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05 Oct 2019 09:45 #147178 by pl7i92
Replied by pl7i92 on topic moving problem
robert yoiu shoudt open a new tread and telling where you are only Basic location
somone will connect you and get a visit
there are Linuxcnc people almost everywhere

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05 Oct 2019 09:56 #147180 by RoberCNC
Replied by RoberCNC on topic moving problem
You mean local physical help?

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05 Oct 2019 10:36 #147183 by rodw
Replied by rodw on topic moving problem
Just reading through the last few pages, I think there are a few issues that when combined are reducing torque to a stage that missed steps occurs then the gantry racks and stalls totally.

First is the voltage. It seems low to me. Most steppers run at 48 volts or 70 volts. But I thought you said you are running 36 volts. If you double the voltage you more than quadruple torque. Use the highest voltage your drivers can handle. This could be the simplest fix.

Then you are starving your steppers for current. You said they were good for 3 amps but you limited them to 2 amps. Its OK if the total amperage of your steppers exceed your power supply amperage by 40% (Eg 10 amp supply can handle 14 amp of steppers.)

Then there is the misalignment between the stepper and the ball screw. You need to use misalignment couplings but don't use the cheap helical aluminium ones. They do not handle a lot of torque so will introduce backlash when they twist. Use an Oldham style coupling and check torque requirements against what the coupling can handle.

Until you get your head around this, I would suggest you don't exceed 400 rpm on rapids (2000 mm/min o 5mm ball screws)

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05 Oct 2019 11:40 #147187 by tommylight
Replied by tommylight on topic moving problem

rodw wrote: First is the voltage. It seems low to me. Most steppers run at 48 volts or 70 volts. But I thought you said you are running 36 volts. If you double the voltage you more than quadruple torque. Use the highest voltage your drivers can handle. This could be the simplest fix.

That is true, although i never suggest using anything over half of the rated voltage for the cheap drives, they just tend to blow up at random when anywhere near that limit.

rodw wrote: Its OK if the total amperage of your steppers exceed your power supply amperage by 40% (Eg 10 amp supply can handle 14 amp of steppers.)

That is also true, as a general rule.
The actual math is much more complicated and having some more info can result in using i.e. 100V/1A power supply to drive 100A motors if and only IF the voltage needed for that motor to draw 100A is 1V. This is of course in ideal conditions and does not include the losses in the drive and cables and the delay in reaching that current due to inductance.
Since stepper motors mostly use current and inductance as information, the lower the inductance the better it is for the power supply as it is possible to use lover voltage and still get decent rotational speeds. Also as a general rule, more power supply voltage= less current needed.

rodw wrote: Until you get your head around this, I would suggest you don't exceed 400 rpm on rapids (2000 mm/min o 5mm ball screws)

400RPM is achievable, but i would not go that far as steppers will have at least 10 times less power at that speed.

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05 Oct 2019 11:54 #147190 by RoberCNC
Replied by RoberCNC on topic moving problem
I can not agree more with you Rodw, I suffer the sum of small details. I am solving the problem of misalignment first, the couplings I use are CM30C, the oldham did not know. As for the voltage, I had been told that with that it was enough (obviously wrong), it is the next thing I have in mind to solve, from what I have seen there are those who use only one source for all steppers, who uses one every two ... I think I will decide on one for every two drivers, what I am not sure about is the voltage, maybe two of 70V would be enough?
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05 Oct 2019 19:28 - 05 Oct 2019 20:06 #147219 by RoberCNC
Replied by RoberCNC on topic moving problem
I think I have greatly improved the alignment of the ballscrews, if I have done the measurements well below the tenth and still the problem persists (I have only joined one sides stepper to the gantry) so there is only the problem of voltage and torque as rodw pointed out, I'm going to order two 72V sources and I'll have to wait for them to arrive :whistle: :whistle: .

Rereading the post I have observed what you say Tommy about not to exceed half of the nominal in the cheap units, which I think is my case. You mean I shouldn't power the drivers with more than 40V?
Last edit: 05 Oct 2019 20:06 by RoberCNC.
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08 Oct 2019 18:34 #147481 by RoberCNC
Replied by RoberCNC on topic moving problem
While the power supply arrives I have been testing and it seems that it is going well, at absurd speed but well, yes, I have observed that the steppers get very hot, to the point that I am not able to grab them for more than 6 seconds. Is that normal?

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08 Oct 2019 21:40 #147501 by Clive S
Replied by Clive S on topic moving problem

RoberCNC wrote: While the power supply arrives I have been testing and it seems that it is going well, at absurd speed but well, yes, I have observed that the steppers get very hot, to the point that I am not able to grab them for more than 6 seconds. Is that normal?


No that is not normal. You will need to turn the current (Amps) down on the drives . Some say you can run them about 50c but in my humble onion 40 - 45c should be max
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08 Oct 2019 23:48 #147511 by tommylight
Replied by tommylight on topic moving problem

Clive s wrote:

RoberCNC wrote: While the power supply arrives I have been testing and it seems that it is going well, at absurd speed but well, yes, I have observed that the steppers get very hot, to the point that I am not able to grab them for more than 6 seconds. Is that normal?


No that is not normal. You will need to turn the current (Amps) down on the drives . Some say you can run them about 50c but in my humble onion 40 - 45c should be max

That is quite normal for stepper motors, they can handle over 100C. Grabbing them for 6 seconds would roughly be 70 to 80c, so not bad, yet.
When it burns your fingers, that is to much.
You can always turn the current down just a bit and have them powered and working for 15 to 30 minutes and test again, they should be warm, and as a rule of thumb, if you can keep the hand on them all the time, that is safe always.
Have the motors working, not stationary, as the drives lower the current at idle.
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09 Oct 2019 07:02 #147536 by RoberCNC
Replied by RoberCNC on topic moving problem
OK, so it's about finding a balance between voltage (torque) and amps, is there any kind of formula that applies and relates everything? It's amazing everything I learn :) :)

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