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Offline NormB

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Motor Tuning
« on: January 08, 2010, 05:17:20 AM »
I have watched the video tutorial here on motor tuning and am still comfused.  I understand how to control changes but what is right?  What do you look for in making these changes.  I ran this machine in Mach2 but the setting are completely different in Mach3 so the numbers do not translate at least I am not able to translate them. 

My system is using 270 oz stepper motors 200 turns with gecko g540 driver and the lead screw is 4 turns per inch so calculating the turns per is easy 8000.  Now the fun begins.  Moving the sliders to adjust speed etc.  What are you really looking for to optimize the system for best speed and movement.

I should probably mention I use the for routing wood the machine is 24 x 48 my normal feed rate in hard wood is around 50 ipm and a max cut depth of around 1/8 inch.  I know the feed rate is controlled in my G-Code file.  The motor tuning has some affect on this does it not?

Norm

Offline Hood

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Re: Motor Tuning
« Reply #1 on: January 08, 2010, 05:58:09 AM »
The motor tuning sets the Max velocity, ie your rapid speed so you are wanting at least your max feed rate plus a wee bit more.
 Its all trial and error, machine design and personal preference as to what is right. For example on my mill that has steppers I can get the rapids to 2500mm a min but the accel cant go over about 40 with that rapid. I can however drop down to about 2200mm/min and get the accel up to 120 or more. To me that is a much greater benefit as I will never need 2500 cutting steel and the increased accel makes code actually run faster so cuts cycle time. Another benefit to greater accel is less corner rounding in CV, although that never bothered me anyway as cutting  metals (steels/stainless etc) feeds are not super fast.The machine is rigid enough to stand the higher accel  but with a router you may have to lower the accel a bit as it may jump about and flex. So as I said, all trial and error and personal preference.

Hood

Offline NormB

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Re: Motor Tuning
« Reply #2 on: January 08, 2010, 06:20:12 AM »
Once again thank you, I now have a better understanding as to what each adjustment is doing and I do understand the tradeoffs between accel and rapids.  Cutting wood is a bit faster than metal, however hard wood has to be cut much slower than soft wood.  I will begin to play with the adjustments tonight and see if I can strike a happy medium that works for me.

Thank you again.
Norm

Offline RICH

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Re: Motor Tuning
« Reply #3 on: January 08, 2010, 07:32:06 AM »
What are you really looking for to optimize the system for best speed and movement.

You can have speed and movement but you just can't forget about the power delivered to the axis.
As the stepper rpm increases the torque decreases. Max power from the motor will accur  when stepper rpm  vrs  torque no longer
changes significantly along the motor curve ( graph of motor speed to torque ). So that is why you back off the velocity / acel settings from where the stepper starts to skip.  Some may call the backing off "headroom"  or allowance for cutting such that you
can run reliably without skipping steps. Some steppers are provided with those graphs and so you can intiialy know what to expect for motor application to the work .  Without the graph it is more trial and error.  In the end though, by trail and error you find the place that satisfies your use.  So it's a comprimise on the required power to do work in considering the other things required, like speed and movement.
A little insight into what is transparently happening as you play with the tuning,
RICH

Offline NormB

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Re: Motor Tuning
« Reply #4 on: January 08, 2010, 08:24:34 AM »
Thank you that also helps..... I guess I have never had to do this until now, so it'snew and I am uncertain moor understand more clearly.  When I purchased my router I was running Mach2 and the setup parms were given to me by the designer and motor tuning was already setup with his numbers.  So I never experimented with them at all.  I do know this since my playing up to this point in Mach3 the motors can run VERY smooth compared to Mach2 and the setting I was using.  What I am not certain of is how do you know you are missing steps?  As I played with the tuning last weekend I found I can move the Y axis fairly fast and the motor is smooth.  I am not sure I I missed steps though.  I guess that is what I am talking about with optimizing the drives.  Making sure I am getting the best performance for both accuracy and sped I can get.

Offline ger21

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Re: Motor Tuning
« Reply #5 on: January 08, 2010, 08:33:17 AM »
I should probably mention I use the for routing wood the machine is 24 x 48 my normal feed rate in hard wood is around 50 ipm and a max cut depth of around 1/8 inch.  I know the feed rate is controlled in my G-Code file.  The motor tuning has some affect on this does it not?

