We have recently found remote-controlled micro-quadcopters, so light that you can use them inside without risk, even in an office environment. Some models are even equipped with a camera, allowing you to fly in FPV (First Person View). If you like learning new things, it's ideal to lighten the rainy days that we have been having early this year.
You can imagine several ways to detect an object that rapidly goes through a gate. We were looking for something easy to implement, robust, not too expensive, and which didn't require to add anything to the quadcopter, in order not to weigh it down.
The small quadcopter that we want to detect in flight
A first idea is to use a Yocto-RangeFinder, which is a priori able to detect the flying object easily at a distance of 50cm. But if we want to multiply the connected gantries, the budget becomes consequent. Moreover, there is also a risk that the detector doesn't notice a quadcopter that flies too fast.
We therefore decided to take advantage of a characteristic common to all quadcopters: they are carried by the air they blow down and you can easily detect this air flow. We have therefore built a simple racing gate with cardboard, with a small seesaw at the bottom. This seesaw swings when a quadcopter goes through and this is detected by a simple Yocto-Proximity, cheap and robust to light changes.
The working principle of our connected racing gate
Our gate is 3cm thick, which enables us to easily fix it almost anywhere, for example with magnets. It's a simple cutting in a cardboard sheet, folded and glued. The seesaw is also made of two pieces of cardboard, mounted together, with a carbon rod as axel and another one as stop. If you don't have carbon rods handy, sewing pins will do as well. The hardware budget is therefore minimal. The Yocto-Proximity mounted on the side very easily detects the seesaw lever: the measured proximity value is of 130 when the seesaw is idle and the beam reflects on the opposite cardboard side, and goes down to 30 when the seesaw is triggered. We simply put a threshold at 80, with a hysteresis of 10.
To avoid detecting the quadcopter twice, because of the seesaw bounce due to the successive passage of two propeller pairs, we modified the standard firmware of the Yocto-Proximity by adding a debounce setting, enabling it to ignore state changes of a duration below a given threshold. This new feature is already available.
The new configuration parameters of the Yocto-Proximity
For a small DIY accessible to everyone, the result is rather convincing. You can download the cutting file here. To your remote controls !
Quadcopter detection, in slow motion