All these parts are controlled by the GEAR button!

(1) delete everything but the hinge rotator and cockpit

(2) grab a block or something to attach the gear to

(3) stick the hinge on the bottom

(4) get a fuselage and make it .25 by .25 by 1.0 and stick it to the hinge

(5) grab a shock and attach it to the bottom of the small fuselage

(6) get one more fuselage and make it .25 by .25 by .25 and stick it to the bottom of the shock

(7) grab a resizable wheel and attach it to the tiny fuselage

(8) Go into XML and set disableAircraftCollisions to True on the hinge rotator, the two smallest fuselages, the wheel and the shock

(9) copy the wheel to the other side

(10) go into the nudging tool scroll down and change the button from selected parts to connected parts

(11) select the hinge and nudge it up about this high

if you have any questions please ask me in the comments!