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Mach Discussion => General Mach Discussion => Topic started by: Randaltb on March 03, 2013, 01:57:51 AM

Title: Lost at low speeds
Post by: Randaltb on March 03, 2013, 01:57:51 AM
I am new to CNC and Mach3...
I have converted an old RF30 and can't get it stable.
I am not sure if it is in Mach3 or the motors?

My system seems OK at full speed but gets lost at lower speeds.
I read another post with a similar issue but did not see how it was resolved.

So here goes:

If I jog the Y axis 1.00 at %100 ~15 IPM the system seems to be with in .001.
If jog the Y axis 1.00 at %40 ~6 IPM the system is way off, and very inconsistent.
I am not addressing backlash here because it happens moving the same direction, repeatedly.


I did some testing with a dial indicator in the vice jogging at %100 15 IPM.

- Set zero and jog away 1.00 then back within ~ .0005 from where I started.
- Set zero and jog away 3.00 then back within ~ .001  from where I started.
- Set zero and jog .1 ~ .001  from where I started 5 times in a row.

Now turn the jog speed down:

- Jogged .1 three times same direction 1st step off ~.001 2nd step ~.005 3rd step ~.007.

Not sure what going on?
I am pretty sure the motor tuning step counts are close because at high speed it repeats 5 times in a row, but at slow speeds it won't repeat.

Info about my system:
- RF30 Drill Mill.
- Ethernet Smooth Stepper. (added afterwards thinking it would solve the issue...) nope, but it looks cool ;)
- Parallel break out board.
- Wantai DQ542MA Drivers, set at 1000 Pulse/Rev. (Were set at 1600, same issues but worse)
- Wantai 57bygh115-003 Motors. 425 in/oz
- 36 VDC 10A supply.
- Mach3 (Licensed)

Steps taken so far:

- Increases the wire size from power supply to drivers. (In case there were to small)
- Disassembled the Mill X and Y completely, cleaned and reassembled. ( It moves smooth, no binding, with about .008 BL)
- Put a fluke meter on the 36 volts and ran motors. (34VDC +_ .3 all the time)
- Tried setting motor tuning 7-15 IPM and tried acceleration (.5 - 10)

Not sure what to try next.
 ???
Title: Re: Lost at low speeds
Post by: Chaoticone on March 03, 2013, 11:02:07 AM
Quote
I am pretty sure the motor tuning step counts are close because at high speed it repeats 5 times in a row, but at slow speeds it won't repeat.


This is a hard known number and does not change.  This needs to be the very first thing that your posotive about.

http://www.machsupport.com/forum/index.php/topic,12512.0.html#new
http://www.machsupport.com/forum/index.php/topic,16315.0.html#new

Double check this and we can go to step 2.

Brett
Title: Re: Lost at low speeds
Post by: Randaltb on March 03, 2013, 12:25:26 PM
OK I'm new to this but here it goes.

- My steppers are also 1.8 degrees. so (200 pulses per revolution)
- Micro stepping = 10. So 200 X 10=2,000 (Not sure about this but seems true)
- Motors X & Y are direct 1:1 via solid coupler.
- My table is 10 turns per inch so .1" per turn of the shaft.


so:
1.0 divided by 0.100=10. So 2,000 X 10=20,000.

So 20K..
Looking at my tuning setup I am real close. 20063.
I added the 63 to make it move the full distance based on 1.0" move with a dial indicator.


---
Also on the side of the Driver(s) it has a list of dipswitch settings for Pulse./rev I picked 1000.
Originally (out of the box) it was 1600, but the motors would skip every time I reversed the table, moving to 1000 seemed to help.




Title: Re: Lost at low speeds
Post by: Randaltb on March 03, 2013, 12:36:14 PM
Oops I misspoke!
looking at Mach3 tuning again, actually I have the Axis "steps per" set at 16018 . not 20065...
Title: Re: Lost at low speeds
Post by: Chaoticone on March 03, 2013, 12:54:27 PM
Quote
- Micro stepping = 10. So 200 X 10=2,000 (Not sure about this but seems true)

Also on the side of the Driver(s) it has a list of dipswitch settings for Pulse./rev I picked 1000.


