Hello!
I am trying to figure out which optical flow options are best to start with. When new hardware experimenting starts i usually read everything i find in wiki and discussion before jumping to baskets, right now i am bound to buy the cheerson cx-of between many options found in above mentioned sources. As i can see latest posts on these can be outdated i am looking for suggestions, am i in the right path to succeeding in opticl flow control with these sensors? BTW…don’t ask me why but i’d like to use it on a serial port.
Thanks in advance for any opinion
Best,
Claudio
Hello
What is the use case:
- Indoor/Outdoor
- Maximum altitude usage for OF
- GPS/Non-GPS
The PX4FLOW is still the best unit for outdoor, high altitude (up to 100 Meter) and can be use with or without GPS. Ouubvioisly, it require a suited RangeFinder to make it work , I use the LidarLite V3 or the Benewake TF02 ot TF03.
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Hello PPoirier,
thanks very much for your reply, really appreciated. Main use is outdoor, final use would be to follow auto missions with altitude lidar integration (have a couple of tfmini-s on their way) and obstacle frontal avoidance (just finished setting up maxbotix i2c sonar, right now being tested in flight). Optical flow use, in my newbie opinion, would be to sustitute the sonar for frontal obstacle avoidance as i got the impression, from the forum and wiki readings, that the sonar is somehow a critical sensor.
Please do not skip on correcting me on any point, my experience is near to zero and my curiosity and openmindness is maximum 
Thanks again,
Happy landings
Claudio
Main issue with sonar is that signal get “washed” by airflow, giving bad readings.
TFMini is ok but limited to 6 Meter outdoor.
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This is my test with “clone” of CX OF sensor from AliExpress.
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Hello PPoirier,
…so the advertised tfmini 12m is on the optimistic side…nice to know! Will start experimenting with these and then eventually switch to tf02 or tf03, hoping that scaling the performance distance would not take such a big effort. What i haven’t seen often covered is using them for frontal object avoidance rather than position gps-less hold. Have seen this: Avoidance Experiments with the POC and Benewake TFMINI ,maybe one day i will understand how you did it, right now i’d be happy to use one just for frontal obstacle avoidance 
Can’t wait to receive themand start experimenting, the fun side of all that
Thanks again!
Claudio
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Hello Alberto,
thanks very much for sharing, will look into it right now!
Thanks!
Claudio
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Hi @ppoirier,
I going to use PX4FLOW for about 100 meters altitude,
Can you explain what features the ground texture should have?
and another question, how can I use it with GPS? (i using arducopter v4)
Thanks.
we are using LightWare SF20 / LW20 (Range finder) + PX4FLOW Optical Flow Camera Board without Sonar (Position hold), no GPS, we tuned the EK2_RNG_M_NSE. Both indoor and outdoor flying are fine. 9-inch propeller drone, 2.3kg. EK2_ALT_SOURCE still use Baro.
Worth understand the Understanding Altitude in ArduPilot.
Thanks, Great!
Can it be set up as GPS backup? (i.e use optical flow when GPS is lost)
And does this module operate at night?
In order to get proper velocity estimation at 100 meters you need a RangeFinder with that range and you will probably need to change the lens on the OF according to this table
https://docs.px4.io/master/en/sensor/px4flow.html#optics
As for ground texture, the OF KLT algorithm is extracting fom a 64 x 64 pixel matrix tfor estimation and the pixelsize is 24 micro meters, so depending on the lens, the surface must have relatively large texture in order to estimate the velocity.
And Yes, the OpticalFlow is fusionned on the EKF and is complementary to the the GPS.
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Thanks dear @ppoirier,
Could you please explain how I set up EKF to combine with GPS?
Because when I set EK2_GPS_TYPE, it only takes one source.
You should use EKF3 and follow wiki
My 4.1.4, 4.1.5 experience sharing.
Has anyone used the Matek Optical Flow Lidar sensor with Copter?
https://a.co/d/cc50Yjv
It should work as it has the Ardupilot settings. Quality and performance, not so sure. I didn’t use it before but from the same IC family. PMW3901 vs PAW3903
the only difference I see is the low-light operating condition.
But if you need a height like 100m, then can consider standalone optical flow + external rangefinder, which is my setup (Hereflow + LW20/C set to rngfnd1).
Thank you for the feedback. I want an indoor alternative to GPS or mocap.
Make sure of this setup.