Calculations to setup my Drives in PnCConf

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14 May 2021 12:15 #208799 by Craig E
Hello Everyone,
As I wait for my 7i96 to arrive I was going through the documents and trying to setup my drives and machine in PnCConf.
My Drives are not listed on the timing Wiki. I am also looking for advise on IPM for my axis.
I designed and am building my machine it has 4ft Gantry for X axis and 2ft dual motor Y axis 1ft Z axis.
I have the same brand Steppers and drivers but different sizes for each axis,
However they all have the same timing specs and max RPM
1) question: what feed rate would you suggest? I know 60 IPM is the default should I leave that for each axis? I am an engineer but I have no machining experience. is there any rule or standard I should use? I was thinking that I would want more speed on X axis maybe 100 IPM? But I am just guessing and that make me nervous.
2) question on Dive setup: is there a formula to calculate the numbers for Step Time, Step Space, Direction Hold, and Direction Setup?
My info on my machine is all axis have 5mm pitch ball screws. All Stepper have 200 set/rev, and max RPM of 3000,
the Drives all have a max Freq of 200Khz, Min Pulse width of 2.5 us and min direction setup of 2.5 us, and step on falling edge.
max Jitter on my RPI4 is 85000 I hope that is all the information that is needed.
I know I don't what to set everything to it max setting. so any suggestions?

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14 May 2021 21:26 #208858 by rodw
Its very complex and there are many more variables at play than you have provided.
you could start here
www.machinedesign.com/motors-drives/arti...rs-for-linear-motion
But be warned the last engineer who ventured in there emerged 3 months later before he had a usable model!
But given the forces involved, he could predict the required motor voltage and current required for a given motor and also the heat buildup to make sure it didn't melt down.

So then it was up to you to select a motor that fell with in the current and voltage ranges available. eg. if the model says you need 130 volts and you can't find a driver that can deliver more than 70 volts, you can't use it!

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15 May 2021 23:03 #208996 by andypugh

My Drives are not listed on the timing Wiki.


Use 5000ns, it will almost certainly work fine.

1) question: what feed rate would you suggest? [/quote]

Experiment to see what the machine can do before stalling, then work out of that is enough for your purposes.

If it isn't, then consider different gear ratios (for example). Or higher-voltage drives.

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17 May 2021 20:24 #209272 by Craig E
Thanks for the warning I am not going to go into deep calculation I am too impatient. I have already picked my motors and drives as a pair. So I hope they work.

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17 May 2021 20:32 #209277 by Craig E
Andy,
To make sure I understand, I can use 5000 ns for all 4 of the drive settings?
It just a hobby machine so I am not really concerned about run time just what quality. I will start the default feed rates and play with them after I have a few projects under my belt.

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17 May 2021 23:25 - 19 May 2021 12:44 #209291 by andypugh

To make sure I understand, I can use 5000 ns for all 4 of the drive settings?.


Direction hold and setup often need to be longer. As you only ever change direction at zero speed there is very little advantage in making then short, so try 20,000 there to be conservative.
Last edit: 19 May 2021 12:44 by andypugh.

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18 May 2021 13:06 #209347 by Craig E
Thanks Andy!

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