Recently, I destroyed the TFmini Lidar in my companies copter. I was flying into a very high powered (30 W) infrared laser at 100 meters height (a Wind-Lidar to measure wind speed), and forgot to put tape on the optics of the TFmini .
Now I would like to replace this sensor. However, I never really noticed any obvious benefit of the TFmini in the flight modes I am using (Loiter, Auto and Stabilize).
I have seen the new Hex HereFlow, and I wonder if that gives any benefit in these flight modes. Will it help to make GPS position hold (loiter) more reliable? We recently had some problems with GPS position hold when we needed to fly in between buildings.
Question: Is the velocity and (relative) position estimate of the optical flow sensor fused with the GPS position estimate?
Dear William,
Yes, the Hereflow when set up correctly will work in a similar way as the PX4flow, where optical flow data will be fused in the onboard EKF frame work to provide position and velocity estimate.
When GPS data is available, both data will be fused together to provide a more reliable estimate.
For queries about our products, you are encouraged to post in our Cubepilot forum: discuss.cubepilot.org
Thank you!
Best regards,
Betty
Furthermore, I read this
The good news is that this implementation is compatible data available on the existing MAVLINK optical_flow message and has also shown it is possible to estimate height above ground without use of a range sensor (if you have a independent measure of velocity like GPS), or can it can constrain drift when GPS is not available if you have a means of estimating height above ground, eg laser).
The best lens to use will depend on the range of speed and height the optical flow is required to operate over. For position and low speed loiter control with copters, a narrow fov lens like the 16mm one fitted as standard to the PX4Flow is a better choice. For fixed wing applications where terrain height estimation is required and the sensor is there to augment the GPS and provide the ability to ride out periods without GPS, a larger fov, smaller focal length lens will be a better choice.
(from https://groups.google.com/d/msg/drones-discuss/SqgXeojbiZU/GHRgYbYHDIsJ)
That makes me confident that optical flow will make the position, velocity and even altitude estimate more reliable when I have the HereFlow installed (but I still need the TFmini to remove position glitches of the GPS).
Yes the opticalflow will improve the positionning of your copter, specially if you have a mid game GPS like ublox m8n. Indeend, the OF will provide velocity input in the EKF, so you can get ride of some error from the integration of the Accelerometer data !
As you are flying between buildings, you will gain some stability when gps is disturbed.
Infortunaly, as all sensors, OF doesn’t work well on all conditions, so you will need to test for effectiveness.
On the benefit of TFMini, you should be able to see easily on low alt. Without it the alt will variate on a 10-30cm range depending on the wind. With, it should stay around 10cm !
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