Let's Make Robots!

IR Versus Ultrasonic rangefinder on grass.

Hi, I'm pretty much new to robotic, even though I've worked with kit like fischertechnik and Lego NXT.

I know the base of it, and i'm good with electronics.

 

but here it is i want to build plane that coud fly by itself using rangefinder (Ir or ultrasonic) to keep a distance from the ground, but i've read that IR sensor aren't good outside and that ultrasonic doesn't work good on absorbant material (Grass).

Since it's a plane I also have to consider weight in my choice.

Wich sensor would be the best for this task ?

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If it's an airhog it is definitely too small to carry the extra electronics.  There are a few options, however, that works incredibly well and are pretty cheap overall:

    * GWS Slow Stick
    * GWS E-Starter
    * GWS Formosa

No, I'm not a rep for GWS but their planes are really inexpensive and will handle a lot of abuse.  I've broken the fuselage in half on the E-Starter and with some 5 minute epoxy and 20 minutes later I was flying again.  The wing loading is pretty well and they'll hold a bunch of stuff.  You can mount cameras and other crazy things.  The slow stick has the best lift to weight ratio, but will be blown around in a breezy location, unless you chop the wing a little bit.

There are a lot of people who add altimeters, GPS and other instrumentation to their planes which work quite well.  One place you should find a lot of help is http://www.rcgroups.com/, they've helped me a lot and could point you in the right direction.
Wow - good tips! GWS Slow Stick is now on whish-list!
I'll try with de air hogs first then when i'll fail i'll get one of those.

The plane i'll use is a Air hogs defender, it's a stryofoam plane for kids, it's made to be crashed so no probleme for this and it's a very slow flying plane and very simple, the faster the motor spins the higher the plane goes and for direction you just slow down one of the two motors.

For the landing it's simple, you just slowly crash it :)

No way an Air hogs defender will carry the extra weight!

And yes - there is the "roll"-problem, but there IS however also the speed to consider. Trust me :) You will get results after things has changed. It takes up to 20ms for a ping to return. And you will get a lot of noise, so you would have to do several sonic pings to get an average.. an average of something that by then is changed.

I do not mind if you do not trust me :) But I know what I am talking about, I am just trying to save you time & trouble :)

Make a quite easy test, compared to trying to make it fly: Put your equipment (SRF05 or IR) on a broomstick, and wave it around, while having cables down to your hand holding it.. See if you get reliable data fast enough to have a plane react (it does take time from the plane reacts to the direction is changed).. or just an enormous amount of jumping numbers.. 

Making a skidding / sliding Wall Racer is nothing compared to navigating a plane.

Of course there are (fun) ways to make "robots" control planes (in fact I am on a project with a guy right now) - but mounting an SRF05 or SHARP IR on an Air hogs defender.. is NOT going to give good results :)

I'll try build a "first robot" first, maybe I'll try this project later. when I'll be better with programming.

I do believe you, but I take this as a challenge :P

Btw, ultrasound take 20 milisec to bounce back, but in theory IR goes a the speed of light, am I right ?

It does sound like a fun project, and a foam plane shouldn't cause too much damage when everything goes horribly, horribly wrong :) I agree that it wouldn't be a good first robot project, but you should definitely try it as a third or fourth robot. I'm actually tempted to give it a try myself once I finish my current project... :

Dan

It's true. The compressed air plane would hardly carry the battery.
It is a small RC plane, not a compressed air plane.
Ah, sorry. The airhogs I know of were a compressed air single-cylinder engine.