Rods "Spaceship" Scratch built Plasma Cutter build

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15 Oct 2020 06:35 #186155 by rodw
Well, I broke my config on the last upgrade to the official 2.8 release version (via run in place).

So I rebuilt my config again from scratch which took a lot of time but it needed a bit of a clean up.

While I was at it I finally added an ilowpass component to smooth out motion on my pendant MPG and add a few features specifically for the Lam Technology drives.

The first is wiring in the Lam fault signal so Linuxcnc knows if something goes wrong and pauses with an amplifier fault.

The second is much more interesting as it uses a custom component that senses when a joint (motor) is accelerating, decelerating, cruising at cut velocity or at rest. When the drives are under acceleration or deceleration, the motors are driven at 6 amps and when at rest or at cut speed (constant velocity for some) the current is reduced to 50% or 3 amps (settable in the Lam drivers).

Here's a video example.



So it will be interesting to see how this goes on a real job. We ran a job the other day where the motors overheated and started to loose steps. I reduced the amps back to 5 and it cut fine. In testing today we lost steps massively and one motor stopped working. I'll run the same job once I'm happy I have it all working correctly as a real test.

Now we have the fault signal to catch this fault but time will tell if 50% current reduction is too much.
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15 Oct 2020 07:58 #186161 by machinedude
looks like you got her cooking pretty good Rod. better think about beefing up the frame work :) otherwise you won't be able to keep the water in that water table very long :)

impressive acceleration though :)

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15 Oct 2020 08:08 #186163 by rodw

looks like you got her cooking pretty good Rod. better think about beefing up the frame work :) otherwise you won't be able to keep the water in that water table very long :)

impressive acceleration though :)

Yeh, it is really a lot to do with it being on casters and I have adjustable feet with a M30 thread to add yet once I know exactly where it will live.

36 metres per minute and 5 metres /sec/sec acceleration.

It actually made the 120 amp plasma cutter overheat the other day at 40 amps. I think it must have been becasue if an obscene number of pierces in the job with no time to cool down becasue of the super fast rapids.

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15 Oct 2020 09:01 #186168 by machinedude
well that makes sense if you think about it. moving that fast cuts into the duty cycle of the plasma cutter. not as much time to catch a break in between cuts should give it a harder workout :)

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15 Oct 2020 09:37 #186172 by pinder
I like those speeds.
:)
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15 Oct 2020 10:37 #186177 by rodw
yeh a huge project to get that far. There is an insane amount of engineering behind the motor selection

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15 Oct 2020 10:58 #186181 by my1987toyota

yeh a huge project to get that far. There is an insane amount of engineering behind the motor selection


true . But It does give you a whole new level of appreciation of what it really takes to design and build tools.
It's always hilarious to hear people who have never done anything intricate say " oh it can't be that hard."
And yes I have even said that myself in the past .( usually before I try to build something ) :P
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15 Oct 2020 10:59 #186182 by Mike_Eitel
Are you driving the motors with higher amperage than they are defined?
Are you aware that you might drive them into magnetic nonliniarity, means you just force them to heat-up more.
Generaly with permanent magnets: Don't know the correct point, but pushing to much current into a magnet can demagnetize permanently. Fx.: Connecting a dc motor directly with a low impedance source with too high voltage... Killed on the first occasion..

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15 Oct 2020 11:58 #186186 by rodw

Are you driving the motors with higher amperage than they are defined?
Are you aware that you might drive them into magnetic nonliniarity, means you just force them to heat-up more.
Generaly with permanent magnets: Don't know the correct point, but pushing to much current into a magnet can demagnetize permanently. Fx.: Connecting a dc motor directly with a low impedance source with too high voltage... Killed on the first occasion..


Yeh, thats OK. They are industrial quality motors, not a cheap and nasty Chinese stepper. The Nema 34's are rated for 7 amps and I don't drive them past 6 amps. But the voltage is pretty hot! Some other motors I looked at could be overdriven by their specs but their torque specs did not suit the application. I have some 2 amp Sanyo Denki Nema 24's which are amazing and I don't give them their full 2 amps either. They in particular are an amazing motor. I run them with a 3 amp driver with the same voltage and features. I did manage to drive them with acceleration of 8 m/sec/sec but I backed them off to 5 m/s/s to be the same as the NEMA34's

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15 Oct 2020 12:06 #186187 by rodw

yeh a huge project to get that far. There is an insane amount of engineering behind the motor selection


true . But It does give you a whole new level of appreciation of what it really takes to design and build tools.
It's always hilarious to hear people who have never done anything intricate say " oh it can't be that hard."
And yes I have even said that myself in the past .( usually before I try to build something ) :P


Yeh I designed and built this table fro scratch (about 5 to 8 times) and it took me 3 months to make the z axis in my spare time! But boy did I gain some confidence in machining after that!

I started playing with an engineer in the US who spent about 3 months building an engineering model and I scoped 100's of motors to validate the model before settling on what I used. He found a lot of errors in the published mathematical models so it was a hard slog for both of us! One day we might sell a table or controller package based on "the model" but I would not hold your breath. The Covid lockdown did not last long enough!

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