# COMMUNITY : FORUMS : TECH

## Gs to Speed Converstion

I am looking for the math equation that converts G load to speed using Arduino (https://www.adafruit.com/products/2796)?  I am building a high power rocket data logger/controller. I need to know the speed by using accelerate of the bird. Yes I might be able to use GPS info, but at super sonic speed GPS can not keep track of the speed. The bird is a 2 stage bird. I want to stage when about 40% of the speed has bleed off.

Thanks

Rocket Nut

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Kiteman3 months ago

Assuming constant acceleration and straight-line flight...

v = u+at

Final velocity = initial velocity + (acceleration*time)

Initial velocity = zero, so...

v = at

"a" = acceleration in m/s/s

1g = 9.81m/s/s

So, v = (number of Gs) * 9.81 * (time of flight in seconds)

See:

https://en.wikipedia.org/wiki/Equations_of_motion#...

Rocket Nut (author)  Kiteman3 months ago
Thanks I think that will work.
3 months ago

It better, or my students are in deep trouble... LOL

Rocket Nut (author)  Kiteman3 months ago

I was looking over your equation, I might see a problem tho. What happens when the booster burns out and the G load drops to zero, then the "v" drops to zero (v = 0 * 9.81 * (time of flight in seconds). So how do I know when the 40% speed reduction has been activated, and fire next stage?

3 months ago

That's why I said "assuming constant acceleration"!

I've asked somebody with more rocketry knowledge than me to have a look - we'll see if he's able when time zones catch up.

Rocket Nut (author)  Rocket Nut3 months ago

May be I should mention what Accelorometer I plan to use. It's from Adafruit (https://www.adafruit.com/products/1231).