FAN: Kick start fan when the increase is more than 50%

[jschuh]

Large increases in fan speed can suffer from acceleration lag, so this
change kick starts the fan for a change of 50% or more in the same way
that starting the fan from 0% does.

Signed-off-by: Justin Schuh code@justinschuh.com

[KevinOConnor]

Thanks. In general it looks fine to me. Could you elaborate on the "acceleration lag"? What are the adverse effects a user experiences when fan acceleration lag occurs?

-Kevin

[jschuh]

I would describe the artifact as a more pronounced seam on the print. That stated, I really only encounter it when using this patch I wrote for Prusa Slicer. The scenario is using a very low fan speed for interior perimeters and infill (e.g. 10%), combined with a higher fan speed for the exterior perimeters (e.g. 70%). There's a range where the fan doesn't seem to spin up fast enough as it starts the outer perimeter. I noticed that I didn't see this artifact when the fan switched from being off entirely, so I made this change and it appeared to resolve the problem I was seeing.

Not too scientific, I know, but I figured I'd post the patch and see if it was useful for anyone else.

[JohnEdwa]

The master build of Cura also has a similar "Infill fan speed" option, and I'd suspect it'll eventually make its way to the main build too, as it's been shown to increase layer adhesion and part strength.
I've noticed the same issue and something like this would help get the fan going faster.

[KevinOConnor]

Makes sense. Thanks.

-Kevin