The SF11/C laser altimeter - awesome performance for $249

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 ;). 

Views: 10728

Comment by Thomas Stone on January 29, 2016 at 9:07am

Great! Should be very popular.

Does the SF11 have the same APM compatibility as the previous SF10? 

Comment by Hector Garcia de Marina on January 29, 2016 at 9:12am

Hi,

nice! it is very light and the price is getting affordable. However I have some questions regarding the post itself.

Is the study of the presented plot reported somewhere? is the measured ground mostly flat? what are the ranges in the roll angle there?

In my opinion, if you really want to know what is the altitude w.r.t. your vertical and you expect high bank angles, you should add a gimbal (like with cameras) to your altimeter (more weight and problems maybe I know...), even if the terrain is "almost flat".

Comment by Ken Gracey on January 29, 2016 at 10:49am

Hector - if you know the angle of the UAV couldn't you use some trigonometry to calculate the distance to ground? I see your points, though, as this assumes the ground must be flat and you're not looking at trees or buildings. 

Comment by Ken Gracey on January 29, 2016 at 10:53am

Parallax will have these sensors in stock late next week, by the way. - Ken Gracey

Comment by Shawn McCracken on January 29, 2016 at 12:29pm

Are we currently able to implement terrain following using one of these on a multirotor during mapping missions created with MP? I am very interested in using this to maintain consistent altitude over forested mountain areas.

Comment by bw4257 on January 29, 2016 at 2:13pm

Developer
Comment by Andrew Tridgell on January 29, 2016 at 6:17pm

I've been testing the SF11/C for a while now and I can highly recommend it. It offers far more range than the PulsedLight Lidars and is much more reliable.

I recommend running it via the serial interface for best results.

Thanks to LightWare for sending me a unit to test!

Comment by Thomas Stone on January 29, 2016 at 7:09pm

@Tridge

Thanks for the testing and recommendation. I assume the installation instructions for SF11/C are the same as shown here.

Also, what do you set your RNGFND_MIN_CM to?


Developer
Comment by Andrew Tridgell on January 29, 2016 at 7:24pm

@Thomas, I've been using 5 for RNGFND_MIN_CM. Works nicely on my plane.


Developer
Comment by Andrew Tridgell on January 29, 2016 at 7:45pm

The graph above shows flight results with a SF11/C connected as the primary rangefinder (on serial) and a PulsedLight BlueLabel Lidar connected as the secondary rangefinder on I2C. The CorrectedBaro reading is the barometric altitude corrected for attitude (ie. divided by cos(roll)*cos(pitch) and clipped at 130m). You can see the following features:

  • the LidarLite starts to lose signal at about 20m, although it still has some signal up to nearly 60m.
  • the LidarLite gives some spurious (short lived) ranging results while above its maximum range
  • the SF11/C shows a range of 130m when it has lost signal (this is settable). So the flatlines at 130m are the parts of the flight where the SF11/C is not giving ranging data
  • the barometric altitude doesn't match exactly with Lidar range as there are small variations in the terrain, especially when the aircraft is rolled over for a turn and is pointing outside the flight area

The SF11/C is a great Lidar, easily the best I have tested

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