This is a simple demo showing how a simulator using Processing can look like with only a few lines of code:
I used something similar for my quadruped robot and was asked how I made it. So today I finally found the time to write a blog post and a small tutorial about it:
http://coretechrobotics.blogspot.com/2015/07/creating-robotics-simulator.html
Basically, you can use Processing and the CAD files of your robot to create a simulation. Then you figure out inverse kinematics, movements, etc and finally copy the code to Arduino. Processig is very similar to Arduino, so it's much easier to learn and there are lots of libraries.
I dont just want to advertise my blog here, I really think it's a shame that so few people are using Processing in their projects.