Losing My Way
30 Jan 2015 01:29 #55455
by jorsborn
Replied by jorsborn on topic Losing My Way
Hmmm... that's no doubt a misunderstanding of the units on velocity. I guess I assumed it was inches per minute. Through my experiments I start to stall at around 350 ipm and so I chose 120 ipm as a maximum velocity. I guess that's 120 ips though. ![:) :)](/media/kunena/emoticons/smile.png)
I will take your suggestion on the acceleration and see if that gets me anywhere.
![:) :)](/media/kunena/emoticons/smile.png)
I will take your suggestion on the acceleration and see if that gets me anywhere.
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30 Jan 2015 01:43 #55456
by ArcEye
Replied by ArcEye on topic Losing My Way
A lift from the docs
Your figures would be high for a metric machine, but when you multiply by 25.4, they are astronomical.
For strong Nema 23s (3 Nm +) with a good high voltage supply, I would probably use somewhere between 25-30mm/sec max velocity and 80-120 mm/sec/sec acceleration
All depends on how many pulses you can get, which depends upon the base-thread being fast and without hiccups and the amount of gearing, multi-stepping and axis weights etc.
That equates to approx 1.2 in/sec and 4.8 in/sec/sec respectively using the higher end of the figures, so you will see that almost exactly matches my divide by 100 and 10 recommendation
Regards base-thread, I usually multiply the best latency figure by 3 and try working down once the speeds are sorted.
regards
MAX_VELOCITY = 1.2 - Maximum velocity for this axis in machine units per second.
MAX_ACCELERATION = 20.0 - Maximum acceleration for this axis in machine units per second squared.
Your figures would be high for a metric machine, but when you multiply by 25.4, they are astronomical.
For strong Nema 23s (3 Nm +) with a good high voltage supply, I would probably use somewhere between 25-30mm/sec max velocity and 80-120 mm/sec/sec acceleration
All depends on how many pulses you can get, which depends upon the base-thread being fast and without hiccups and the amount of gearing, multi-stepping and axis weights etc.
That equates to approx 1.2 in/sec and 4.8 in/sec/sec respectively using the higher end of the figures, so you will see that almost exactly matches my divide by 100 and 10 recommendation
Regards base-thread, I usually multiply the best latency figure by 3 and try working down once the speeds are sorted.
regards
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30 Jan 2015 02:30 - 30 Jan 2015 02:35 #55459
by jorsborn
Replied by jorsborn on topic Losing My Way
With the acceleration and velocity lowered as you suggest the problem becomes even more pronounced. I can stand at one side of the gantry and watch the other side begin to move before the side that I am standing at. I believe I am observing this only when there is a change in direction... almost like backlash.
Any thoughts on that?
Any thoughts on that?
Last edit: 30 Jan 2015 02:35 by jorsborn.
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30 Jan 2015 07:44 #55472
by andypugh
That's probably not what you want![:-) :-)](/media/kunena/emoticons/smile.png)
You say you have one set of step/dir pins driving both stepper drives. Are you sure that the output pin can source (or sink) enough current to trigger the pins?
If you have access to both sides of the drive input optos you would probably want to run the slaved inputs in series. But I don't think the G540 supports that wiring.
Go back to two separate sets of parallel port pins run from the same step generator, if you still have the unmodified cable.
This really sounds like a problem outside the software, but it's hard to guess where. As an initial experiment double the step time and make the dir setup time something like 10x longer. You never change direction at high step rates, so it won't matter.
Replied by andypugh on topic Losing My Way
I can stand at one side of the gantry and watch the other side begin to move before the side that I am standing at
That's probably not what you want
![:-) :-)](/media/kunena/emoticons/smile.png)
You say you have one set of step/dir pins driving both stepper drives. Are you sure that the output pin can source (or sink) enough current to trigger the pins?
If you have access to both sides of the drive input optos you would probably want to run the slaved inputs in series. But I don't think the G540 supports that wiring.
Go back to two separate sets of parallel port pins run from the same step generator, if you still have the unmodified cable.
