I have auto bed tramming working on our Rumba. I used the most recent stock Marlin firmware. It has sections for the Rumba and all the latest toys. I only had to edit Config.h and all is good.

Enable ABL, measure and set offsets, set servo angles. I have the servo plugged into the bottom left three pins of EXP3. CHANGE PIN OUT ON SERVO CONNECTOR or you will cook something. Just move the ground to the middle pin and +5 is on the bottom.

I think auto bed tramming is almost necessary with a wooden Y bed that is 300mm square. That is not going to stay where you want it for very long. Mine is warped after only a few weeks of printing.

swirvbox