Building Avionic System

[jetsman97]

Hey guys,
I am a team leader of Avionics for my University's new Rocket Club. We are planning on launching a rocket with a helix solid fuel grain hybrid engine that our propulsion team is building. I am in charge of the Avionic System and have a few questions regarding the battery.

The rocket is supposed to reach a height of 1km and have a maximum acceleration of 5G. The system we are building is meant to be used for:

• ignition (heating a resistor surrounded by flammable chemicals)
• parachute deployment (sending a signal to a parachute deployment mechanism designed by the structure team)
• record video of the flight an save it onto an SD card
• transmit to ground station via a telemetry device data captured from sensors such as:
  • velocity
  • acceleration
  • pitch/roll/yaw
  • flight path
  • temperature
  • pressure

We believe a lithium-ion battery should be enough to power the system since there are no motors needed to power rotating fins or anything of that nature. We want to combine all of our components via a PCB. My question is, if all the part require a different voltage:

1. How can I know which battery to get?
2. Will a single battery be able to power a whole circuit board?
3. Do I need to ensure every component operates at the same voltage?
4. What parameters should I be looking at in order to decide on the voltage of battery to get?

Thanks!!

 

[user 30299]

Hey guys,
I am a team leader of Avionics for my University's new Rocket Club. We are planning on launching a rocket with a helix solid fuel grain hybrid engine that our propulsion team is building. I am in charge of the Avionic System and have a few questions regarding the battery.

The rocket is supposed to reach a height of 1km and have a maximum acceleration of 5G. The system we are building is meant to be used for:

• ignition (heating a resistor surrounded by flammable chemicals)
• parachute deployment (sending a signal to a parachute deployment mechanism designed by the structure team)
• record video of the flight an save it onto an SD card
• transmit to ground station via a telemetry device data captured from sensors such as:
  • velocity
  • acceleration
  • pitch/roll/yaw
  • flight path
  • temperature
  • pressure

We believe a lithium-ion battery should be enough to power the system since there are no motors needed to power rotating fins or anything of that nature. We want to combine all of our components via a PCB. My question is, if all the part require a different voltage:

1. How can I know which battery to get?
2. Will a single battery be able to power a whole circuit board?
3. Do I need to ensure every component operates at the same voltage?
4. What parameters should I be looking at in order to decide on the voltage of battery to get?

Thanks!!

Have you selected the components for each of the conditions?

Also do you have a drawing that shows a proposed layout of the components?

I don't know if anyone can help you without that most basic information - unless they
share with you a setup that they already have on the bench or in a rocket.

 

[Steve Shannon]

Hey guys,
I am a team leader of Avionics for my University's new Rocket Club. We are planning on launching a rocket with a helix solid fuel grain hybrid engine that our propulsion team is building. I am in charge of the Avionic System and have a few questions regarding the battery.

The rocket is supposed to reach a height of 1km and have a maximum acceleration of 5G. The system we are building is meant to be used for:

• ignition (heating a resistor surrounded by flammable chemicals)
• parachute deployment (sending a signal to a parachute deployment mechanism designed by the structure team)
• record video of the flight an save it onto an SD card
• transmit to ground station via a telemetry device data captured from sensors such as:
  • velocity
  • acceleration
  • pitch/roll/yaw
  • flight path
  • temperature
  • pressure

We believe a lithium-ion battery should be enough to power the system since there are no motors needed to power rotating fins or anything of that nature. We want to combine all of our components via a PCB. My question is, if all the part require a different voltage:

1. How can I know which battery to get?
2. Will a single battery be able to power a whole circuit board?
3. Do I need to ensure every component operates at the same voltage?
4. What parameters should I be looking at in order to decide on the voltage of battery to get?

Thanks!!

Given the low altitude goal I would assume this is intended to be a single stage rocket. As such you need to be aware that ignition of the rocket motor must be controlled by the LCO at whatever launch you intend to fly your rocket. And it’s done quite simply by connecting two wires to an igniter that isn’t inserted in the motor until the rocket is on the pad and pointed away from all people.
Instead, your self contained avionics might serve as a circuit that has the ability to inhibit the ignition circuit unless all internal systems check out.
Also, the single most important function of any on-board avionics is that which controls parachute deployment. It should really be separate from anything else that could cause a failure. In fact, in larger rockets it’s customary (and even sometimes mandatory) that function be provided redundantly.
As far as your questions regarding which battery, etc, you will need to add up all the loads to determine the total load and you’ll need to understand how long you need to provide the voltage and current needed to support that load. It’s pretty straightforward math. A single battery certainly could, but consider reliability; is it wise to use a single battery?
As far as your question about how you’ll know which battery to get, that points to you doing a bunch of research to determine the types of batteries that are available, what their characteristics are, and what their voltages and capacities are. There are lots of different kinds. I would start by reading the threads here which discuss such things.

