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Author Topic: What's the best way to determine motor velocity?  (Read 13116 times)

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Offline chad

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Re: What's the best way to determine motor velocity?
« Reply #30 on: May 04, 2006, 05:14:24 PM »
sshneider, #1 is not true.

My understanding is (Brian correct me if i am wrong) fro will go beyond the motor tuning max. The motor tuning will dictate what a GO speed is. I think the conventional wisdom dictates that the fro is used primarily to slow down a job, or speed up a little bit. I think the way the pros use it is to fine tune a running program and not as the global speed knob. In other words set your F rate at the speed at, or faster than you want to cut and use the fro to adjust down.
If you are at 290% then you should have set your F much higher, this way you are still within the tuning.

I would tune to the skip point then back off 15% for safety and crank up your F to match, or back off another 20% and you can go higher on the FRO.

?!? 

chad
Re: What's the best way to determine motor velocity?
« Reply #31 on: May 04, 2006, 06:56:59 PM »
I Like to post my program VERY close to the cut rate that I wish to use... I never go over 150% because there is no need... That is just me.
Fixing problems one post at a time ;)

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Re: What's the best way to determine motor velocity?
« Reply #32 on: May 04, 2006, 07:09:18 PM »
AHA (Said the Blind Handyman as he picked up his hammer & Saw  ;)  )

Slowly things are becoming clearer.  Chad & Brian Thank you for helping me to understand.

Sid

Offline ger21

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Re: What's the best way to determine motor velocity?
« Reply #33 on: May 04, 2006, 07:40:55 PM »
I'm pretty sure FRO DOES speed up rapids. If you don't want it to, check "NoFRO on queue" in Config>State. The downside to that is that FRO will not respond immediately because the moves are buffered.
Gerry

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Re: What's the best way to determine motor velocity?
« Reply #34 on: May 04, 2006, 09:37:28 PM »
My x and y are pretty fast but my z tops at 6 in/min. This morning I took on milling some wood. Not knowing much about milling wood I f'd in the speed at 10 in/min. Everything worked as expected but I was in a hurry and the wood was cutting pretty good so I FRO'd to 180% because I know that's my FRO limit, any faster and my z starts skipping steps or hanging. I finished the job with x and y speeds at 18 in/min but z never went beyond 6 because thats the limit. I know though that if I'd FRO'd to 250 or 300% my z would have skipped steps. Even if  programmed it at 2 in/min, like I do in steel, I'd be skipping steps if I FRO'd above about 200%. In the last example the resultant z speed would have only been, at FRO of 300%, 6 in/min, still within the capability of the z. Curious isn't it. Is this pretty much the way it is?

BTW, this is a great discussion.

Jim
Re: What's the best way to determine motor velocity?
« Reply #35 on: May 05, 2006, 12:29:36 PM »
I Agree Jim,  Great Discussion!

I think that the primary principle that I have come to understand in this thread is to write your code with an F that is close to where you want to be runing with maybe a little 'wiggle room'.  This is a great idea if you are an experienced operator but if your a newbie then I guess you're in for some trial and error time.

I think one of the things that is confusing is the wide range of the FRO.  If  most dudes only tweak their FRO 20-50% above the F rate then why does FRO go all the way to 300%?  In other words, if travel at the speed of light is impossible, why put a warp drive button on the dashboard?

That's kinda why the doo dad macro pump that Brian worked up is pretty awesome.  It's kinda of a 'governor' if you will.  It keeps one from jackin' things up too far.

In summary, I think that the best procedure (IMHO) for finding motor velocity would be to set your Feed Rate at the highest you ever anticipate runing your machine.  HIGHEST = F x FRO% (you're going to have to do a little math to figure out what this number is).  Then find the max velocity you can run without missing steps.  Then use Brian's Macro Pump and set the Max DRO so it corresponds to the the HIGHEST value.  Does that make sense?  To me it seems like if you follow this method you have a fail safe way to not overspeed your machine.

Happy Cinco De Mayo!

Sid

Offline ger21

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Re: What's the best way to determine motor velocity?
« Reply #36 on: May 05, 2006, 07:35:05 PM »
Just use FRO for ONLY slowing down the machine, and you won't have any problems. Our router at work goes from 0-110%. We leave it all the way up, and program fast. If we need to slow it down, we can, but we never need to go faster than we program.
Gerry

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