I’m using a here 3+ with a cube orange (not +) and ardupilot 4.1.5. I’ve done 100+ successful flights without any manner of symptom or error. However, the cold start of the GPS/drone rarely takes a long time to acquire a home position. I’d like to know if this is expected and normal behavior.
The procedure is:
- start with a drone that hasn’t been turned on in 12hr+ to ensure cold start conditions
- turn on controller or laptop to see when it acquires home position
- turn on the drone and time the acquisition of home position
Obviously step 3 is a composite score of the autopilot booting, gps booting, gps acquisition rate, and autopilot algorithms. Qualitatively, I have seen no indicators that it is autopilot driven.
Typical results are a 80-100 second cold start. Occasionally it will take more - 3 minutes, 5 minutes, or even 10+ minutes (after which I stop timing).
The frequency is wildly inconsistent. At worst (week of Oct 16) it exceeded 2 minutes 4/15 times at 134, 381, 410, and 600+ seconds. I flew after the 410 second acquisition and observed no performance degradation in the air. Those were with AP 4.1.5. I’ve since updated to 4.5.6 and upgraded 1 drone with a here4, and I am 1/9 over 2 minutes, with a 180s start on the here4. Before August, I can only recall this happening 1 time (the drones were manufactured Q2 2024), but I also hadn’t noticed it was happening at all so that may not be reliable information.
Hot starts (any start within a few hours of a cold start) are not affected and are consistently 45-55 seconds. I can collect parameters if needed, but seeing that it works correctly in flight I’m guessing that isn’t the issue. Even if a cold start is slow, I can’t eyeball any degradation in the GPS position’s stability after a hot start.
Lastly, I have experienced this across 3 here3+ and 1 here4. I have controlled my data for the following and seen no correlations:
- Atmospheric and solar weather
- Orientation: both drone and GPS right side up and level
- Environment: the drone elevated 18" off the ground on a plastic bucket, on asphalt or grassy field, with no obstructions in a 45 degree cone pointing upwards from the drone
- I have avoided any emitter strong than my telemetry radio (RFD900)
- Geographic location: tested at 8 locations across two states in the mid west USA
- Satellite count/HDOP: when home position is slow to acquire, the satellite count is slow to go up, but does go up. In the 600 second case, it acquired 14 satellites within a few minutes and still wouldn’t acquire home. I’ve never seen any anomalous behavior between HDOP with respect to satellite count.
I did see strong correlation when flying at the edge of lake michigan, but that exhibited the additional symptom of an abnormally unstable GPS position. Myself and those I worked with attributed that to GPS multipathing off the water, which have seen before in other products we have that use a different uBlox module. I believe it was a different issue, but it is the only other issue we’ve had with the Here3+.
I have not tried connecting the drone/GPS to u-center via droneCAN. I have no idea what I would look for, or how I would compare that data to my existing data.
Thanks for any insight and a mostly exceptional product.