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Half Speed Drive
« on: June 25, 2019, 02:25:27 PM »
Been away a while so I'm a bit rusty.
I'm using Aspire 4.5
I have a rectangle 300 x 300
I set my tool speed at 100mm/sec
When I run my code on Mach 3 My axis only run at half the speed
Probably quite simple but where am I going wrong.
Heres my gcode generated by Aspire maybe someone can set me correct.
I have never actually tested the axis speeds before, I was thinking of attaching a laser head and I saw a sample file depicting a feed of 100mm/sec so I wanted to see if my machine axis would travel at that speed. Seems quite fast!! ?

( 300box )
( File created: Tuesday, June 25, 2019 - 07:20 PM)
( for Mach2/3 from Vectric )
( Material Size)
( X= 500.000, Y= 500.000 ,Z= 20.000)
()
(Toolpaths used in this file:)
(Profile 1)
(Tools used in this file: )
(1 = End Mill {3 mm})
N100G00G21G17G90G40G49G80
N110G71G91.1
N120T1M06
N130 (End Mill {3 mm})
N140G00G43Z19.050H1
N150S12000M03
N160(Toolpath:- Profile 1)
N170()
N180G94
N190X0.000Y0.000F5994.4
N200G00X-150.000Y-150.000Z3.175
N210G1X-150.000Y-150.000Z-0.500F127.0
N220G1X150.000Y-150.000Z-0.500F5994.4
N230G1X150.000Y150.000Z-0.500
N240G1X-150.000Y150.000Z-0.500
N250G1X-150.000Y-150.000Z-0.500
N260G1X-150.000Y-150.000Z-1.000F127.0
N270G1X150.000Y-150.000Z-1.000F5994.4
N280G1X150.000Y150.000Z-1.000
N290G1X-150.000Y150.000Z-1.000
N300G1X-150.000Y-150.000Z-1.000
N310G00X-150.000Y-150.000Z3.175
N320G00Z19.050
N330G00X0.000Y0.000
N340M09
N350M30
%

One step at a time!
Re: Half Speed Drive
« Reply #1 on: June 25, 2019, 02:49:06 PM »
Hi,

Code: [Select]
N210G1X-150.000Y-150.000Z-0.500F127.0This is  a Z axis plunge cut and should happen at 127mm/min.
Code: [Select]
N220G1X150.000Y-150.000Z-0.500F5994.4This is an XY cutting move and should be executed at 5994.4mm/min, or near as dammit 100mm/sec.

That's pretty quick for a hobby machine. What is your max X and Y axes velocity in your motor tuning page?.
Mach will go up to that max speed and no higher even if the Gcode insists that the machine go faster.

Craig
My wife left with my best friend...
     and I miss him!
Re: Half Speed Drive
« Reply #2 on: June 25, 2019, 04:42:16 PM »
Thanks Craig, Velocity was set at 3000mm/min that's 118" per minute .
Why that speed, I dunno, I just saw a guy using 'Lightburn software' and he set initial bur speed of 100mm/sec. I thought it was pretty fast so I started to investigate the speed of my machine.

My axis settings are
400Steps, 3000mm/min. 575 Accell, 0.056g's
Does this look correct ?
One step at a time!
Re: Half Speed Drive
« Reply #3 on: June 26, 2019, 01:55:25 AM »
Hi,

Quote
My axis settings are
400Steps, 3000mm/min. 575 Accell, 0.056g's
Does this look correct ?

Well 3000mm/min is as fast as your machine can go. Thus your G1 move which called for a feed speed of 5994mm/min
will never exceed 3000mm.min no matter what.

As to does it look correct...who knows.

The general idea is that you have the velocity and acceleration settings as fast as your steppers will allow WITHOUT losing
steps. The maximums depend on your steppers (inductance especially), the drivers (voltage supply especially) and the mass
and drag of your machine.

All steppers lose torque as they speed up. Low inductance steppers may retain 25%-33% of their torque at 1000 rpm
with a good high voltage driver. High inductance motors may have as little as 5% of their torque at 1000 rpm, especially
with weak and/or low voltage drivers.

As a rule of thumb I would set the maximum speed of an axis as that speed it would attain if the stepper was doing 500rpm.
Most steppers, unless you've bought some real dogs, will have about 50% of their holding torque at 500 rpm. If the steppers
are adequate to accelerate an axis and exert the required thrust for cutting at slow speeds then with any sort of luck it will
still have enough at 500 rpm.

So if you have direct coupled 5mm pitch ballscrews for example then I would start with the motor tuning velocity of 5 x 500 =2500mm/min.
Another rule of thumb is to start with the acceleration of 10% of the velocity, ie 250mm/s2.

