Marlin 1.1.9 for Robo3D R1+ & Fan speed hotend temp protection

Hello everyone

I recently finished updating my printer to 1.1.9 (decided not to go for 2.0 for now). Since my code is in github I thought it would be nice to share. You can use it at your own risk and/or use the diff to see what I changed to fit my robo

https://github.com/tomerorian/Marlin/

Included in that github repo is my small change to the part cooling fan speed algorithm ported from my previous 1.0 RC6 build (yes yes I was way behind).

The feature makes the fans ramp up slowly to the speed you specify in your slicer instead of just going immediately at the desired speed. In addition (and this is the important part), it checks the hot end's temperature sensor and decreases the fan speed if it drops below a configureable threshold. This lets you have maximum part cooling while avoiding cooling the hot end too much and shutting down the printer.

My dual cooling fans were just cooling way too much when there is a flat surface to reflect the air back at the hot end, this eliminated the need for me to configure a different fan speed depending on the print. been running with 100% fan speed from layer 2 for years now with no problems

The feature is enabled in the repo by default, but is controlled by the FAN_TEMP_SAFE_CHANGE flag in Configuration_adv.

P.S: My build: Robo3D R1+, E3D v6 hotend, dual duct fans, the common LCD and some lighting mods

Enjoy.