The Telemetrum is an all-in-one flight computer manufactured by Altus Metrum. It acts as a dual-deploy altimeter, GPS tracker, and data transmitter.
- Recording altimeter
- Supports dual deployment
- 70cm ham-band transceiver for telemetry downlink
- Barometric pressure sensor good to 100k feet MSL
- 1-axis 200-g accelerometer for motor characterization
- On-board, integrated GPS receiver
- On-board non-volatile memory for flight data storage
- USB for power, configuration, and data recovery
- Integrated support for LiPo rechargeable batteries
The Telemetrum has four key elements for operation. These elements correspond to the three sets of wire terminals, plus the battery plug:
- BATTERY: This plug is for a dedicated lithium polymer battery. It is sized for typical consumer batteries that are usually used for drones and other hobby electronics.
NOTE: The positive and negative terminals of the battery plug on the Telemetrum are opposite from typical hobby battery connectors. Make sure to check the connector on the intended battery and switch the wires around if they are incorrectly oriented. Failure to do so may result in hardware damage.
- SWITCH: Terminals for attaching a power switch. This allows the Telemetrum to be turned on and off. The Telemetrum will not power on if it does not have a switch (or a closed loop of wire for testing purposes) wired into these terminals, regardless of whether there is a battery attached.
- DROGUE: Terminals for attaching the e-match wires for drogue parachute separation. The e-match attached to these terminals will fire at apogee by default, or after a specified delay that can be changed in the settings.
- MAIN: Terminals for attaching the e-match wires for main parachute separation. The e-match attached to these terminals will fire at a specific altitude that can be programmed in the settings.
The Telemetrum functions both as a dual-deploy altimeter and a data transmitter. These two functions will be detailed below.
When the Telemetrum is powered on, it will sound a series of beeps. The full meaning of these beeps can be found in the manual, but the correct series is as follows:
- Series of beeps indicating battery voltage in decivolts
- Either "dit dit" (idle mode) or "dit dah dah dit" (pad mode) depending on the context of the power on state
- "Dit dit dit" (repeating) indicating continuity on both the drogue and main ignitors
It is imperative that settings and continuity are double checked using these beeps both before the vehicle is brought to the pad and after the vehicle is set up on the pad. Failure to do so may result in premature deployment or failure to deploy, which can cause harm to the vehicle and/or personnel on the ground.
The Telemetrum has a built in 7-inch antenna to establish a communication link with a dedicated ground station. This antenna operates at around 433 MHz, so the ground station antenna must operate at the same frequency range.
While on the pad, the Telemetrum will begin transmitting its data to the ground station. Throughout the flight, it will continue to do so (assuming it has power). At different stages of the flight, the real-time data shown on the ground station will vary:
- LAUNCH PAD: The Telemetrum is waiting to detect a launch event. Ground Station data includes battery and ignitor voltages, on-board data logging confirmation, and GPS information.
- ASCENT: This includes the Boost and Coast states, during which the rocket motor is firing, and after motor burnout, respectively. Ground Station data includes current and maximum height and speed, latitude and longitude, and ignitor voltages.
- DESCENT: This includes the Drogue and Main states, during which the vehicle is descending under the drogue and main parachutes, respectively. Ground Station data includes speed, height, elevation, range, bearing, ground distance, latitude and longitude, and ignitor voltages.
- LANDED: The final stage of the flight, once the vehicle has fully come back to the ground. Ground Station data includes bearing, ground distance, latitude and longitude, and maximum height, speed, and acceleration.
In addition to its real-time flight data transmission, the Telemetrum records a plethora of flight data to its own onboard storage. This can be used post-flight to analyze flight characteristics in detail. A more detailed description of these functions can be found on the AltOS page, but some basic functions are briefly listed below:
- Table View: A list of many relevant flight statistics can be viewed in a table. This table can also be viewed during the flight if desired.
- Flight Graph: Many different types of flight data can be graphed with respect to time in order to view characteristics of the flight as a whole and make correlations at certain key points in the flight.
- Map: AltOS can use the recorded GPS information to map the flight path over a sattelite image of the launch site. Additionally, the GPS data can be exported to Google Earth to view the flight path in 3D.
When powered on into Idle mode, the Telemetrum can be used for ground testing separation charges. Typical altimeters require a convoluted process involving using a vacuum or something similar to simulate a pressure change that would trigger the separation charge. The Telemetrum simplifies this process by enabling remote triggering using the ground station antenna. Once a link is made, the separation charge can be safely triggered at a distance when ground testing. This increases the efficiency of the testing process.