motors tend to run really hot (500C) when at rated current. If you back off a bit to 4-4.5A they will run cooler
and most likely still have enough 'grunt' to do the business.
Craig
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Hi,
if you want your machine to run at production speeds and duty cycles then you need AC servos.
Stepper motors have great torque at low speeds but are limited in resolution and speed and run hot all the time.
Servos have somewhat lower torque for the same size motor but maintain that torque right up to rated speed
and have usually a 3-4 fold temporary overload rating, they run quietly and coolly, with superb (100 fold better)
resolution.
The DMM 400W, 200V servos I linked to earlier with the 200V driver and cables is about $450USD. Note that the driver is
wired directly to 230VAC, ie no external power supply is required.
A Delta A2 or B series 400W servo, driver and cables (again 230VAC input) are about $500USD.
Either of these servos will 'eat your steppers for lunch.....any time any where'.
Craig
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That's fantastic thank you for an excellent explanation, i always say everyday is a learning day.
I've just checked my voltage supply and stepper motor drivers see attached
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Hi,
by the way if you look at the Delta A3 series they have a 24 bit multiturn absolute encoder with battery backup.
Thus you can use 8 bits of the encoder for the number of complete revolutions (+- 127) and still have 16 bit resolution (131071
count per rev) within any one turn.
When you turn the machine on the battery backup means you don't even have to home the servo, it just picks up from
where you left off at the last session.
These are the latest and greatest from Delta but all the major manufactures are going that way, that is multiturn high
resolution encoders.
Apparently DMM have, although not widely publicized, a 30 bit multi turn absolute encoder option for their servos....amazing!
Craig
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Hi,
that power supply is too whimpy for the 5.6A stepper.
You would be advised to get a toroidal transformer type power supply, that are much more rugged and forgiving than
switch mode supplies like the one you have pictured.
Craig
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My 3.3 amp power supplies aren't going to cut it either are they :(
this is the one that is packaged with those motors
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Hi,
by the way if you look at the Delta A3 series they have a 24 bit multiturn absolute encoder with battery backup.
Thus you can use 8 bits of the encoder for the number of complete revolutions (+- 127) and still have 16 bit resolution (131071
count per rev) within any one turn.
When you turn the machine on the battery backup means you don't even have to home the servo, it just picks up from
where you left off at the last session.
These are the latest and greatest from Delta but all the major manufactures are going that way, that is multiturn high
resolution encoders.
Apparently DMM have, although not widely publicized, a 30 bit multi turn absolute encoder option for their servos....amazing!
Craig
Wow, but this is getting expensive with servo motor suggestions, it's just for a bit of hobby fun in my little garage :)
I'm going to order those motors as they are a direct physical swap for what i have now and also those higher power supplies, my stepper controllers will still be fine...
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Hi,
Wow, but this is getting expensive with servo motor suggestions, it's just for a bit of hobby fun in my little garage :)
Understood. What I would like exceeds my budget also. Good servos have come down in price however. You don't
need multi turn encoders etc, even 'plain old 16 bit incremental encoders' will still outperform any stepper ever made.
Some time ago I bought a second hand Allen Bradley (US made-quality) 1.8kW servo and servo drive to make a spindle motor.
Its power and flexibility has to be experienced to be appreciated.
A stepper is like a horse and cart......a modern AC servo a high power 4x4 truck!
I would still recommend a toroidal power supply. For example:
https://www.automationtechnologiesinc.com/products-page/torroidal-power-supplies/unregulated-1300w-65vdc20a/ (https://www.automationtechnologiesinc.com/products-page/torroidal-power-supplies/unregulated-1300w-65vdc20a/)
This has 20A output so would do all your steppers with just the one supply.
Craig
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Craig,
One more question, would you leave the Z motor as is, the travel is only 170mm. The reason for asking is if doing a lot of carving work where the z will be changing height rapidly and my xy travel is speed up then I'm thinking I should match all the motors?
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Hi,
I would change the Z axis motor also. It may not have to travel far but it does need to accelerate fast, otherwise
the X and Y axes have to slow down to allow the Z axis to keep up.
