Monday, February 4, 2013

Quad Copter Design

My senior design project is to design and build a quad copter frame. The end goal is to build a sturdy enough frame that can withstand impacts and crashes. I will also attempt to make it fly after assembly.

Step 1: Design
Step 2: Materials
Step 3: Building
Step 4: Landing Gear

Github link to all of the SolidWorks files for the quad copter.

Parts List:

The electronics for the quad copter were already predetermined before I picked up the project.

Motor: AeroQuad BP A2217-9
Prop: AeroQuad APC 10x4.7
ESC: HobbyKing FlyFun 30A ESC
ArduPilot 2.5
Battery: Zippy 30C Series 2200mV Battery

Frame: (All from McMaster)
3x 24'x24'x0.125' ABS plastic (3 frames total)
1x box of 1.5" nylon threaded standoffs
1x box of 1.25" nylon threaded standoffs
1x box of .5" 4-40 nylon bolts

Step 1: Design
Many designs were considered. I frequented the forums at for inspiration and design challenges that others faced. I had to make the frame sturdy and modular for components to be added at a later time. Here is some of the early designs that I came up with.

The red quad copter was designed to have the motors on the bottom of the arms, the picture is not upside down. I needed more room for the extra components, like Raspberry Pi (used for processing 3D stereoscopic and sending over wifi; future post?). Out of those three, I liked the 3rd (red) one the best. It had a modular design and offered the most room inside the dome-like roll cage.

For the final design I decided to flip the quad copter around so that the motors are on top of the arms and that the dome is on top. This is to make sure the electronics are not on the front line when the quad crashes or lands hard. The arms were shortened about an inch to reduce weight. The total distance from arm to arm is a little under 2 ft. The Robotics team wants the 2 camera mounted underneath the motors, so I added some mounting holes. I am not sure how much this will effect the motor performance. The cameras will need to be mounted using some kind of dampening material to reduce the vibes from the motors. The batteries are also going to have to be mounted on the bottom of the green circle to lower the center of gravity for stability.

Here is a top down view showing prop clearance.

The 2 yellow and 2 green circles are going to be bolted together to squeeze the slotted pieces together. The blue pieces that create the dome are going to be attached to the arms by a hinge. This is so when the 2 yellow pieces at the top are unbolted, the blue dome pieces can spread apart and the red center piece can physically be taken out to easily work on the electronics. The arms are going to be held together by putting bolts through either side of the threaded standoffs.

Step 2: Materials
I considered a few materials to use for the quad copter, such as carbon fiber, ABS plastic, wood, and aluminum. Wood is really good for vibration dampening and cheap; but it would break too easily on bad landings. Aluminum is too heavy and terrible for vibrations. I almost chose carbon fiber, but my university, University of Cincinnati, does not have a water jet. Getting carbon fiber cut is around $150/hr plus setup fees. ABS was chosen because it is really cheap, light, strong, and I can get it laser cut at my university.

Step 3: Building
The parts were laser cut at my universities design center. Here is some pictures.

Here are some pics of it assembled with motors and a demonstration of the roll cage design.  

The total weight of the quad copter with all of the necessary components and landing gear (not shown above) is 2 lbs 14 oz.

Step 4: Landing Gear
A few different ideas were considered for the landing gear design. The final decision came down to either buying a pre-made landing gear for a large RC helicopter or using foam. The problems with the pre-made landing gear are that they are heavy (up to ~1 lb) and there would have to be an adapter plate that attaches the landing gear to the quad copter. A multi layer foam was chosen for the final design. The multi layer foam is more dense on the top for support and the bottom half is less dense for impact absorption. A slot was also cut out to house the battery.

Here is a video of the last flight before I graduated...

Unfortunately, one of the motors broke in that crash and I wasn't able to get a new one before I left the project :(
The good news is that only some nylon screws broke. The frame was intact with no structural damage!