This really sounds like a problem outside the software, but it's hard to guess where. As an initial experiment double the step time and make the dir setup time something like 10x longer. You never change direction at high step rates, so it won't matter.
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30 Jan 2015 15:47 #55478
by jorsborn
Replied by jorsborn on topic Losing My Way
No, I am not sure about the drive strength of the parallel port on this motherboard. However, I do know that this problem is persistent through two other parallel ports (one on another motherboard and one on a PCI card). That means nothing, I know. I was wondering if the output voltage of the parallel port might be too close to Vin min on the gecko. I was thinking maybe I'd try to wire in a small board with some optocouplers and a 5V supply. That's a bit of work so I was leaving that until I get absolutely desperate.
The G540 does not support a slave configuration. I'll return it to two separate step/dir pins on the same step generator and make the modifications to the step timing as you have suggested. Fingers crossed....
The G540 does not support a slave configuration. I'll return it to two separate step/dir pins on the same step generator and make the modifications to the step timing as you have suggested. Fingers crossed....
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30 Jan 2015 19:32 #55482
by andypugh
You can test the DIR pin voltage fairly easily with a multimeter (though you would need a break-out cable or a parport cable with a removable backshell).
You might not need to add extra optocouplers, you could just pull-up the pins to USB 5V with (say) a 500R resistor.
But first you need to be sure that it really is a drive-signal problem. It doesn't 100% sound like one.
Replied by andypugh on topic Losing My Way
I was wondering if the output voltage of the parallel port might be too close to Vin min on the gecko.
You can test the DIR pin voltage fairly easily with a multimeter (though you would need a break-out cable or a parport cable with a removable backshell).
You might not need to add extra optocouplers, you could just pull-up the pins to USB 5V with (say) a 500R resistor.
But first you need to be sure that it really is a drive-signal problem. It doesn't 100% sound like one.
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20 Feb 2015 21:26 - 20 Feb 2015 21:26 #56148
by jorsborn
Replied by jorsborn on topic Losing My Way
I sent the G540 into Gecko and they did find that two of the drives had damaged opto-isolators. They did not provide any information so I can't tell if it was the input or output side which was damaged. I just assume these are the opto-isolators for the step and direction inputs too. Anyway, I was happy about that but after installing I found the problem still exists. This time I decoupled the motors from each side of the gantry and ran them with no load. The problem is quite obvious. Have a look for yourself...
I think this pretty well rules out any kind of mechanical issue. I also believe it points to the G540 still. If I swap the motor, the problem follows the drive, not the motor. Keep in mind that this is using one step and direction signal applied to both motors so they should both be receiving the same input.
Next I plan to do some testing to see if one is simply lagging or if one is moving when it shouldn't (noise?). Regardless, I think this implicates the G540 still.
www.dropbox.com/s/1xrnv6fybi8wvy8/2015-0...%2010.59.08.mp4?dl=0
I think this pretty well rules out any kind of mechanical issue. I also believe it points to the G540 still. If I swap the motor, the problem follows the drive, not the motor. Keep in mind that this is using one step and direction signal applied to both motors so they should both be receiving the same input.
Next I plan to do some testing to see if one is simply lagging or if one is moving when it shouldn't (noise?). Regardless, I think this implicates the G540 still.
www.dropbox.com/s/1xrnv6fybi8wvy8/2015-0...%2010.59.08.mp4?dl=0
Last edit: 20 Feb 2015 21:26 by jorsborn.
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20 Feb 2015 21:55 #56152
by alan_3301
Replied by alan_3301 on topic Losing My Way
was it always making that horrible noise?
It sounds like the stepper is stalling, but much worse.
You can check the resistance on all the motor coils and compare them to another motor.
It sounds like the stepper is stalling, but much worse.
You can check the resistance on all the motor coils and compare them to another motor.
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20 Feb 2015 21:57 #56153
by jorsborn
Replied by jorsborn on topic Losing My Way
No, the noise you hear is a vibration caused by the temporary arrangement. If I were to tighten the motor frame to the bracket and hold the bracket with a clamp you would not hear that.
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