Overall acceleration is the most important tuning objective. High acceleration promotes accurate toolplath following
without corner rounding that happens with CV tooplaths. Additionally most Gcode jobs spend more time accelerating
than actually at full speed. Therefore cycle times are commonly more favorably affected by high acceleration than
high max velocity but low acceleration.
Craig.
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Hi,
I would change the Z axis motor also. It may not have to travel far but it does need to accelerate fast, otherwise
the X and Y axes have to slow down to allow the Z axis to keep up.
Overall acceleration is the most important tuning objective. High acceleration promotes accurate toolplath following
without corner rounding that happens with CV tooplaths. Additionally most Gcode jobs spend more time accelerating
than actually at full speed. Therefore cycle times are commonly more favorably affected by high acceleration than
high max velocity but low acceleration.
Craig.
Many thanks again, ;D
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Hi Marky88,
I have been wanting to swap out my steppers for servos for a while. I have just (10 minutes ago) ordered a Delta B2
series 400W servo, drive and cables, price $460USD including shipping to New Zealand. I still have to pay 15% tax
when it enters the country so will cost $872NZD by the time I get it.
When I built my machine I bought secondhand 23size 5 phase Vexta steppers with low lash (less that 3 arc min) 10:1
planetary drives. Despite the small motors the 10:1 reduction means I get great torque, just over 700 oz.in. They drive
directly a 20mm diameter 5mm pitch ground ballscrew which gives a stall thrust of over 1400kg force or 14kN.
The only downside is the gear reduction means its slow, I have them tuned for 1200mm/min. I can get them to do 2000mm/min
but I have to run them at max current (1.4A per phase) and they get hotter than I like. So I run them at 1.1A per phase.
The vagaries of 5 phase steppers is that four phases are energized at any one time so 1.4A phase rated is equivalent to 2.8A
in a 2 phase stepper. At reduced current and consequent less torque I've found that 1200-1500 mm/min is reliable.
At 1200mm/min the ballscrew rotates at 240 rpm and so the stepper is rotating at 2400 rpm. You might ask 'can a stepper
do that speed' given the nature of this thread. 5 phase steppers are a bit specialist. Among the advantages they have over regular
two phase steppers is smooth operation without the vibration propensity of two phase steppers, high speed operation
and 500 full steps per revolution compared to 200 full steps per revolution for a two phase stepper.
The drivers I use are specialist Vexta 5 phase drivers. They don't require a power supply, you wire them directly to 230VAC.
I have measured a peak output voltage at the stepper of 150VDC. So you can see that Vexta drives have a very high voltage output
which goes a long way to secure the high speeds that can get.
Even secondhand the steppers and drives were not cheap, $278USD each plus shipping for the motor and gearbox and $147USD
each plus shipping for the drivers.
These steppers have been absolutely superb....once I had them tuned they never missed a step (except when I crash!) and I get
repeatable resolution of 1um. They have been so good I don't think I'll sell them....I'm so impressed with them. I'm sure I'll
find other uses for them. Of course I've only ordered one servo so far...I'll have to save a few more pennys before I can
buy another two!
Craig
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I'm just a little bit jealous now Craig, ;D
Have you got any pictures of your machine/setup?
I'm going to give those motors a go first, I've negotiated a discount and can get the motors and power supplies for £236 delivered which is a bargain for the upgrade.
As i'm not used to using such a small machine what speed do you think is reasonable with light cuts in say mdf, at work I can run at 8mtrs/minute with a 12mm tool cutting through 19mm thick veneered mdf board in one pass :)
Of course I'm not looking to do that on my little toy :)
Hi Marky88,
I have been wanting to swap out my steppers for servos for a while. I have just (10 minutes ago) ordered a Delta B2
series 400W servo, drive and cables, price $460USD including shipping to New Zealand. I still have to pay 15% tax
when it enters the country so will cost $872NZD by the time I get it.
When I built my machine I bought secondhand 23size 5 phase Vexta steppers with low lash (less that 3 arc min) 10:1
planetary drives. Despite the small motors the 10:1 reduction means I get great torque, just over 700 oz.in. They drive
directly a 20mm diameter 5mm pitch ground ballscrew which gives a stall thrust of over 1400kg force or 14kN.