If the drives are set to take 1000 steps per rev on a 1.8 degree stepper motor, this is 5 microsteps per each 1.8 degree full step.  So it would be 200 x 5 = 1000 x 10 (.1 lead on the screw) would make the steps per 10,000

Brett
Title: Re: Lost at low speeds
Post by: Randaltb on March 03, 2013, 01:03:02 PM
OK silly question...
If the stepper motor is 200 steps per rev (1.8 Degrees), what is the proper setting for the driver?

Not sure I see the relationship between them.
My little brain doing no real math etc, says 200 steps = 200 pulses, or a multiple such as 10 x 200 = 2000.

Basically what drives the setting on the Driver?
I pulled the 1000 setting from the air, just because I was having skipping issues at 1600...

Cheers




Title: Re: Lost at low speeds
Post by: Chaoticone on March 03, 2013, 01:18:33 PM
Well, 10,000 steps per will give you .0001 resolution.  What you need or want, I have no idea.  It also means that at a kernal speed of 25KHz you can travel at 150 IPM (if your machine is capable of that).  I would set the micro stepping to where I could get the reseloution, and speed I want as smoothly (best sound) as possible.  Its best if your steps per divide by your desired resoloution equaly as well. If your trying to get a resolution of .0001 and your steps per were 16,000, you could'nt hit your resolution evenly so it would have to be rounded to the nearest possible step.

https://www.youtube.com/watch?v=bngx2dKl5jU&list=HL1362334138

Brett
Title: Re: Lost at low speeds
Post by: Randaltb on March 03, 2013, 01:58:51 PM
 
When you say round to the next step, I assume Micro Step?

Base on the video you linked more micro steps just adds resolution, not real accuracy, or torque.
--This explains why the motors skipped at 1600 and not 1000...

So what I gather so far is:
- I want fewer micro steps for torque and more micro steps for resolution.
- But to few steps and I get ringing etc. and to many steps low torque.

So the answer to my earlier question about best Pulse/rev is to set it where I get enough torque, and still maintain accuracy needed.
Since .0001 is beyond my machines ability to repeat any way, I should drop to 400 pulses/rev and get more force and still have about .00025"   (.1/400)

Am I making any sense here or wanting off down the wrong road?

BTW. Thanks for the help I might actually learn something ;)




 
Title: Re: Lost at low speeds
Post by: Chaoticone on March 03, 2013, 02:35:38 PM
Quote
When you say round to the next step, I assume Micro Step?


Exactly

Not sure you will get much more torque, I'd say that has more to do with the drive really but yes, if you change your steps per to 5000 by changeing the microstep option from 1000 to 400 you will get a res. of .00025.  If you avoid microstepping all together you will get a res. of .001 either would work but I think it will be much smoother at 10,000.  You will just have to play and see what suits your needs best.

Brett
Title: Re: Lost at low speeds
Post by: Randaltb on March 03, 2013, 05:50:15 PM
OK short update.
I changed the X and Y to 400 from 1000 and adjusted steps per in motor tuning.
Still had the issue but much less.

So I decided to crank the acceleration way up I went for 1.5 to 55.
Wow night and day, still is off a bit but much better.

note: with it set up this may the motors do make much more noise, and if I get below 10 IPM It creates a vibration in the stock.

So any feed back on acceleration would be helpfull, such as is 55 to high?
Like you said Chaoticone  I think 10000 will be smother, maybe with acceleration  cranked up it might work...

Thanks again.
Now to start asking how to deal with backlash 0.o
Title: Re: Lost at low speeds
Post by: Chaoticone on March 03, 2013, 06:14:13 PM
The higher the number in accel, the faster you will be able to ramp up velocity.  But if you try to do it faster than your machine can stand it will skip steps and possibly stall.  In other words, the faster it will go from stopped to wide open.  But, this is all a balanceing act.  I want my accles and vel to be as high as the machine can stand (takeing into consideration tool load + 100% safety factor) but what that will be for you is anyones guess.  You will just have to play and see.  I do think you will like the 10,000 steps per better though.  Have a look in the members doc board.  There is some information to help you with your backlash.

Brett