Mechanical Design

Overall Concept

Our overall design consisted of 4 omni-directional wheels, a flywheel shooter, and two bumpers.  The square design for both our bottom and top base were used in order to help our robot square off when it hit the corners.  

Flywheel Shooter

After creating several prototypes for a shooting device, we eventually settled on using a flywheel.  This design was chosen because nearly every variable was manipulable.  The speed of the flywheel could be adjusted via a potentiometer.  The angle that the ball could exit the flywheel could be changed using the corresponding pin-slots.  Furthermore, if LeBot James was shooting too far to the left or right of the hoop, the entire shooting apparatus was also able to rotate and be locked in place.

Bumpers 

Our bumper assembly consisted of two major parts: a bumper (shown above) made from Masonite, and a Pololu Snap Action Switch. The bumper was placed beneath the chassis and extended in front of the omni-wheels.  This location was chosen after several hours of experimentation.  Several problems arose with placing the assembly above the chassis.  These problems include spacial limitations as well as not being able to sturdily mount the Snap Action Switch.  In order to accurately detect that the switch was depressed, it was imperative to have it rigidly connected to the body of our robot.  By having a bumper with a long edge and filleted corners, the robot was able to hit the wall at several locations and accurately detect making contact.  The pin-slot was designed to ensure that the bumper never extended in such a way that our robot out of the 1 cubic foot spatial limitation.

Chassis

Our Chassis was designed to contained 4 omni-directional wheels, each connected to a Jameco HN-GH12-1634T-R 12 Volt Motor.  The motors were connected using laser cut parts that were fit into slots in the chassis.  In order to have enough support for all of the weight that we anticipated our robot having, our chassis was made out of 0.25" duron.  In order to decrease weight in our chassis, holes were cut out using a LaserCAMM.  We used a rigid shaft coupler in order to connect the wheels to the motor shaft.  In order to reduce the bending moment of the long metal shafts, a ball bearing inserted into a mounting plate was later used on the opposite side of the wheel.

Omni-Wheels

The omni-directional wheels were one of our first major design decisions.  Our team decided that having the flexibility to move in all directions would allow us a lot of flexibility in our early design stages.  We later learned that this added some complication to our robot.  Having four motors to drive all the wheels weighed a good amount and having to control 4 wheels instead of 2 often led to confusion and extra troubleshooting.  That being said, our strategy evolved over time and changed considerably from our first iterations.  The wheels served it's purpose in being adaptable to all of these strategies.  

Overall Mechanical Lessons Learned

  1. Plan ahead.  Reserve LaserCAMM machines ahead of time and anticipate many iterations of the design.
  2. Allot several days for integration of all systems.
  3. Design mechanical systems so that they are all manipulable and easily replaceable.
  4. Use materials that will not change over time.  For example, do not rely on the use of rubber bands or tape as their effectiveness may change.  Instead, opt for screws, nuts, bolts, etc.
  5. Try to reduce any friction or bending moments that the motor may need to overcome.  Having a solid chassis that moves without too much power from the motor is necessary before any additional features can be added.