Why is the drone home point when RTH never accurate

[IflyinWY]

Would someone like to explain how the bird can (theoretically) hold it's position in the sky to within 1 meter or less, but can't find the point it took off from? I'm not trying to be dense here.

I realize there may be signal issues because of buildings or the OP's house.

My RTH typically hits within 24 inches. Next time I am in a canyon I will test RTH and see if it wanders off target as it descends.

 

[N017RW]

Position hold is also augmented by the IMU and this augmentation is minimized during any control input???

 

[Rob2160]

Would someone like to explain how the bird can (theoretically) hold it's position in the sky to within 1 meter or less, but can't find the point it took off from? I'm not trying to be dense here.

I realize there may be signal issues because of buildings or the OP's house.

My RTH typically hits within 24 inches. Next time I am in a canyon I will test RTH and see if it wanders off target as it descends.

It uses the Visual Positioning System when close enough to the ground to lock onto one position if the ground texture is suitable. If you are above the VPS altitude and using GPS only it will move very slowly as the computed GPS position wanders slightly a few meters. If you are watching it the entire time it won't appear to be moving - but if you take off and land 10 minutes later using RTH the distance it has moved can be noticed much easier. Sort of like watching the minute hand on a clock. You can't see it moving, but in 10 minutes it is in a different position. The quad will drift around very slowly and when you hit RTH it might land perfectly at the home point or slightly off.

 

[30secs]

I think DJI has designed an underlying "failsafe-failsafe-RTH" system in the P3. I haven't had the chance to prove this (cold in Aus to fly).
What used to happen in previous models was when RTH was triggered, it would fly straight up to the nominated RTH height (usually 20m).
This scared a lot of pilots when they unintentionally activated RTH. Eg trying discharge battery with props on or accidently turning off the controller whilst the props were running or knocking the controller and the 4xAA batteries fell out etc...

Its common sense if you think about it... if the phantom is a few meters away, why would you need to activate RTH when you can simply land it your self or hit the auto land.

I might start a thread on it as I cannot find it in the "extensive DJI" manual.

Very smart insight. I think you are correct about that. Now.. I want to turn off the controller while the phantom is next to me just to see what happens..

 

[IflyinWY]

Very smart insight. I think you are correct about that. Now.. I want to turn off the controller while the phantom is next to me just to see what happens..

Please take video...

 

[30secs]

If GPS is so inaccurate, how does the p3 sit so still in the sky?

 

[N017RW]

The IMU is also active and senses 6 DOF plus the barometer.

 

[30secs]

The IMU is also active and senses 6 DOF plus the barometer.

What's dof?

And doesn't the barometer only senses altitude?

 

[Thrifty64]

Just my 2 cents: Before flight I always, let it completely warmup, calibrate compass, get home point, and acquire as many satellites as possible. I don't use RTH home often but when I have it has always been within 2 feet.

 

[N017RW]

What's dof?

And doesn't the barometer only senses altitude?

DOF = Degrees of Freedom.

Assuming the P3 is comparable, the P2 IMU has...
3 axis (DoF) gyro
3 axis (DoF) accelerometer
it also includes the barometer (1 DoF) which is not typically considered part of the inertial package.

That now actually adds up to 7.

Now add a 3 axis GPS and 3 axis Magnetometer and you have a total of 13 DoF.

The P3 may have a redundant IMU or whatever (I don't recall) but you can also add the two axis VPS and 1 axis sonar for 16 DoF on the P3.

As far as the last question... altitude is part of sitting 'still'... No ???

 

[adjmirealty]

OP when you say balcony what sort of position are you talking about ? side of a high building ?
try it in an open space and see how accurate it is without gps being blocked on one side

My balcony on second floor big balcony about 15 feet deep and 40 ft long

 

[adjmirealty]

If GPS is so inaccurate, how does the p3 sit so still in the sky?

It's inaccurate to your exact home point when it returns it thinks it's feet from the home point... But GPS is dead on when you fly and for stability

 

[taroh]

If GPS is so inaccurate, how does the p3 sit so still in the sky?

