With a range in excess of 100m and able to measure over water, the SF11/C is the most cost effective laser altimeter for drones on the market today. Compatibility with Pixhawk and derivative flight controllers and its multiple interfaces including serial, I2C, analog and USB make the SF11/C the easiest plug-and-play solution for altitude holding, terrain following and safe landing.
The SF11/C was developed to handle the unpredictable real-world conditions that sensors face when attached to a drone. Environmental factors including vibration, wind, noise, temperature fluctuations and extreme contrasts in lighting from brilliant sunshine to pitch dark are all managed by the SF11/C, and whilst all this is going on, the SF11/C measures to rapidly changing terrain, giving stable results over wet and dry surfaces without producing false readings.
Tests conducted by the Center for Research into Ecological and Environmental Modeling at the University of St Andrews in Scotland demonstrated the abilities of the SF11/C over wetlands and open water. Their requirement for consistent results under these difficult conditions were easily met by the SF11/C, contributing to important conservation work.
An important characteristic of the SF11/C is its long measuring range. This is especially useful during changes of roll or pitch angle. Data from the IMU is used to correct for geometric effects during such maneuvers, but this only works correctly when there is valid measurement data from the laser. The long measuring range of the SF11/C makes this possible as you can see from the graph below.
The green line is the roll angle, the purple line is the barometric height referenced to sea level and the red line is the uncorrected, AGL altitude from the SF11/C. During tight turns the measured distance increases significantly but the long range capability of the SF11/C keeps the ground clearly in view.
More details about the SF11/C can be downloaded from the website. The SF11/C is manufactured by LightWare Optoelectronics (Pty) Ltd based in South Africa. LightWare has been designing and manufacturing laser altimeters for the drone market for 5 years and is committed to providing high quality products to the industry. The official distributors in the USA are Parallax and Acroname.
Special thanks go to the dev team for their contributions to the driver software and Tridge for his tireless and occasionally incendiary flight testing ;).
Comments
How does the SF10/C and SF11/C handle trees? Does it use multiple reflections to determine the ground returns versus the canopy returns?
Hi Cool Dude,
The data looks completely normal when connected to the Lightware terminal, so I'm inclined to think that the sensors are fine. As for parameters, I'm using the same ones you posted on this page.
Hi @nasa1092 can you download the Lightware terminal from http://www.lightware.co.za/shop/en/content/8-software and try it after connecting it using USB. Then you will have the proper test of the system as bad param values in the pixhawk will not effect it's reading. Then you will be able to debug if you unit really has any issues. My SF11 works fine. I took my drone to 75 meters and the reading in the log I get are correct.
Hey guys, I've got a couple of SF/11Cs and I've been having a lot of trouble getting useful data from them. When connected to the Pixhawk's Serial 4 port, the 'sonarrange' parameter reads 130 (the default no-return value) nearly all the time. When it does return altitude readings, they are few and far between. Thinking that perhaps I didn't have enough available UARTs on the Pixhawk (I'm using GPS and two MAVlink telemetry connections), I also tried the SF11/C with an analog connection. This produces good range readings on or near the ground, but in the air the analog voltage goes straight up to 2.56V regardless of altitude. Even when I land, the reading usually stays at maximum. I've tried I2C as well, which is totally non-functional and reads zero constantly. I followed the rangefinder configuration guides in the Ardupilot documentation to the letter, and both sensors work perfectly fine when connected to the Lightware terminal over USB.
Thoughts?
Hi all,
I have got one of these SF11/C units on a quad and it is performing very well. I am extremely surprised at how accurate it is up to 100m+ very cool!
I do have one issue and I think it's Pixhawk related. When using RTL or Land, the copter now descends very very slowly. There are two stages to the landing usually, a faster speed controlled by WPNAV_SPEED_DN (310) and a slower speed that usually kicks in around 15-20m that's LAND_SPEED (75). Both of these parameters are unchanged after the LIDAR install, but now the copter descends at LAND_SPEED the entire way down. This can take a very long time from 100m and uses a ton of battery. Is this a bug or can I fix this?
There is a 'Zero datum offset' setting in the SF11 settings menu (Via USB). It's possible this may have been changed to something other than the default 0.00m.
Could you also confirm the distance error (using the USB connection) against some known distances (Maybe 2m or so)?
RNGFND_TYPE,8
RNGFND_MAX_CM,10000
RNGFND_MIN_CM,5
RNGFND_GNDCLEAR,10
RNGFND_SCALING,1
SERIAL4_BAUD,19
SERIAL4_PROTOCOL,9
This seems to be OK to me.
Oh, and RNGFND_SCALING
Hi Cool Dude, can you verify what settings you are using for the following parameters:
SERIAL4_PROTOCOL
SERIAL4_BAUD
RNGFND_TYPE
RNGFND_MIN_CM
RNGFND_MAX_CM
RNGFND_GNDCLEAR
Hi guys. I recently received my SF11/C sensor. I installed it on my 3DR quad using serial interface to port Serial 4 port of PIXHAWK. However the reading I get a not good. It added an offset of about 1 meters. Even after that the readings seem to be scaled a bit depeding on how high the copter is. Is anyone else having this issue. Earlier I had Lidar lite V2 ( I2C ) installed on the same copter and it seems to be working fine. Using lidar lite the plot of sonar alt/baro Alt pretty much matched but not using the SF11. I am using ArduCopter 3.3.3.
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