Mechanical Systems
We designed two custom PCB boards for each robot. The first board primarily connected the motors to the Roboclaws and provided a bus to the second board which housed the AND-gate, voltage regulator, battery connector, and connections to the Odroid. The design was completed in Eagle, a free PCB board CAD tool. It is used heavily by the hobby and academic community. These boards proved to be very helpful as they significantly cut down on wiring and made constructing a second robot much simpler. It was also quite humorous that they served as fuses a couple times. When a dangerous current spike occurred the thin copper traces connecting the power sources would break, killing the surge. In retrospect, we should have made the voltage source traces larger and also have put in more circuitry to control the voltage from the batteries, which was often a little to large for the motors. Our board files are also available in the repository.
We relied heavily on CAD to design the layout of our physical system. We pretty much 3D modeled every part on our robot in Solidworks. This allowed us to verify everything would fit together before cutting anything and helped us get a visual for what the robot would look like. Doing so also made it convenient to have the laser cutter cut all the hardware/fastener holes so there was a minimum of drilling the plastic tiers. Our 3D files are available in the repository. We discovered GrabCAD was a great resource for finding a couple parts (including the Odroid) that had already been modeled. If you choose to use GrabCAD as a resource, be sure to contribute back to the open source community and upload the parts you model. Solidworks is an excellent choice for 3D modeling as is an industrial standard. The complete robot assembly is listed as robot.SLDASM. All the individual parts can be opened from this assembly view. The three tiers of the robot were fabricated based on these models. The tiers are a 3D part, but the BYU ECEN shop requires a 2D .SVG file. In order to have these laser cut follow the following instructions:
- Open tiers.SLDDRW (this is the 2D drawing file which contains all three tiers)
- Export this Solidworks drawing as an Adobe Illustrator file (.AI)
- Use an online converter to convert from .AI to .SVG
- Ensure there is at least one dimension on the part so that the shop can appropriately scale the .SVG file if the dimensions are not included.
We initially chose to do the typical hexagon shape. However, we soon realized that by going with a half-circle shape we could gain substantially more surface area on the front for controlling the ball. This gave us greater control and was advantageous in sweeping the ball away from opponents.
In retrospect, we could have saved a ton of time if we would have made custom cables for everything so that there would be no mis-wiring or headaches when trying to switch out parts. Custom cables could have been constructed by supergluing breadboard jumper wires together in configurations that matched the socket shapes of the PCB headers, Roboclaw pins, etc.
We ended up with several damaged Roboclaws throughout the course of the semester. It was hard to explain what caused each issue, but it became clear that covering these things to prevent any kind of short would have been a great idea. It would have been awesome to have insulated these things with some sort of wrap or enclosure.
