altitude sensors anyone?

[DavidGitz]

Is it possible to change your competition strategy? i.e., since you are indoors, fly closer to the ceiling and monitor your clearance to the ceiling itself.

What exactly is your motivation behind wanting to get your range at that far away? Their may be ways around this limitation, depending on your reasons. And since it is an indoors environment, are you able to place static objects ahead of time? Probably not, but it's a thought.

[Bryan Herbst]

Originally Posted by DavidGitz

Is it possible to change your competition strategy? i.e., since you are indoors, fly closer to the ceiling and monitor your clearance to the ceiling itself.

What exactly is your motivation behind wanting to get your range at that far away? Their may be ways around this limitation, depending on your reasons. And since it is an indoors environment, are you able to place static objects ahead of time? Probably not, but it's a thought.

The collegiate FIRST pilot is happening at championships. The field will be very similar to the FRC field, and will have a net over it (if I remember correctly). Though definitely a fantastic new way of looking at the problem, that won't work.

As for other suggestions- Kinect would be so much fun, but these are light quadrocopters (powered by arduinos), so I have a feeling that would be too heavy.

The other problem here is that there are platforms that robots must land on, so I am not sure how much help sonar will be. Not exactly sure what the altitude will be used for, but this may cause an issue.

[Chris Hibner]

For a sonar or light-based ranging system, I would recommend a Kalman filter strategy for error/noise rejection.

If you want to get fancier, add 6-axis inertial measurement unit along with the ranging system, and tie it all together with a Kalman algorithm strategy. This can work quite well.

[reversed_rocker]

thanks for all the help

so first of all, i think it's especially important to mention that we're using 2 controllers. one processor for controls and one for fancy sensor inputs (image analysis and whatever else we throw on there). the second processor may be an ARM 3530, so i think kalman filters on the matbotix sonic rangers will do the trick. After reviewing the rules, i found out that the ceiling is 16 feet high, so that should be within the 255 in range of the range finder.

i was going to play around with using the camera and an optical flow algorithm to do position hold, but unless you're looking at a fixed object on the ground with a known size and shape, you cannot use the camera to determine altitude.

[Gdeaver]

There are some high resolution pressure sensors available. With the proper calibration you might get 1 foot accuracy. Turbulence with a copter could be the killer. A tube with properly designed holes may help. They use SPI or I2C so the audrino low analog is not a n issue.

[Tom Line]

The maxbotix sensors are accurate over long distances (VERY accurate) but only if they are held still. They also have a noticeable lag time along with an overshoot-then-leveling-off issue when used with the analog (I'm not sure if the digital connection has the same problem).

I would consider combining two sensors. The ultrasonic for longer distances and the sharp for closer in where speed is important.

Sharp does have some longer range rangefinders (1.5m) that might work:

http://www.robotshop.com/sharp-gp2y0... campaign=jos

[kamocat]

I have found that using the measuring the digital pulse on the Maxbotix SONAR is much less noisy than the analog signal. (It also doesn't have the trouble with maximum slew rate).
Granted, this is with FRC hardware. The characteristics of your control system will be different. (You may have little enough noise on your 5v power supply, and a pulse-length-measurement that is not as accurate as an FPGA, and so analog may be a better choice.)

EDIT:
about those rangefinders: They have a MINIMUM distance around 5-10 inches. (it will say on the datasheet). If you get closer than that, you will get false readings.