Norm

My machine is very similar to yours, but I have a Xylotex drive. Same screws, and about the same size. On my dual driven X axis, my motor tuning is set to 150 ipm. I think the accel is about 9 or 10. My Y axis (along the gantry) is set to 185 ipm, same accel. With a G540, depending on voltage, you should be able to go a bit faster.

I do my cutting, with 1/4" bits, between 125 and 150 ipm, at about 12,000 rpm, with about the same depth of cut as you, 1/8". A general rule of thumb when cutting wood, is to cut as fast as you can, as long as you still maintain an acceptable cut quality. At my day job, on a big commercial router, we routinely cut hardwood at 400ipm. I should be getting a new job Monday, where they have a router capable of much higher speeds than that. Probably 1000 ipm. :)

When you're cutting a bit faster than the 50ipm you're using, you'll see that acceleration is very important. I traded a bit of top speed for faster acceleration, which allows me to get sharper corners in CV mode.
« Last Edit: January 08, 2010, 08:38:16 AM by ger21 »
Gerry

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Offline ger21

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Re: Motor Tuning
« Reply #6 on: January 08, 2010, 08:37:34 AM »
What I am not certain of is how do you know you are missing steps? 

You'll either see it in your finished parts, or here the motors make a grinding noise, or even stall. I've been running my machine for about 4 months now, without a single missed step. Two days ago I ran my first detailed 3D carving, with a 1/16" router bit. About 10 minutes in, the bit had lifted above the work and stopped cutting. The Z was missing steps (or stalled) on the way down. I lowered the Z acceleration, and re ran it, and it came out perfect.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline NormB

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Re: Motor Tuning
« Reply #7 on: January 08, 2010, 08:40:54 AM »
Oh a new term, CV mode? God, I have a lot to learn. Thank you for that information that will really help me. I will use your numbers as a starting point to see if how it does.  I can adjust from there if necessary. :)

Norm :)

Offline RICH

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Re: Motor Tuning
« Reply #8 on: January 08, 2010, 09:36:50 AM »
"What I am not certain of is how do you know you are missing steps? "

You may want to take a look at the Gecko site as it has a lot of info about steppers.
Explained more clearly in the proper context than i can.

Mach will send all the required pulses to the driver / motor based on you settings ( velocity and Acel ).
The motor should properly use those pulses to do work. A pulse changes the position of the rotor ( steps) in the stepper via the electrical field.The number of pulses  over a time determine how many steps the motor will do. There is limit on how fast a stepper will turn. There is also a limit as to whether the motor can step based on the load / torque presented to it.  

You need some level of power ( torque x speed) from the drive system just to move the axis Assembly.
So like stated before, the motor torque available is the smallest at the highest rpm ( velocity ) of the motor.
So if the load presented to the motor is greater than what the motor can do, the motor skips. The pulses are sent but the motor can't  "step" / it's stalled.

So in initial motor tuning you set the velocity real high to turn the motor as fast as possible to find where it will skip /
not have the power to move the axis. That's one reference setting. Now you lets say that you usually do a max cut of
1/8" deep in hardwood ( there is  a difference between Pine and Bambinga, heck wait until you do Ebony and hit rock in it!). Well that cutting presents another load to the motor. So you reduce the setting ( velocity and acel) until you can do the cut  without the motor skiping. Because you lowered the motor speed the motor torque has increased. The motor has a rated torque for a given set of electrical conditions. So now you have another reference
 for the motor tuning. Want to set it for the  worst case of what your cutting ? That's your choice.

Lets say you decide to set it for Pine. But you hit a knot in the Pine, and all of the sudden the motor skips because it can't deliver the power, position is lost  and who knows where the axis may go! You will hear the motor skip.

Lost steps is something different in that so many pulses should make the motor step so many times.
 Steps can be lost due to electronic items in the pulse stream (break out boards) or the pulse itself ( bad pulse signal).
Need some special equipment to actually measure the pulses  or look at them.

Long winded reply,
RICH

Offline NormB

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Re: Motor Tuning
« Reply #9 on: January 08, 2010, 10:10:05 AM »
now that was very enlightening Rich, Thank you for the input, I have downloaded the specification sheet etc. from the Gecko site.  A little reading is in order now Think. 

I really understand much better the relation now, I had a pretty good idea before with previous comments but you added a little more perspective to the relations.  My worst case scenario is usually white oak.  I do cut pine etc walnut but if I can cut white oak all domestic hardwoods are good to go.  Blood wood I would have to take a look at that one.  Like cutting concrete. *L*