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Speed of stepper motors
« on: November 10, 2015, 01:12:44 PM »
Hello!

I'm a newbie in Mach3, and I have some problem with the speed of the axis in my Mach3 CNC machine. I think this is probably a really easy problem to solve, so for a pro this might take a sec!   ::)

I have set the system to metric, e.g. in mm's. By measuring the distance the axis move when I use the program, I have calculated the "Steps per" to be 200. My stepper motors turn 200 steps per revolution, which means that one motor revolution moves the axis 1 mm in linear distance. The kernel speed is 25KHz, so the maximum velocity should be 25KHz/200 steps per unit = 125 mm/s

However, this feels like a very low velocity? This is the maximum velocity the machine will move, right? What can I do to make it faster? Or am I missing something completely now?

/ Johanna
Re: Speed of stepper motors
« Reply #1 on: November 10, 2015, 01:19:44 PM »
That is not how you work out the velocity....!

Firstly your stepper motor drivers, what microstepping resolution do you have them set on?

Next what leadscrew or ballscrew pitch do you have?

Presume you have no gearbox and they are direct drive?

How big is your machine... Not its physical size but how much travel does each of the axis have?

Presume all the leadscrew for all the axis are the same?

Rob
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”
Re: Speed of stepper motors
« Reply #2 on: November 10, 2015, 01:26:15 PM »
How big is the machine (the carriages)... What sort of a machine is it ... Is it a milling machine / engraver like the 3040 cncs or is it something else?

Do you have a photo?

Rob
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”
Re: Speed of stepper motors
« Reply #3 on: November 10, 2015, 01:29:46 PM »
Thanks for your quick response!!
The drivers are set at full step.

About the ballscrew and the leadscrew, the problem is that they are in the machine and I can't determine their pitch. I am fixing an already existing machine, and making the controller between the computer and the motors.

Yes I presume they are direct drive.

The travel in Z-, Y- and X-axis is about 40 cm.

The machine is an Emco F1-CNC

/ Johanna
Re: Speed of stepper motors
« Reply #4 on: November 10, 2015, 01:33:52 PM »
If I test and put the "Steps per" to for example 4000, then the axis move a lot faster, but the distance they move does not match the distance in the "Distance Window" in Mach3
Re: Speed of stepper motors
« Reply #5 on: November 10, 2015, 01:39:07 PM »
Hang on trying to review some specs of the f1 (I have an fb2... Not converted to CNC yet)

Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”
Re: Speed of stepper motors
« Reply #6 on: November 10, 2015, 02:02:32 PM »
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”
Re: Speed of stepper motors
« Reply #7 on: November 10, 2015, 02:06:49 PM »
We use drivers HY-DIV268N-5A and the stepper motors are KL23H
Re: Speed of stepper motors
« Reply #8 on: November 10, 2015, 02:13:34 PM »
Seems they are 2mm pitch, with a 2:1 gear reduction (if you are using the existing stepper motors), then each stepper will be 200 steps full scale resolution...

The manual lists the resolution as 0.001mm / step...

so 2 / 2 / 200 = 0.005 mm / full step..... the problem is the commong uStep resolutions are:
full step, half step, quarter step, 8th step and 16th step....
which would give the following resolutions per step
full - 0.005
half - 0.0025
quarter - 0.00125
8th - 0.000625
16th - 0.0003125


the manual lists the maximum axis speed as 1200mm / min ....

So I'd suggest setting up the maximum axis velocity as 1200mm / min

Then you are going to need to do a bit of exploration as to the step resolution .... I'd suggest as a start (given you have them as full step) as 1 / 0.005 = 200 steps per mm.... (which is what you did in the first place....)

I'd start off with the acceleration as about 40 mm/s/sec .....

given 1200mm/min = 20mm / sec >>>> and a good starting point is about 0.5sec to achieve full speed....

Then you will need to do some tuning....


as far as the Kernal speed.... leave it as 25kHz  .... given 200 steps / mm x 20 mm / sec = 4000 steps per second (maximum).... hence 4kHz...

Rob
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”
Re: Speed of stepper motors
« Reply #9 on: November 10, 2015, 02:18:13 PM »
..... if I was setting up my machine.... I would try to set it up on quarter uStep driver setting ....

So I'd get 0.00125mm / micro step and that would allow for backlash compensation

1 / 0.00125 = 800 steps / mm >>>>> 800 steps / mm x 20mm / sec = 16kHz kernel frequency ..... so leave it at 25kHz ( minimum setting ).

Rob
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”