I've been wanting to get into electronics and find a new project. I even bought a 3D printer for whatever it was I was going to build. After watching a lot of YouTube videos of James Bruton (http://xrobots.co.uk) I discovered the BB-8. So I decided that that was challenging enough and that was what I was going to build. I even joined the R2D2 Builder's Club (http://www.astromech.net). I should also probably say that I have no design or electronics experience, I'm a total newb. I'm a software analyst by profession and have been programming most of my life, so that is my only advantage here. All of the work I do here will hopefully become open-source. I wished I could have also made a video log of this on YouTube, but video editing is very time consuming. I may do that for other projects. Well, I'm getting impatient, so lets get started!
The obvious question is how? Word is going around that this is actually done with a holonomic design with a chassis inside the sphere, but we don't know for sure. We, the R2 Builders Club, don't know for sure if this is how the Lucas Film version works, but it seems to be the most practical concept out there considering how it moved on stage. So that means I'm going with a holonomic robot with three omni wheels. The head is probably the most challenging part of the design. I'm not going to write an entire article on how to move BB-8's head because if you're like me you've already read a 100 of those articles. I've decided on a simple idea that gives me a full range of movement and rotation, that being a gimbal system much like what you see in an analog joystick on a game console's controller. That involves three motors. Two are for X and Y axis and a third for rotation. I do not yet have a drawing of this to show you, as this design will be fully planned out later. I just needed a practical idea before I got started with the chassis.
Now that I know how it's going to work it's time to get it down on paper, er I mean screen. For this project I am using Autodesk 123D Design, because everyone else is using it for this kind of work and it's pretty easy to get the hang of (especially since I already have experience with more hard core 3D modeling appplications).
The CAD shown in the picture on the right isn't something I cooked up overnight, it was two months in the making. So as you're reading this now I am probably much further along in the project than I am writing about. What's missing from the CAD right now is the mounts for the Arduino, XBee, and Motor Driver. Also the gimbal to move the head around is not yet designed. Shown in the picture are two mounts for speakers, a mount for two batteries, mounts for three motors, and audio boards (trigger, amp, power distribution). Unfortunately I am limited to a 6" x 6" x 6" build area with my 3D printer so the chassis interior will be 6" in diameter. I still have to break up the chassis into parts as I can't truly print 6" x 6".
Also consider the wheels in the CAD aren't at the right angle to make good contact with the interior of the sphere, that's because this setup is only for testing on flat surfaces. The areas where the motors attach also have extra bolt holes so that I can unbolt the motor and adjust its negative camber. Based on my calculations and testing with 3D models, that needs to be a 33 degree difference. I have been able to test this physically and it seems to be just about right.
For the printer I'm using a Lulzbot Mini. It's my first 3D printer so I'm not trying to go all out, but at the same time I needed something to get the job done. If you want to learn more about this 3D printer, check out the Lulzbot website.
For creating the gcode I'm using Cura which I then send to my Raspberry Pi B+ with Octoprint to start the print without being tethered to my computer. I'm in the process of also adding a camera to that so that I can monitor the print visually as well and maybe even get some timelapse videos without setting up my camcorder.
I hope to keep this updated, so check back with http://www.xeekworx.com/bb8 for more articles as I progress. Initial updates should come pretty quickly since I'm really about 30% into the project already.
The deadline for this project is December 1, 2015 before the Star Wars movie comes out on December 15, 2015.