Improve SKR mini E3 + Ender 3 settings

[salami738]

Requirements

Thanks for working on the great Marlin firmware!

Description

The BigTreeTech SKR mini board is used often in Creality Ender 3 printers, because it is a dropin replacement (same size, holes and connectors) for the stock mainboard.
Some of the constants are not optimal for this board.
I made a few improvements based on own tests and the sources from: https://github.com/bigtreetech/BIGTREETECH-SKR-mini-E3/tree/master/firmware/V1.2
The ender 3 uses a 24V heated bed as default, the defaults file uses constants that are not usable for this type of bed (not heating to the target temperature, always 10° below)

Benefits

• more driver current for the TMC2209 drivers (they can handle about 1.5A)
• PID control optimized for stock Ender3 heated bed
• More capabilities of the TMC drivers used (hybris threshold)
• The default Ender3 heated bed is very uneven -> use more probe points
• The used STM32 cpu has plenty of RAM -> use greater buffers

Related Issues

I did not make a issue yet. Should I?

[thisiskeithb]

Keep in mind that you're editing the stock Ender-3 configs located in the BigTreeTech folder, not Ender-3 Pro (the only difference is the status screen).

[salami738]

The pid changes and Hybrid threshold are ok?

[thisiskeithb]

PIDTEMPBED isn’t necessary on the Ender-3 (it uses bang-bang by default).

Enabling hybrid threshold on both E3 mini configs would be a good idea.

[salami738]

PIDTEMPBED

why not make PID the default? bang-bang is worse than PID and PID works well.
hybrid threshold is now enabled for both board versions.

[thinkyhead]

Thanks for your contribution! Unfortunately we can't accept PRs directed at release branches. We make patches to the bugfix branches and only later do we push them out as releases. Please redo this PR starting with the bugfix-2.0.x branch and be careful to target bugfix-2.0.x when resubmitting the PR. It may help to set your fork's default branch to bugfix-2.0.x.

See http://marlinfw.org/docs/development/getting_started_pull_requests.html for full instructions.

[thinkyhead]

It wasn't hard to rebase. To update your working copy use the Git Console and…

git fetch origin
git checkout 2019_fix_ender_defaults
git reset --hard origin/2019_fix_ender_defaults

[salami738]

It wasn't hard to rebase. To update your working copy use the Git Console and…

git fetch origin
git checkout 2019_fix_ender_defaults
git reset --hard origin/2019_fix_ender_defaults

Thanks for the information, I will use that if i have to make a PR again. Thanks for reviewing and merging.