 

[waltr]

Steve Shannon has very good points and questions.

-Anytime there needs a high current source for igniter, etc a separate battery for this is recommended. Reason is if the load pulls the battery Voltage too low and it is power other circuits (processor) that circuit could reset or stop working.

- WHY send all the data down on Telemetry??? I think it is better to simply store ALL the data on board in FLASH or SD Card then download after recovery.

-Telemetry can be use to obtain real time system and rocket status. Send down Altitude, Drogue/main chute deployment, Descent rate under chutes (tells you the chute properly deployed). Battery Voltage, and other status info.

- Video can/should be a separate sub-system. Use a commercially available camera then mods for use in a rocket.

-You gave acceleration and altitude goals but nothing about size and weight of rocket. Or what the motor's average thrust will be. What is the Size and Weight allowed for your payload? These should be the specs that drive the payload design constraints.

- LiIon or LiPo will both work. You will need to determine what Voltage is required by the electronic which will tell you how many cells in series you will need. Then you will need to determine what the current draw of the systems and for how long to calculate what capacity (Amp-Hours) is needed.

-Sensors...
What sensor does Velocity? Three ways I know of:
Pitot tube, Integrate Accelerometer, Differentiate Altitude. Each has pluses and minuses.

Pitch, roll, yaw. Best way is integrating a GYRO sensor. Study the sensor carefully since these tend to have big offsets and long term drift.

Temperature: will this be internal circuit temperature, then one could use the thermometer build into the Barometric sensor. Or external temperature, then needs a probe to the outside air.

Flight path: This is very difficult and there is NO one sensor to do this. There are some IMU's available BUT these are all for Ground based robots that use Earth's gravity vector as a reference. A rocket in flight has NO Earth gravity reference therefore requires fusion of multiple sensors, properly calibrated using different algorithms than earth based systems, This is best left for Post-flight analysis.

Since it is only going to 1km (3274 feet) the entire flight will be visible. Therefore the sensor/telemetry is not needed to asses real time time status. Your eye ball will do it.

Final: Reliable Recover is a MUST, therefore best to keep recovery electronics separate and ideally redundant to ensure safe recovery. NAR statistics of rocket flights shows that 70% of failures is due to recovery systems, chute not deploying, become tangled, or parts break.

Hope this gives you good questions to take back to the Avionics committee

 

[jderimig]

We believe a lithium-ion battery should be enough to power the system since there are no motors needed to power rotating fins or anything of that nature. We want to combine all of our components via a PCB. My question is, if all the part require a different voltage:

1. How can I know which battery to get?
2. Will a single battery be able to power a whole circuit board?
3. Do I need to ensure every component operates at the same voltage?
4. What parameters should I be looking at in order to decide on the voltage of battery to get?

Thanks!!

Answers not in asking order.
3. No but its definitely easier to design if they do. If they dont you will need different voltage regulators for each component voltage requirement and level shifters if you want the components to communicate with each other. So you want all the components to work at their rated Vcc levels, nowadays most common is 3.3v.
2. Yes
4. The minimum battery voltage needs to be higher than the voltage regulator voltage + the voltage regulator drop out voltage + any voltage drop of your polarity protection circuit + allowance for battery voltage drop due to discharge and internal battery resistance. But not too much higher or you will needlessly throw away energy in your voltage regulator and heat it up.
3. Determine the current consumption of your pcb, multiply that by how long you want the battery to last to determine the Ah rating needed for your battery.

 

[cerving]

Look at the spec sheets for the components that you are using in your avionics package, add any losses in the circuitry (they probably will only be significant in the power supply), and that will give you a rough idea of your current draw. After you actually build the circuit, use a recording DVM to gauge the current through the various functions of your avionics to get the actual (vs. predicted) current draw. Then, size your battery accordingly for the amount of time that you think you'll have it on. Basic Electronic Design 101...

 

[user 30299]

Steve Shannon has very good points and questions.

-Anytime there needs a high current source for igniter, etc a separate battery for this is recommended. Reason is if the load pulls the battery Voltage too low and it is power other circuits (processor) that circuit could reset or stop working.

- WHY send all the data down on Telemetry??? I think it is better to simply store ALL the data on board in FLASH or SD Card then download after recovery.

