Launch Model Rockets Wirelessly with This LoRaWAN-Enabled Controller

Getting a model rocket off the ground

Whether it is a NASA Saturn V, SpaceX Falcon 9, or even a hobbyist's 1:40 scale model, launching rockets into the air is a large challenge due to aerodynamics, weight management, and determining how to do it all safely. Wanting a way launch his model rocket from a distance without the need for running a long pair of wires to a battery, Milos Rasic from element14 Presents designed his own launch control system from scratch that operates wirelessly thanks to LoRaWAN.

Ignition circuit design and verification

Unlike commercial designs that utilize liquid oxygen and kerosene to generate thrust, hobbyist rockets rely on solid-fueled rocket motors that burn either zinc-sulfur, black powder, or a sugar-potassium nitrate mixture, and all of them need a source of ignition to begin combusting- typically a very hot piece of wire.

Although a LiPo battery pack could provide enough current to sufficiently heat the wire, its low voltage and slow charging time made it a less-than-ideal choice, which is why Rasic opted for a pair of super capacitors instead. Run in series, the capacitors are charged via two MOSFETs, which are, in turn, balanced by a set of op-amps to ensure an equal charge between them. One relay in the circuit is responsible for connecting the battery to the charge circuit, while two others either discharge the capacitors in case of an emergency or allow current to flow into the ignition wire for launch.

Assembling the device

After verifying his circuit worked correctly, Rasic soldered all of the components onto perf board and added it into a water resistant box that already had 3D printed gaskets terminals attached to its sides. In order to receive the charge, arm, and launch commands from afar, Rasic integrated an Arduino MKR WAN 1310 board that operates using the LoRaWAN wireless communication protocol. Finally, several LEDs were added to indicate the current status of the system, such as if it is connected, if the capacitors are charged, or if the device is armed.

Adding a wireless controller

An igniter by itself is quite useless without a way to control it, so Rasic quickly moved onto the next step of creating a terminal for the user to interact with. The top panel prominently features a 16x2 LCD screen which is flanked by a key slot to its left and a USB port for programming the other Arduino MKR WAN 1310 to its right. Below are indicator LEDs, a switch for charging/discharging the capacitors, another switch for arming the system, a rotary encoder for selecting menu items on the LCD, and lastly, a large "FIRE" button that ignites the rocket motor.

Rocket and launchpad construction

Both the rocket and its launchpad were designed from the ground-up to be 3D printed, with the latter also containing a metal plate to prevent the plastic underneath from melting. The launchpad's tripod design provides ample stability while the central rod gives the rocket a vertical path upon launch. Further assisting in guiding the rocket are its four fins and precisely modeled nose cone which aid its aerodynamic profile.

Lift-off!

Once Rasic was confident his model rocket would successfully take off into the sky, he brought out the pad, rocket, igniter, and controller into a field and began the charging sequence. One minute later, he flicked up the "Arm" switch and pressed the FIRE button to send his creation flying from a safe distance. To see this project in action, you can watch Rasic's video here on the Element14 Presents YouTube channel.