Construction

I found that JavaScript was too slow to run even one motor at full speed, 50 rpm. I needed a new language that was compiled rather than interpreted. I chose Python. It was fast enough to run all three motors at full speed and much more.My program was able to run the stepper motors at full step and half step. I was happy to get the motors to half step because that meant that I would have better precision movements of my robot. The bigger breadboard was too big to fit in the robot so I chose to use 4 smaller breadboards that I attached together in a square. This allowed the wires from the bottom of the breadboard to be fed up through the hole in the middle of the breadboards and the wiring was very compact.

Designing the Frame

To make the frame I first designed it on the computer using SketchUp and Omnigraffle. Then, to test out the design, I cut the pieces out of cardboard and hot glued them together. I bought some screws to attach the cardboard pieces together. Since one robot was going to be inside the ball and one on top, the wheel and motor assembly had to be positioned perpendicular to the surfaces of the ball. I did not know the correct angle ahead of time and could not measure it until I had made a frame and installed the wheels. I decided to allow the wheels to tilt into whatever position they needed to make good contact with the ball. Allowing the motors to tilt also allows the robot to drive on level surfaces for testing. After I had settled on a design that I liked, I chose the material I would use to make the final robot. I wanted to see all of the wire and motors so I used .093” sheets of acrylic to build the frame. I stuck the template onto the acrylic with a glue stick. Then, I cut the pieces out on the bandsaw and drilled the holes.  

    Frame Template PDF

Assembling the Frame

When all of the parts were cut out, I had to glue them together. I used Loctite 2 part plastic glue. This glue melts the plastic and fuses the 2 pieces together. Once the pieces were glued, I attached the separate pieces of the frame together with the screws.

Once the frame was assembled I attached the motors. I attached the wheels and then it was time to measure the angle the wheels had to be at to make good contact with the inside and outside of the ball. I marked the positions of the screws and drilled the holes.

The next step in assembly was to attach the electronics. I put colored hubcaps on the wheels and used those colors throughout my robot. The blue motor wire had blue shrink tubing, was attached to the blue breadboard, and had wires going up to the BeagleBone Black that were kept together with more blue tubing. I did the same process for all of the motors and carefully wired up the robot. The colors allowed me to quickly find and fix any electrical problems and they helped with programming. I attached the BeagleBone Black onto the top of the robot with foam tape.

Batteries

I was almost done with the frame of the robot. All that I needed were batteries to power the motors and the BeagleBone Black separately. The BeagleBone Black only needs 5 volts and 1 amp, so I chose to use a cellphone charger with the same dimensions of the BeagleBone Black. The batteries for the motors were harder to find. I first went to Batteries Plus to see if they had any 6 - 12 volt batteries that could supply 1 amp, had around 2 amp-hours of capacity, and that could fit in the tiny space in the bottom of my robot. It was then that I realized that I should have designed the robot with the batteries in mind. I ended up trying CR123 batteries that are used in cameras. They are 3 volts and with 3 batteries in series and 2 groups of the 3 in series wired in parallel, I figured that they would give me the right amount of power and run time. I tested out many configurations of the batteries to try to fit them in the robot. I ended up putting a battery pack containing 2 batteries in parallel in each of the 3 sides of the robot. I then wired the 3 battery packs in series to give 9.7 volts and 1 amp.

The batteries did not have the run time I wanted so I needed a new plan. I bought 2 USB battery packs used for charging cell phones. They delivered 5 volts at 1 amp and claimed to have 2600 milliamp-hours. I thought that these batteries would be great. They should power the robot for around 2 hours and they were pretty inexpensive. I found out that they do not have 2600 milliamp-hours as they only lasted about half an hour in the robot. I bought 4 of them, 2 for each robot and when I got them 2 could not hold a charge and were totally dead. It turns out they were not very high quality batteries. I bought 2 more expensive batteries and am hoping they last longer. I also decided to power the robot from a wall adapter that delivered 9 volts and could supply 2.5 amps, plenty for the motors.

Building BB-8's Body

Now that I had the robot part done, I needed the ball for the robots to go into and to balance on. My first idea was to cover a playground ball with paper maché 1 inch thick on all sides. I planned to cut the ball in half and think of some way to make the two halves lock together, and then come apart when twisted, in order to remove the robot. After the first layer of paper maché, I realized that this plan would take far too long. I remembered a video I had watched about a different person making a BB-8 robot. He mentioned that he used a hollow styrofoam ball that came in 2 parts that locked together. This was a very good idea and much faster than the paper maché plan so, I decided to order some styrofoam balls online. I turns out that very few of these balls are made in the U.S., so I had to order a 50 cm diameter ball from the U.K. The head is also a sphere so, I ordered a smaller 30 cm diameter ball as well. I wanted to paint the designs on the ball to make my robot look like the droid in the Star Wars Episode VII trailer. I decided that gesso, a paste that is typically brushed onto canvases to prepare them for paint, would help the paint stick to the styrofoam and provide a little protection to the ball. I applied two coats of gesso and let them properly dry. I made the designs on the ball and the head using templates I found online and the video of BB-8 on stage at the Anaheim Star Wars Celebration. I traced the outlines of the shapes onto the ball and then painted the surface. I used acrylic paint and mixed the colors to match BB-8 as closely as possible. I dipped a Lego piece in paint and used it for the circles around the ball. I made the eye piece from a plastic Christmas ornament painted black.

Artwork Template PDF