Are GPS/ Non-GPS automatic transitions supported in Copter 4.3, when I use GPS and optical flow sensor?

ArduCopter Copter 4.3
1

Hi everyone,
I would like to build a drone with 2 F9P GPS modules. Is it necessary to use a optical flow sensor, for environments with weak GPS signal? Is there any other reason, for using a optical flow sensor in my construction?

2

@LeoSeg,

If you’re flying outdoors at altitudes above 30m then I don’t think an optical flow sensor is going to add much value.

AP Copter-4.3 does support GPS/Non-GPS transitions including GPS<->Optical flow but it’s not a common setup.

3

Hi Mr Randy. Thank you for replying. I really admire your work!!!
I want to ask you:

  1. Could I use the optical flow sensor only for the secondary source of horizontal velocity (parameter EK3_SRC2_VELXY=5) ?
  2. At altitudes lower than 30m, would the sensor help significantly ?
  3. Are optical flow sensor data used for others flight modes, except FlowHold mode ?
1 Like
4

Hi @LeoSeg,

  1. yes, the optical flow sensor can be setup as a secondary velocity source so that both the GPS velocity and the optical flow velocity are fused into EKF’s final estimate as long as EK3_SRC_OPTIONS = 1.
  2. In practice, I don’t think the optical flow will help much if the vehicle is flying outdoors and you’re using the F9 GPS which is quite a good GPS.
  3. Yes, the flow sensor is fused into the EKF’s estimate regardless of flight mode so it will be used for Auto, Guided, Loiter, etc… any mode that requires a position estimate. Re FlowHold, in general I don’t recommend this mode because it tries to directly use the optical flow output instead of using the EKF’s estimate (which is a combination of optical flow, GPS, IMU, etc). FlowHold was originally written for the SkyViper commercial drone which didn’t have a GPS and the direct use of the optical flow just doesn’t work well on many vehicles.

Hope that helps.

5

Mr Randy,
Thank you for answering all my questions. You are a great Sir. I have one last question for you. Which optical flow sensor do you reccomend? I think that HereFlow is the better choise!!!

6

Hi @LeoSeg,

Normally I try not to recommend one sensor over another and instead just recommend reading over the various optical flow options listed on the wiki.

… but one important advantage that the HereFlow has is that it has an onboard gyro so that it can provide the sensor’s rotations directly instead of AP needing to use the gyro values from the autopilot (which are slightly different because they are mounted in different locations on the frame).

I have also heard good things about the ArkFlow sensor but I have not tested it myself nor do I know if it has an onboard gyroscope.

EDIT: I think ArkFlow also has an onboard gyro because it uses the same AP driver as the HereFlow.

1 Like
7

Ok Sir thanks for your help. Good luck with your impressive work!!!
Best regards,
George