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[on:]

I am a real new newbie.  I am trying to make a distance measuring in the horizontal distance for around 100+ feet.  I am having trouble, because this is to measure the total distance a remote controlled airplane takes to land.
I first thought to use rpms for the wheel rotation on the ground, but sometimes the airplane bounces to land and I need to total distance from the first time it touches down to the point where it stops. 
I then thought to use a combination of a vertical ultrasound and calculate with the code the horizontal distance over time, and rpms once it stops bouncing and a flex button to switch between both, in other words the flex button is pressed and released by the weight of the airplane it would start the ultrasound and when it is pressed and held it will start the rpms.  the only problem with that Idea is that the bounces will not be exactly parabolic or hyperbolic so it makes the computation a little harder.
my next idea is to drop something on the ground at initial touchdown and then when it stops have an ultrasound measure the total distance from the thing that touched down and the airplane, but I don't know of an ultrasound that could go around 100+ ft distance.
I am really only looking for help with my ideas, or if someone has a better idea on how to do it, could you please help me out?

[Reply #1 on:]

Is there some reason you don't just have a friend stand where they saw the plane touch down and then you can pace off the distance?

A video taken from a fair distance with cones every 10 feet or so along the runway would allow you to determine the landing distance later and without the help of a friend.

[Reply #2 on:]

I just wanted the measuring device to be on the aircraft,  a video is a good idea, but requires me to bring more things to go play than just the airplane.  this would just be something I put on the aircraft. 

[Reply #3 on:]

High precision sub meter GPS? Shouldn't be more than $5000 a unit.

Since you did not mention cost... or allowable weight or dimensions or...

[Reply #4 on:]

low tech - Powder on the runway to see tracks - or paint on the wheels ?

[Reply #5 on:]

If you could use a accelerometer activated/timestamped at first contact of the wheels......(perhaps nunchuck of a wii or something)
airspeed sensor + groundcontact would also be an option (not that accurate though...)

Just to be on a sensor/electronics side of the matter

D.

[Reply #6 on:]

How do you get an accelerometer to measure distance travelled??

[Reply #7 on:]

The Holux M-241 (eBay... about $50) is an amazing device... records GPS tracks, and has excellent, user firendly software to display the track... including the vertical dimension... as an overlay on a Google map. Why track just your landing, when you can track the whole flight? The device can be configured to many modes. For your needs, the x/y/z+time every 5 seconds would be the thing.

62 grams, incl the single AA cell that it runs on.

Now, you're not going to connect that to your Arduino... but you are going to use an Arduino to record the time  of first contact with the ground. (Low torque microswitch on a landing gear.) And maybe the time the plane stops. Vibration sensor of some kind? With the times, you can then consult the Holux log, interpolating as necessary.

[Reply #8 on:]

@robtillaart thinks like a flight test engineer.

On big airplanes we use first landing gear movement to fire a 20ga shotgun straight down onto the ground, shells are loaded with different colored chalk for different runs.  KISS = keep it simple, stupid !

[Reply #9 on:]

@MarkT

Insert Quote
How do you get an accelerometer to measure distance travelled??

Well, it's an integrating process of all the accelerometer data and timestamps, i.e. how long the object is at the different g's.
Starting from last point at standstill, the g's at certain time will give a x speed or distance travelled depending on how you rearrange the formulae for speed and acceleration. integrating all the points up to the time of touchdown will give the final distance travelled.

mind though, you are dealing with 3d motion so, the math is vector math or/and matrixes.
Could be an interesting exercise though....

the games played with controllers with accelerometers do use similar techniques to translate accelerometer-data to movements in the game.

Since the data is postprocessed, then a visual graphics program could be used to visualize the data........


D.