Sonar coating

[Stephanie]

I'm making a sumobot, and read the page about Stampy.

http://www.societyofrobots.com/robot_sumo.shtml

Now, I want to coat my robot with that "sonar absorbing pointy shaped foam". I can't find "pointy shaped foam" around here, so I'll cut it myself.

But... what kind of foam is that? What's the best density? What does that "sonar absorbing" mean? Cutting regular foam in pointy shape makes it sonar absorbing or is it "sonar absorbing foam" cut in pointy shape?

Because if it's the latter, I don't think I'll find special foam around here... The only types of foam I've found were 35, 28, 26, 23 and 18 kg/m3 at a mattress store.

[wil.hamilton]

sonar absorbing...
hmm, i would say it has to do with both the shape and the foam.
sonar uses sound waves to calculate distance.  sound travels relatively slowly in atmosphere, so how sonar works is by making a sound and seeing how long it takes to hear the echo.
the pointy shape of the foam probably serves to deflect the sound waves so they dont bounce back towards the sonar module.  plus, the foam itself probably absorbs some sound being porous.   

[Asellith]

Egg cartons works as a poor mans sound proofing for buildings and is cheap.. Ie free with purchase of eggs. So maybe run some experiments with some different egg cartons and see if that helps then no need to cut foam. I think it has a lot to do with the shape. Also the egg carton might allow the sound waves to enter and be diffused by the air behind it and that's what attenuates the return signal. Take a sonar sensor and test it against some different materials. also I think you need to use the foam style cartons not the cardboard ones.

[Stephanie]

@Asellith

Thank you for the suggestion... I know egg cartons are good, I've used them for sound proofing my house. The only problem is that they're too big for my robot.

@wil.hamilton

Thanks... I'll cut the foam in pointy shape.

But... what kind of foam do I buy?

[wil.hamilton]

i would buy a low density foam, the lower the density the more likely it would be to absorb, rather than deflect, the sound waves

[Stephanie]

What would be good distances for x, y and z?

Also, does anyone know foam densities that work for sure?

[Soeren]

Hi,

Egg cartons works as a poor mans sound proofing for buildings and is cheap.

Egg cartons is very poor in dampening the sound intensity eg. outside a rehearsal room, but it works for getting the reverb down, which is unfortunately called dampening as well. To measure the effect of this dampening, you usually use a ball shaped array of speakers and a sound output that is a bit like a heavy machine gun firing short bursts and then measuring the delay and strength of the return signal.

I think it has a lot to do with the shape. [...]

My office is over-dampened by flat baffles mounted on the wall and ceiling (and the floor is covered in grounded carpet with carbon fibers - glued on to a grounded copper net with carbon loaded glue (expensive beyond imagination).

Take a sonar sensor and test it against some different materials. also I think you need to use the foam style cartons not the cardboard ones.

I agree on the testing with actual sonar and since one is probably used on the 'bot, it won't mean an extra outlay
I'd go for something like whatever_I_could_find and make lots of test to acquire some knowledge and then go buy what works best.
2 layers might be beneficial if different densities are chosen - light stuff on the outside and something like a thin layer of neoprene on the inside against the 'bot.

[paulstreats]

Mentioning carpet...

A piece of carpet or carpet like material might work best.

(a softer material is less likely to reflect sound waves)

[Admin]

What would be good distances for x, y and z?

Also, does anyone know foam densities that work for sure?

If you google around, you'll find some research papers on this.

You can probably find pics of it on company websites, then just imitate the ratio.

Also, sound absorbing wall foam is usually pyramid shaped.

http://www.google.com/search?q=sound+absorbing+wall+foam