measuring ground and airspeed?

[want2learn]

I want to learn ( ) how to measure ground speed and airspeed.

This will be on a ground based robot. Ill be using the $50 robot with an extra mcu and sensors for measuring these parameters.

Which sensors do you recommend?
Will gps provide both?

[SmAsH]

by groundspeed do you mean how fast the robot is moving? because the ground doesnt really move that much otherwise and for airspeed you could use a pinwheel hooked upto a tiny generator and measure the power outputs. but thats just my majorly ghetto way of doing it

[Razor Concepts]

Why do you need to measure airspeed for something thats on the ground 

[want2learn]

I'm trying to learn how to crawl:

I figured it's easier to learn how to use new sensors and how to successfully implement them on something i'm familiar with before experimenting in unfamiliar teritory..

I'll be experimenting with further sensors, same setup before trying to walk.

[paulstreats]

accelerometers are a good starting point. (try to get a 3d one for 3 dimensional movement). Also make sure the accelerometer range covers the level of acceleration you are expecting

[want2learn]

I planned on trying a balancing robot after these trials so I could implement accelerometers in a true application, after first experimenting with them on my $50 testbed

[want2learn]

Just a quick question on accelerometers:  My testbed is going to replicate different conditions on my final robot which will have a vertical movement of several cm (5-10cm guesstimation at this point) with a frequency of 0.8 - 3Hz (varies with speed).
Will this affect the readings I receive in all axis or just the vertical?
Being a variable low frequency, will it be easy enough to filter out?

[paulstreats]

it should only affect the plane it is on (e.g. the x plane).

you can use a capacitor to average the readings and reduce noise.

accelerometers are great in theory, though they can be quite tricky in practice. holding them straight, 1 of the axes (usually y) will always register an acceleration due to gravity(the accelerometer isnt moving but gravity is causing stress on the microstructures causing an acceleration reading on an axis). if the accelerometer is tilted then more than 1 axis will be affected by gravity. The difficuly comes from trying to differentiate which part of the reading is coming from movement and which part is coming from gravity. If your movement make a slight tilting motion as well as a forward/backward motion then it will affect the other axes but only because the gravity reading is switching axes. Getting to grips with differentiating gravity from actual readings is essential for using accelerometers.

[want2learn]

Thanks Paul.

Will an air pressure sensor be more accurate than a small propellor for measuring airspeed.
I've done quite a bit of googling, almost everything I see uses a pitot tube with an air pressure sensor.

[Admin]

Quantitatively, what is your minimum required accuracy?

[want2learn]

1mph will do just fine.
Because this is only for learning at the moment, the cheapest reliable solution will be the best. As long as  I don't end up with a sensor I can't interpret data from I think I'll manage. (Please note I did say think )