Boardcomputer for rocket

Hey you guys,

I am making a model rocket and to make things a bit more interesting I want to build a small board computer which does the following:

IMU with accelerometer and gyro for telemetry
GPS
SD data logging
Transmission of the gps data for localizing the landed rocket
deploy parachute via servo and barometric altitude determination

Now a couple of questions:

1.) Can you point me to source where I can learn how to combine the accelerometer and gyro data?
2.) I want to split the workload and have one arduino handling the IMU and the other pretty much the rest. What do you think of that and how can I have the two arduinos communicate with one another when I am using the I2C connection for the sensors?
3.) Can you recommend some hardware for transmitting the gps data reliably over long distances?
4.) I am planning on using aluminum on some structural parts of the rocket - is there a possibility to use those parts as an antenna?

Thank you for your answers in advance! (=

  1. RTIMUlib for Arduino Of course, no IMU will work with the rocket engine firing, or in free fall.
  2. You could use SPI for interprocessor communications
  3. Define long distance. GSM or satellite modem
  4. Perhaps, it depends on the design

Thank you for your answer (=

1.) Why shouldn't an IMU work when firing? sure, the readings will be influenced by the vibrations but other than that it should work fine.
2.) Sounds good - I will look into it!
3.) well 3-5km would be nice just for peace of mind

Hobbyist assembly build quality and rocket launch vibrations, G shock and T shock sound to me like a bad combination.
It is not that it can't be done - the VT fuse was in production in time to get a lot of hits in WWII. It is that the type of work involved in getting joints to not break is boring stuff which took a lot of people a lot of tries to get reliable.

Before doing any work on your main project, I'd test whether the build quality and solder joints which you can make are sufficient for a basic arduino LED flasher to go up, return to earth, and still work after that. Not unless you can launch an arduino to altitude and return it safely to earth without the battery falling off and comparable inconveniences can you even contemplate an instrumented flight.

3-5km is 9000 to 16000 feet which is definitely not kosher with the civil aviation people. Check the rules for hobby rocket launches in your region.

A weather balloon might get your altitude at lower cost and better reliability than a rocket, with more ascent time to collect data points, and without destructive shock and vibration. See the flying deckchair episode of Mythbusters series I.

Why shouldn't an IMU work when firing? sure, the readings will be influenced by the vibrations but other than that it should work fine.

An IMU contains an accelerometer, which measures acceleration due to gravity, the rocket engine and that due to any other forces on it, such as air resistance. See Launching our products! - News - SparkFun Electronics

IMU operation assumes that the measured acceleration is that due to gravity only.

ad2049q:
3-5km is 9000 to 16000 feet which is definitely not kosher with the civil aviation people. Check the rules for hobby rocket launches in your region.
series I.

Is this for finding it afterwards or altitude of 3 Km.

Be aware that commercial GPS will shut down above 600 MPH.i

ad2049q:
Hobbyist assembly build quality and rocket launch vibrations, G shock and T shock sound to me like a bad combination.

Before doing any work on your main project, I'd test whether the build quality and solder joints which you can make are sufficient for a basic arduino LED flasher to go up, return to earth, and still work after that. Not unless you can launch an arduino to altitude and return it safely to earth without the battery falling off and comparable inconveniences can you even contemplate an instrumented flight.

3-5km is 9000 to 16000 feet which is definitely not kosher with the civil aviation people. Check the rules for hobby rocket launches in your region.

A weather balloon might get your altitude at lower cost and better reliability than a rocket, with more ascent time to collect data points, and without destructive shock and vibration. See the flying deckchair episode of Mythbusters series I.

Thank you for your great answer!
The test you suggested sounds like a great idea!

The GPS is for recovering the rocket. I don't want to go up that high but want to make sure that I can find it afterwards. I am aware of the regulations of my country.

I am interested in rocketry so I will stick to rockets but thanks for the suggestion (=

jremington:
An IMU contains an accelerometer, which measures acceleration due to gravity, the rocket engine and that due to any other forces on it, such as air resistance. See Launching our products! - News - SparkFun Electronics

IMU operation assumes that the measured acceleration is that due to gravity only.

As far as I know a accelerometer measures the acceleration along the three axis. when you then comine this the overal acceleration (R^2 = accX^2 + accY^2 + accZ^2) you can figure out the angles with sin and cos. I mean ideally(^^) the vector of acceleration is parallel to the one of gravity. Isn't this correct?

Boardburner2:
Is this for finding it afterwards or altitude of 3 Km.

Be aware that commercial GPS will shut down above 600 MPH.i

No, just 3km radius around the launchpad.
Yeah I have heard of this. Will the GPS automatically reset itself when the rocket travels below that speed? Otherwise I can issue a reset command when I deploy the parachute with the baromter.

I mean ideally(^^) the vector of acceleration is parallel to the one of gravity.

Why should it be, and what do you do if it is not?

MarkGoingToSpace:
The GPS is for recovering the rocket.

If there is mobile phone coverage i would suggest this is the way to go to retrieve the GPS information.

Be aware of the accuracy limitations though.

If your Rocket lands in tall grass it is possible to get within a few feet and miss it.

A recovery beacon, (Blink sketch for night) or a bleeper helps here.

I lost a quadcopter in a field, waiting until nightfall with a blinking LED found it easily.

MarkGoingToSpace:
3.) Can you recommend some hardware for transmitting the gps data reliably over long distances?

You need to use LoRa.

How much ground (search) range you get depends a great deal on the actual terain, but in practical real world tests I have found LoRa will give around 10 times the distance of previous generation FSK radio modules.

