Flight Computer Power Options

Using Arduino Motors, Mechanics, Power and CNC
1

Hey all, this is my first post so I apologize in advance but this issue has been bugging me for a while.

I'm currently working on implementing flight computer to manage thrust vectoring for a model rocket, but the issue of finding a suitable power source has been giving me a headache. Here is a breakdown of the components I'm using:

Teensy 4.1
MPU6050 Gyro
BME280 Pressure sensor
L7805 Voltage regulator
2x Micro servos (SG90?)

The intended power source for this circuit was typical 9V battery, however, with how often I am updating the postion of the servos (20ms), I believe the current draw is high enough that its causing a voltage drop and the circuit briefly shuts down.

Using 6 AA batteries works well, but this solution is far too heavy for the application. Does anyone know of any suitable power sources that can handle current requirements for the application while not being too heavy? The actual flight time is only a few seconds, so the source does not have to last long.

2

Those are for low power smoke alarms and the like, and can't supply enough current for servos. For servos, you need batteries capable of delivering Amperes (1 A per small servo).

4xAA or 5xAA NiMH would work.

3

Like this?

PP3 WARNING
PP3 WARNING660×810 51.5 KB

Those batteries lack the current capability to be of much use on an Arduino project, especially running motors. Better a lipo cell with a boost converter.

4

Thanks for the quick response.

Even when using 4xAA I still saw occasional shutdowns when I was testing it out, this is what drove me to 6xAA. This is when weight became an issue:

6xAA lithium = ~90g
1x9V lithium = ~34g

Of course the 9V doesn't work so it's a bit of a moot point, but tripling the weight would be a bummer.

The perfect porridge might be to go back to 4xAA and slow down how often I update the servo positions until the shutdown issues are eliminated.

5

Then the batteries you chose can't supply the required current.

It is not a question of battery voltage. With 6xAA you need a step down voltage regulator that must also be rated to easily handle the required current. The L7805 linear regulator can't handle more than 1 Ampere, and it wastes a huge amount of power.

The battery "C rating" is a measure of how much current it can provide. The battery capacity is stated in mAh (typically 2500 mAh for an AA battery). A 1C AA battery can supply 2500 mA or 2.5 Amperes.

6

EE isn't my field so you'll have to bear with me.

I agree that its a current issue, however, if the LM7805 is the bottle neck for my current and not the power source then shouldn't I see the same shutdown issues between 4xAA and 6xAA?

So are you recommending using the 4xAA without the regulator? My only concern with that would be 6V is on the limit for Vin to the teensy 4.1, I could run it through a diode to drop it to 5.3V.

7

4xAA NiMH have a maximum open circuit voltage of 5.6V when freshly charged, 4.8V nominal.

The extremely inefficient, linear 7805 regulator has 2V dropout voltage, which means to deliver 5V, you have to supply it 7V minimum. The 1A current limit is another serious drawback.

EE isn't my field

Clearly, and this is a challenging project, requiring some technical expertise. You have hardly even started with the learning and research needed for a viable design.

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