Hot wire for small robots

I used to do work with hot-wire velocity measurement. There is an empirical correlation - King's Law - between velocity, fluid properties and probe geometry.

I did a search and found this:

http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel3/3573/10682/00496325.pdf?isnumber=10682&arnumber=496325

If that doesn't give you what you need, you will have to go the DIY route.

If I remember correctly, you should be able to program a small microprocessor to give the velocity from hot wire and temperature inputs and a measured current output using the King's Law correlation.

Good luck with the project!

Regards,

Mike

Dear Guest,

So - was this any help - or what? It really is nice to know that when you reply to a post, it has some usefulness.

Mike

Unless relativity is achieved solution is power consuming or weight constarint will come.

Regards

Srinivas

Have you considered a GPS device?

thank you for the answers, however there is no way for us to develope such a device ourselves, actually we're trying to find a solution that is simple to use, small and light weight. But the only thing there is on the market seems to be this: http://www.c2v.nl/fr_index.shtml?/products/sensors/air-flow-sensor.shtml

but it is not available anymore...

does sbdy know another manufacturer or a competitor product of this.. (a bit smaller would be even nicer )

Thanks a lot!

mirko

It is very simple if you do not want to have a high precision. You need two resistors one for measure one for a reference and an OP AMP to generate a constant curent through the measuring wire. The tension at the op amp output is proportional to velocity. The relationship between curent and velocity is not very linear since it depends on the forced or free convection between wire and air. Without a calibration you will only have an indication but you could not use the signal for more than a rough regulation.

May I also suggest a pitot tube similar velocity measure .

There are very small pressure transducers which can be used as difference to determine the pressure drop due to displacement. It could be easier to manage than the hot wire approach. The response is also not linear but much more possible to approximate with a simple function (second degree function drop to velocity)

One of the transducers should measure the stall pressure with its sensitive opening toward the direction of flight and the other at 90°. Since the sensitivity is important it is possible to use the signal with a low amplifier gain. Impedances are high so that curents are small. For the hot wire system you will need more curent.

What is the max weight you can afford to carry? There are light weight hand held wind speed measuring devices some are no bigger than a small mobile phone. Just make sure it has a data logger inbuilt and a USB socket.

thanks you all for the help!

we'll try the hot wire sensor...

I'll let you know about what's our feeling once we receive a demo of it...

M