How to measure the distance covered by iphone during free fall?

Question

During a free fall, the iphone should send acceleration values ​​as 0 on all three axes. So how to determine the distance covered by iphone?

Answer 1

Do not trust Newton’s laws, they ignore air resistance, Iphone rotation, etc. Use an empirical approach instead. Let the device fall from several heights, for example, 1 m, 2 m, 5 m, 10 m, 30 m ... Repeat several times for each height. Every fall, time is measured. Estimated spline results. Calculate the inverse function.

Answer 2

The simplest and most naive implementation is to try the accelerometer data and use the following formula.

v+=a*dt; d+=v*dt; 

But it can give a dream over time, read this to explain why the best solution is: http://gafferongames.com/game-physics/integration-basics/

Answer 3

If your accelerometers report a zero value, you will have a problem determining when your movement is complete.

So, determine the braking on impact, then determine the maximum speed at the beginning of the deceleration, then lean back. Assuming linear motion, lack of final speed and air resistance, linear braking (possibly), and that your phone is still working!

Answer 4

From initial start

distance = 0.5 x acceleration x time ²

Gravitational acceleration = 9.81 m / s ²

I'm going to assume that you are not dropping the phone far enough to reach the final speed. If you do this, I doubt that your application will be very useful in restoring the phone :)

Answer 5

Ignoring Air Resistance:

 float t; // time since drop float distance = 9.81f * 0.5f * t * t; 

For greater distance (falling from an airplane), you can also use location services. CLLocation contains height.

Answer 6

One solution that would take into account the issue of wind resistance is to use the difference between the acceleration from gravity and the actual rate of acceleration you are reading,

d ² x / dt ² = g - | a |

Where g = 9.8 and | a | = sqrt (a ₁ ² + a ₂ ² + a ₃ ² ), where a _n are the readings from the accelerometer on each axis.

Then we calculate the differential equation using the Euler method.

You can even be smart and search for the local g value using GPS.

Answer 7

distance = 0.5 * gravityAcceleration * timeOfFall ²

In the simplest form.

We can safely pass friction and wind in the air, taking into account the coefficient and weight of the iPhone, as well as the distances that the hardware will still be useful in the fall .;)

However, if you are in a free fall with the phone before opening the parachute, there are too many factors to calculate in order to reliably calculate the distance based on the accelerometer itself. In any case, this is hardly suitable for such applications, since the readings are very unstable, and its main goal is to determine the orientation of the device or to determine the potential free fall (in the case of laptops that use similar accelerometer chips).

Answer 8

This is very simplified because you have to consider friction in the air. Air friction causes the device to reach “final” speed. Only at final speed does accellerometer indicate 0.

The formulas given here assume a free fall in a vacuum (without friction).

In other words, it’s quite difficult to calculate the distance traveled (one problem is that the final speed depends on the orientation of the phone when it falls).

Answer 9

Also keep in mind that the phone is VERY likely to crash in any form of falling scenario. As the phone profile changes, the drag and drop will change and the accelerometer will NOT read zero.

Answer 10

The accelerometer will read 0 (or g) on ​​all three axes, regardless of whether it is in free fall or sitting on a table. Therefore, the issue is debatable, since there is no way to determine the distance without the assumption of free fall.