# G's to Velocity ### Help Support The Rocketry Forum: #### RocketNut9

##### Well-Known Member
Does any one have a equation that convert Gs to velocity? I am working on a data logger (logging 10 samples per second) that will record both the Gs and speed (fps) per sample. I been scoring the web but draw a blank.

Thanks:smile:

Rocket Nut

##### Roger Smith
G is a measure of acceleration which is a change in velocity. Acceleration times time equals velocity. If you know the acceleration at points of time you can add the accelerations to determine the velocity.

For example, if the rocket's speed starts at zero and it accelerates at 9.80 meters per second per second (about one G) for one second, its speed will be 9.80 meters per second. If it accelerates at the same rate during the next second, its speed will be 19.6 meters per second.

For your logger, start with a speed of zero and add the acceleration times the length of each time interval to the furrent speed to compute the speed at the end of each interval.

-- Roger

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#### blackbrandt

##### That Darn College Student
You need to take the integral of the G's. Derivative of velocity is acceleration, integral of acceleration is velocity.

#### markkoelsch

##### Well-Known Member
Well, it is initial velocity + the integral of the acceleration.

##### Roger Smith
"Integral," btw, basically means computing the sum of the acceleration times time.

If you were to plot the acceleartion on a simple graph with acceleration as the y axis and time as the x access, you could compute the speed by adding up the area under the curve, similar to how total impulse is the area under the curve of a time-thrust graph.

#### Ravenex

10 samples per second is likely much to slow to accurately integrate in a rocket.

#### RocketNut9

##### Well-Known Member
Thanks for the quick responds.

I was hoping to read the accelerometer, then run it along with time through a equation to get velocity. I guess I will get the speed from the GPS unit.

Again thanks for the info.

Rocket Nut

#### bdureau

##### Well-Known Member
I do not think that reading the GPS would be very precise. I thing that it just measure the distance between 2 points and work the speed out by recording the time it took to reach them.
You will be better off doing it with your barometer assuming that the rocket goes strait and vertical

#### dhbarr

##### Amateur Professional
barometer + accelerometer + Kalman filter = yay, although as previously mentioned 10 samples/sec will be pretty grainy.

#### SpaceManMat

##### Space Nut
You'll want to read the accelerometer as frequently as you can, update your velocity based on it. But then log your accelerometer and calculated velocity at less frequent intervals. This will give you more accurate speed values without your logs getting too big. It's just a matter of taking into account how fast you can sample the accelerometer and do the calculations and how much memory you have for your logs. Don't bother doing unnecessary calculations, just grab the raw data. You can play with the data after you have it downloaded.

#### RocketNut9

##### Well-Known Member
It sound like I bite off more then I chew.:blush:

I don't know how samples per second, because I am going to fire pyros (staging,chute deployment, ETC) based on the data read from the sensors (accelerometer, barometric [alt], GPS). I think I can get 100/sec. The limiting factor in how fast I can read the sensor using I2C serial bus. Then crunch the data after the flight.