No robot is complete without lights and eyes....
This is a pan/tilt assembly for the Martian rover (http://www.thingiverse.com/thing:1318414). Repbaza kindly put a mounting for a standard servo, so it seems rude not to use it.
This needs two standard size servos (it's designed for Futaba s3003) although mine were bought cheaply on E-Bay and are slightly larger than the official dimensions so I suspect that they may be fakes. Any standard servo should fit through. You want one with a maximum 90deg rotation angle.
The holes are splined for a Futaba servo but you can change the spline in FreeCAD for other servos if you wish. It's hard to print the spline shaft accurately enough for a perfect fit so I've printed it 0.1mm too large and use a bit of bicycle inner tube repair rubber around the spline to make a (very) tight fit.
It has mounting holes for five standard 5mm LEDs. I've used three white and two red and use a 4-channel sequencer (http://www.ebay.co.uk/itm/231693026897) to drive them via a few diodes and resistors.
Printed in ABS. Most of it isn't that tricky apart from the spline shafts - hence the 0.1mm resolution.
Original is included in case you want to adjust it. The upper servo has been "padded out" with a larger top to match the dimensions of mine.