The only downside is the gear reduction means its slow, I have them tuned for 1200mm/min. I can get them to do 2000mm/min
but I have to run them at max current (1.4A per phase) and they get hotter than I like. So I run them at 1.1A per phase.
The vagaries of 5 phase steppers is that four phases are energized at any one time so 1.4A phase rated is equivalent to 2.8A
in a 2 phase stepper. At reduced current and consequent less torque I've found that 1200-1500 mm/min is reliable.
At 1200mm/min the ballscrew rotates at 240 rpm and so the stepper is rotating at 2400 rpm. You might ask 'can a stepper
do that speed' given the nature of this thread. 5 phase steppers are a bit specialist. Among the advantages they have over regular
two phase steppers is smooth operation without the vibration propensity of two phase steppers, high speed operation
and 500 full steps per revolution compared to 200 full steps per revolution for a two phase stepper.
The drivers I use are specialist Vexta 5 phase drivers. They don't require a power supply, you wire them directly to 230VAC.
I have measured a peak output voltage at the stepper of 150VDC. So you can see that Vexta drives have a very high voltage output
which goes a long way to secure the high speeds that can get.
Even secondhand the steppers and drives were not cheap, $278USD each plus shipping for the motor and gearbox and $147USD
each plus shipping for the drivers.
These steppers have been absolutely superb....once I had them tuned they never missed a step (except when I crash!) and I get
repeatable resolution of 1um. They have been so good I don't think I'll sell them....I'm so impressed with them. I'm sure I'll
find other uses for them. Of course I've only ordered one servo so far...I'll have to save a few more pennys before I can
buy another two!
Craig
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Hi,
I would guess that the ultimate speed limit will be the rigidity of the machine or possibly the power, or lack
thereof, of the spindle.
As the speed goes up so do the cutting forces and any flexure in the machine can badly degrade the work.
I have two spindles, one German made 24000 rpm asynchronous spindle with ER11 manual tool holder and
a home made Rego-fix ER25 cylindrical in P4 angular contact bearings powered by my Allen Bradley 3500 rpm 1.8 kW
6Nm servo. The high torque slow speed spindle I made so I could machine steel and stainless steel. It works great
but the cutting forces are high. Despite my machine being made of cast iron it still flexes, the rate of metal removal
depends on the amount of flexure I can tolerate with a given operation.
As I said earlier acceleration is the key, less important is the speed. The steppers you have ordered will be an order
of magnitude faster than what you have currently. I suspect they will be faster than the machine can safely and reliably
handle.....machine flexure will determine the limits....not the steppers.
Craig
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Hi,
It's quite a strong machine, 4 " Box section frame with the steel frame gantry with large linear guide rails and blocks on all axis. Twin motors on the Y Axis.
I would say I wouldn't want to go much faster than 5 to 6k mm/min in any case and at that the new motors would only be spinning at 375 rpm max at with my set up. Even though we don't have a torque graph for these motors based on the Leadshine graphs that should be well up in the motor torque range should it not?
Hopefully then I want get any stalling or missing steps etc and very good acceleration speeds?
Mark
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Hi,
if you plan on hooking your new steppers direct to the leadscrews then this is the calculation:
Leadscrew, 16mm diameter, 16mm pitch.
The radius of action (where the ball contacts the groove) will be a little less than the radius of the leadcsrew, say 7mm.
The stall torque of the stepper is 7.5Nm or 0.75kg(force) at 1m which is equivalent to 0.75 X1000/7=107 kg(force)
at the radius of action. The circumference of the circle described by a radius of 7mm is 2x 3.141x7=44mm. If the leadscrew
rotates one turn the axis will advance 16mm. The mechanical advantage of the leadscrew is 44/16=2.75.
Thus the stall thrust of a 7.5Nm stepper on a direct coupled 16mm diameter screw of 16mm pitch excluding frictional losses
will be 107x2.75=294kg(force) or 2.94kN. Not too shabby.
Of course if you had a belt or gear reduction the stall thrust would go up by the reduction ratio and given that these steppers
are likely to be way WAY WAY quicker it would still not count against your ultimate top speed.
Remember that stall thrust is a somewhat slanted or unusual measure of a machines thrust.
