Servo Purchase Recommendations, Yaskawa?
- tommylight
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The bad rep they are getting is costing them much more than 3 sets.
P.S.
Just in case they ever decide to send something my way, i do not do NDA, i do not care about hurting feelings, and i sure as hell do not respond gently to someone suing me for whatever.
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- ihavenofish
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The good thing about delta (drive model -L) and yaskawa and several others is that you can use pulse or analogue. so if analogue doesn't work out well, just switch over.
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Good to know are P44 + P45. Standard setup are 16 + 10
=160000 steps/rev. Little high for hobby machine...
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Tommy I would gladly send you a dmm set if you weren't so damn far away. I would be curious to see what you could do. Still not sure what I will do with them when I take them off.
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- tommylight
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Yes i am !Tommy I would gladly send you a dmm set if you weren't so damn far away.
Andy and Peter (PCW) can do all the testing required also, but try to coordinate with them, we have one thing in common = no time!
Forgot to mention above, the time it takes for testing such things costs much more than 3 sets, and still we are willing to put the time and effort to help others, it is 4:06AM here and have to be up by 9!
Thank you for the offer.
Manufacturers should also take a page from PC equipment manufacturers, they send every damn thing to youtubers and accept feedback and fix things, not all are fair though.
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- ihavenofish
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when you have a pulse controlled drive, it reads that harsh acceleration command and says "yeah, that's not gonna happen" and filters it, creating its own jerk control. new drives can have some very advanced filtering resulting in negligible position deviation. so basically, the problem doesn't exist because the drive is taking care of it and because the control is not reading the encoder other than to log an error (if even that), it cant interfere. you will have a path deviation, however it should be so small it is not an issue in practice.
in analogue mode, linuxcnc is controlling the position loop, and keeps spitting out speed commands to the drive, which the drive/motor can't perform, which in turn causes linuxcnc to keep adjusting and compensating. in theory, your high inertia heavy machine would make this even worse. the result (for me) was a clunky acceleration where the motor would overshoot and then come back. this was literally 2 or 3 encoder counts on the x and y, well under 0.001" deviation, however it was enough to make a violent motion that could damage the ball screws, and occasionally send the motor into resonance (especially the z). i had sanyo servos on a brother tapping centre, so a light high dynamic machine.
Things to note on my experience are that my encoders were 1024 line - 4096 pulse, and the drive had a velocity loop of about 100hz. linuxcnc typically runs its position loop at 1000+hz - so the drive basically does not respond to the control before the control decides to issue another correction.
a delta b3 (and yaskawa sigma 7) has a velocity loop of 3100hz if i remember right, so it is entirely possible that it would behave flawlessly as it has both the velocity loop performance and encoder counts to adapt to the controls unreasonable commands.
my analogue spindle servo (basically an axis drive) worked flawlessly as well, because i assume the way linux controls it is much "lazier" and it's also not driving a heavy linear load. 0 to 6000rpm to -6000 to 0rpm in 400ms. vroom.
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- ihavenofish
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Manufacturers should also take a page from PC equipment manufacturers, they send every damn thing to youtubers and accept feedback and fix things, not all are fair though.
oh, they send out all sorts of things for testing, they just literally don't give a s*** about this market. at all.
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The jerk motion described does sound similar to the issue I had. Even at low acceleration numbers in my INI the motors would lag the command and over accelerate to make up for it. This would cause an over current fault at anything above half speed. We discussed ways to deal with it; lincurve, some PID constraints. The Ferror wasnt horrible but the motors would never work past half speed without the fault. DMM just kept saying it wasn't their fault and the servos are "capable of near instantaneous acceleration".
They work fine in pulse mode and achieve full speed but as an open loop to LCNC. I really want closed loop and specifically to home to index. Most of my work uses pallets and the same couple WCS so I would like the homing to be as accurate as possible. Currently its .0005" in open loop.
I don't blame them entirely. I was attracted to them because of price and had no idea what I was doing at the time (still don't). They are decent for the price and market they are shooting for. Just not the direction I should have went. Hind sight is always 20/20
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- tommylight
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Guessing here, but using buffers for filtering and seting long timings to have clean signals does that.
As for acceleration on older machines, it has to be tuned to every machine, the LinuxCNC default of 750mm/s/s was to much on a Hurco BMC20, but my plasma can do 5000mm/s/s easily, 3D printers do even more.
Basically, LinuxCNC acceleration has nothing to do with slow drives.
Slow drives have something wrong on the feedback side, the input side is a simple power amplifier so the delays there are very short.
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On the Delta Servos, you could set a low-pass or S-curve Filter. Its own chapter in the manual. First step of tuning is set the electronic gear ratio. Should be your smallest unit/pulse. In metric =1µ/puls or 10µ/pulse. Second, could you adjust a low pass filter or s-curve filter. In any way should you are able to avoid the jerk. Your following error rise in this step, but with low gain from lcnc it's okay. Another way is to use one external scale and connect to drive direct and set lcnc PID near 0. To calculate the gain parameter is the tuning software helpful. For sure not perfect, but you are able to get better result as to set the parameter by hand.I don't have a high end machine. It's a 1996 that's getting a retrofit. Will deltas have the same issue with jerk on a large old heavy machine with a lot of inertia?
As I write this line...
What will be happened if all step and feedback commands pass the lcnc low-pass filter? Could it be possible to avoid a jerk by this way?
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