Hello!
There is very simple to do that!
Open the servo "UI" and insert " rightx " (no quotes) in the controller field.
Namnlös.png
If you want to control the speed (a motor) with up and down arrow, just write " righty " (no quotes).
It's wery simple, and this page is wery helpfull http://sketchyphysics.wikia.com/wiki/Beginner.
/hpnisse