Tracking in flight is not an issue, if you use the appropriate GPS. I dont speciufically know of examples with LoRa used to track rockets, but when tracking high altitude balloons, LoRa has a range of circa 400km @ 10mW

srnet:
You need to use LoRa.

How much ground (search) range you get depends a great deal on the actual terain, but in practical real world tests I have found LoRa will give around 10 times the distance of previous generation FSK radio modules.

Tracking in flight is not an issue, if you use the appropriate GPS. I dont speciufically know of examples with LoRa used to track rockets, but when tracking high altitude balloons, LoRa has a range of circa 400km @ 10mW

Which LoRa? When I last looked there were a lot of OEM modules and nothing that looked easy to hook into an Arduino.

Hi,

Of course, no IMU will work with the rocket engine firing, or in free fall.

An IMU contains an accelerometer, which measures acceleration due to gravity,

IMU operation assumes that the measured acceleration is that due to gravity only.

An inertial measurement unit (IMU) is an electronic device that measures and reports a body's specific force, angular rate, and sometimes the magnetic field surrounding the body, using a combination of accelerometers and gyroscopes, sometimes also magnetometers.

The IMU does not assume gravity, it measures the acceleration force that is applied to it, gravity is one of the accelerations, rocket acceleration ,free fall and the sudden stop are all accelerations.

We as the data users ASSUME gravity and add or subtract the phenomenon.

So ALL through the flight all measurements will be valid.

Tom... :slight_smile:

The IMU does not assume gravity

Perhaps there is some confusion about the term IMU. Most hobbyists use an IMU nowadays to estimate body orientation.

The algorithms used to deduce orientation from an accelerometer and gyro combination assume that gravity is the only acceleration present, when including the contribution from the accelerometer data. Here is a good introduction to the theory of attitude estimation.

This method does not work when any other significant accelerations are present. That includes the radial accelerations present when the device is spinning, in which case the gyro is absolutely required. The method does not work in a rocket, either while the engine is firing, or when in free fall.

Of course, it may be of interest to use an accelerometer/gyro combination to measure the rocket engine acceleration, or spin of the rocket body. However an accelerometer used for attitude orientation would probably not be useful to measure rocket acceleration.

The military spend £!!!!!!!! on designing guidance systems for rockets - I doubt if it can be easily done for
a few quid

regards

Allan.

MorganS:
Which LoRa? When I last looked there were a lot of OEM modules and nothing that looked easy to hook into an Arduino.

There are a few LoRa modules out there, and most are easy enough to run with an Arduino. The LoRa RF device is SPI based and in general a lot easier to configure and drive than some of the previous FSK type modules.

You could build a complete working tracker and receiver with DRF1278F, Arduino Pro Mini, GPS, battery and some wire, no other components required. For resiliance however, surviving launch and landing for instance, a PCB is highly recommended.

Take a look at this link;

Easy Build LoRa Tracker

srnet:
There are a few LoRa modules out there, and most are easy enough to run with an Arduino. The LoRa RF device is SPI based and in general a lot easier to configure and drive than some of the previous FSK type modules.

You could build a complete working tracker and receiver with DRF1278F, Arduino Pro Mini, GPS, battery and some wire, no other components required. For resiliance however, surviving launch and landing for instance, a PCB is highly recommended.

Take a look at this link;

Easy Build LoRa Tracker

That looks very promising! Thank you for your help!

jremington:
Perhaps there is some confusion about the term IMU. Most hobbyists use an IMU nowadays to estimate body orientation.

The algorithms used to deduce orientation from an accelerometer and gyro combination assume that gravity is the only acceleration present, when including the contribution from the accelerometer data. Here is a good introduction to the theory of attitude estimation.

This method does not work when any other significant accelerations are present. That includes the radial accelerations present when the device is spinning, in which case the gyro is absolutely required. The method does not work in a rocket, either while the engine is firing, or when in free fall.

Of course, it may be of interest to use an accelerometer/gyro combination to measure the rocket engine acceleration, or spin of the rocket body. However an accelerometer used for attitude orientation would probably not be useful to measure rocket acceleration.

Would it then maybe work if I decoupled the accelerometer during firing? I don't care too much about the data from the free fall. But the firing would be really interesting.

How to real rockets figure out their attitude? Not in detail but what principle do they use?

Hi,

How to real rockets figure out their attitude? Not in detail but what principle do they use?

This may help, Amy talks quick, its loaded with info, the important bit the

And some grassroots stuff.

Tom.. :slight_smile:

allanhurst:
The military spend £!!!!!!!! on designing guidance systems for rockets - I doubt if it can be easily done for
a few quid

regards

Allan.

No but they can be purchased ready made.

MarkGoingToSpace:
How to real rockets figure out their attitude? Not in detail but what principle do they use?

Radio/radar telemetry from ground stations.

Older ICBM use star sghitings for guidance, Do not know about altitude though.

TomGeorge:
Hi,
This may help, Amy talks quick, its loaded with info, the important bit the

Why Does a Rocket Need to Roll Going Into Orbit? - YouTube

And some grassroots stuff.

How a gyroscope guides a rocket - YouTube

Tom.. :slight_smile:

Yes indeed very helpful (=
Bbbuuuuutttt... an IMU consists of a Gyro and a Accelerometer. As far I know the acceleromter is needed to compensate for the gyro's drift. So I don't really see why an IMU would work here. Could someone please enlighten me?

Boardburner2:
Radio/radar telemetry from ground stations.

I highly doubt that this is enough. Especially looking at the selflanding first stages from spaceX^^