it wouldn't work along the side wall unless you were able to move the goal to the inside of the playing field while you are moving parallel with the wall picking up balls...
Well...I don't know if you've thought of this but couldn't you grab and/or - hmm.."or" - hold the goal along the side that's parallel to the wheels? This way you can have a grabber on the side perpendicular to your wheels and therefore be able to obtain balls from the railing at the same time that the goal that you're holding on to is facing the inside of the playing field.
