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Max Velocity in MACH3
« on: July 20, 2011, 09:45:46 AM »
Hi everyone,

First of all. I am new to Mach3 software although I am working as a CNC service technician for more than 10 years.
I recently bought DMM-Tech CNC kit. I prefer servo motors than stepper.

Peak 7.2Nm(1015 OZ-In) high torque AC servo motor, 3 Axis CNC kit for MACH3
- 3 x Peak 7.2Nm(1015 Oz-In), rated 2.9Nm(408 Oz-In), Peak power 900W, AC servo motors
- 3 x Dyn2-H AC servo drives for very smooth,quiet,very high efficient driving
- 1 x DMB4250-8B breakout board, fully buffered Opto-isolated I/O, isolated PWM analog output
for spindle speed control,and charge pump. Hardware generated X secondary X' for CNC Gantry with
jump selectable motor turning direction.
- 1 x 6ft DB25 parallel port cable
- 1 x 6ft USB cable
- 2 x 120 or 220Vac input, 350w,+48Vdc, 7.3A output DC power supply
- 3 x 1ft cables between breakout board and drives
- 3 x 10ft differential signal encoder extension cable
- 3 x inductive, non contact , LED indicated proximity Home/Limit Switches
- 1 x Emergency STOP Switch
- Necessary Cables, DMM software for tune up servo

I installed the program for tune up the servo which came along with the kit. The motors are running very well. I was very satisfied. I can easily control them and turn them to the maximum speed of 1000 rpm.

But when I installed the Mach3 R3.043.022 software and tried to tune up the motors I run into a problem. I can't reach the maximum speed for the motors. The maximum speed of the motors should be 1000 rpm. With Mach3 software I can achieve only 915.6 m/min. Calculated value using 10 mm pitch is 91.56 rpm max. The kernel speed is set to 25000kHz. I tried with higher kernel speed and it gives me higher velocity but I really don't want to increase Kernel speed. It's not recommended they say. Or someone can explain it how much can I increase it?
The Mach3 software is somehow limited the velocity. How is this determined or calculated? Or is this because I am running in demo mode with Mach3?

Motor tuning and set up:

Steps per: 1638.4   (16384 encoder steps / 10 mm pitc ballscrew)
Velocity: 900         (Mach3 calculate the max Velocity to 915.6 - I set it to 900)
Acceleration: 200
Step Pulse: 5 us     (defined in http://www.machsupport.com/forum/index.php/topic,18355.10.html )
Dir Pulse: 5            (defined in http://www.machsupport.com/forum/index.php/topic,18355.10.html )

How can I achieve higher speed? Is there any chance to do that? My motors should turn with max 1000 rpm and with 10mm pitch ballscrew they should give 10000 m/min max feed.

For further information's please don't hesitate to post me.

Thanks for help.

Offline Hood

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Re: Max Velocity in MACH3
« Reply #1 on: July 20, 2011, 09:58:32 AM »
The combination of Kernel speed and steps per unit will determine the max velocity you can theoretically achieve.
The kernel sets the max pulserate for each axis so at 25KHz that is the max that Mach will put out per axis. If you have 1638.4 steps per unit then you could achieve max Velocity of  25,000/1638.4 = 15.26mm/second so 915.53mm/min.

Increase the Kernel to 45KHz will give you a max theoretical Vel of  45,000/1638.4 = 27.46mm/s = 1647mm/mim

So as you can see it is the relation of the kernel speed to your steps per unit that will determine the max Velocity you will achieve.

Setting to 45KHz should not be a problem for most computers and some can reliably run at the max 100KHz but it is best not to set it higher than you actually need.

If you need even more, for example I need 666KHz for one machine then you need an external pulsing device, I use the SmoothStepper, it can pulse up to 4MHz

« Last Edit: July 20, 2011, 10:00:19 AM by Hood »

Offline Hood

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Re: Max Velocity in MACH3
« Reply #2 on: July 20, 2011, 10:05:40 AM »
Oh just another thing to mention, often servo drives can electronically gear the steps.
What that means is for example for every pulse Mach puts out the drive sees it as 4 pulses (if 4:1 electronic gearing is set) This can allow you to achieve higher Velocity but it is at the expense of resolution so its not a route I like to take personally.
Re: Max Velocity in MACH3
« Reply #3 on: July 20, 2011, 10:11:07 AM »
Dear Hood,

Thank you very much for this helpful information. I will certainly use an external pulsing device since I am using my machine for a 3D foam cutting machine. I certainly need more velocity on the motors.
I will also examine the second thing too before I decide permanently.

Thanks and best regards,