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PID Weirdness

Posted by DaHai8 
PID Weirdness
March 17, 2018 07:32AM
I have a JGAurora A3 and a JGAurora A5 3D Printer.
I just installed a new Thermistor in the A5 as the old one was crapping out.
It's the same type as what I have in the A3 - I bought both thermistors at the same time.
I did a PID autotune afterward on the A5 and got these results:
Kp 37.52
Ki 5.87
Kd 59.94
But on the A3, the PID autotune results were much different:
Kp 22.2
Ki 1.08
Kd 114
So I tried a print on the A5 with the A5 PID results and the nozzle heater was all over the place.
Halfway through, I applied the A3 PID results and this is what happened: The A3 PID results were amazingly smooth (see attached image)

Why did I get such wildly different PID results for the same thermistor and why are the results for the A5 so bad???
open | download - A5 PID v A3 PID - weirdness.png (111.4 KB)
Re: PID Weirdness
March 19, 2018 02:19PM
Don't know why you got different tuning results, but the dirivitive is all about putting the brakes on overshoots, so it makes sense that increasing that value would somoth it out. Might even be able to go up a bit more. Give it a shot.
Re: PID Weirdness
March 20, 2018 09:39AM
Ok, so use the A5 PID results, but set the Kd to what the A3 used, like:
Kp 37.52
Ki 5.87
Kd 114
I'll give it a try.
Re: PID Weirdness
March 22, 2018 03:00AM
I eventually ended up with these settings after doing manual tuning with the hot-end heated up:

Kp 18.5 
Ki 0.8 
Kd 135

The fact that its still very spiky and jumps around seemly randomly makes me thing that I still have a connection issue somewhere.

Thinking along that, I have a 5v fan plugged into the mainboard (MKS GEN L v1.0) near the thermistor connector. Its on a set of pins just marked 5v & Gnd and not part of any bundle. Perhaps that could be sending noise over to the thermistor connection?

Next time I'm poking around inside, I'll disconnect that fan temporarily and see if it helps.
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