Welcome to PhantomPilots.com

Sign up for a weekly email of the latest drone news & information

  1. lot49

    Joined:
    Oct 9, 2016
    Messages:
    11
    Likes Received:
    6
    So, this morning I set up a waypoint mission along a river for a couple hundred yards and then lifted the P4 up over the trees and circled back towards take off/start of the mission and ending it to form a sort of question mark shape. At the start of the mission, I was approximately 15 or 16ft off the water but 6ft above take off (on the bank) and the altitude reading was 6ft. At the end the mission, the altitude reading was 256ft. Don't know if it matters, but where I ended the mission, the land is about 40ft higher than the take off. I then flew back to the start of the mission (let the P4 fly itself about half way and then took over) and brought it down closer to the river as I approached the start. But at the point where the P4 looked like it was back to 15ft off the water, the altitude reading was 22ft instead of 6ft..... At that point I wasn't sure if the altitude reading was off, or if it had switched from altitude over take off to altitude over the land/water below, but even if it had, the 22ft still seemed too high. Unfortunately, being a newbie I didn't think to check the VPS. Anyhow, I decided not to run the mission because if the drone used 22ft as it's altitude when it was really at 15ft (over the water, 6ft over take off) and dropped to the start point altitude of 6ft, it would drop into the water.

    Later today I was flying over a field (no mission) and lifting the P4 over the trees at the end. When I started over the field, it was 15ft off the ground (that was the reading and it appeared accurate) and I then brought it up to 200 or so as I cleared the trees. But when I brought the P4 back around and dropped back down to the field, at the point where the altitude reading was 25ft, the VPS indicated 6ft (I thought to look at it this time...) and visually the VPS was the correct reading......

    Is the altitude reading really this variable and inaccurate, or is something else going on?

    Thanks and sorry for the long post, but I wanted to include as much detail as possible.

    Cheers,
    Scott
     
  2. msinger

    Approved Vendor

    Joined:
    Oct 30, 2014
    Messages:
    19,034
    Likes Received:
    5,603
    Location:
    US
    It's not uncommon for the altitude to be off since it's just a calculation. The altitude reported by the VPS is usually pretty accurate since it's using sensors to determine the altitude. Try calibrating the IMU on a level surface to see if that resolves your issue.
     
  3. lot49

    Joined:
    Oct 9, 2016
    Messages:
    11
    Likes Received:
    6
    Will do. Thanks msinger!
     
  4. GMack

    Joined:
    Jul 26, 2016
    Messages:
    575
    Likes Received:
    147
    I don't know, but mine starts at zero and then fluctuates during the flight over flat land with about a 20 minute flight. Flying straight and level it may show 20 feet, then drop to zero feet. Back to starting point and landing it shows -30 feet. This is with Go 3 on iOS ver. 9.3.5 and P4 all updated. Weird. I don't know what effect this bizarre altitude drifting would have on some autonomous flight app.

    I installed the new RC 1.8 and ran through all compass, IMU, and VPS calibration with Assistant 2 (ver.1.0.6) and will check same flight path next week and see if it's any better.
     
  5. lot49

    Joined:
    Oct 9, 2016
    Messages:
    11
    Likes Received:
    6
    Meant to ask before, altitude is based on the take off point, right? And is there a way to switch it to based on the topographical elevation directly below the P4? Anyhow, the altitude variance is something to consider in regards to low altitude waypoint flights. We'll see after I re-calibrate the IMU if there's an improvement, but if not, then it seems like anything under 30ft or so for a waypoint might be dicey....

    Had another, unrelated, waypoints mission scare a couple days ago. At the end of plotting a mission on the same stretch of river, but ending it still down at river level, when I started the mission and initially hit "ok" for the P4 to fly itself to the start (thinking I would take over), the app then froze during the uploading waypoints screen...I couldn't cancel the upload or do anything else, either with the app, or the controller. Fortunately, even though it cut across a curve in the mission path that followed a bend in the river, the P4 barely - like by a couple feet - missed the trees on the inside bank.... Then when it got to the start of the mission, I noticed that only the first waypoint showed on the map, but the P4 flew all 5 that I plotted. At the end of the mission, I finally regained control.

    If that weren't enough, here's a pic of my P4 rescue at the same point on the river on Monday. This time it was just bad flying on my part. Took off and headed up the river, as I'd done a bunch of times already, looked away from the screen for a second, looked back and there was the branch up lose and personal. Guess it wasn't solid enough for obstacle avoidance. Anyhow, neck deep where the ladder is set and it's mid-October in northern NH....Oh yeah, and the branch started to crack just as I got to the P4... It came through unscathed and dry, me not so much.
     

    Attached Files:

  6. Meta4

    Meta4 Moderator
    Staff Member

    Joined:
    Jan 8, 2014
    Messages:
    7,750
    Likes Received:
    3,462
    No ... Except for close to the ground readings with the VPS, the altitude data comes from a barometer which has no way of telling what is below it.
     
  7. lot49

    Joined:
    Oct 9, 2016
    Messages:
    11
    Likes Received:
    6
    Thanks Meta4.
     
  8. Erised

    Joined:
    Apr 2, 2016
    Messages:
    814
    Likes Received:
    336
    I can't help you with your situation but I must say that your framing and content of the picture is very nice even with the ladder!
     
  9. lot49

    Joined:
    Oct 9, 2016
    Messages:
    11
    Likes Received:
    6
    Ha! Thanks but only by chance, that shot was after I got it down and in my nearly hypothermic state, I wasn't thinking too much about framing....:)
     
  10. skyeboysteve

    Joined:
    Jun 7, 2015
    Messages:
    174
    Likes Received:
    64
    Location:
    Texas, USA
    Is there any way to prevent these large variations in reported altitude readings? I've noticed this more with my P4 than P3P... but it really hit home for me this morning... I flew a simple waypoint mission clearing 12 feet tall brush by at least 10 feet. I flew the mission several times with my P3P with no issue. However, when flying the same exact mission with the P4... after one pass with no issue, on the second mission (with Litchi iOS) [and having not landed between running missions], it actually clipped the top of the brush. Fortunately it didn't crash, and simply hovered as I switched into Sports mode a little too late--after the horses had already left the barn. Sure enough, when I looked at it's reported altitude, with VPS indicating 9 feet above the level I took off from, the altimeter was showing 25 feet.
     
  11. Rich C.

    Joined:
    Nov 7, 2016
    Messages:
    50
    Likes Received:
    17
    Interesting. I live in the Nevada High Desert, HAAT is over 4000 feet. The bird seems to calculate my altitude based on what the barometric pressure sensor tells it. Interesting that even though I'm 4000 feet above sea level, when I fire up the bird in the house, the altitude is recorded as 65 feet, which is stupid. I don't trust the displayed altitude. The system seems a bit primitive. We don't all live at sea level.
     
  12. skyeboysteve

    Joined:
    Jun 7, 2015
    Messages:
    174
    Likes Received:
    64
    Location:
    Texas, USA
    In all fairness... the barometer isn't calibrated to pressure altitude at sea level--it just compares the pressure from the pressure it sensed from where it was turned on. Unfortunately, the two P4s I've flown, seem to have barometers that are less accurate than GPS-altitude (which is pretty poor). Flying inside a house might also be a little confusing to it... Air bouncing off walls from the prop wash or even the AC kicking on and off could affect the air pressure enough to give some wild altitude readings.
     
    Rich C. likes this.
  13. Rich C.

    Joined:
    Nov 7, 2016
    Messages:
    50
    Likes Received:
    17
    That's reasonable. Thank you.

    Cheers