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Motors unable to run slow/missing steps
« on: February 17, 2009, 02:01:36 AM »
Hi everyone. I'm struggling a bit to get my motors running right. I'm running Mach 3, with a Gecko 540 and Kelling 48V power supply & motors on a Taig mill.

I managed to calibrate everything fine, so each axis moves what it says it should when I ask it too. I tried some of the wizards in Mach 3 and they all seemed to work ok.

My problems come when I tried to cut my first proper part. I generated the g code in meshcam and I was really conservative with the feed rates (didn't want to do any damage). It seems my motors just don't run at all if the feedrate is too low. By low I am talking about 4ipm (100mm/min). Surely I should be able to run the motors this slow?

The part I test cut looks a mess. It's all of about the right dimensions but the circular pockets are all out of round, and the external walls are a bit chewed up where I'm guessing the mill has lost/gained steps.

Any ideas why my motors stall at low speeds? Is this normal???

Thanks for any help guys!

Rich

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Re: Motors unable to run slow/missing steps
« Reply #1 on: February 17, 2009, 02:36:44 AM »
Its certainly not normal, you should be able to crawl along at almost zero speed and have plenty of torque, maybe your motors are just on the small side for the cuts you are trying to take?
Hood
Re: Motors unable to run slow/missing steps
« Reply #2 on: February 17, 2009, 03:46:08 AM »
The motors should be fine, they are 280 Nema's so they should be way more than man enough for what I'm asking (0.3mm depth cuts in alu with a 3mm endmill).

Any suggestions as to what settings I can try to tweak to help this?

Thanks!

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Re: Motors unable to run slow/missing steps
« Reply #3 on: February 17, 2009, 04:30:43 AM »
Could it be backlash? When you cut a circle in a single pass  where does  it go wrong?
Hood
Re: Motors unable to run slow/missing steps
« Reply #4 on: February 17, 2009, 04:55:14 AM »
I'm as sure as I can be its not backlash. When I use the wizards in Mach 3 it cuts perfect circles, rectangular pockets or hole patterns.

Its just when I try to run a programme for a part it starts missing steps. It also seems quite jerky when going round profiled corners too.

My big concern is that my motors won't run slowly, could this be a motor tuning issue??

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Re: Motors unable to run slow/missing steps
« Reply #5 on: February 17, 2009, 05:37:50 AM »
Very unlikely, if your motors were not tuned it would mean you would miss steps all the time due to accel being too fast, it would happen the faster you went rather than the slower. Poor resolution could make motors jerky at very slow speeds but unless your ballscrews have a huge pitch thats not it.
 You say wizards are fine then it cant be motor tuning as wizards just produce code, sounds like it may be your code, especially when you say it jerks round corners. That sounds like your code is made up of lots and lots of tiny lines instead of arcs, you could try  G64 (Constant Velocity) if you are not already in that mode.
G61 is Exact Stop and if that is in your code it will slow and stop at every line before it starts the next which will give you jerky movement if your code is bad (lots of small lines rather than arcs)

Hood
Re: Motors unable to run slow/missing steps
« Reply #6 on: February 17, 2009, 06:41:09 AM »
Ah ok. I should explain that when I say the wizards are working fine, they only work fine at higher speeds. If I try to run a wizard with a slow feed the motors just dont move. I think that is the root of all my problems. I'll check my code out for what you have suggested also.

Thanks!

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Re: Motors unable to run slow/missing steps
« Reply #7 on: February 17, 2009, 06:44:13 AM »
Well that is a strange one, if you command a G1X100F100 (If mm or G1X4F4 if imperial) does the axis move correctly?
What is the Steps per unit you have?

Hood
Re: Motors unable to run slow/missing steps
« Reply #8 on: February 17, 2009, 07:13:59 AM »
Steps per unit is 1574.803.

I'm using mm and a 100mm move does indeed give a 100mm translation.

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Re: Motors unable to run slow/missing steps
« Reply #9 on: February 17, 2009, 08:35:55 AM »
Well thats ok, was thinking maybe your resolution was low so at slower speeds it would cog a bit but thats obviously not going to be the case.
What is the feed like if you feed the axis at G1X100F100 with MDI? Then try doing G1Y100X100F100 and see how that is.

Hood