Microstepping and Jog rate.

[leeleatherwood]

Hello, I am completely new to the CNC world. I have bought and assembled a 4AUPC kit with the 305oz motors from HobbyCNC.com, it works great i suppose. I am using the latest version of EMC2 (which i love BTW!) and I am trying to get everything working on the bench before i assemble the motors on the machine.

The question i have is with the Microstepping rate. When I am following the "Quick Start Guide for Stepper Configurations" the formula is as follows:

steps * usteps * pitch * ratio

So for my setup using 1/8th microstepping, and a 10tpi leadscrew:

200 * 8 * 10 * 1 i come up with 16000.

I input this into the stepper_in.ini and when i load up EMC2 it gives me an error saying my rates are too high. I have tryed lowering the MAXVELOCITY but that seams like it would defeat the purpose since it would only make things slower.

So what I do is set my board to 1/4" microstepping and adjust the settings in the Stepper_in.ini accordingly. Things run fine now... but I cannot get it to JOG faster than ~50ipm. The motors will turn about a half turn (accelerate) and then lock. If i slow it down to 49ipm it will run fine. This JOG rate seems very slow because i have seen people getting over 250ipm on the machine I am building. (using MACH3)

I also know that the motors and controller are both capable of that speed because if i leave the controller on 1/4 microstepping but i change the Stepper_in.ini to reflect 1/8 microstepping, the motors will spin very fast without locking...

Does anyone have a similar setup to mine and can lend assistance? Is EMC2 capable of doing what i ask? I sure hope so, I like the interface alot better than Mach3's.

I really dont want to reformat the machine to install windows and Mach3 just for testing purposes.

EDIT: Oh yeah, the system i am using is pretty powerfull, AMD Athlon XP 1900+, 512mb ram, ASUS A7N8X Deluxe motherboard (nForce 2)

In the bios i have tryed both ECP and EPP.

[sansbury]

Have you tried reducing the BASE_PERIOD from the default of 50000? RTFM section 5.3.2:


BASE_PERIOD = 50000 Base task period, in nanoseconds - this is the fastest thread in the machine. It’s units are nanoseconds. This is a fairly conservative value but if you are installing on a very old, slow processor you may have to make this a larger number or the machine may lock up or reboot.
You might want to make this value smaller if you have a fast computer because this value sets the maximum number of stepper pulses you can get from your machine.


Basically the formula is

Steps / second = 10^9 / 2 * base_period

So 50000 gives you a max of 10k steps/second. In order to hit 250ipm with your setup, you'd need (250*16000) / 60 = ~67k steps/second. If I do the math I end up with a base period of 7500 to generate pulses that fast.

I run a base period of 45000 on an eight-year old doorstop so I'd guess that your machine should be capable but I have no idea whether this is something that scales linearly, exponentially, or chaotically.

[Big John T]

Here is some really good info...

http://wiki.linuxcnc.org/cgi-bin/emc...StepGeneration

John

[leeleatherwood]

Thanks guys. That info really helped, I have everything running smoothly now at 8x Microstepping and I have gotten it up to 60~ IPM jograte running on just a 12v testing powersupply. Any faster on the Jograte the motors will start to stumble and/or lock, again i think that is only due to the powersupply.

[sansbury]

Are the motors hooked up to anything or are you just spinning them freely? 60ipm with 12V on those motors actually sounds pretty fast to me, all things considered. In any case you will almost certainly get a lot more with 24V+ going in. 35V seems to be the safe sweet spot.

[leeleatherwood]

Originally Posted by sansbury Are the motors hooked up to anything or are you just spinning them freely? 60ipm with 12V on those motors actually sounds pretty fast to me, all things considered. In any case you will almost certainly get a lot more with 24V+ going in. 35V seems to be the safe sweet spot.

Well, they have a slight load on them. Basically a 6ft section of threaded rod and the friction from the nut allows them to run to 60ipm without locking.

With no load they lock at anything over 52-53ipm.

As long as i can get at least 120ipm Jograte with 36v I think I should be fine.