Our team at AmadorUAVs has decided on building a smaller quadcopter, mainly for use as a test bench for technologies that will be going on our main drone — such as the autopilot, image recognition, and cargo drop systems. Currently, our club has very little funds so it is impractical to jump straight to the hexacopter we have planned to build for the competition. In addition, if anything goes wrong (which is very plausible), we would not want to risk a $2000 drone getting destroyed. This smaller drone that we are designing will be a great transition step to help all our divisions become familiar with designing, constructing, and programming a drone, making the final production task a lot easier. It would also help greatly in searching for sponsors that could give us funds and propel us forward as a club and a team.
Our mechanical division first started designing the drone in mid-February. We are using the CAD software Onshape to aid us in the design process, mainly because we can collaborate real-time as it is an online software. Our plan for the design of the drone is a very simple, rectangular plate that all electronics attach to from the top/bottom. The arms of the drone are slightly thicker and they extend from the corners of the plate. They are secured on top by screws.
The arms of the drone were subject to many early changes in design. We wanted them as light as possible without sacrificing strength. The final design has an integrated truss, mainly to cut out material and make the arms lighter. One aspect of the arms that provided a lot more strength is the lip around the entire arm. This was taken from iron beams used in construction and prevents bending in the arms. To test the strength of the arms, our team used FEA (Finite Element Analysis). One constraint was that our arm had to fit 7040 propellers while being able to fit on the 3D print bed (215 x 215mm). We had to make a lot of adjustments to arm angle and length until they fit on the bed diagonally. This was one of the most difficult parts of the design.
To manufacture the parts, we plan is to 3D print the center plate and the arms using PLA plastic. This plastic is very inexpensive and quite strong. We also don’t want to waste filament so we plan on doing a 75% gyroid infill on with our arms. We will do 100% infill on the center plate because it is only 3 mm thick.
We are using a 4 cell 5800 mah battery that was left over from our previous airplane project (it ended quite badly). We don't want to spend more on another battery so we will use this one even though it is a little too big.
We are using four Racerstar BR2212 1400KV Brushless motors. These are compact, inexpensive motors. We chose 1400KV because we were prioritizing torque over RPM. We are looking to fit 7040 propellers onto this drone so that we get good control in slow flight.
The ESC we chose is the Turnigy Multistar BLheli_32 ARM 4-in-1 32bit 31A 11g Race Spec ESC. This is a 4 in 1 so it is cheaper and smaller than 4 separate ESCs.
The Raspberry Pi and Navio are on another smaller plate that is on top of the larger one. It is held up by standoffs. The main reason for this is so that we have enough room to put all the other electronics.
We plan on 3D this design and trying to get it in the air by the first week of April. There will be a follow-up post talking about whether this drone was successful or not!
Links for parts :
ESC — https://hobbyking.com/en_us/turnigy-multistar-blheli-32-4-in-1-32bit-31a-11g-race-spec-esc-2-4s.html?countrycode=US&gclid=Cj0KCQjwhuvlBRCeARIsAM720HrHxmZkGSVQeT9lDkxv122XBvK2agKG5JH0nf3yB-rI6de7x1UtsrUaArO2EALw_wcB&gclsrc=aw.ds