S3 Fun with speeds and limit switches

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twforeman
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S3 Fun with speeds and limit switches

Post by twforeman » Wed May 27, 2015 12:33 am

I finally installed a full set of limit switches on my S3 and started playing around to see what kind of speeds I could run the machine at. These are all just air moves, no cutting involved yet.

I currently have the max travel rates set at 14,000 mm/min. That's pretty quick. I tried 15,000 and got some interesting resonance from the machine.

14,000 mm/min is a pretty impressive thing to see. :)

I'm also here to tell you that if you run the machine at 14,000 mm/min (or even only 10,000 mm/min) and ram it into the limit switch, it will over-run it a bit before it actually stops. Which means that it will probably ram the end plate. But it will stop pretty quick. The mounts I designed should prevent limit switch destruction in the event of an over-run although the levers on the switches might get bent if you do it a lot. :)

The annoying thing about tripping a limit switch is the dance you have to do to unlock the machine - although it's no different than what you have to do on an S1 or S2.

Grbl detects the switch change of state as a limit trip, no matter whether it's going from open to closed or vice-versa.

Which means you have to do the following after hitting a limit switch:
  1. Send Grbl a 'soft reset' to get it out of alarm state.
  2. Send a $X to Grbl to unlock the machine.
  3. Move the axis that hit the limit away from the switch - which will send Grbl into alarm state again as the switch opens.
  4. Send Grbl another 'soft reset' to get it out of alarm state again.
  5. Send Grbl another $X to unlock the machine again.
  6. Move the axis that hit the limit away from the switch.
  7. Now you can re-home the machine because Grbl unlocks the motors when you hit a limit switch and it doesn't know where it is.
A 'soft reset' is ctrl-x, and since I use UGS it has a 'soft reset' button. Carbide Motion must have some equivalent, but I'm on a Linux laptop and can't run it to see.
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chamnit
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Re: S3 Fun with speeds and limit switches

Post by chamnit » Wed May 27, 2015 12:41 am

Hard limits resetting is pretty annoying. I plan on addressing some of that in the next major release. However, if your GUI will allow it, you should be able to run a homing cycle immediately after a hard limit because the homing cycle will detect it's on the switch and immediately locate position. If you can't home, it's best to power down the SO3 and manually move the machine off the switches. Power up and then home.

twforeman
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Re: S3 Fun with speeds and limit switches

Post by twforeman » Wed May 27, 2015 12:52 am

Actually, I just tried it. I'm using the CarbideMotion 0.9g build and hitting a limit switch:

Code: Select all

ALARM: Hard/soft limit
[Reset to continue]
I send it a soft reset which tells me this:

Code: Select all

CarbideMotion 0.9g
['$H'|'$X' to unlock]
Sending $H puts it immediately into Alarm state.
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chamnit
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Re: S3 Fun with speeds and limit switches

Post by chamnit » Wed May 27, 2015 1:49 am

Ok. Then they probably enabled the two homing switches on one pin option in the firmware. It does this because Grbl can't tell which side it's on when triggered. It's the right thing to do but an annoyance.

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Re: S3 Fun with speeds and limit switches

Post by WillAdams » Wed May 27, 2015 2:22 am

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rtlflatt
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Re: S3 Fun with speeds and limit switches

Post by rtlflatt » Wed May 27, 2015 3:16 am

cant u change the grbl compile option for homing sequence is this case? so it home z first like usual but then instead of x/y at same time do x and then y after it finishes? i havent tried this but that was how i was interpreting the comments for that setting
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twforeman
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Re: S3 Fun with speeds and limit switches

Post by twforeman » Wed May 27, 2015 12:35 pm

It doesn't matter what order it homes the machine in.

If you trip a limit, you need to get off the switch.

If you have a limit switch on each end of the axis and you trip the one on the non-home end then if it tries to home it will go the wrong direction for the pull off and you will be even worse off.
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chamnit
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Re: S3 Fun with speeds and limit switches

Post by chamnit » Wed May 27, 2015 2:39 pm

Oh, forgot to say, running at 14000mm/min is awesome! With travel upgrades, this seems like a great speed to move those longer lengths.

Dallas
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Re: S3 Fun with speeds and limit switches

Post by Dallas » Mon Nov 09, 2015 6:33 pm

I either need to upgrade my dust collection adapter or keep my darn mitts off the machine when it's running. Yesterday, I was proactively vacuuming up big piles of sawdust off the waste board to keep the rails clear while the machine was running when I touched a limit switch with the vacuum hose.

Party over. :(

That's the second time I've committed that particular sin.

I was 20 minutes into a 30 minute job when it happened (hence the big piles of sawdust). It sure would have been nice to restart the machine. I'm going to print out Tim's list of steps and scotch-tape it to the wall next to my Shapeoko.

To be clear though, in order to reset Carbide Motion, I'll need to type 'l' on the keyboard to enter the log screen... And then do what exactly to achieve a 'soft reset' (step 1 of Tim's list)? I presume I can skip steps 3-6 since the machine didn't actually hit the limit switch itself.
  • 1. Send Grbl a 'soft reset' to get it out of alarm state.
    2. Send a $X to Grbl to unlock the machine.
    3. Move the axis that hit the limit away from the switch - which will send Grbl into alarm state again as the switch opens.
    4. Send Grbl another 'soft reset' to get it out of alarm state again.
    5. Send Grbl another $X to unlock the machine again.
    6. Move the axis that hit the limit away from the switch.
    7. Now you can re-home the machine because Grbl unlocks the motors when you hit a limit switch and it doesn't know where it is.
Once I re-home the machine, (by setting zero with the Carbide Motion software, I presume), what do I do to restart the job?

Thanks for your help.

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