THEN you start tuning. As it turns out fast axis speed often does not result in good high sped cutting performance but rather
maximum acceleration does. For this reason I suggest keep upping the acceleration until you can get the motor to stall when issuing
MDI's like:
g0 x0
g0 x300
g0 x0
g0 x300
g0 x0.
Once you have found the maximum acceleration (when it starts losing steps or stalling) back off by 25%. Now try upping the speed
using the same approach.

Craig



My wife left with my best friend...
     and I miss him!
Re: Half Speed Drive
« Reply #4 on: June 26, 2019, 07:22:27 AM »
Thanks Craig.
I'm using pretty hi power 2Nm steppers on all axis (See pics) Drivers are MSd542 from Motion control products and my machine uses 10mm Ball screws (See pics)
So my thinking is the machine should be no slouch.
In the motor tuning my steps per are set to 400, this allows for a maximum speed of 3750mm/min (Cant go any higher ??)
My stepper drivers are set  to 1000 pulse/rev (can I set different than that)
What do I need to change to allow me to run my X & Y axis at 6000mm/min
It's a pretty robust construction as you can see from the pictures
I hope you dont mind me posting and asking these questions.
One step at a time!
Re: Half Speed Drive
« Reply #5 on: June 26, 2019, 08:08:10 AM »
Hi,

Quote
In the motor tuning my steps per are set to 400, this allows for a maximum speed of 3750mm/min (Cant go any higher ??)
My stepper drivers are set  to 1000 pulse/rev (can I set different than that)

I take it your ballscrews are direct coupled? If so the steps/per unit are fixed by the pitch of the ballscrew and the microstepping
regime you have in place on your stepper drives.

A two phase stepper advances 1.8 deg/step or 200 steps per rev. If you use a five microstep per full step regime that would
mean 1000 pulses would produce one revolution of your stepper. One revolution of your stepper will cause 10mm of axis
travel, assuming direct coupled ballscrews. Thus the 'steps per unit' value in your motor tuning page should be
1000 (steps)/10 (mm movement) =100 'steps per'

Note this is DETERMINED by the pitch, any gear or belt reduction and the microstepping regime.......it is not a free choice.
To test whether you have done the calculation correctly zero the axis and MDI:
g0 x200......the axis should move 200mm, not 199 or 201 but 200mm EXACTLY. This sets the basic accuracy of your machine.
You will do NOTHING successful until you have this perfect.

With 10mm pitch ballscrew and the stepper doing 500 rpm the axis would travel at 5000mm/min. Per my previous recommendation
I would suggest that is a reasonable value for max velocity in the motor tuning page.

Are you using a parallel port? If you are the parallel port has a limited maximum output pulse rate, called the kernel speed.
Machs default parallel port kernel speed is 25kHz.

At 500rpm and 1000 pulse per rev each stepper will require a maximum pulse rate of 500 x 1000 /60=8333.3 pulse per second.
So 500 rpm will mean that Mach can loaf along at about 1/3 its default kernel speed and still produce enough pulses to spin your
steppers to 500 rpm. In fact you could, with the same default kernel speed, have Mach signal your steppers (1000 pulse/rev)
to spin at 1500rpm for an axis speed of 15000mm/min. I would expect your stepper to wimp out and stall long before
you could get that fast though.

Quote
I'm using pretty hi power 2Nm steppers on all axis
2Nm is not earth shattering, although I'm sure will be adequate. The important specification is the inductance. Low inductance
steppers spin faster without losing torque. What inductance are your steppers? Less then 1mh is very good to good, about 2mH
is average and 4mH or more is poor.

Note that first time stepper buyers tend to buy on the basis of holding torque.......the higher the torque the better right?
Well......no actually. It is quite possible to wind a motor to have high torque but commensurately high inductance. Thus it would
have a spec of 4Nm and 6mH and so would be lucky to have 0.2Nm at 1000 rpm. The same size motor wound differently
might have only 2Nm holding torque but a commensurately low inductance of 0.9mH and so still have 0.6Nm torque at
1000rpm. Thus the lower torque motor is better overall because it maintains its torque at speed.

The classic way to overcome the drop of torque with speed is to use a high voltage driver. About 80V is the current state
of the art maximum voltage for two phase steppers. What voltage power supply are you using?

Craig
« Last Edit: June 26, 2019, 08:16:36 AM by joeaverage »
My wife left with my best friend...
     and I miss him!
Re: Half Speed Drive
« Reply #6 on: June 26, 2019, 05:11:03 PM »
Ok, all screws are 5mm pitch and directly driven from the steppers.
The steppers are wired 'Bi-Polar' parallel.
X axis is 2 phase 1.8deg per step. Rated voltage is 2.73 current 4.2A Resistance 0.65Ohm/phase and an  inductance of 3.2 mh/phase Hold torque 3Nm
Y axis is 2 phase 1.8 deg per step 1.93v 4.2 Amp 0.46 Ohm and 2.2 mH/phase Hold torque 2.0Nm

My supply voltage is only 30Volts, I guess I should double that!! ?
My steps per are set to 400, I guess I should halve that ?