Its more realistic to assume that approximately half of the available torque (equivalent to thrust) is used to accelerate the
axes and mass of the workpiece/gantry or whatever and the other half be available to supply the cutting forces required.
A detailed calculation would require much more data on the kinematics of the machine and a much more thorough knowledge
of the cutting forces, the sort of thing professional mechanical engineers thrive on. Its dubious that as hobbyists we need that
sort of detail. If however you were designing and building a $100,000 plus machine for production work you want/absolutely
need to know before you start....and after all mechanical engineers want a job too!
Craig
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Hi.
if you follow the calculation so far try imagining this:
Desired theoretical max top speed=6000mm/min. Therefore the leadscrew must rotate at 6000/16=375 rpm.
If you had a 3:1 belt reduction the stepper rpm would be 375x3=1125rpm. The low inductance steppers are
such that you will retain approx. 50% of holding torque at 1125 rpm so the available torque from the stepper
at 1125 rpm we estimate to be 0.5x7.5=3.75Nm. With a 3:1 reduction the torque at the leadscrew is3x3.75=11.25Nm.
The resultant thrust as a result of mechanical advantage of the leadscrew, indentical to my previous post, is
2.94 x11.25/7.5=4.41kN or a little over 400kg(force).
Allowing 50% for acceleration that still allows 200kg(force) for cutting forces at 6000mm/min.
As you can see using a belt or gear reduction would allow you to exploit the full potential of your new steppers
and still go as quick as you dare.
Craig
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Hi,
as a matter of comparison the servo that I ordered today has a rated torque of 1.27Nm and a rated speed of 3000rpm.
If this were fitted to your machine through the same 3:1 reduction I am proposing then the calculation is something
like this:
max speed is 3000/3 x16=16000 mm/min
torque at the leadscrew is 3x 1.27=3.81Nm so the thrust of the axis is 3.81/7.5 x2.94=1.49kN
So a servo equipped machine is about 2-3 times faster but about half the static thrust. With a servo however a short term
overload does not cause a stall as it would with a stepper, the servo just 'digs in'. The overload torque of my new
servo is 3.8Nm so its short term thrust at 16000mm/min is 4.48kN, ie about the same as your stepper but at nearly
three times the speed. Additionally my servo gives has an ultimate resolution of about 0.2 arc min or on a 3:1 reduction
16mm pitch leadscrew a linear resolution of 0.05um!!!
That sort of performance doesn't come cheaply but this calculation shows just how superior servos are in practice and why
they dominate in pro equipment.
Craig
-
Hi,
as a matter of comparison the servo that I ordered today has a rated torque of 1.27Nm and a rated speed of 3000rpm.
If this were fitted to your machine through the same 3:1 reduction I am proposing then the calculation is something
like this:
max speed is 3000/3 x16=16000 mm/min
torque at the leadscrew is 3x 1.27=3.81Nm so the thrust of the axis is 3.81/7.5 x2.94=1.49kN
So a servo equipped machine is about 2-3 times faster but about half the static thrust. With a servo however a short term
overload does not cause a stall as it would with a stepper, the servo just 'digs in'. The overload torque of my new
servo is 3.8Nm so its short term thrust at 16000mm/min is 4.48kN, ie about the same as your stepper but at nearly
three times the speed. Additionally my servo gives has an ultimate resolution of about 0.2 arc min or on a 3:1 reduction
16mm pitch leadscrew a linear resolution of 0.05um!!!
That sort of performance doesn't come cheaply but this calculation shows just how superior servos are in practice and why
they dominate in pro equipment.
Craig
Hi Craig
My new motors and power units have arrived, I should be fitting them soon.. :)
At 16000mm/min my ball screws would be spinning at 1000rpm as direct drive which is probably not advised for longevity. What would you recomend that max rpm of the 16mm dia 16mm pitch screws, also where do you think my new motors will start to max out rpm and acceleration wise?. Is there a calculation to getting the acceleration setting close to start with?
Mark
-
Hi,
in the NSK ballscrew technical literature there is a calculation that can be done to arrive at the recommended top
rotational speed for a given diameter ballscrew.
