Over the last couple of days I have been testing the Lidar based auto-landing code that will be in the upcoming 3.1.1 release of APM:Plane. I'm delighted to say that it has gone very well!
Testing has been done on two planes - one is a Meridian sports plane with a OS46 Nitro motor. That is a tricycle undercarriage, so has very easy ground steering. The tests today were with the larger VQ Porter 2.7m tail-dragger with a DLE-35 petrol motor. That has a lot of equipment on board for the CanberraUAV OBC entry, so it weighs 14kg at takeoff making it a much more difficult plane to land well.
The Lidar is a SF/02 from LightWare, a really nice laser rangefinder that works nicely with Pixhawk. It has a 40m range, which is great for landing, allowing the plane plenty of time to lock onto the glide slope in the landing approach.
APM:Plane has supported these Lidars and other rangefinders for a while, but until now has not been able to use them for landing. Instead they were just being logged to the microSD card, but not actively used. After some very useful discussions with Paul Riseborough we now have the Lidar properly integrated into the landing code.
The test flights today were an auto-takeoff (with automatic ground steering), a quick auto-circuit then an automatic landing. The first landing went long as I'd forgotten to drop THR_MIN down to zero (I normally have it at 20% to ensure the engine stays at a reasonable level during auto flight). After fixing that we got a series of good auto flights.
The flight was flown with a 4 second flare time, which is probably a bit long as it allowed the plane to lose too much speed on the final part of the flare. That is why it bounces a bit as it starts losing height. I'll try with a bit shorter flare time tomorrow.
Here is the video of one of the Meridian flights yesterday. Sorry for missing part of the flight, the video was shot with a cell phone by a friend at the field.
Here is another video of the Porter flying today, but taken from the north of the runway
I'd like to thank Charles Wannop from Flying Finish Productions for the video of the Porter today with help from Darrell Burkey.
Comments
Hi Joe and Gisela,
The flare timing is just used for when to initiate the flare, and is based on vertical time to touchdown, not horizontal time. Once that triggers the plane then just uses the EKF and TECS to target a constant sink rate (defaulting to 25cm/sec). From that point on it doesn't use the Lidar as its all based on the EKF inertial estimate of sink rate.
Paul and I had a closer look at the logs from the flights yesterday and worked out that the main cause of the bounce is that when the plane starts the flare it overshoots on pitch, causing it to bleed off too much airspeed, so the sink rate then climbs. Part of the reason for that is we use a smaller time constant in the landing for TECS, so the pitch loop is a bit twitchy. To fix that we've changed the timing of the bring in of the sink rate target to happen over 1s rather than 0.5s, and we will also use a small amount of pitch damping. We're hoping for much softer touchdowns today.
btw, I should have mentioned your earlier work on Lidar landings in my post, sorry about that! I know we're just playing catch up with features you've had for ages, but catch up can be fun sometimes :-)
Cheers, Tridge
Well done Andrew!
Good to see you are using the Lightware Laser Rangefinders to benefit here!
We now have 4 different plane types - from 5kg up to 66kg - all working well in auto takeof and autoland using those LRF's - they certainly have extended the envelope for this mode!
Just an idea - we gave up on timed flares - the only way to make the autoland 'universal' is to ensure a controlled rate of descent - as the real pilots do...That way the flare is automatic, and lasts as long as it needs, in a closed loop control mode.
Soft Landings.
Regards
Joe and Gisela.
The Nampilot(s)!
Hi Andrew, thanks for clarification.
Congratulations! Very cool stuff.
I uploaded some still photos from this morning's test flights to the Canberra UAV Flickr site as well. Have a look to get a peek at all the cool things CUAV are up to these days.
@Vishal, also, it isn't really expensive for what you get. The LightWare Lidars are really top quality and very reliable. If you are building a big plane then they are well worth the expense.
@Vishal,
The folks at PulsedLight are working on a really affordable one that looks very promising.
I tested an early prototype of it which had a range of about 10m. The final version should be closer to 40m, which is ideal for landing.
LIDAR is quite expansive. Some times back I saw LIDAR module in just 45US$ on Kikstarter but I do not know the status of that wether it actually manufactured and delivered to customers or not.
Wow, wonderful !
A heartfelt thanks to Andrew and Darrell for the opportunity to shoot the session this morning :) Very exciting stuff.
Charles.
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