3-4 Design basic stock-parts Rocker-bogie Chassis

Mechanical engineering is not a strong suit of mine, so I thought to start off with it would make sense to build the first prototype of porter bot as a stock parts bot, with no custom parts.  The basic structure of the rocker bogie suspension was familiar to me from seeing some other projects posted on the web (here and here).  I knew I wanted to design the bot in a 3D drawing or CAD program.  After investigating some possible offerings, like SketchUp and SolidWorks, I settled on an open-source animation and modeling software package called Blender.  It was free, had wide community support, and had some integrations with a physics engine called Bullet Physics.  Eventually I want to simulate the porter bot in different physical environments to facilitate unit testing before going commercial, so that was a big selling point for me.  Blender is not ideally suited for CAD modeling since it's aimed more at animation or game development tasks, but I thought it had a very good tool-set for being free and was far easier to install and manage than other open source modeling packages I've tried like Rhino. 

After deciding on Blender, I had to figure out where to get robot stock parts.  There are surprisingly few robotics parts vendors online; I ended up relying on McMaster Carr for general parts, Lynxmotion (now part of Robotshop) and their Servo Erector set, and ServoCity for the actual Hi-tec servos.  I decided not to do a hardcore engineering analysis for the first prototype, but happened on a very helpful paper sponsored by the South Korean government that did a theoretical study on the best configuration for a rocker bogie suspension.  I used their general recommendations and then used my best estimate of the dimensions of each of the stock parts online to design the robot in Blender.  

Porterbot version 1.0

After ordering all the parts based off my Blender design, the total came to around $700 (not including the cost of the i.mx53 android brain), which is a lot steeper than I expected.  I don't think the costs are intrinsically that high (after talking to some roboticists with more experience than me), so hopefully I can build the basic chassis and suspension for half that cost when I start looking at putting porter bot into full production.  Stay tuned for details in the coming weeks as I start to make Porterbot version 1.0 a reality.