Cheerson CX-OF low cost optical flow sensor testing

ppoirier · January 4, 2019, 3:48pm

Yes altitude holds by tfmini
Set ekf3 altitude source to rangefinder

rmackay9 · January 5, 2019, 1:10am

Nicely done. Strange that EK2 didn’t work, it should.

I just want to be clear to others reading this thread that I recommend EKx_ALT_SOURCE be left at the default of 0 (for barometer). It should not be set to “1” for Rangefinder.

In @ppoirier’s test environment which is indoors with a flat floor it’s perhaps OK but in 99% of situations I do not recommend setting the altitude source to range finder. I dealt with yet another user support issue yesterday caused by a user setting this parameter to range finder. I feel like I’m constantly fighting a battle to stop people from changing this parameter because it rarely goes well.

ppoirier · January 5, 2019, 1:42am

Yes I agree about usage of the rangefinder as the primary altitude source is not recommended for normal flights.

I generally start tests in stabilize , doing the usual trim and PID land, check the logs, confirm rangefinder reading and stability and then use it as primary source.

Start in stabilize, takeoff and then switch to alt hold, check for stability and response. Land and takeoff in alt hold mode to confirm.

As for loiter, set ekf home , hold quad a simulate a flight , confirm that vehicle movements ate showned on map. Takeoff in AltHold , make sure vehicle is stable and switch to Loiter, get ready to switch back.

Last test I did is takeoff in guided an did different guided “fly to” and land.

catalyst1 · January 7, 2019, 1:30am

Any kind soul able to nudge me in the correct direction for downloading 3.7 Dev?
I have a few CX-OF sensors that I would love to integrate to a pixracer to offer more test results.

Thanks yall! (Happy 2019 everyone!)

rmackay9 · January 7, 2019, 1:31am

@catalyst1,

We included CX-OF support in Copter-3.6.4 so it’s available in the stable release. I’ll update the notes above, thanks!

catalyst1 · January 7, 2019, 1:34am

awesome sir!
I’ll load it up to get it tested!

anbello · January 17, 2019, 2:35pm

What I described above as a strange behavior:

… when I switch from Loiter to FlowHold I see the Copter oscillate quickly in roll and pitch (like if the Roll / Pitch PID was bad tuned), then if I move the quad a little bit around (with RC) the oscillation disappear and the Copter remain stable.

should be a normal behavior from what I read in the wiki:

Because no Lidar is used in this mode, the optical flow sensor is used both to estimate the vehicle’s height above the surface and the vehicle’s speed. Soon after takeoff or after there have been large changes in the height above the surface the vehicle may wobble as it learns the new height and velocity.

ppoirier · January 17, 2019, 3:31pm

Well, that is a proof that the wiki is pretty complete , thanks to @rmackay9

BTW I see you can adjust parameters

github.com

ArduPilot/ardupilot/blob/master/ArduCopter/mode_flowhold.cpp#L133


/*
 calculate desired attitude from flow sensor. Called when flow sensor is healthy
*/
void Copter::ModeFlowHold::flowhold_flow_to_angle(Vector2f &bf_angles, bool stick_input)
{
   uint32_t now = AP_HAL::millis();


   // get corrected raw flow rate
   Vector2f raw_flow = copter.optflow.flowRate() - copter.optflow.bodyRate();


   // limit sensor flow, this prevents oscillation at low altitudes
   raw_flow.x = constrain_float(raw_flow.x, -flow_max, flow_max);
   raw_flow.y = constrain_float(raw_flow.y, -flow_max, flow_max);


   // filter the flow rate
   Vector2f sensor_flow = flow_filter.apply(raw_flow);


   // scale by height estimate, limiting it to height_min to height_max
   float ins_height = copter.inertial_nav.get_altitude() * 0.01;
   float height_estimate = ins_height + height_offset;

Gino_Nencioni · January 22, 2019, 9:52am

hi @ppoirier could kindly explain me how to force the drivers to “other board”…thx in advanced!

ppoirier · January 22, 2019, 10:15am

In order to force the sensor on these board, you have to copy and paste line 108 to line 122

github.com

ArduPilot/ardupilot/blob/master/libraries/AP_OpticalFlow/OpticalFlow.cpp#L108


    // possibly have pixhart on external SPI
    backend = AP_OpticalFlow_Pixart::detect("pixartflow", *this);
}
if (AP_BoardConfig::get_board_type() == AP_BoardConfig::PX4_BOARD_SP01) {
    backend = AP_OpticalFlow_Pixart::detect("pixartPC15", *this);
}
if (backend == nullptr) {
    backend = AP_OpticalFlow_PX4Flow::detect(*this);
}
if (backend == nullptr) {
    backend = AP_OpticalFlow_CXOF::detect(*this);
}
#elif CONFIG_HAL_BOARD == HAL_BOARD_SITL
backend = new AP_OpticalFlow_SITL(*this);
#elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_BEBOP
backend = new AP_OpticalFlow_Onboard(*this);
#elif CONFIG_HAL_BOARD == HAL_BOARD_LINUX
backend = AP_OpticalFlow_PX4Flow::detect(*this);
#elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_CHIBIOS_SKYVIPER_F412
backend = AP_OpticalFlow_Pixart::detect("pixartflow", *this);
#elif defined(HAL_HAVE_PIXARTFLOW_SPI)

ppoirier · January 22, 2019, 10:17am

I think @rmackay9 is working on a PR for this

rmackay9 · January 23, 2019, 11:21am

I must admit that I don’t actually know exactly what’s required to make it available for all boards. Perhaps it’s moving this chunk to be below the “#end”

if (backend == nullptr) {
    backend = AP_OpticalFlow_CXOF::detect(*this);
}

Gino_Nencioni · January 23, 2019, 11:47am

Big thx!!!
Now works fine!!!
Thx Again.

Eosbandi · February 3, 2019, 12:26am

I can confirm it does not get detected on MiniPix either.
Apparently AP_FEATURE_BOARD_DETECT is 0 on a number of ChibiOS boards. Moving detection outside of the #if AP_FEATURE_BOARD_DETECT makes it detected.

Amit · February 12, 2019, 10:02am

Thanks, this looks great.
Does the optical flow sensors can be use for an autonomous mission without GPS like the Zed camera?

rmackay9 · February 12, 2019, 11:43pm

@Amit, yes, but like the ZED camera there will be some position drift and that drift increases if the vehicle flies higher… so it will probably work OK if the vehicle stays below 20m and the mission isn’t too long.

anbello · February 13, 2019, 8:26am

@rmackay9 This is true only with optical flow + range finder, with only optical flow in flowhold is not possible, do I understand well?

rmackay9 · February 13, 2019, 11:10am

@anbello, with optical flow + range finder all modes should work without GPS including Auto mode. FlowHold mode will work even without the rangefinder.

Eosbandi · February 13, 2019, 7:09pm

@rmackay9 Any news on EKF switching to optical flow only in case of in flight GPS failure ?

rmackay9 · February 15, 2019, 2:54am

@Eosbandi, No progress on that issue I’m afraid. I think the first step is probably to confirm whether the issues exists when using EKF3. txs!