Unlike Cycles Render mode, BGE has no Rigid Body Constraints in the physics panel. I can add hinges/etc but no physical motor force to move them. I believe the logic blocks allow you to, however it only allows translational motor servo for location OR simple motion where it rotates buuut teleports instead of passing coordinates in between. (edit, no it doesn't teleport)
The simple way is to use the "angular velocity" field of the simple motion brick. But that doesn't give you any angular-speed ramp-up the way things in the normal world work.
Another way is to use torques, and to set the rotational damping in the physics really really high. This gives you the required ramp up, but also affects how the object responds to impacts.
The normal solution I use is to code it. This can either be done by directly applying torques to the object (ie the KX_GameObject.applyTorque() function), or it can be done by creating a constraint and setting the various parameters. As you are making a game, I highly suggest learning python - it really will make things significantly easier.