MHello,
I'd like to share my experience and experiments with the use of the sonar on my quad.
The config is the following:
-Quad 3DR base frame rev C
-880Kv motors, 11 x 4,7 props
-4S 4500 ma battery
-Sonar MB1260 XL-MaxSonar-EZL0 (bought in the 3DR kit)
Having followed all advices to habve the sonar work properly, I have shielded the cables, moved it away from propo wash, away from ESCs, i have a filtered power on it, etc.
On the bench and in certain flights the sonar seems to work fine : the sonar alt follows closely the barometer alt value.
But , erratically and without any explanation I can find, the sonar does not work in certain flights or even in certain parts of the flight as shown in the graph above. The sonar alt value (in red) is completely erratic and not close at all to the true barometer alt (in green).
In another flight log I found this : where the sonar seems to work fine for most of the log and then breaks down for no reason:
In flight I experienced a very bad ALT HOLD with the sonar enabled : the quad did very rapid vertical movements about 1 meters amplitude (wihout any wind). Once the sonar was disabled, I had then a PERFECT ALT HOLD.
my conclusion is this sonar being used only for under 7 meters altitude, it is absolutely useless and does not bring any added value. On the contrary its usage reveals dangerous as I experienced.
I do not see what could cause such an erratic behaviour of this sonar, except a too sensitive piece of equipment not made to be used on a drone.
Funny enough, I see the 3DR store removed this model from the sensors list. Does this mean 3DR admits there is indeed an issue with this Maxbiotic 1260 model ?
Replies
So the Sonar works just fine under 7M then? If so that actually makes sense, because the Sonar is only used for low altitudes, and terrain following.
From the Manual:
ArduCopter supports the MaxSonar line of sonars for low level terrain following and in the future collision avoidance. Sonar is NOT necessary for altitude hold and will not work above 10m. Even if you have a sonar sensor, you should disable it in the Mission Planner hardware setup page unless you specifically need it for terrain following on a particular mission. Sonar tends to be a somewhat noisy data stream and will not do as a good a job in altitude hold as the built-in baro sensor on APM 2.5.
very strange, in the 2. recording between line number 42 and 45 barometer's values seems to be zero.
A usefull way way will be to calibrate the sonar as static values, the altitude versus the output signal.
With so oscillating output signals it will be a advantage to use average values during several seconds
From most of my research sonar is only good for very low altitudes (on average 1-3 meters)
The various models available all have unique charicteristics, in levels of sesitivity and spread patterns, Because of this the code used to drive a specific sensor model must also be unique for its calculations to perform well, Since the technology is forever changing and improving no one code gets developed far enough to work flawlessly in conjunction with a flightcontroller (in most cases)
@Hugues,
Since your sonar seems to function well for a certain period of time and then become sporadic for no apparent reason at all could indicate an intemittent connection in your cabling or a possible marginal component in either the sonar or the power filtering circuit that is vibration sensitive. These kind of intermittent issues can drive you crazy until they are either resolved through a process of elimination type of troubleshooting or the system is replaced by a more reliable one.
Regards,
TCIII
Edit: oops, sorry. my bad, made an error in conversion 1068cm => 10.68m. clearly you said it is under 7m.
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My experience in using sonar is NONE, but went through the specs[1] and found that "Maximum range of 1068 cm (420 inches)"
Is it possible you've used it beyond that range?
Ruwan
[1] http://www.maxbotix.com/Ultrasonic_Sensors/MB1260.htm