Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: richyrich212 on October 24, 2010, 08:06:30 PM
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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
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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
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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.
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Maybe some noise from THC, do you use shielded cable in you setup.
Jeff
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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.
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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
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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.
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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 !!!
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i set it at 20% and all things is ok.
i think problem is noise in system.
or GND issue
Amir
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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
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It depends on what your max speed in motor tuning is set to
yes.
my mistake. i forget about max speed.
thx for Correct my mistake and sorry for it.
Amir
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he he - that's ok Amir ;D
so what is your max speed set to? and do you use a THC300 or similar? I think it would be useful if we could share settings and experiences.
Cheers
Ian
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yes, i build my THC300 and use it.
i set velocity for Z axis about 100IPM.
THC would not work with the Smooth Stepper.
i think we can use modbus+SS for plasma machine
Amir
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My current setup is as follows:
z-axis is direct drive rack and pinion 848 steps per rev.
THC300
accel is set @ 100 in/s
velocity is set @ 200 ipm
THC rate is set @ +20
My setup is currently off site. I will tune later on in the week and ill report back with my findings. In the meantime would others like to post there z axis specifics and info!!!!
I think this will help me and other people tune, their machine.
Surely some of us have struggled with this in the past
Thanks
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With a Z velocity of 200IPM, your THC Rate needs to be much lower than 20. My Z velocity is 30 on a lead screw and a THC Rate of 10 - 15 works best. With your Z velocity, I would start at 10 and work back from there. That, or slow down your Z velocity in Mach. Why do you need 200IPM on the Z?
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Thanks everyone for all the help. I successfully got my THC tuned !!!!! ;D My final numbers were as follows:
acel = 75ipm
velocity = 75ipm
thc rate = 9
Thanks again to anyone who had input !!!