After we completed the design of the Buffalo rocket back in 2021, we started to build a launchpad from which it could lift off. This launchpad served us well for multiple years. Yet early in 2023 after completing the design of the Buffalo L rocket, we adapted the launchpad to better suit Buffalo L’s uses.

Physical build

The launchpad is built out of 15mm screen printing plates which were connected by dowels instead of screws to make the launchpad more appealing. For the same reason, all wires are led inside the launchpad.

For the exhaust trench a sewage pipe T-piece with 110 mm diameter was used. One of the connections is led outside, one up to the launch structure, and one is covered by a Plexiglas pane. This transparent panel allows camera shots of the flames and exhaust of the rocket engines.

All other designed parts represented in gray are 3D-printed out of polylactide (PLA).

Leveling screws on the four edges of the launchpad allow for manual adjustments to the launchpad level. Further, two metal hooks at both sides of the launchpad can be used to tighten the launchpad to the ground.

Launch Structure

For the original idea of our hold-down clamp design, we took inspiration from the YouTuber (T-Zero Systems).

All rockets that lift off from this launchpad use an engine cluster. Even though all the electric ignitors are triggered simultaneously, the startup time of the used engines varies by a few milliseconds. This slight variation can result in thrust imbalances at the first few milliseconds of the flight, which would cause the rocket to steer off in an unintentional direction. By clamping the first few ms of the burn-duration we ensure that all engines are up on thrust.

This mechanism works by clamps that hook into the lower body of the rocket and remain attached until the four representative servos are controlled. Control of the servo unlocks the part that prevents the clamp from retracting. The clamp then retracts by the force of a spring.

Controller Enclosure

For easy accessibility, the launchpad computer is mounted to the outside of the launchpad. Consequently, the launch computer must be protected from the engine’s thrust, which is done by this enclosure. The enclosure features air inlets, as well as a perplex pane to be able to view status LEDs.

The wiring of the launchpad is led on the inside to protect it from the environmental conditions and for a neater look.

Launchpad Computer

The Launcher Rev. B is the second launch computer we designed for this launchpad and replaced Launcher Rev. A during the launchpad upgrade works in 2023.

Power Supply

As with most of our controllers, this launch computer is powered by a three-celled LiPo battery, step-down regulates the voltage using a 5V buck converter (LM2596S-5.0) and a 3.3V linear regulator the AP2112K-3.3.

The power-on switch is a rocker switch. Additionally, there’s a arm switch that disconnects the battery voltage from the pyro channels. If this switch is turned off, the pyro channels can not be used. This adds a layer of protection to safely operate next to a launchpad with loaded pyro channels.

Microcontroller

The microcontroller is the ESP32-WROOM-32E-N8, which allows the launch computer to communicate with the flight computer using ESP-now. The microcontroller is programmed via the micro USB port and through the USB-to-UART bridge CP2102.

A voltmeter allows the microcontroller to assess the battery voltage.

Outputs

It is equipped with four servo ports to release the clamps of the launch structure. Additionally, it incorporates two D-class amplifiers the MAX98357, and two speaker outputs for stereo sound. Further, it has a port for an RGB LED strip, and an anemometer input to assess the ground-level wind speed upon flight.

This launch computer features six pyro channels with which the ascent engines of the rockets are ignited. The pyro channel architecture is the same as that of the Buffalo Rev. E flight computer, featuring continuity detection and status LEDs.

Countdown Display

Another output of Launcher Rev. B is this self-designed countdown display PCB. It was designed to improve the readability of the countdown time, as common displays feature way smaller digit sizes.

This PCB features a display with a 0.8-inch digit size and incorporates the TM1637 LED display driver chip for ease of control.

Software

The launch computer cooperates with the flight computer to establish the launch sequence. They communicate with each other via the ESP-now protocol and exchange data.

Before we upgraded our CTS (control and telemetry system) to JM Mission Control (learn more on the Buffalo L project page), the user connected his/her phone to the flight computer via Bluetooth. Via this connection, the user was able to send a launch request. The launch request was then handled by the flight computer and forwarded to the launch computer. The processing of the flight computer’s launch request and the sequencing of the launch pad’s tasks follows this structure:

After transitioning to an RC-controlled launch, the process remains the same, except that the user communicates with the flight computer with the RC controller instead of the phone with Bluetooth.

Video of First Launchpad Version

Project by Johannes Moser

Launchpad