SF02 Laser Rangefinder Flight tests:
I recently purchased three of the SP02 Laser Rangefinders from Laserman, and have fitted one to one of our SurVoyeur mk-II planes. I had intended to fly earlier this week, but was beset with PC hard disc failures so spent a few unpleasant day resurrecting PC's...
Anyway, back on line and we flew today with excellent results.
The rangefinder was fitted in a housing and mounted in the internal bay of the aircraft, with the lenses looking out the fuselage underside. Here are some pictures:
Rangefinder lenses from under fuselage
Rangefinder connected to autopilot
Rangefinder fitted internal to Fuselage
Fuselage under view with rangefinder lenses and ultrasound ranger visible.
The Plot below shows the SF02 rangefinder plotted against Baro Alt ( as a function of height above ground) and the Ultrasound rangefinder)
IMU-Height is Baro_height above ground
LRF Height is the SF02 height , active from 30 meters AGL only.
Ultrasound is the Ultrasound sensor height AGL, active from 6 meters AGL only
The SF02 performs very well. The terrain was soft desert sand, with patches of very coarse gravel, interspersed with desert brush and bushes.
At the price , this is a brilliant piece of equipment, and cannot be beat!
We are working at replacing the Ultrasound sensor with the SF02, which will allow vastly improved autoland, completely eliminating any destabilization due to errors and differences in baro-alt and actual height above ground when starting the landing flare.
Thank You Laserman!
Joe
The Nampilot
Comments
I believe Andrew is working on just that...
Has this been integrated with APM?
Hi Joe,
I've sent you a PM asking info on the survoyeur plataform.
Thanks!
Hi Gary,
I was using the analog output, with the fast upate rate, not averaged
Laserman does have faster scan devices - take a look at his web site.
Regards
joe
Thank you for this review, Gisela and Joe,
And objective real use application done by those who really want to make use of it.
Even though its a bit slow for my scanned App, it seems like an easy (and relatively inexpensive) way to get started.
Were you using the straight sample or the 4 to 1 averaged sample?
"Yes it would appear smoothed, but that is not really true - it is the baro alt that is noisy"
Exactly the first thing I thought.
"Using a laser ranging device, or a radio altimeter ( Radar, FMCW type or other) is the only way to discover how bad the Baro Alt measurement really can be"
Or carrier phase differential GPS. I've tested a lot of baro sensors over the years with that. It's always nice to have a higher accuracy measurement source when testing a given sensor. If your higher accuracy source is cheap enough to be integrated into your system to replace or compliment what you've already got, all the better.
Laser rangefinders are nice if your landing area is relatively smooth and uncluttered. Basically a necessity for fixed-wing aircraft. For rotary-wing, when landing in tight spots, they can be problematic ... unless you get into scanning systems, but this is a lot more complicated and costly.
@ Vladimir-
It works fine on grass although I have only flown over a grassed soccer field - the grass was only about 50mm tall. However, I flew over bushveld, with thorn trees that have new leaf growth, and then onto a flat salt pan to land, and it registered the tree tops perfectly! As the plane passed over the trees on the flat area the step in height ( about 4 to 5 meters , the height of the trees) was clearly seen. This really is a brilliant piece of equipment. I am still amazed at the performance for the price. A world beater!
Regards
Nampilot
@JackCross..
Yes it would appear smoothed, but that is not really true - it is the baro alt that is noisy - and shows very nicely the pitfalls in static and dynamic pressure measurement and airdata port placement. This landing was in rather turbulent conditions - winds gusting from 3m/s to 7m/s in seconds, and so the aircraft was quite agile in pitch to maintain height. It is precisely the change in pitch angle which the Dynamic airdata source Pitot tube sees that causes a change in dynamic pressure without any actual change in speed, with resultant throttle activity. This always feeds back into height control as well. This is a problem with Pitot tubes ( see my blog on Pitot tubes and airdata sampling on DIYDrones) and without calibration them in a wind tunnel, very difficult to eliminate. In addition, the static pressure source location is as critical, any change in pressure at that point will be seen as a height change as well ( and, differentially, a speed change too..). A poorly placed static port can suffer from pressure change due to aircraft forward motion, prop rpm, side winds, fuselage pressurisation, etc.
The change in pitch and roll angle in the straight on approach has less effect on the laser rangefinder since for low angles change ( sub 10 or so degrees) the change in the hypotenuse length ( laser line of sight) is not significant.
EVERY single plane I have built and fitted with autopilots ( 9 different planes so far) has had its own pains to find the best position for the static port location. Never vent simply to the fuselage interior..The combined Pitot Static tube is best, but more pipes to plug in before flight, etc, and they are difficult make, or rather time consuming. The one from Sparkfun ( I think , or is it 3DR, not sure.) is not very good - the dynamic port inlet shape is very poor, and will have significant errors at pitch/yaw angles greater than a few degrees. Also the static ports are located to close to the tube tip.
Using a laser ranging device, or a radio altimeter ( Radar, FMCW type or other) is the only way to discover how bad the Baro Alt measurement really can be - unless you have an absolute reference, you have no idea if the baro-alt variation is because of pressure variation, or the aircraft actually not at desired height. The lousy thing is that the height control is based on pressure alt, so it is a chicken and egg thing - if the plane was at the correct height, but the pressure was incorrect, then the plane is brought in line with the pressure alt, and when the pressure 'normalises', the aircraft is forced to another height. So you wobble up and down, thinking the height control is poor, when actually it is the pressure source that is poor!
Excuse the dissertation...
Joe
The Nampilot
Great. :)
You test it on hard surface? How it's work on grass or similar?
@Crashpilot1000 - Because they are not given away free....
@Vladimir - The lenses are inside of the fuselage, ie, they do not protrude, so are somewhat out of harms way. However, they do become dusty, and all we will do is clean them before each flight, as we do the camera lens ( IR Camera), so no big deal. The rangfinder still works with half the lense blanked of with a piece of tape opaque to the laser light, although the range reduces a little. The demo done to show this gave a range of 30meters instead of 40, which is very good.
Nampilot
-
1
-
2
of 2 Next