Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: rwiebe89 on November 28, 2017, 11:07:41 AM
-
I am new to this forum, so I apologize if this is posted in the wrong section or redundant.
Earlier this year I put together my first CNC router. https://www.smw3d.com/r7-cnc-diy-kit/ I used a Mach3 usb board https://buildyourcnc.com/item/electronicsAndMotors-electronic-component-breakout-Mach3-USB-Board with the other components from the kit.
Everything was working great until I started a cutting project that lasted about 1 hour. Running at 30 IPM, it will lose either X or Y positioning and try picking it up again from 1/8" off to 4" off. I also notice that when I bump up the jog rate to 150% for positioning the router, it will stutter or pulsate. Slower feed rates do help eliminate this.
I believe I set up my motors correctly in Mach 3, but has anyone else ran into these issues, or have suggestions on what it could be? It's really frustrating being almost done with a project and then have it ruined because it loses position.
Thanks!
-
What are you using for motors, drives, and power supply?
What is the pitch of the leadscrews?
What are your velocity and acceleration settings?
-
Nema 23 2.8A/Phase, 24v 8.3amp power supply, drivers: https://www.amazon.com/gp/product/B016ZJS1FA/ref=oh_aui_detailpage_o05_s01?ie=UTF8&psc=1
Pitch is 2mm.
Velocity and acceleration I'll need to look up when I get to my laptop.
-
Simple answer, you are losing steps because of lack of torque at the speed you are trying to run. That comes from motors too small, or motors with high inductance. Nema 24 is a frame size and the range of torque for that size can be 3 or 4 to 1 from one motor to another. A motor with high inductance will greatly reduce the available torque as the speeds go up.
It can also be from a power supply that is too low of a voltage or actually can’t supply enough current when all three motors move at the same time. Switching power supplies cannot absorb the regenerated power from the motors where an old fashioned linear can. Your screw pitch is also very fine and if it isn’t a ball screw there will be lots of friction losses at higher speed, plus the motor needs to turn much faster.
For comparison I got the lowest inductance motors I could find. They are driven by 80 volt rated drivers supplied by a massive 1500 watt 68 volt linear power supply. The machine has 5mm pitch ball screws and this gives me rapids of 300 ipm and cutting speeds of 200 ipm in plastics and wood. It never misses steps.
The good news is you can incrementaly improve what you have. In order of cost/benefit: 36 power supply would be a good step. Motors with a higher torque rating and lower inductance in the same frame size. Coarser pitch or ball screws.
-
Sorry, I was mistaken. It's 8mm/revolution. I have my drivers set at the highest amp (3.5amp). For the steps/rev, I have it set in the 10,000 range in Mach3. The machine has a max feed rate of 240 IPM with a suggested of 60, so I'd expect it shouldn't struggle at all at 30IPM. After all, the machine was designed to cut that fast. My Mach3 velocity is set to 90 IPM, and acceleration to 10 in/sec^2.
Am I setting up the motor tuning in Mach3 correctly? What about the settings on the motor driver? Is it better to have higher or lower pulse/rev?
Thank you all! I value your input greatly!
-
Hi,
what number of microsteps?
Craig
-
400 microsteps on the drivers.
I have to be completely honest here, setting this up was completely hit and miss. Knowing what microsteps to pulse/rev ratio to put into Mach3 was guess work. Yes, I did calculate the correct pulse/rev and it is accurate w/in 0.002", which is fine for me and a wood router, but at the end of the day, I went with what sounded didnt make the motor growl at me or go to fast.
-
Hi,
is that 400 pulses per rev? That would be called 'half-step'. A normal two phase stepper is 200 pulse/rev.
At 'half step' 400 pulse per rev. At '4 microstep' 800 pulse per rev. At '8 microstep' 1600 pulse per rev.
If that is correct your steps per mm would be 400 (pulse/rev)/ 8 (mm/rev)=50 steps per mm.
If in inch units 50 (step/mm) x25.5= 1270 steps per inch.
Seems like a large discrepency between what you've set and these numbers.
Can you post the manual for your drivers? I suspect, as it stands, there is some confusion between microsteps and pulses
per rev.
Craig
-
Here is the driver I have. If you zoom on it, you will see the pulse/rev on the front of it. I believe I set it at 400, but I could be wrong as I am out of town and away from my machine.
I also attached a screen shot of my mach3 motor setup.
-
Here is a picture of the driver showing the different options. I have it set to the highest amperage, and I believe 400 pulse/rev.
-
If your drive is set to 400 steps/rev, that would mean your screws have a 1 mm pitch.
Does the machine move the correct distance?
With 1mm pitch screws, 30ipm would be about 750 rpm, which you'd be unlikely to get with only 24V.
Also, you shouldn't have it set to 4 amps with a 2.8amp motor, as it'll damage the motor.
-
It is a 8mm pitch. I've confirmed this with the manufacturer. I could be wrong on the 400 steps/rev (is this the same as pulse/rev?).
Regardless, in your experience, what conditions would cause a skipping/pulsing effect on a jog, but diminish at lower speeds?
-
Hi,
I think ger21 is right, without the correct steps per unit you could be demanding that your stepper go way too fast and it will
fail to do so and quite probably give you the symptoms you describe.
You cannot guess about these things, if its not right, everything else is rubbish.
Microstepping is used because it results in smoother motion of the stepper motor. Most people use '8 micro steps' or maybe '16
microsteps'. You could use even more if you wish but then Mach may not be fast enough to drive the machine to high speeds.
As a consequence 8 or 16 microsteps is a good compromise. It sound like your driver is set to '2 microsteps'. I really want you
to study the manual to resolve this. I would set the switches to '8 micro steps' which is the same as 1600 pulse/rev or
1600 steps/rev.
Note that is steps per rev, so if the machine moves 8mm per revolution of the screw then the steps per mm would be 1600/8
or 200 steps per mm, or in inches, 200 x 25.4= 5080 steps per inch.
What are the native units of your setup? Look under Config/Select Native Units....you can use either but once you choose it
then leave it alone. If you want to run some Gcode in inches use G20 or in mm use G21, don't fiddle with the native units.
Craig
-
Do you think having too many steps specified in Mach3 (ie 10,000+) will result in these conditions? Best to keep in the low thousand range?
I guess I am having trouble understanding why the such wide range in microsteps on the driver when you can do your speed manipulation in Mach3?
-
Hi,
there is ONE right number for your machine...it is the number of pulses that Mach has to issue to get the axis to move one unit, whatever units you
choose. If you put the wrong number, say 10000, when your machine is actually 5080 Mach will issue 10000 pulses and you expect the machine to move one
inch but it in fact moves closer to two inches.
What is the native units of your machine?
Craig