AUSROC 2.5 Throttle Valve Controllers

Lunar Numbat is group of Australian (and New Zealander) engineers and technologists (and space geeks) developing innovative mission-critical technology as a partner to White Label Space, and in the process aiming to lower the barrier to entry to Space Science by using and developing Open-Source technologies and inexpensive hardware combined with our skill and expertise.

Over the last few months, one of the development tasks being undertaken by the Lunar Numbat team has been the development of embedded controllers which receive instructions from a flight vehicle’s central computer over a CAN (Controller Area Network) connection and translate these throttle position instructions into signals which control the powerful motors which drive the valves that admit propellant into the rocket engines.

This system has been developed primarily for ASRI‘s AusRoc 2.5 research rocket, however a derivative system may have other applications to other vehicles in the future, such as the descent engine on the White Label Space GLXP lander.

Here’s a picture of some of the fruits of our labors over the past few weeks:

Throttle controller boards

Two of these boards will be used to control the AusRoc 2.5 rocket engine; one controlling the kerosene valve and the other controlling the LOX valve. These boards are based around an Atmel ATmega328 microcontroller, which communicates over CAN through a Microchip MCP2515 CAN transceiver. (At the moment the real linear pots aren’t installed, so a couple of conventional pots are connected for testing.)

The 24 V power supply rail from the main avionics fairing is wired down to the throttle fairing along with the CAN link, and this supplies power to the Rutex motor controller and is regulated down to 5 V to run the interface controller and AVR microcontroller.

These embedded microcontrollers measure the position of the propellant valves through a pair of linear potentiometers attached to the valve assembly and send the appropriate motion control information to a Rutex R2020 motor control board connected to each of the motors, which control the powerful motors through a H-bridge running at 50 volts.

Powerful motors and high-torque gearboxes are required, since we require very reliable, very fast but still carefully controlled opening of a fairly large, heavy metal valve, even when it is under the pressure of a full, pressurized fuel tank… or cryogenic liquid oxygen at 90 K:

One of the propellant valve motor and gearbox assemblies

One of the valves mated with its gearhead assembly:

Motor and gearhead

At this point we need to write the software for the system, assemble the linear potentiometers and their associated mechanical components to measure the absolute position of the valves, and of course perform tests and then some more tests, and hopefully within the coming months we will be starting to integrate this system with ASRI’s rocket engine to perform some cold static testing of propellant flow into the engine.

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