-Telemetry can be use to obtain real time system and rocket status. Send down Altitude, Drogue/main chute deployment, Descent rate under chutes (tells you the chute properly deployed). Battery Voltage, and other status info.

- Video can/should be a separate sub-system. Use a commercially available camera then mods for use in a rocket.

-You gave acceleration and altitude goals but nothing about size and weight of rocket. Or what the motor's average thrust will be. What is the Size and Weight allowed for your payload? These should be the specs that drive the payload design constraints.

- LiIon or LiPo will both work. You will need to determine what Voltage is required by the electronic which will tell you how many cells in series you will need. Then you will need to determine what the current draw of the systems and for how long to calculate what capacity (Amp-Hours) is needed.

-Sensors...
What sensor does Velocity? Three ways I know of:
Pitot tube, Integrate Accelerometer, Differentiate Altitude. Each has pluses and minuses.

Pitch, roll, yaw. Best way is integrating a GYRO sensor. Study the sensor carefully since these tend to have big offsets and long term drift.

Temperature: will this be internal circuit temperature, then one could use the thermometer build into the Barometric sensor. Or external temperature, then needs a probe to the outside air.

Flight path: This is very difficult and there is NO one sensor to do this. There are some IMU's available BUT these are all for Ground based robots that use Earth's gravity vector as a reference. A rocket in flight has NO Earth gravity reference therefore requires fusion of multiple sensors, properly calibrated using different algorithms than earth based systems, This is best left for Post-flight analysis.

Since it is only going to 1km (3274 feet) the entire flight will be visible. Therefore the sensor/telemetry is not needed to asses real time time status. Your eye ball will do it.

Final: Reliable Recover is a MUST, therefore best to keep recovery electronics separate and ideally redundant to ensure safe recovery. NAR statistics of rocket flights shows that 70% of failures is due to recovery systems, chute not deploying, become tangled, or parts break.

Hope this gives you good questions to take back to the Avionics committee

Some of their conditions almost makes it sound like the team is in a competition - or it's a Capstone project. I'm working with a
university team, in a competition, where they have to send the rocket's telemetry info to a base unit during the launch, along with
pictures once the payload touches down. They have the added challenge that only lithium ion batteries can be used in the rocket
and payload.

 

[Rob Campbell]

First, you need to work out your power budget. What functions are your avionics systems going to perform. Once you have the functions, do market research to estimate voltage and amperage required to operate. Then determine how long the system will be on. This will determine the capacity of the battery you need. As you select components and subsystems, refine the power budget. Once refined, selecting the battery should be straightforward.

 

[gldknght]

Something else that you mentioned, but no one else has commented on..."a helix solid fuel grain hybrid engine that our propulsion team is building." Is this a commercial motor, or one you are completely building from scratch?

If it is not a commercial motor, you must have at least one member of your launch team be certified TRA level 2. And you must do your launch at a TRA sponsored launch. NAR does not allow experimental or "homebuilt" motors.

Here https://www.tripoli.org/Certification is where you can find the certification process.

 

[Titan II]

If it is not a commercial motor, you must have at least one member of your launch team be certified TRA level 2. And you must do your launch at a TRA sponsored launch. NAR does not allow experimental or "homebuilt" motors.

This only applies if you launch under the TRA umbrella. There is a vast amout of rocketry going on that has absolutly nothing to do with TRA or NRA.

 

[cerving]

Yup. Take a trip out to FAR sometime... there are some individuals and schools doing some pretty amazing work.

 

[BigDeal4]

Hey guys,
I am a team leader of Avionics for my University's new Rocket Club. We are planning on launching a rocket with a helix solid fuel grain hybrid engine that our propulsion team is building. I am in charge of the Avionic System and have a few questions regarding the battery.

The rocket is supposed to reach a height of 1km and have a maximum acceleration of 5G. The system we are building is meant to be used for:

• ignition (heating a resistor surrounded by flammable chemicals)
• parachute deployment (sending a signal to a parachute deployment mechanism designed by the structure team)
• record video of the flight an save it onto an SD card
• transmit to ground station via a telemetry device data captured from sensors such as:
  • velocity
  • acceleration
  • pitch/roll/yaw
  • flight path
  • temperature
  • pressure

We believe a lithium-ion battery should be enough to power the system since there are no motors needed to power rotating fins or anything of that nature. We want to combine all of our components via a PCB. My question is, if all the part require a different voltage:

1. How can I know which battery to get?
2. Will a single battery be able to power a whole circuit board?
3. Do I need to ensure every component operates at the same voltage?
4. What parameters should I be looking at in order to decide on the voltage of battery to get?

Thanks!!

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