Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: filo4078 on October 11, 2011, 12:33:15 PM
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Hi all
This may be something or nothing.
I have just converted a 7x14 mini lathe to two axis CNC. Everything works fine but when I increase the jog above 5% the drives start to loose steps and grind to a halt.
If i'm set to 5% and below everything is fine.
My config is as follows:
3.06Ghz processor.
TB6560 driver card. DIP switches set to 75%, FAST, Half step.
57BYGH603 stepper motors. 1.0amp 1.8 step angle 14.5 kg.cm running at 24vdc.
Using this information I have set the Mach3 steps per unit to 4000 which gives me the correct travel as per the DRO.
I have the step/dir timing set to 1us.
I have the acceleration set at 0.6 seconds and the velocity at 200in/min.
The kernel speed is 60,000hz.
Any help would be appreciated. It might just be that my motors are not man enough to go any faster which is fine as I can work with it as it is.
Cheers
Phil
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Correction:
Driver card set to:
Current (amps) 75%
Decay mode FAST
Microstep setting 1/2
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First thing to say is you should not have the kernel any higher than you need. Next is likely you would be better set to 1/8 stepping. You then need to set the steps per unit correctly and then set Velocity and Accel on Motor tuning page, the latter two need trial and error to set as there is no hard and fast numbers that will work on all machines as there are so many variables.
Hood
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Hi there
So, I set the board to 1/8th microstep.
The Mach3 steps per unit works out at 32000!! to get the correct travel. However, no increase in speed despite playing with vel/acc graph.
Are the motors supposed to get hot when running?
Cheers
Phil
PS I lived in Aberdeen for 10 years. The granite city.
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Phil can you attach your xml please.
Aberdeens quite a nice place, its about 70-80 miles up the coast from me.
Hood
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Are the motors supposed to get hot when running?
They can get hot if the drive current setting is to high and when they get hot they can start to act wierd.
Any motor which is doing work will increase in temperature. No increase in temp and they are not doing much work.
You don't want to exceed their rated temperature.
If they get hot ( can't touch and leave your hand on them ) you are over 140 deg F and you'll get a burn.
If they get hot quickly upon engagng them and not running your current setting is to high.
FWIW,
RICH
RICH
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XML attached.
The motors are not so hot that I cant touch them.
Cheers
Phil
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With an accel rate set to .6 /sec/sec it would take forever to get up to speed with a max vel of 200in/min. with short moves involved you have to accell up to speed then slow down to a stop in the givin move. You may NEVER get any speed with some code.
Just a thought,
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Ok first glance at XML looks fine except from as Terry says accel is slow and also so are your Velocities.
Can you just clarify what you are meaning by this " Everything works fine but when I increase the jog above 5%"
What is the 5% you are talking about?
Hood
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When I had the velocity set to 200in/min I couldn't go above 5% in the slow jog % box in the manual screen. Since I have lowered the velocity to 10in/min and the accel is set to 0.5 in/sec/sec now I can go to 100% but these numbers are academic as the overall velocity is no higher than before. I hope this makes sense cause i'm confused as hell...lol.
When I say everything works fine, this is what I mean. My lathe is only 14" across the bed so 10 in/minute is slow but workable. I would have thought that for a rough cut I could have got 20-30 in/min but i'm no expert in machining. I'm an electronics man, not a turner. It's just something I fancied learning.
I should also add that i'm working with delrin 150 so I should be able to go quite a bit faster than working with alloys.
Also, my steppers are only 1 amp rated, I suspect they are underrated.
Cheers
Phil
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When setting up the motor velocity and accel you should be able to test from within the motor tuning page as you tune by pressing up and down arrows on your keyboard.
Forget the slow jog, you need to find the sweet spot for your rapid as if you rely on a slow jog % your motors will stall as soon as you either command a G1 move faster or command a rapid move (G0)
You could try setting Sherline mode as enabled and restarting Mach to see if its any better, the other thing is run drivertest.exe (with Mach closed down) and see what it looks like.
What voltage are you using for your power supply to the drives?
Hood
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Unless I missed it in my quick read, the motor voltage has not been stated. A common problem with newbees and steppers is to supply the voltage that the motor spec states. Steppers should run on 3 to 6 times their 'rated' voltage. I have not messed with steppers in a long time and I don't recall exactly the technical reasons why the stepper rating is so far below the correct operating voltage, the rating is voltage per phase or per winding or something like that. In any case, a stepper will be very lethargic running at its 'rated' voltage and the proof here is the inability for the stepper to accelerate to keep up with the step stream. Steppers are very slow in any case and certainly should be able to reach the few hundred RPM they are capable of. If your voltage is correct, I would suggest you remove the motor from the machine and try to spin it up on the bench. Even an 'un manly' stepper can reach full speed with zero load :P.
Steppers draw full power whether they are moving or not, that is why they hold so well, and as a consequence they are designed (insulation and lubrication temp specs primarily) to run hot . . . that's hot, not warm. Perfectly normal, even if they are not moving. Imagine a skinny old guy with his neck stretched out as far as it will go, holding his breath with his face beet red and his eyes bugging out . . . that's how steppers are all of the time . . :D
However, they will only get to a certain temp and then just stay there. On the other hand, a normal DC motor under a heavy load (holding up an uncounterweighted Z axis, or otherwise held off of its commanded position for example) will continue to heat more and more until it self destructs, so you do have to pay attention to temp on those motors.
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I found from testing here that some steppers will start to act funny at higher temps no matter what the rating is, missing steps, etc, etc. The higher voltage will allow higher rpm as the pulsing goes from a rather dc to a ac and that frequency gets limited similar to an RC circuit. In fact, one can actually mount the motor and turn the shaft at different rpm and measure the voltage generated from it and see at what rpm it drops off. Any voltage in excess of that is useless and the drives may not be able to handle it.
Irrelevant of the above, I would imagine that the torque is at the bottom of the motor curve when at 200 in/ min. The motors are underrated for even a small metal lathe in my opinion even with the gearing.
Fwiw.....
RICH