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The never ending THC Saga !!
« on: October 24, 2010, 08:06:30 PM »
Hi guys,

After months and months  I am still  continually struggling to get my THC 300 to operate correctly !!!!!

Originally I was trying to get the THC  to work with the smooth stepper but after a lot of questions, I was told that the THC would not work with the Smooth Stepper.  After reverting back to my PMDX breakout board and a second PP port.   I was able to get the THC somewhat functional.  My THC seems operate but has very erratic movements and causes the z axis to oscillation when the THC is under control.  When this is happening the up and down LEDS blink very quick rate.    When I turn the THC  off the oscillation goes away.

 Anyone have any input on this??

I am almost ready to sell this machine for scrap metal  !!!!!!

Any help is very much appreciated


Online BR549

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Re: The never ending THC Saga !!
« Reply #1 on: October 24, 2010, 08:41:51 PM »
Have you tried SLOWING down the Z axis acceleration and velocity rates. IF it is too fast it tends to overshoot the setpoint and that can set up an oscillation.

There have been discussions of this I believe do a search on here and the yahoo site.  Then try the CandCNC site for trouble shooting guides on hi s products they operate in a similar fashion.

Just a thought, (;-) TP
Re: The never ending THC Saga !!
« Reply #2 on: October 24, 2010, 08:54:54 PM »
I have not tries slowing down the Z axis acceleration and velocity rates yet.   My machine does appear to be overshooting !!!!         I will test this and report back.
Re: The never ending THC Saga !!
« Reply #3 on: October 24, 2010, 09:32:23 PM »
Maybe some noise from THC, do you use shielded cable in you setup.

Jeff

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Re: The never ending THC Saga !!
« Reply #4 on: October 25, 2010, 04:01:57 AM »
This is classic behaviour of the THC300 and it's like with Mach. You need to turn down the value in the THC RATE DRO.

The THC Rate tells Mach to move the Z at that percentage of the max velocity set in motor tuning. If you have it set too high then you will get the huge oscillations. Set it too low and it won't cope with large warpage. It's a balancing act. For example my Z velocity in motor tuning is set to 3 m/min and for flatish steel I set THC rate to around 10. You may need to go even lower. A tip: the min that you can set the DRO to is 5. If you need lower, you need to directly edit the xml. The tag is thcspeed.

Just as an aside, Z acceleration is not relevant. THC's ignore acceleration and move the Z axis at the set speed without an acceleration ramp.
Re: The never ending THC Saga !!
« Reply #5 on: October 25, 2010, 10:56:58 AM »
Quote
Just as an aside, Z acceleration is not relevant. THC's ignore acceleration and move the Z axis at the set speed without an acceleration ramp.

i think must use "THC rate" in mach for decreasing overshooting

Amir
**Even a clock that does not work is right twice a day**
Re: The never ending THC Saga !!
« Reply #6 on: October 25, 2010, 12:21:57 PM »
slow down the z axis. i have it set at 8 percent. unless you are using very uneven material, the response of the thc should be able to keep up.
Re: The never ending THC Saga !!
« Reply #7 on: October 25, 2010, 12:31:04 PM »
ostie01   >   I use  sheilded cables with ferrites on each end of the cable.  I haven't put a scoped on the parallel cable to view the input but noise is a possibility.


stirling   >   Your explanation off the "THC Rate " field describes everything to a tee !!

My z is set to 200ipm  with a 100 accel.     I wanted to keep my accel as fast as possible, so I wouldn't run out of speed when cutting thin warped material.    Currently my THC Rate is set to default value .  (20 I think)  


I will test asap and report back.    Thanks for all the help thus far !!!





Re: The never ending THC Saga !!
« Reply #8 on: October 25, 2010, 12:32:20 PM »
i set it at 20% and all things is ok.
i think problem is noise in system.
or GND issue


Amir
« Last Edit: October 25, 2010, 12:39:04 PM by manmeran »
**Even a clock that does not work is right twice a day**

Offline stirling

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Re: The never ending THC Saga !!
« Reply #9 on: October 25, 2010, 01:30:05 PM »
i set it at 20% and all things is ok.

Yes but Amir - ALL systems are different. It depends on what your max speed in motor tuning is set to. IF for example your max speed was 10m/min then your Z would move at 20% of 10m/min i.e. 2m/min. BUT if for example your max speed was 2m/min then your Z would move at 20% of 2m/min i.e. 0.4m/min. These would give very different results regarding the oscillations