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So the PID auto-tune is usually performed while every other system on the printer is idle.

What about the cooling capacity of the filament? Simple.

When performing the PID auto-tune, simply manually extrude filament (with the knob on the ez-struder) at what might be your maximum rate. Depending on your ambient temperature, the filament itself can be cooling the nozzle to some extent. Factoring this in to the auto tune will provide higher sustained temperatures while at maximum extrusion ("flow") rates.

Thanks for the tip!
It is one of those why didn't I think of that!

I've been thinking about this too, great solution!

Could this be baked into the PID routine in the firmware somehow?

I think this would solve or help my clogging on larger prints that I try to run a little faster. I've done large prints over 10" tall and the quality of the filament extruder keeps getting worse going up. It gets smaller and crunchy.

The PID needs to be stable under all conditions, even when not extruding. You don't want the temperature to oscillate when you're printing slow or something.

On the other hand the PID autotune is very conservative. I have found that you can at least double the values it comes up with for the P and I terms. I usually hand tune starting with the Ziegler-Nichols method and then tweak from there.
http://en.wikipedia.org/wiki/Ziegler%E2 ... ols_method

Oh the third hand, I have been playing with the dead-time control. It works a lot better for things that have a lot of phase lag, like the bed. The hot end I'm still playing with it, maybe it's better maybe not.

I invariably end up tweaking the PID values by hand, the autotune does not do a very good job for high powered heaters like the 40W cartridge a lot of people use.

Bot does have a point. If it is going to oscillate under conditions it was not tuned for, then I would much rather it oscillates while I am not printing. So using Ziegler-Nichols method during slow extrusion may be a better approach. Or one could run tests with no extrusion and maximum extrusion and use the feedrate as a modifier for the pid control parameters. A smith predictor could be applied or even a disturbance observer. Which would also help with nozzle cooling due to air flow.

If I remembrr correctly people were discussing tuning the pid while the nozzle was close to the build surface to simulate the effects of the fans.

If the PID is tuned properly it shouldn't oscillate under any condition I get less than 1C oscillation whether extruding at 100 mm/s or sitting idle.

Yeah, if you extrude too fast while doing the pid, you'll get about a 2-3 degree fluctuation only when the printer is not extruding. When it is extruding the temperature fluctuates by 1-2 degrees around the target. Previously my printer was falling ten degree short of the target. Doesn't hurt to try. Takes no time at all.

I honestly think that people should try out the dead-time heat manager . It doesn't take ANY calibration (well, it takes a 30 second "calibration" if you can even call it that) and it works GREAT. It is SUPER EASY to set up as well. I get <2 degree fluctuations when just sitting there and <1-2 degrees when extruding and printing. I have my bed setup with the dead-time manager as well and it's within .5 degrees at all times and NEVER overshoots as it did with PID management.

After some testing my printing temps are basically 100% stable. less than 1 degree of fluctuation while printing. Now to install those layer fans...

How do I set the PID to work both with layer fans and without?

Pid should be able to compensate for that. Especially with the I component.

But you could re tune it while the fan is on. And have 2 pid values. (Which you would have to switch manually unless you are willing to rewrite part of the software.)

bot wrote:After some testing my printing temps are basically 100% stable. less than 1 degree of fluctuation while printing. Now to install those layer fans...

How do I set the PID to work both with layer fans and without?

Depends how many and how powerful, for the most part it shouldn't be an issue but if your heater block isn't insulated, it can sometimes require messing with the I value.
I run a 40mm squirrel cage fan and I don't have to touch my PID settings to run with the fan on or off, and the fan is powerful enough that at 100% my 40W heater cartridge can't get the temperature over 230.