About two years ago I motorized a Bruder toys Mercedes Unimog in 1:16 scale and equipped it with (Atmel AVR-based) IR remote control. Because the Bruder chassis front axle did not have steering (fixed front axle), I constructed an steering front axle using aluminium profiles (see last photo).
Now, with a reprap printer available I constructed the front axle again in openscad and printed it. It has an adjustable tie rod (vitamin, non printed) and is controlled by a micro servo at the front (see photos). The axle can steer and tilt. The construction principle is just a basic Achsschenkellenkung (German), I believe in English it is called Ackermann- or A-steering.
I reused the vitamins from the old aluminium profile axle, particularly the ball couplings for the tie rod and the servo connector.
Update 2013-09-20: The servo connector arm broke after a few days of operation. I have made the connector thicker and removed the inner connector bar and replaced it with a hull from the servo attachment point to the axle arm, thereby hopefully eliminating any notch stress. (see updated scad and stl files)
The scad code is commented and mostly parametric.
The frontaxle_complete* files show all parts combined.
The following parts need to be printed: _body, _armright, _armleft and _servoconnector. The arms need to be printed upside down, so the arms for the tie rod are at the print bed. The arms left and right are modelled with a support column which is cut off after printing. If you want to print with the support your slicer offers, you can disable the support in the scad file.
The servo connector is attached to the underside of either the left or the right axle arm by both the M3 bolt used for steering the arm and an additional 3mm alignment hole. I have simply glued a short length of 3mm filemant through the servo connectors alignment hole into the the axle arms alignment hole for fixing the servo connector to the arm.
The Vitamins should be obvious from the photos. All bolts and nuts are M3. The arms have both a nut trap on the inside, use a nyloc nut to fit the wheel axle there.