A Tensegrity Micro Quadcopter

 

Is this the world's smallest tensegrity quadcopter?

It uses a HubSan X4 quadcopter with a carbon rod tensegrity frame around it so as to be as light as possible. In order to make this I had to go through several evolutions and spreadsheets of component weights in order to find a combination of materials and techniques that would be light enough to fly. My first evolution was completely 3d printed with larger elastic bands, which proved much too heavy. After that, I tried 20cm carbon rods and settled on 3d printed end caps to hold smaller elastic bands, which I had to cut and tie together to make them long enough to work.

My original idea was to mount the motors directly to the carbon sticks in order to reduce weight and also to de-couple the flight controller sensors from the motor vibrations. This was my main idea behind this build. I thought that separating the flight controller from the motors and not having them on a rigid frame would greatly reduce the vibration noise from the motors and props and lead to a better flight characteristic. However, my first attempt with the motors attached to the sticks was both too heavy and also led me to believe that the layout has some inherent problems. As the motors are in pairs on separate sticks, they were moving independently of each other. These were only small movements, based on the amount of flex in the tensioned tensegrity frame, but it's enough to cause control problems. I noticed online that another similar project also had problems in this regard [Roman Fedorenko Medium link].

In addition to the vibration issue, the main reasons for building tensegrity drones is that the frame is crash resistant and they can also change their shape by changing the tension in the wires in order to squeeze through smaller gaps [Morphing Drones link]. NASA even tested the idea for landing spacecraft on other planets [NASA Super Ball Bot link].

My main interest was in seeing how it would fly, which is shown in the video - badly! The problem is the elastic bands, which are causing it to vibrate. Also, there's a lot of mass in places that the flight controller isn't expecting, so it acts like a pendulum. If you're wondering why it doesn't look like a regular icosahedron in the video, then that was because it had already hit the wall a few times before I managed to learn to fly it so that it stayed in front of the camera in the limited space.

This was my first attempt at a tensegrity drone, but I'm going to try and evolve this design a bit more before I release any of the build files for it. I'm still experimenting with the 3d printed clips that hold it together. If you look carefully, there are only three clips holding the orange quadcopter frame to the black carbon sticks. The 3d printing on the fourth one broke in half when I tried to attach it, so I ended up tying the back right corner to the frame with cotton thread. Also, the bands need replacing with tensioned threads to remove the vibrations coming from the elastic. I'm just in the process of working out how to tension it all at the moment, so things are going to change a lot in the next evolution.

Hopefully, I should get this working and flying well soon, at which point I will publish an article on how to make your own one.