The principle determinants are the diameter of the screw and the maximum un-supported length. For instance I did the
calculation for my ballscrews (20 diameter,400mm max unsupported length) and it advised me that the maximum recommended
speed before the onset of ballscrew whipping was 2500 rpm. As these screws have a pitch of 5mm that would be equivalent to
12500 mm/min, a factor of ten faster than I actually use them. Since the rotational limit was that much higher than my intended
use I quietly forgot about it.
Two days ago I took delivery of my new Delta 400W B2 series servo and drive. I was of the opinion that I was going to have
to buy a 3:1 or a 5:1 planetary reduction box to bring the rated 1.27Nm torque of the servo up to around 4-5Nm to match
the thrust capabilities of my existing steppers/10:1 planetary combination. The torque/stiffness of the Delta servo is very
high indeed, far FAR exceeding my expectations. I am inclined now to try the servo in my mill direct coupled as see what
happens. If I do then I would anticipate that the servo could, if I allow it, drive the ballscrew in excess of the 2500 rpm
recommended maximum that I calculated six years ago when I was designing it. For the first time I am going to be able
to push the boundaries and see what happens.
You are aiming for about 6000mm/min or the screw rotational speed of 375rpm. Unless your screws are very long or the
non driven end is left un-supported, ie no bearing block, then I don't think you will have any problem. Whether you could
drive then to 1000 rpm or 3000 rpm with a direct coupled servo is another question.
Is there a calculation to getting the acceleration setting close to start with?
A professional mechanical engineer would probably come up with a reasonable prediction. It would require detailed measurements
of your machine, particularly the rotational inertial moments of the screw/stepper rotor combination and the mass of the
gantry/table/workpiece that is being accelerated. All in all it is probably beyond us and experimentation at with the machine
with the steppers installed will yield the required limits faster and more reliably than any calculation we could perform.
If you have followed my previous calculations then a sketchy calculation is this:
stepper torque at 375 rpm (estimated)=6Nm
thrust at 375rpm considering the mechanical advantage of the screw=235kg(force) or 2.35kN
assuming half the available thrust is consumed combating cutting forces then the thrust available for acceleration
is about 1.2kN
According to Newtons Law a=F/m thus with a gantry weight of 100kg
a=1.2K/100=12 m/s2 or about 1.2g. This is a very VERY respectable result for a hobby machine.
Note that I have not allowed for any rotational inertia in this calculation so I would expect it to be optimistic but none the
less even without a belt reduction I suspect your machine will accelerate very smartly. With a belt reduction
it would be stellar!
The procedure goes, set the max velocity in Machs motor tuning to be a very low value, say the equivalent of only
100 stepper rpm and then increase the acceleration in steps until you find a maximum where either the steppers stall
or the machine starts flexing alarmingly or the machine starts bouncing all around the workshop. Then back
of 25% from that maximum. Now start increasing the max velocity until the same conditions indicate a practical maximum
and then back off 25%.
Methodical experimentation is the key......persue the limits of just one variable at a time until you have arrived with a clear
and repeatable result. Then and only then move onto the next variable by setting all previously discovered at a level that
will not unduly interfere with experiments concerning the current variable.
Craig
-
Hi,
Excellent information thank you, I'm possibly going to try cutting some aluminium and again possibly use Imachining, that's if I can get enough speed from the axis. Servo's certainly would be the way to go but I'm not ready yet to take that leap.
I guess running these new steppers to around 600 rpm would still be viable, torque would be less than 375 rpm obviously. You did say they were many times faster because of the lower inductance compared with the old ones.
Is there much gain to be had on running either or/and higher kernal speed and 10 micro stepping rather than 8, more micro steps would be a smoother drive but not sure if I would be then better with a smooth stepper board, even drop the parallel port set up and go with the ESS network port smooth stepper.
With my current high torque slow speed steppers i tried to cut a 700mm diameter at 5000mm / minute as a test on them and they slower axis didn't sound so great when it was nearing a stop as it was cutting the circle. Having not done that before it maybe the same with all steppers?
So for instance 10000 mm/min, 625 stepper RPM
(200*10000)/60 = 33333khz
So 25000 khz is not enough for this speed.
-
I understand the test, would you just manual jog (at full velocity) one axis at a time back and forth between the limits or create a program to interpolate both axis running together for X and Y? What sort of velocity increments 500 ok? and fine tune from there. Maybe 100 increments for acceleration?
