VL53LOX Rangefinder for Landing Flare

ArduPlane Plane 3.9
1

I am experimenting with and hope to use a VL53LOX rangefinder to help with determining the altitude at which to flare in an auto-landing. On the bench I observe that the unit can deliver reliable distance of up to 110cm, or about one meter.

Arduplane has two related parameters:

RNGFND_LANDING. If set to 1, then the autopilot will use the rangefinder for both the landing approach and flare.

RNGFND_MAX_CM. The maximum reliable distance in centimeters that the rangefinder can measure. I set this to 100cm (1 meter) based on its performance on the bench.

I understand that the landing approach will start far above 1 meter in altitude.

During the landing approach will the autopilot use barometric pressure for altitude until the rangefinder delivers a value of 1 meter or less?

Thanks,

Paul

2

1 meter of rangefinder is useless for a plane.

The plane will use for altitude what the EK2 will consider more reliable generally the barometer but it could be also the Gps .

In theory the AP will switch to rangefinder as primary altitude when during LAND mode EK2_RNG_USE_HGT condition will be satisfied and the message “rangefinder engaged at xx m” is recorded in the log.

3

VL53 will not work outside over non highly reflective surfaces such as grass or dirt.

4

I think your are right Andras. I can only get reliable readings when moving a piece of white paper or my silver laptop case in front of the VL53.

Thanks all for your information. I will have to wait until more choices for inexpensive rangefinders are available and supported.

Paul

5

Check this : https://www.robotshop.com/eu/en/benewake-tfmini-micro-lidar-module-12-m.html
However I don’t follow how is the driver development going…

6

Andras,

That looks like a nice small. lightweight unit and the seven meters is likely enough range to make it useful for landing.

Hopefully it will be supported by Arduplane soon.

Paul

7

Actually you can uses ‘‘as is’’ in lightware serial mode, you just need to change mode on the TFMINI,
I get good reading up to 5 Meter Outdoor

8

Are the instructions to configure the tfmini included in this thread?

https://discuss.ardupilot.org/t/how-to-make-the-tfmini-rangefinder-talk-i2c/24403/150

9

Yes:
It comes preconfigured in binary output at 115200 Bauds and we can change the mode by issuing these commands through the Benewake console (http://benewake.com/en/down.html110) or using Realterm:
The command of standard output is 42 57 02 00 00 00 01 06
The command of pix format output is 42 57 02 00 00 00 04 06

The pixformat send clear ascii distances in meter and we can read directly this format x.xx (cr-lf). Within this mode it can be used with ArduPilot by choosing Lightware Serial @ 115200 Bauds

You might have to change the scale to Centimeter:
Modify output unit to mm output: 42 57 02 00 00 00 00 1A
Modify output unit to cm output: 42 57 02 00 00 00 01 1A

10

ppoirier,

Looks like an interesting unit. Concerned about some issue with distances between something like 50 and 150 centimeters (“blindspot)”

Thanks,

Paul

11

Looking at the WIKI, I think the TFMINI has not sufficient range, most of use cases are above 6 Meter …
When using a rangefinder for landing the altitude given by the rangefinder is used only in the landing approach and to determine the flare point, and is designed to allow the aircraft to more accurately follow the glide slope and to flare at the right time.