Sketchyphysics for Google Sketchup
I have seen that many users on LMR use google's free sketchup design software to get a rough overview of the appearance of the complete robot. Did you know though that with the assistance of a plugin it is possible to make these robots "come alive" and be controlled.
Sketchyphysics is a free plugin created for google sketchup that incorporates the newton physics engine to sketchup. The plugin will only recognise grouped objects but includes options to set the engine to recognise that object as a sphere, a box, a convex hull and so on or also the option of not recognising it at all but wheres the fun in that. 2 boxes can also be grouped together the go on and create an L shape otherwise not possible to be recognised by the engine.
Joints can be grouped to an object which can then be connected to another object to allow them to interact. Joints include: Motor, servo, slider, piston, hinge, spring, corkscrew, gyro, ball, universal and fixed. By making a simple box and then taking 4 cylinders each grouped with a hinge you can then set the hinges to be connected to the box and get a small trolley that can be pushed along. alternatively you could attach a motor and make a motorised trolley.
This basically means that you could make each individual component such as a leg or wheel of your robot into a group which you should be doing anyway and then just add the sketchyphysics joints and the robot will be able to move around. Unfortunately IR sensors and such are not possible so it is not a suitable bed for testing code although it does support control of motors or other similar powered joints by either: onscreen click and drag sliders, keyboard, wired versions of xbox 360 gamepads (ps3 has limited support) or by a specialised form of ruby code. Ruby code may be used to execute some behaviours of your robot.
The most recent version can be found for download on this page: http://sketchyphysics.wikia.com/wiki/SketchyPhysicsWiki
And also many examples of existing models of varying quality can be found under: http://sketchup.google.com/3dwarehouse/search?q=sketchyphysics&styp=m&btnG=Search&scoring=d