"The procedure goes, set the max velocity in Machs motor tuning to be a very low value, say the equivalent of only
100 stepper rpm and then increase the acceleration in steps until you find a maximum where either the steppers stall
or the machine starts flexing alarmingly or the machine starts bouncing all around the workshop. Then back
of 25% from that maximum. Now start increasing the max velocity until the same conditions indicate a practical maximum
and then back off 25%."
-
Hi,
changing the microstepping will marginally affect smoothness but will have no effect on stepper torque and therefore acceleration.
Lower microsteps will bring the required pulse frequency down and allow you to go faster at 25kHz kernel or alternately increase
the kernel speed to as much as your PC can handle.
If you use an ESS then it so fast that kernel speed is irrelevant and is worthwhile aside from being smoother motion and the PC very much
less inclined to stutter and stall.
To really effect an increase acceleration without losing top speed you need a gear or belt reduction of 2:1 to about 4:1.
If that does not appeal try direct coupling to the screws first. If that's adequate all well and good. If you want more torque
at speed and maintain your top speed a belt reduction may well be the only way to achieve it.
I understand the test, would you just manual jog (at full velocity) one axis at a time back and forth between the limits or create a program to interpolate both axis running together for X and Y?
You need to create a program that goes back and forth multiple times but only one axis at a time.
g0 x0 y0 z0
g0 x100
g0x0
g0x100
g0x000
g0x100
g0x0
etc...
Try a low acceleration and work up, I should suggest a large increase to the extent it stalls in acceleration phase then back off.
You don't want or need to take all day over this, be reasonably aggressive in your increments and narrow the increments as you establish
the outer limits and refine you guesses.
Craig
-
Hi,
I've got this torque curve for my new motors but don't understand it, sorry not very good with graphs and I'm just trying to learn more about the mechanics of my components.
Torque is the motor torque in Nm.
Pulse rate?
400 pulse rev?
The leadshine graphs you popped up had Rpm on the bottom line hence my confusion. How do i convert the pulse rate shown here to Rpm
Mark
-
Hi,
Torque is the motor torque in Nm.
Pulse rate?
400 pulse rev?
The driver in this measurement is set to half stepping, that is 400 pulses per rev as compared to 200 pulse per rev for
full steps. Thus 400 pps (pulse per second) is 1 revolution per second. So 1000 rpm is equivalent to (1000/60)x400=6666 pps.
Pulse per second(half stepping regime)= RPM/60 X400
Torque at low rpm =5.5Nm = 3.7ft.lb =718 oz.in
Torque at 1000 rpm (6666pps)=1.8Nm=1.2 ft.lb=235 oz.in
Ratio of torque @1000rpm compared to 0 rpm =1.8/5.5 =33%
Craig
-
Hi
Thanks, I'm slowly picking it up :)
These motors are rated at 7.5nm holding torque in the spec (see attached) so I'm now confused why the graph shows only 5.5nm at zero now.
Mark
-
There not quite as we presumed then given that graph if only 33% at 1000 rpm
"The low inductance steppers are
such that you will retain approx. 50% of holding torque at 1125 rpm so the available torque from the stepper
at 1125 rpm we estimate to be 0.5x7.5=3.75Nm. "
-
Hi,
the graphs are representative only, that they will exactly describe every motor is fallacious.
Also note that the 33% retained torque at 1000 rpm was measured with a driving voltage of 60V, the result
might be closer to 50% if you used 80V.
These motors are still many fold better than what you had. Try them out.
Craig
-
;D
looking forward to seeing the difference, keep in touch re how you get on with your servo's please.
Hi,
the graphs are representative only, that they will exactly describe every motor is fallacious.
Also note that the 33% retained torque at 1000 rpm was measured with a driving voltage of 60V, the result
might be closer to 50% if you used 80V.
These motors are still many fold better than what you had. Try them out.
Craig
-
Hi,
I have taken delivery of the Delta 400W B2 series servo and drive. Its fantastic.
