Rods "Spaceship" Scratch built Plasma Cutter build

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02 Jul 2020 09:21 #173388 by rodw
Actually, this shot I took today shows the detail reasonably well



The open frame driver is a LS1073a which is functionally equivalent to the DS1073a, the smaller 3 amp version of the 6 amp DS1076a I'm using on the DIN rail. The open frame one is a bit cheaper and what was available in Australia. I prefer the enclosed version.
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02 Jul 2020 11:50 #173401 by tommylight
Please tell me those are not daisy chained ground wires, please please pleaseeeeee. :)

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02 Jul 2020 12:15 #173405 by rodw

Please tell me those are not daisy chained ground wires, please please pleaseeeeee. :)


Nah, they are in a star to a common ground.

I've been looking at the LAM boost function and its a bit different to what I thought. the manual says:

The BOOST input allows to manually reduce the current even while motor is rotating. This feature can be useful to reduce the heating when the whole torque supplied by the motor is not required (for example when the load moves at constant speed).


So that is an interesting scenario. They actually suggest you reduce the current when you get to cut speed. That will be easy to do.

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02 Jul 2020 13:50 #173417 by tommylight
Yeah, but that will bring the motor closer to stalling, by a lot.

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02 Jul 2020 13:51 #173419 by tommylight

Please tell me those are not daisy chained ground wires, please please pleaseeeeee. :)


Nah, they are in a star to a common ground.

Oh good, almost had a heart attack there . :)
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02 Jul 2020 13:57 #173420 by rodw

Yeah, but that will bring the motor closer to stalling, by a lot.


maybe not, elsewhere they say
In other words, even doubling the current, a double torque is never obtained from a motor. For this reason it is usually superfluous to over supply the motor of more than 30% of the nominal current. 

So pick your figures and you can still get motor rated torque when not accelerating and +30% when accelerating

Do the Sanyo Denki's quote max current or RMS (effective )current do you know?

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02 Jul 2020 14:44 #173423 by tommylight
I have 2.4A Sanyo motors wired to LS1076 set at 2A, and they get very hot, like 65 to 67 degree C at 27C ambient temp when running all day non stop. Since i know temperatures here can sometimes reach 41 or 42 C and that would result in a 80 to 85C on the motors. I am sure they will handle more, but no reason to push them any further, i did try to stop the gantry by pushing as much as i can on it, it did not stall at 12M/M, so i consider that way to much power for a plasma cutter.
Lam can claim all those things as they are sure their drives are by far the best at what they do, so where a normal motor wired to a normal quality drive will heat less as the speed goes up, motors wired to Lam will heat more at speed, and that is due to very fast switching and reaching the rated current at any given speed.
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02 Jul 2020 14:54 #173425 by rodw
Yes, it will be interesting to see how mine go. Our model says they can accelerate at 5 m/s/s which means they can get from 0-15m/min in 50 milliseconds. The Moons are equally as nice too.
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02 Jul 2020 15:52 #173429 by tommylight
Oh i did try mine at 6m/s/s and the result was interesting to say the least, max velocity at 24m/m the machine started moving when changing direction, like the whole machine was moving a little (1 to 2cm) back and forth over the floor, everything was shaking and it did not last to do a video as it started ripping the teeth on the small belts ! :) Had to change both belts and set it back at 1.5m/s/s.
Thinking about it, the LAM version of lowering the current after acceleration seems very smart for plasma use, the biggest risk of stalling is while accelerating, so that makes sense. My idea of boosting current is much more suited for mills and stuff with bigger forces in use.

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02 Jul 2020 21:19 #173453 by rodw

Oh i did try mine at 6m/s/s and the result was interesting to say the least, max velocity at 24m/m the machine started moving when changing direction, like the whole machine was moving a little (1 to 2cm) back and forth over the floor, everything was shaking and it did not last to do a video as it started ripping the teeth on the small belts ! :) Had to change both belts and set it back at 1.5m/s/s.
Thinking about it, the LAM version of lowering the current after acceleration seems very smart for plasma use, the biggest risk of stalling is while accelerating, so that makes sense. My idea of boosting current is much more suited for mills and stuff with bigger forces in use.


I wondered about that. Sounds like you came up against the limitations of Linuxcnc's trapezoidal acceleration profile. I think it will need jerk limited (S curve) profiles to support those numbers... but my pinion teeth might be a bit stronger
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