The main mechanical function of our BB-8 was to get a small robot to drive within a sphere. We built a bottom heavy robot inside of a spherical shell to mimic the functionality of BB-8.
Creating the Sphere
Making the Ball Openable
Fabricating a sphere that is smooth inside & out is hard enough, but building it such that we could easily access the robot inside made it even more challenging. Our team decided to short cut the main fabrication portion by repurposing a 13" hamster ball. Hamster balls are meant to be assembled and then only opened from a small door so we had to make some modifications so that it could open and close in a way that let us access our robot. We cut off the flares on the tabs that locked the ball in place and then drilled holes where they used to be to put screws through.
Smoothing the Inside
Unfortunately, the inside of a hamster ball is also rather uneven. Our robot often got stuck inside the ball trying to overcome the bumps with the small 38mm omni wheels. We first attempted to smooth out the bumps by adding some duct tape. We quickly realized that did not do as much as we hoped. We then tried adding pipe cleaners underneath the duct tape on either side of the bump to create a more gradual slope when approaching stiff edges. This immediately improved the performance of our robot. In addition to adding pipe cleaners and duct tape, we also filled the inside of our ball with epoxy. Epoxy is harder to get as an even coating so we had to be very careful about the way we applied and smoothed it.
Building the Chassis
Chassis Design
Our chassis was designed to have no overlapping parts so that each piece would be easily accessible. This wound up coming in quite handy when our motor shield burst into flames. Not only could we quickly replace the Arduino, we were also able to easily rewire our batteries to send less power, which caused the fire in the first place. We also added a geometric dome to enclose our electronics. This was meant to protect our circuit or give it a bit of cushioning in case our robot flipped over in our ball. Since our chassis did not have any overlapping parts, this meant that we could still easily access our batteries to remove and charge them. They were purposefully kept separate and accessible so that we could house our electronics.
Recyclable
Our chassis is fully recyclable using only metal, and MDF. We laser cut our chassis out of MDF and sheet metal bent all of our mounts. We used the plasma cutter to cut our some of the larger holes and shapes. Our Arduino mount had flares that were challenging to bend because they required 2 bends very close to each other. To over come this, we used blacksmithing techniques and bent our metal with an “anvil” and hammer.
Future Steps
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Add a head that stays on top
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Find a more rigid ball or more flexible epoxy
Unfortunately, the hamster ball was rather flexible while the epoxy was not. This meant as the ball would flex, the epoxy would crack. This would leave weird epoxy flakes on the inside of our ball that began to gunk up our wheels.
- Redesign the motor mounts so that the wheels have a larger point of contact with the ball
Right now, each wheel connects to the sphere on only one point. Angling the wheels will give more points of contact for a smoother driving experience.
CAD Models
This hexagonal chassis has a mount in the center for placing the Arduino and three edges on the bottom for mounting motors. The motors and batteries are mounted on the bottom of the chassis. Images of the modeled chassis and its components are shown below.
