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- schmidtmotorworks
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Great news! You'll soon be making chips...
John
Yah, I can hardly believe it.
I learned so many things in this project.
Thanks for everyone's help, I never could have got this far alone.
Now the main thing that seems to be left is PID etc.
The machine has a whole new personality, it's like "CNC extreme makeover".
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It still runs smooth but a little more than twice as fast as i expected so I will probably start adjusting the pots tonight. Is it correct to do this before PID have been established, or will I need to come back and do that again later?
You probably don't need to do any twiddling, if "some" PWM is a certain speed and "some more" PWM is "more speed" then that is all the PID controller really needs to work with.
They have big problems if "some more" = "more speed" and then "a bit more" = "a bit less speed". You should never get than problem with an electric motor, but it plays havoc with an engine idle speed controller.
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- schmidtmotorworks
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www.pidtuning.net/
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That is all you need really... set up a motion trigger on the scope and watch the following error as you tune. Following error smaller you did good, bigger and back that setting to the level before.
John
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I am thinking of buying this PID tuning tips book, does anyone knw if it is worthwhile?
For $97? I wouldn't think so.
At least try the simple method here, to get yourself closer:
linuxcnc.org/docs/html/motion_pid_theory.html
You can set up a simple bit of G code to do 1" (or 25mm) moves in a loop, then tweak the PID until it looks good on Halscope.
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- schmidtmotorworks
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This is what I have figured out so for, please tell me if I'm basicly on track.
I'm going to set up HALScope to monitor two things.
1. "pid.(whatever axis goes here).error"
2. "axis..(whatever axis goes here).motor-pos-cmd"
I also have to set up a command and a trigger that will execute the command and record the results.
Then I will tune P,I,DFF0,FF1,FF2 to mnimise the error.
Is there any special stragey for FF0,FF1 and FF2? or just more of the same?
You can set up a simple bit of G code to do 1" (or 25mm) moves in a loop, then tweak the PID until it looks good on Halscope.
I don't think I understand this one, does the loop run continually and I watch the scope or is it triggered?
Any detail about how to set that up would be appriciated.
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- schmidtmotorworks
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schmidtmotorworks wrote:
It still runs smooth but a little more than twice as fast as i expected so I will probably start adjusting the pots tonight. Is it correct to do this before PID have been established, or will I need to come back and do that again later?
You probably don't need to do any twiddling, if "some" PWM is a certain speed and "some more" PWM is "more speed" then that is all the PID controller really needs to work with.
They have big problems if "some more" = "more speed" and then "a bit more" = "a bit less speed". You should never get than problem with an electric motor, but it plays havoc with an engine idle speed controller.
OK thanks is there any rule of thumb I can use for setting the velocity, with the motor off? Some % higher?
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..motor-pos-fb1. "pid.(whatever axis goes here).error"
2. "axis..(whatever axis goes here).motor-pos-cmd"
Makes is clear how the position is following command.
I don't think I understand this one, does the loop run continually and I watch the scope or is it triggered?You can set up a simple bit of G code to do 1" (or 25mm) moves in a loop, then tweak the PID until it looks good on Halscope.
Any detail about how to set that up would be appriciated.[/quote]
Yes, just set up the G-code to run continuously.
O1 REPEAT
G0 X1
G0 X0
O1 ENDREPEAT
In the Axis gui there is a utility (machine->calibrate) that lets you adjust the PID controller parameters on the fly.
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- schmidtmotorworks
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So I will put this in a file and run it? (this will be the first program I have run in EMC)
O1 REPEAT
G0 X1
G0 X0
O1 ENDREPEAT
Then in Halscope (if I understand correctly) I think I need to set up a trigger, is there some way I can make some part of the program the trigger?
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Indeed. call the file something like "test.ngc"So I will put this in a file and run it? (this will be the first program I have run in EMC)
O1 REPEAT
G0 X1
G0 X0
O1 ENDREPEAT
Also note that I forgot something, you need to say how many repeats.
O1 REPEAT [100]
Yes, you can set it to trigger on a rising edge of ...motor-pos-cmd. At the top of the screeen there is a slider for zoom and one that lets you position the trigger point (so you can graph the time before the trigger too)Then in Halscope (if I understand correctly) I think I need to set up a trigger, is there some way I can make some part of the program the trigger?
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