The Goal

In model rocketry, commonly used means of measuring altitude such as the use of barometers bear the disadvantage that an altitude can only be measured to a reference point. This can result in difficulties during landings on uneven terrain, as the starting altitude is different from the landing altitude.

To that end, a classmate and I (Johannes) worked on the goal of introducing radar technology into model rocketry to create a means of measuring relative altitude during landing sequences. We tackled this goal during our high school graduation project and cooperated with Infineon Technologies and utilized their 77 GHz Pico radar that is commonly used in cars for adaptive cruise control.

Further, we set out to create a rocket capable of parachute landings with which we could test this altitude measuring system.

Such a drop test should happen according to the following procedure:

The rocket automatically detects fall and deploys its airbrakes.
It measures the distance to the ground using radar.
And deploys the landing legs based on the radar’s measurements.

Through more than 700 working hours per person, we developed two rockets (Buffalo Pro and Buffalo Max).

Buffalo Pro

Physical Design

We based our first project prototype on the existing Buffalo rocket. We added landing legs and airbrakes. Further, we upgraded the parachute deployment system.

The goal of Buffalo Pro was to test the airbrakes, the landing legs, and the parachute system.

Landing Legs

Our landing leg design functions as follows: In the deployed state, rubber bands pull together the upper and lower support beams. However, a stopper integrated into the lower support beam prevents them from moving any closer together. This creates a stable configuration.

When an upward force is applied to the landing leg in this position, it attempts to rotate the joint between the two support beams. However, the stopper prevents this rotation, transferring the force to the rocket body instead.

The deployment process is initiated by the force of the rubber bands. These rubber bands rotate the joint from the folded state into the stable deployed position. Initially, another rubber band holds the legs in the folded state inside the rocket body. This holding rubber band is burnt through with a heating wire, allowing the deployment process to start.

Airbrakes

Airbrakes are flaps that fold out of the upper part of the rocket body into a horizontal position. The airbrakes of Buffalo Pro have two functions:

First of all, they provide stability when the rocket is falling, because there are three identical flaps distributed equally around the perimeter of the rocket, resulting in an effect similar to that of fins.

Secondly, they provide a space to mount our radar. This way, the radar is concealed for the ascent, and the aerodynamics are unaffected, but for the fall, the radar can see the ground clearly and get good measurements.

However, ultimately we haven’t installed the radar on this prototype, as our primary focus was testing the landing mechanisms and our fully functional rocket was ready soon enough to install the radar there.

Parachute Deployment System

We optimized the parachute system that I used in the Buffalo rocket to account for Buffalo Pro’s needs. The principle of it is that a sliding plate, which is guided by aluminum rods, pushes the parachute out of the rocket through force provided by springs.

The rods are themselves guided through bearings in the rocket body, and are secured against pulling out by screws. The springs are located around the aluminum rods, completely encasing them. They are tensioned by pushing them down and then securing the sliding plate through a cable tie. If the parachute should be deployed, the flight computer heats up a heating wire, which burns through the cable tie and releases the force of the springs, which then push out the parachute. The laces of the parachute are mounted on the sliding plate, and the parachute opens in the airflow.

Buffalo Rev. D

For the Buffalo Pro rocket, we implemented the existing flight computer, Buffalo Rev. D that we previously used on the Buffalo rocket. As this flight computer previously didn’t have to control the landing mechanism, we had to make several upgrades.

Power supply upgrade

The thrust vector control system for the Buffalo Pro rocket, utilized in the launch and landing attempt, used stronger servo motors than the Buffalo rocket used. In addition, the first versions of the parachute deployment system for the prototype used a servo too. All the servo motors connected to the board use the +5V regulated power supply; therefore, the current drawn from the voltage regulator drastically increased to more than two amps. As the on-board linear voltage regulator (LDO) is only able to provide up to one amp of current under perfect conditions, the on-board voltage regulator had to be bypassed. Now the +5V power supply is provided by an external buck converter that can provide up to three amps of current. Another benefit that is reaped by using a buck converted instead of a linear voltage regulator, is the reduction in power losses

Pyro channel extension

Buffalo revision D has only one pyro channel on board that is normally intended to ignite the rocket’s engine. For this project, a minimum of three pyro channels are needed. One to burn through the rubber band holding back the landing legs, one to burn through the rubber band that pushes the airbrakes to fold into the rocket before their deployment, and one to burn through a cable tie that holds back the slider plate that then pushes out the parachute.

To satisfy this need, an adapter board was soldered that features two additional pyro channels.

Indicator improvement

The flight computer already uses an RGB LED to indicate several flight states and errors that might occur. As the process of soldering this RGB LED to the board is prone to error and the RGB LED’s brightness is inadequate, an external RGB LED board is used instead. This extension board features two LEDs instead of one and thus increases the brightness of the indicator. The soldering process of the external board is also easier, and less prone to errors.

Buffalo Max

Physical Design

Structure

The whole rocket Buffalo Max consists of separate interchangeable modules that are 3D-printed from PLA plastic. This allows us to compose, change, and rotate the modules in the best way possible for a specific application. The modules are held together through three M3 threaded rods that run down the side of Buffalo Max. They are held by three nuts on each end, making assembly and disassembly much easier. Additionally, the rods improve structural rigidity in terms of bending and pressure, which is handy for hard landings. In the following chapters, the different modules shall be discussed.