About two months ago we added altitude hold using the Maxbotix sonar to the ArduCopter (you can find instructions re how to set it up on the wiki). At the moment on the we recommend the LV-EZ4 and XL-EZ4 but that's not based on a lot of research or experience so the question to the community is:
Which one of the Maxbotix sonars is best for our purpose?
Above you can some pics extracted from the datasheets of the four sensors. Each is a 1 foot grid and shows the theoretical range within which the sonar can sense a 3.5 inch pole (look at the black lines, not the red dots)
The first choice is whether the extra cost of the XL over the LV is worth it - according to the data sheet the XL's range is 80% better (nearly twice the range) which makes me think "yes".
The next choice (for either LV or XL lines) is between the EZ0 (fat-beam but longer range) or EZ4 (narrow-beam but shorter range). We went with the EZ4 because we thought the narrow beam would make the altitude correction using roll/pitch work better but I guess we might be able to correct for the fat-beam of the EZ0 in the code and then we'd benefit from the longer range..but perhaps we would also get more false readings?
So my guess is it should be the XL-EZ0 or LV-EZ0 but it would be great if people especially those who have played with sonars could voice their opinion/experience. Also at least one person has had trouble with the XL-EZ4 over carpets and grass so if people have experience over various surfaces we'd love to hear about it!
Comments
Hello, this is Tom Bonar from MaxBotix Inc.
When operating MaxSonar sensors on UAV's we recommend the XL-MaxSonar-EZ sensors over the LV-MaxSonar-EZ sensors. The XL sensors have better noise immunity then the LV sensors and the XL sensors also operate better over environments with grass and noise. Our engineering team recently did an evaluation of our sensors for use on a UAV that can be seen at the following link http://www.maxbotix.com/articles/067.htm.
Another reason the XL is recommended is the longer maximum range of 765cm (300inches) versus 645cm (254 inches).
Please let me know if you have any questions.
Best regards,
Tom Bonar
Technical Support
of MaxBotix Inc.
Phone: (218) 454-0766 ext 2#
Fax: (218) 454-0768
Email: thomas@maxbotix.com
Technical support and sales are subject to
the terms and conditions listed on our
website at http://www.maxbotix.com/
@FDC,
Sorry for the crazily late reply..ArduPilot (or rather ArduCopter) works with a sonar for altitude hold so it should be fine. Check out the wiki. It's the same as for a multicopter.
Heey guys I am new on this field and I am working on an Autonomous Heli. I want to mount a MaxSonar EZ1 with the Ardupilot. Do you think this is possible? I really do not want to work with a regular Arduino since I am running out of space and weight capability on my 180-EFL Heli. Any Ideas. Any converter that I can use for these TTL and PWM signals..
Just to confirm my vague sentiments from earlier.
EZ0 is the only choice. Black is for our voltage, red is for 3.3v so with any variance in the supply voltage you want the most accurate ranging with both voltages. Simples (joke for the English).
@Randy
The difference between the AE and all the other ones is the analogue output is changed to analogue envelope output. This means that instead of a voltage based distance reading you get a signal of the entire reflected echo for the envelope (the interval where no ambiguous signals can be picked up).
This means that with an AE sensor, a custom waveguide, a linear rail and some processing a synthetic aperture sonar system can be made. The "processing" is not exactly simple but could be cheated with some signal processors from radio swap meets or if you feel like doing compression algorithms across aperture and azimuth you can do it that way too.
John,
If you could do a test and post results here, that would be really great. We have spare PWM inputs for extra radio channels on the back of the APM although I'm not sure if it would be compatible with the PWM coming in from the sonar. Still, I think if we found that the PWM input was more reliable we would try to find a way to use that instead.
@Randy All I can say in regard to analog vs. PWM is what I've seen anecdotally on my sensor. I can do a test program that collects both at the same time to see if the noise is from the sensor or from how it's read. I just figured I'd through in my 2 cents :) on what protocol we should standardize on in case that would affect the hardware choice.
John,
I thought the major difference between the AE and XL lines was just the pwm output.
I've noticed with the analog input that we get jumps in the values fairly often. Do you think this noise would be reduced if we used PWM?
That's really too bad they dropped PWM support on the AE line.
Perhaps I am the only one have noisy ADC with the Maxbotix, but I switched the code to use the PWM output and I've found it to be significiantly more reliable and then I also don't have to worry about how I physically wire the sonar w.r.t. other devices as the signal is digital and not analog.
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