If Phantom stays rock solid, it's done by gyro/accelerometer, not by GPS. Minimum resolution of GPS is around 3-6 feet.

 

[IflyinWY]

DOF = Degrees of Freedom.

Assuming the P3 is comparable, the P2 IMU has...
3 axis (DoF) gyro
3 axis (DoF) accelerometer
it also includes the barometer (1 DoF) which is not typically considered part of the inertial package.

That now actually adds up to 7.

Now add a 3 axis GPS and 3 axis Magnetometer and you have a total of 13 DoF.

The P3 may have a redundant IMU or whatever (I don't recall) but you can also add the two axis VPS and 1 axis sonar for 16 DoF on the P3.

As far as the last question... altitude is part of sitting 'still'... No ???

Are you sure about all this information you are teaching the newbies? It would be a shame to mislead them.

And DOF??? When exactly did you decide to comandeer this "DOF" thing, and relate it to the Phantom?
Was it here, where you were the only one who knew how it related somewhat to the discussion?
http://www.phantompilots.com/threads/your-calibration-opinion.22677/#post-208017

My apologies to the OP, sincerely, but I can't stand by and watch a bunch of, or for that matter any BS being fed to the new folks.

If you know it, say it.
If you think it, say so.
If you've made it up, put on your clown face when you post it.

Quit messing with me 7RW

 

[N017RW]

Are you sure about all this information you are teaching the newbies? It would be a shame to mislead them.

And DOF??? When exactly did you decide to comandeer this "DOF" thing, and relate it to the Phantom?
Was it here, where you were the only one who knew how it related somewhat to the discussion?
http://www.phantompilots.com/threads/your-calibration-opinion.22677/#post-208017

My apologies to the OP, sincerely, but I can't stand by and watch a bunch of, or for that matter any BS being fed to the new folks.

If you know it, say it.
If you think it, say so.
If you've made it up, put on your clown face when you post it.

Quit messing with me 7RW

Is this a Joke?
I hope so, arrogance and ignorance don't go well together.

 

[Chris Vedeler]

If you request the RTH within a 65ft radius of the home point, it will land wherever it's currently at (which is pretty dumb, honestly). This confused me at first too, but it's apparently by design. From the manual (pg 14):

Are you sure that is right? I think the 20 meters is the default RTH height and simply the example used in the manual. I have tested my RTH with a 75 meter height and the bird less than 20 meters from home and it went straight up to 75 meters, flew the few meters until over home and went straight down to land within a meter of home.

 

[N017RW]

Are you sure that is right? I think the 20 meters is the default RTH height and simply the example used in the manual. I have tested my RTH with a 75 meter height and the bird less than 20 meters from home and it went straight up to 75 meters, flew the few meters until over home and went straight down to land within a meter of home.

It seems Mr Ward is referring to or confusing the RTH with the minimum Home Lock radius???
Page 55 of the P3 manual specs that minimum radius to be 10 meters.

 

[Dave Ward]

It seems Mr Ward is referring to or confusing the RTH with the minimum Home Lock radius???
Page 55 of the P3 manual specs that minimum radius to be 10 meters.

This is from page 14:

I've had this happen myself. The first time I triggered RTH from the tx, the drone was hovering about 40ft away and descended straight down instead of going up and coming back to the home point. Luckily, that was a safe, flat spot, but my confidence in convenience RTH was definitely shaken a bit after that.

 

[N017RW]

I must have an old version of the manual (v1.0) as that is not on my page 14.
I have not looked for an update in months. Guess I will now.

 

[Chris Vedeler]

This is from page 14:

View attachment 24867

I've had this happen myself. The first time I triggered RTH from the tx, the drone was hovering about 40ft away and descended straight down instead of going up and coming back to the home point. Luckily, that was a safe, flat spot, but my confidence in convenience RTH was definitely shaken a bit after that.

That isn't in my manual. I have V1.0 2015.04