Nano Rocket #3 : Making Sense of the Acceleration Data

RE: Nano Rocket #3 : Making Sense of the Acceleration Data

DAB — Tue, 12 May 2020 18:42:51 GMT

You have keep the relationships in mind when dealing with acceleration.

You have distance in each dimension, x,y,z.

You have velocity in each dimension, Vx, Vy, Vz

You have acceleration in each dimension Ax, Ay, Az.

Acceleration is the rate at which the velocity changes. So if Ax = 0, that just means you are moving at a constant velocity.

Velocity is the rate of change in distance. So if x1 = x2, then Vx = 0.

When you go from X0 to X1 in a given time interval t, then you get Vx= X2-X1/t. When V goes from 0 to Vx, then Ax = Vx-0/t.

DAB

RE: Nano Rocket #3 : Making Sense of the Acceleration Data

dougw — Tue, 12 May 2020 18:02:05 GMT

Dave is right. NASA uses this concept to "simulate" "zero g" on their vomit comet...

https://www.youtube.com/watch?v=2V9h42yspbo

If you are in free fall, you are accelerating, but don't feel the force of gravity.....until you hit the ground (where you "might" feel the deceleration of the impact...) [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-5c409c60-ccac-4938-a165-bec3cffc5b5c/contentimage_5F00_1.png:16:16]

RE: Nano Rocket #3 : Making Sense of the Acceleration Data

beacon_dave — Tue, 12 May 2020 17:33:14 GMT

"... or the sensor does not detect gravity when in free flight..."

Or rather in free fall there is no measured displacement of the mass within the sensor itself ?

I think some of the confusion might arise from how we look at the acceleration values of the sensor compared to how we look at the acceleration of the object to is attached to that we actually want to measure.

For example the Z axis of the sensor will output:

+1 (or +9.81m/s^2) when stationary the right way up (+ve displacement)

0 when on its side or in free fall (no displacement)

-1 (or -9.81m/s^2) when stationary upside down (-ve displacement)

Whereas when we look at the box on the table we see:

0m/s^2 when it's on the table (box velocity is constant at 0m/s)

+9.81m/s^2 when it is in free fall (box velocity is increasing at a constant rate by 9.81m/s for every second of fall)