My microstep drivers ar set to 2000 pulses per revolution.   
Physical movement of x & y axis shows 5mm movement per 1 360deg turn of the stepper.
One step at a time!
Re: Half Speed Drive
« Reply #7 on: June 26, 2019, 06:22:59 PM »
Ok, all screws are 5mm pitch and directly driven from the steppers.
The steppers are wired 'Bi-Polar' parallel.
X axis is 2 phase 1.8deg per step. Rated voltage is 2.73 current 4.2A Resistance 0.65Ohm/phase and an  inductance of 3.2 mh/phase Hold torque 3Nm
Y axis is 2 phase 1.8 deg per step 1.93v 4.2 Amp 0.46 Ohm and 2.2 mH/phase Hold torque 2.0Nm

My supply voltage is only 30Volts, I guess I should double that!! ?
My steps per are set to 400, I guess I should halve that ?

My microstep drivers ar set to 2000 pulses per revolution.   
Physical movement of x & y axis shows 5mm movement per 1 360deg turn of the stepper.
also read somewhere that a stepper should by driven by 32 times it's rated voltage, is that correct ??
One step at a time!
Re: Half Speed Drive
« Reply #8 on: June 27, 2019, 04:22:23 AM »
Hi,

Quote
My steps per are set to 400, I guess I should halve that ?

For a given set of parameters (pulses/rev, ballscrew pitch, gear/belt reduction) there is one and only one right answer. You
cannot set it at will UNLESS you also change the parameters that determine it.

Are you going to change ballscrews? No, I didn't think so. The parameter of ballscrew pitch is fixed.

Are you going to put gear or belt reduction instead of direct drive? No, I didn't think so. The parameter of gear/belt reduction
is fixed.

Are you going to change your stepper drive microstep regime. You certainly can, it easy and costs nothing.
On the one hand you want to set the pulses per rev (PPR) as high as you can to get the smoothness of motion that
microstepping offers. On the other hand high PPR means high pulse rates and so Machs parallel port may limit the ultimate
speed of your steppers.

The calculation with the existing PPR setting of 2000:

25,000 /2000  x 60 = 750 rpm. With a 5mm pitch means a max velocity of 3750 mm/min

If you want to go faster then you have a couple of choices:
1) increase the parallel port kernel........OR
2) get an external controller like a SmoothStepper which can output up to 4Mhz....plenty.....OR
3) reduce your microstepping regime to 1000 PPR say.

If you choose the later then the same max speed calculation becomes:

25,000 / 1000 x 60 = 1500 rpm or (5mm pitch assumed) 7500mm/min.

I rather doubt you'll be able to get your steppers to go anything like that speed, especially with such a low voltage supply,
however Mach's parallel port will give you that head room.

The potential resolution assuming 1000 PPR, 5mm pitch and direct drive is:

5 / 1000= 0.05mm......which is probably quite adequate for  a router.

If you assume 1000 PPR the last parameter is now determined. The 'Steps per Unit' in the motor tuning page is:
1000 / 5 =200 steps per unit. Once again this is fixed by other choices you have made, the ONLY way you can change it is by
revisiting the choices you made for those parameters.

To get your steppers to go as fast as you can you should use the highest voltage that your drivers can handle. They are rated to 50V.
You should be using a 48V supply. I have seen different recommendations for the voltage, including one formula that looked
interesting but the bottom line is use the highest you can, in your case 50V.

I have Vexta 5 phase steppers with genuine Vexta drives. Each drive has its own power supply built in, you just hook it up to
230VAC and the drive does the rest. The DC voltage the drives use to move the motors is about 150VDC!!! It really makes
those steppers sing. They can do 3000 rpm with pretty good authority, ie not losing steps, but I run them at 2400 rpm max
just to be on the safe side. I doubt you'll find any drives for two phase steppers to match those but it does show the principle.....
high voltage equals high speed.

Craig
My wife left with my best friend...
     and I miss him!
Re: Half Speed Drive
« Reply #9 on: June 27, 2019, 09:10:45 AM »
Clear! Thanks Craig,
Those Vexta's are serious stuff, and pricy. I have seen 5phase with driver (Used) at £145.00 ea but I don't think I want to go down that route. I have been using my machine as it it for 8 years or more with no issues and have created some very nice work (Se sample)
With the plan to install a laser head I thought I would investigate my speed so I will proceed as follows.

Reduce the Pulses/re from 2000 to 1000
Upgrade my Power supply to 48VDC
Reduce steps per from 400 to 200
Then I will carry out some accuracy tests at various speeds.

Maybe later I will upgrade my CNC4PC c11 Controller for a more advanced one.

Meanwhile many thanks.

George
One step at a time!