What is the best sensor for terrain follow

Hi guys,
What is the best terrain-following sensor for Low altitudes(1M) and Speed of 5 m/s?
I tried Lidar, due to its Narrow FOV(field of view), lidar is following terrain accurately when mission speed is less than 2m/s.
Suggest me a sensor which is having the capability to follow terrain accurately at low (less than 2 meters)mission altitudes and high speeds(>=5 meters).

Thanks and regards
Mohan

I guess it is less a problem of the sensor, but more a problem of physics. A sensor that is looking straight down can only meassure what is directly below the copter. This means the faster the copter flies, the more the sensor would have to meassure in flight direction. Due to the way a copter flies, the problem gets worse, because the copter pitches down to fly forwards, which means the sensor meassures behind the copter. I would mount the sensor on a servo to keep it meassuring straight down, or even use a lua script to make it meassure ahead of the copter with higher flight speeds.
That is all just brainstorming, I never used a lidar on a copter.

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Thank you,

Actually planning for this.

How we will achieve this? Please provide any reference link!

Thanks and regards
Mohan

We use lidar on auto mission tested altitude of 1.5m at 4.5 m/s without any issue. You need to change the parameters to change the default horizontal speed from 2m/s to your desired horizontal speed. I can let you know the parameter name when I go back to office tomorrow. Or if anyone else knows it they can post it here.

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@JackJavan Thank you for your reply, Sir.
we are used TFmini 2pro and its data rate is 1000Hz. Can please suggest to us some efficient lidar settings.
We will wait for your reply.
Thank you @JackJavan

Thanks and regards
Mohan

Hi Sir, Good morning,

Can edit this WPNAV_SPEED For terrain follow.

Ek2_rng_use_spd that’s the parameter

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@JackJavan Sir, Thank you very. We test with this parameter tomorrow. Sir sensor data frequency rate how much? Present We are using 1000Hz, Is this OK?

What parameter are you talking about. Let me know the name

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Tf02 pro(lidar) data rate sir. The data rate is the sensor side parameter. Default it is 100Hz, we are increased it to 1000Hz. Which lidar sensor you are used, @JackJavan sir.

We use a Lightware SF11c to fly at 2m AGL at 5m/s. This has been a pretty robust setup. If I remember correctly you can tune how aggressively the aircraft sticks to the lidar height. Too much and the aircraft will be bouncing all over the place and too slow and it wont react quick enough. Sorry, I can’t remember the parameter off hand. One thing to watch out for though is that thick fog or dust can affect the lidar and so you may need to change to last pulse (in the Lidar’s setting) to help combat this. However for flying over water you need ‘first pulse’ otherwise the lidar will in effect read the height from the sea bed.

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Hi @Carapau Sir, Thank you for your Suggestions, we will try to test

These parameters if our TF 02 pro having.
Sir, when we are working with OA_TYPE=3, then Terrain follow is not working. What is the reason for this.

Thanks and regards
mohan

OA_Type is referring to object avoidance I think rather than terrain following. If I am correct, providing you have set your rangefinder to be orientated downward and you have set the max and min heights for the rangefinder to work then the terrain following is done automatically. The parameter to adjust how agressively the lidar is followed is RNGFND_GAIN. So, the parameters to look at are: RNGFND1_ORIENT, set this to 25 for downward facing. RNGFND1_MIN_CM to set the min distance that the lidar can detect. RNGFND1_MAX_CM for the maximum distance it can reliably read. You will also need to set RNGFND_OFFSET to ensure that the range finder is reading 0 when the aircraft is on the ground (ie how high is it mounted from the undercarriage of the aircraft).

Also, read this link- not the best but a start: https://ardupilot.org/copter/docs/terrain-following-manual-modes.html?highlight=surface%20following

Finally I am by no means an expert on this so use my guidance at your own risk! Test test test if you can.

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I use the sf11, is impressive how its work, now ligthware has faster but smaller lidars than this, mail them for recommendations for your specifications.
Here my tests some years ago https://diydrones.com/profiles/blogs/sf-11-laser-altimeter-an-usefull-tool-for-agriculture-purpose

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Hi, @Carapau Sir Thank you for your valuable suggestions.

But Consider this link He is showing this is for the only analog sensors. But TF02 pro is the digital sensor. How could use RNGFND_OFFSET Parameters, Please any idea?

We did today OA with Bendy ruler with terrain following. The response is ok, But not good.

Thank you for this link. we already did this experiment with our drone, results are not satisfactory. In loiters, modes surface is working good and satisfied. But in auto, we are not satisfied.

Tomorrow we will apply your modification to our Drone. Then we will give feedback.

Thanks and regards
Mohan

Hi, @cala2 Sir
Thank you for your response. we will follow your link and make changes according to that link in our drone.

Thanks and regards
Mohan

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If its not working in Auto but fine in other modes it could be that you have the wrong terrain type selected in Mission Planner. When writing waypoints make sure that ‘Frame’ column is set to ‘Terrain’ and not ‘Absolute’ or ‘Relative’. Just above the list of waypoints is a line with ‘WP Radius’, ‘Loiter Radius’, ‘Default Alt’ and then a box where you can select the altitude/height type. This is the default setting for the Frame column. Be aware though that if writing multiple missions or if re-starting MP then this can sometimes revert back to ‘Relative’

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@Carapau Sir Thank you,

I will follow next time.

ok, Sir. I will check the next missions. (i.e Today)

Thanks and regards
Mohan