I was of the opinion that I would have to use a gear reduction (3:1 to 5:1) to match my existing steppers and integrated low lash
planetary 10:1 drives. The manufacturers spec on the Vexta stepper and gearbox is 705 oz.in. That results in over
1400kg (force) of stall thrust, really rather more than my machine could hope to contain. I was of the opinion that
if I had a servo/gear reduction that could deliver half, say 350 oz.in, that would be still every bit good enough for my mill.
The manufacturers spec on the 400W servo, without gear reduction is 1.27Nm (cont) or about 166 oz.in Now that I have the servo
in hand I'm thinking that I may try direct coupling it. That would save the cost of a low lash planetary gearbox which would
be advantageous. What I have discovered is that while the continuous rating is 1.27Nm the overload rating makes it behave
as if its considerably more torquey than its spec.
When you load a stepper to near its max spec it starts losing steps when it does not stall completely. A servo on the other hand
just 'digs' in and produces the torque demanded until it current overloads or faults following error. In short the overload
capacity really allows for a servo to 'punch well above its weight'.
I have to shift house over the next two weeks and so will have to put this on hold for a while....but I am extremely impressed
with this servo and drive. I want one more for the X axis, and another but with a electromagnetic brake for the Z axis.
Craig
-
That sounds like it's going to work well, are you looking for another 2 it sounds like you only have one at the moment?
I picked up a bargain today, a 27" touch screen monitor and large gas strut monitor and laptop arm. It's bigger than I need but for £30 it was a bargain I couldn't resist.
I'm researching into making a vacuum table now without having to buy and run a large noisy industrial type pump.
Do you know much about smooth stepper boards, I would like to get a better quality break out board and smoother stepper like the Warp9 ess one. With this i presume I can use a more modern computer with windows 10 and use the Ethernet port and drop the parallel port?
I'm presuming the pc connects to the smooth stepper with the Ethernet cable then the smooth stepper to the break out board with a parallel cable?
Hi,
I have taken delivery of the Delta 400W B2 series servo and drive. Its fantastic.
I was of the opinion that I would have to use a gear reduction (3:1 to 5:1) to match my existing steppers and integrated low lash
planetary 10:1 drives. The manufacturers spec on the Vexta stepper and gearbox is 705 oz.in. That results in over
1400kg (force) of stall thrust, really rather more than my machine could hope to contain. I was of the opinion that
if I had a servo/gear reduction that could deliver half, say 350 oz.in, that would be still every bit good enough for my mill.
The manufacturers spec on the 400W servo, without gear reduction is 1.27Nm (cont) or about 166 oz.in Now that I have the servo
in hand I'm thinking that I may try direct coupling it. That would save the cost of a low lash planetary gearbox which would
be advantageous. What I have discovered is that while the continuous rating is 1.27Nm the overload rating makes it behave
as if its considerably more torquey than its spec.
When you load a stepper to near its max spec it starts losing steps when it does not stall completely. A servo on the other hand
just 'digs' in and produces the torque demanded until it current overloads or faults following error. In short the overload
capacity really allows for a servo to 'punch well above its weight'.
I have to shift house over the next two weeks and so will have to put this on hold for a while....but I am extremely impressed
with this servo and drive. I want one more for the X axis, and another but with a electromagnetic brake for the Z axis.
Craig
-
Hi,
That sounds like it's going to work well, are you looking for another 2 it sounds like you only have one at the moment?
Yes, only one at the moment. Partly budget, partly I wished to establish how it works in practice. I may well for instance require a gear
reduction, in which case I really want to know BEFORE spending more money.
Do you know much about smooth stepper boards, I would like to get a better quality break out board and smoother stepper like the Warp9 ess one. With this i presume I can use a more modern computer with windows 10 and use the Ethernet port and drop the parallel port?
I'm presuming the pc connects to the smooth stepper with the Ethernet cable then the smooth stepper to the break out board with a parallel cable?
I've used an Ethernet SmoothStepper (by Warp9TD, don't be fooled by a Chinese ripoff) and Mach4 for five years, highly recommended. Yes you can use just about
any PC you like including laptops and 64 bit OS's including Windows 10 which were precluded by Machs parallel port.
Yes you hook one (or up to three) parallel port boards by parallel cable to the ESS.
