Rolling Chassis Concepts

Goal

Low fidelity prototype of three chassis designs using laser-cut cardboard, 3d printed parts, bamboo skewers, straws etc...

Must be actual size and have functionality of final design. i.e. wheels must steer, body must articulate, etc. No electronics, just mechanics.

Definition of Chassis: 

"An example of a chassis is the underpart of a motor vehicle, consisting of the frame (on which the body is mounted). If the running gear such as wheels and transmission, and sometimes even the driver's seat, are included, then the assembly is described as a rolling chassis." - Wikipedia

My Project

I was unsure how to approach this project, so I started off by sketching a few chassis variations.  I experimented with two, three, and four wheel chassis.  For three wheels, I could have one wheel in the front, with two driver wheels in the back, or vice versa. A two wheel chassis could have a third object acting as a support (as long as the surface area of the third leg is small, it shouldn't produce enough friction to impede movement).

When designing my chassis in Adobe Illustrator, I made sure to measure the size of my gear motors and Arduino to make sure everything would fit in the final design.

For assembly, I used cake pop sticks as dowels and laser cut all my chassis pieces out of pieces of cardboard.  After gluing and putting together all my parts, I secured the wheels of each chassis with zip ties.

My designs all used differential steering, which is when one wheel would move faster than the other, in order to turn the vehicle.  If the wheels rotate in opposite directions, the vehicle would spin in place.

In the two designs below, the motors would be attached to the wheels in the front and the Arduino would be hidden inside the compartment in the back.

After designing and making three chassis designs, I felt that I could still design a better chassis.  Having four wheels would make it difficult to turn the vehicle, even with differential steering, since the back wheels would resist the turning motion.  Three wheels could work if one of the wheel pivots.

To solve this problem, I looked into caster wheels, which would be able to turn in multiple directions.  Caster marbles turned out to be even better, since there are no constraints on the direction of the marble.  Whichever way the driving wheels (wheels being controlled by the motor) are moving, the marble would follow.  The next chassis I made features two driving wheels in the front and two caster marbles in the back.

I 3D printed marble casters (http://www.thingiverse.com/thing:8959) and inserted marbles.  The print didn't come out perfectly clean, so I had to clean up a bit of the stray filament. 

After assembling all my laser cut pieces, I zip-tied the casters onto the chassis.