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
@Laser Developer
Very helpful. Thanks again!
In the ArduCopter documentation, it suggests that RNGFND_MIN_CM should be set to 5cm for the SF10 (link). So I assumed that it might have a better short-range performance.
@Thomas Stone - thanks for promoting our products. Like most suppliers we work very hard to make the best products that we can and your support is most welcome.
Our distributers tend to stock products that suit their preferred market and none of them stock all our products. If you need to verify the production status of one of our products then please check our website or drop a note to Tracy or Nadia. In some cases, our customers get the agents to stock particular products just for them as part of a long term OEM arrangement and these are not always shown on their web-store.
The region below 10cm is a bit of a "grey" area for most types of laser range finders (not just ours). There are complications caused by the effects of parallax between the outgoing and return beams, the potential for multiple reflections and the problem of different optical path lengths being followed by different rays. This can lead to slightly different performance between one unit and the next so I can't make any specific recommendations. Here is an example of an SF11/C at really close range:
The best solution is to always mount the laser as high off the ground as possible. Ideally you should try to get above 15cm but I know it's not always practical. Some customers make special brackets to raise the laser higher, like this one using an SF10/A on a low wing design:
@Laser Developer
Many thanks for the helpful information. We have recommended the SF10/11 rangefinders for many commercial precision landing projects. (btw, I saw the 'discontinued' notice by this distributor: link)
One more performance question: Which unit do you recommend for ~10cm distance sensing? Does the SF10/A have a lower min distance than the SF11/C?
Do you have the opportunity to test your equipment at temperatures down to -40 degrees Celsius?
Thank you.
@Vadzim - thanks for your questions. I must mention that it is impossible for us to deliver to many of the former Soviet block countries. There are restrictions on both the export from here and the import on the other side.
In answer to your questions:
1. We have tested many of our products down to -20C but we don't offer the extended temperature as standard.
2. Fog and cloud are often reflective to light depending upon the droplet size. This means that the laser will read up to a distance somewhere inside the fog or cloud but not all the way through.
@Thomas - The SF10 series is still in production and will only be superseded when we have a product with identical specifications. Many of our customers are working on long term projects and you can imaging that once they have certified a laser altimeter for their application they need to have a continuous supply for many years into the future. For this reason we try to keep products going as long as possible even if newer technology becomes available. Some of our industrial products have been around for more than 12 years.
The reason why the SF10/A is sometimes used for short range applications is because it has a higher update rate than the SF11/C (32 vs 20 readings per second). The higher speed alters the control loop characteristics and for some customers the faster response is important.
As far as the short range accuracy is concerned, now that version 1.2 of the SF11/C is available there isn't much to choose between the 11's and the 10's. The graph below is from an SF11/C and SF10/A that I just grabbed off the production line and tested straight out of the box. The short spike at 1m is residual laser firing noise and causes the greatest measurement errors. Beyond that the SF10/A is slightly more accurate. Note that I've taken the readings using the factory test functions at millimeter resolution otherwise you can't see the difference:
Good afternoon.
I produce gasoline helicopters for commercial applications.
I'm looking for an inexpensive alternative to radio-wave radar.
I have a few questions.
1. In my latitude, almost half a year, the ambient temperature is below 0 gr Celsius. I need to use it to -30 degrees Celsius.
2. How does the fog on the height measurement. In our latitude, often is present fog. Or do I have to fly in mountainous terrain dominated cloudy.
Will I be able to use your sensors?
Thank you.
@Laser Developer
I am interested in your comments regarding short-range performance. Are you recommending the SF10/A for short-range applications? I thought this series of units was discontinued.
@Shawn McCracken - the SF11/C has good long range performance over ground and trees. The update rate is 20 readings per second (current revision) but I don't know if this meets your requirements. Do you have a specification that you need to meet?
Hi Laser Developer, ok thanks for your fast reply! I'll send the unit to you today. I'll send you a PM for the shipping details etc. Greetings, Steven Verver
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