C10 breakout boards at $23.00 each are a cheap option. They are bi-directional. Note they do not have any relays, PWM output or opto-isolated inputs. If you want
those you have to add the handful of electronics parts to do so OR buy a more sophisticated board. I use Homann Design MB2's (from Australia) which are very similar
to the C10, ie bi-diectional, no PWM, relays or opto-isloated inputs. They are very flexible.
CNCRoom do a three port board (MB03 approx $180) especially for the ESS, all ports are developed but require you stick with the circuit arrangements and pin-out choices
made by the manufacturer. You lose some flexibility, on the other hand you get a quality, sophisticated and complete breakout board solution in one hit.
When I transitioned from a parallel port, with which I'd had great success, to the ESS, I able to increase my G0 axis speed by 33% without losing steps and run a little
cooler. I had not expected that smoother more consistent pulses that you get with an ESS would have been that significant....but it was. As far as I am concerned the parallel port
is for those on a budget or those who just aren't bothered about a lesser standard of performance.
Craig
-
Sounds like I'm on the right track for further upgrades then,
The Ess smoother stepper form warp 9. A newer PC with windows 10 which I prefer and already have a spare of.
With regards to a bob, I want a decent one with plenty of connections for inputs and outputs. I want to control spindle on/off and also the RPM, The usual E stop, ideally pump on/off , a probe, limit and homing switches as well as all the axis XYZA. Feed speed control via remote hand controller.
I like the idea of going to mach4 too....
Got my eys on a few here but I presume the USB type will now work with the ESS smooth stepper if it requires parallel port connection to a bob?
https://www.ebay.co.uk/itm/3-axis-mach4-board-interface-usb-cnc-motion-control-card-2000khz/303252148651?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
https://www.ebay.co.uk/itm/CNC-200-KHz-4-Axis-USB-Mach3-Motion-Control-Card-Breakout-Interface-Board/123698623045?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
What about this one, it doen't mention mach 3/4 compatible though.
https://www.ebay.co.uk/itm/Spark-Concepts-CNC-XPro-V3-Control-Board-Good-condition/303286057224?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
Spec here
http://www.spark-concepts.com/cnc-xpro-controller-v3/
Now updated with this one, again doesn't mention MAch3/4
http://www.spark-concepts.com/cnc-xpro-v4-controller/
I also want a hand controller that I can control feed and spindle speed with a rotary dial/knob. I think this one will cover that.
https://www.makers-hut.com/product/mach3-4-axis-wireless-electronic-handwheel-manual-controller-mpg-usb-handle/
-
Hi,
With regards to a bob, I want a decent one with plenty of connections for inputs and outputs. I want to control spindle on/off and also the RPM, The usual E stop, ideally pump on/off , a probe, limit and homing switches as well as all the axis XYZA. Feed speed control via remote hand controller.
If you want that on one BoB then you need the MB03 from CNCRoom.
All of those controllers you have linked to are junk Chinese.....stay away from that rubbish!.
That wireless pendant is more XHC Chinese junk and won't work with Mach4 anyway.
If you want a pendant try VistaCNC. I use a VistaCNC P1A and it works with Mach4.
https://warp9td.com/ (https://warp9td.com/)
https://www.cncroom.com/ (https://www.cncroom.com/)
http://www.vistacnc.com/ (http://www.vistacnc.com/)
Craig
-
Hi Craig
I checked with the supplier of my new motors and they have just stated the maximum rpm is 300, this leaves me way short of target velocity. Does this sound correct to you that a Nema 34 stepper is maximum 300 rpm?
Or am I getting confused as using microstepping changes the rpm effectively allowing the motors to spin faster. I've attached the 400 pulse revs as per their torque graph and one at 8 stepping.?
"Hello
The RPM is 200~300 rpm/min
How many 34HS9456 do you willing to buy?
What king of machine do you use?
------------------
Yolanda
Sales Manager
ChangZhou Longs Motor Co.,Ltd
Skype:yolanda-momo1"
"Hello
maximum RPM is 300
How many 34HS9456 do you willing to buy?
------------------
Yolanda
Sales Manager
ChangZhou Longs Motor Co.,Ltd
Skype:yolanda-momo1"
-
Hi,
Does this sound correct to you that a Nema 34 stepper is maximum 300 rpm?
No, that does not sound correct. Fit the motors and try them out.
Craig