What battery do I need if I want to power a PixHawk as my flight computer?

jetsman97

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I'm on a rocketry team at my university and I was told we're looking into using a PixHawk with Ardupilot as our flight computer. We are building a hybrid engine and from our calculations, we expect a burn time of 5 seconds and a maximum altitude of about 1050 meters. The lithium-ion battery should have a capacity of at least 5Wh and hopefully be under 50 grams. How do I know what voltage and current I need? I tried looking on the PixHawk website but couldn't find this exact information. Thanks!!
 

waltr

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Did you read the Manual?
If you still have questions I'd suggest to contact them directly.

Battery Capacity requirement will depend on what the Pichawk draws and what all other devices connected also draw.
Capacity is typically in units of A-Hrs for batteries. W-Hr can be used but one must consider the dropping Voltage of the battery as it discharges.
You also need to consider the total timer the unit is powered on. This includes the Launch setup, flight and the recovery )this can be hours if flight is not nominal).

Seems you also need to study power requirements, basic electronic engineering. I say it this way since you are at University and there to learn.
Quick overview---
Current is DRAWN from a source (Battery) by the LOAD.
Voltage is Supplied by the Source.

I quick look at the Pichawk schematics (on their web site) indicates it requies 5V Regulated source. The Manual indicates the Pichawk's power comes through a power module.
 

jetsman97

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Did you read the Manual?
If you still have questions I'd suggest to contact them directly.

Battery Capacity requirement will depend on what the Pichawk draws and what all other devices connected also draw.
Capacity is typically in units of A-Hrs for batteries. W-Hr can be used but one must consider the dropping Voltage of the battery as it discharges.
You also need to consider the total timer the unit is powered on. This includes the Launch setup, flight and the recovery )this can be hours if flight is not nominal).

Seems you also need to study power requirements, basic electronic engineering. I say it this way since you are at University and there to learn.
Quick overview---
Current is DRAWN from a source (Battery) by the LOAD.
Voltage is Supplied by the Source.

I quick look at the Pichawk schematics (on their web site) indicates it requies 5V Regulated source. The Manual indicates the Pichawk's power comes through a power module.
I did. Is it possible to use a power module on a lithium ion battery? The manual only discusses attaching a LIPO battery from what I've seen.
 

OverTheTop

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Normally flight computers like the pixhawk run on a dc supply provided by a BEC, battery eliminator circuit. For higher currents, when big servos are used for example, SBECs are used as they dissipate less power. Switchmode BEC.

The output of those is usually 5v.

Input can be anything up to the rating of the BEC. 2s to 4s is typical, some even higher.

Have a look on www.hobbyking.com for examples.

If you are running Ardupilot you might want to consider running LUA scripts so you can customise features for rocketry. For that I think you need a FC with 2MB of flash memory to store the firmware.
 

Titan II

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I did. Is it possible to use a power module on a lithium ion battery? The manual only discusses attaching a LIPO battery from what I've seen.

The manual clearly discusses the use of LiIon:

 

waltr

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Yes, the Manual does discuss LiPo and LiIo batteries.

That is why I asked if you read the manual. Diagrams clearly show the Battery connected to the power module (or BEC) to power the Pichawk module with 5V.

Another thing I noticed when reading the Manual...
They assume that the main battery will be powering the MOTORS to Fly a Copter or Airplane. Motors require a lot of power therefore the battery must be Large (lots of A-Hrs) to get any reasonable amount of flight time. The Pichawk then draws very little current in comparison to the motors and is not speced since the motors wil determine length of time the batteries are good for not the Pichawk.

If you want just enough battery capacity to run the pichawk then you will need to actually measure its current draw (then add some as a safety factor). My guess is the pichaw may draw between 100 and 500mA at 5V without anything else connected. If servos are connected then the current draw of the servos in 'stall' must be considered.
 

G_T

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And don't forget to derate your battery capacity based on potential temperature range.
 
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