by the term "robot" we mean a mechanical device which performs automated tasks, either according to direct human supervision, a pre-defined program or, a set of general guidelines, using artificial intelligence techniques
so do you want simulation tools for the elctronic circuits that you will employ or the mechanical part or what???
Rossum's Playhouse (RP1) an open-source robot simulator
This is a modest, two-dimensional robot simulation intended to aid developers implementing control and navigation logic. It allows applications to build a data-configurable robot which can interact with a simulated landscape or solve a virtual maze". Its written in JAva so its platform independent and has a client server model so the clients ( the robots ) can be written in language of choice.
it already hav some built in robot types like fire fighting, line followin robot