Altitude is not always accurate.

[N017RW]

Why would it need to know those things (in this application)?

I would imagine that at the time of manufacture the barometer is calibrated to a known pressure for pass/fail testing and validating proper operation.

Having said that, once it's installed in the Naza it is simply an in-flight relative pressure measurement. As others have said it assigns the take-off pressure as Zero feet above the ground.

AGL, AMSL, serve no function to the flight controller in this application.

Sure atmospheric pressure changes would have an effect but how much change would you expect during the duration of a flight?

 

[WessexWyvern]

Why would it need to know those things (in this application)?

I would imagine that at the time of manufacture the barometer is calibrated to a known pressure for pass/fail testing and validating proper operation.

Having said that, once it's installed in the Naza it is simply an in-flight relative pressure measurement. As others have said it assigns the take-off pressure as Zero feet above the ground.

AGL, AMSL, serve no function to the flight controller in this application.

Sure atmospheric pressure changes would have an effect but how much change would you expect during the duration of a flight?

Because a barometric altimeter senses pressure and pressure varies depending on ambient conditions, not just with altitude and the phantom has no indication of the altitude it is starting off from. This is why I asked whether it indicates above MSL or AGL, if it's AGL then yes, it only needs to sense change as you have said.

 

[N017RW]

While I agree there are other conditions which alter barometric pressure at any given point at any given time, I addressed that in my last sentence.

It seems the designers determined it doesn't need those other things in this application (a hobby grade aircraft) since there is no need for any other reference other than the take-off point to operate as intended.

My comments are within the context of Naza MCs.

 

[WessexWyvern]

It is still only accurate assuming a standard lapse rate of 2 deg c per 1000ft though. I agree it's near enough for hobbyists but the op was asking why his altitude reading wasn't always accurate.

 

[N017RW]

I guess it's only natural to expect such performance from something you paid $600-$1200 for but the reality is the Phantom is constructed from the manufacturer's low-tier components.

 

[dbfletcher]

I also posted about my phantom losing accuracy in altitude as it flew. When first powering up, it would normally show 1-3ft in altitude when sitting on the ground before launch. After i fly around for a while and come back to a 5ft hover, it would typically report that altitude as 30-40 ft. I tried the advance IMU calibration as suggested and got the green tick.. but i still have the same issue. I did the calibration after letting the Phantom "cool down" for 5 hours.. and started the calibration withing 1 minute of plugging the batter in and connecting to my computer. It seems as it heats up that is where the problem start to manifest so in my mind it makes sense to do the calibration when an typical operation temperature rather than cold. I havent tried it yet, but the cold IMU adv. Cal didnt seem to help at all.

Doug Fletcher

 

[PsychopathRC]

I also posted about my phantom losing accuracy in altitude as it flew. When first powering up, it would normally show 1-3ft in altitude when sitting on the ground before launch. After i fly around for a while and come back to a 5ft hover, it would typically report that altitude as 30-40 ft. I tried the advance IMU calibration as suggested and got the green tick.. but i still have the same issue. I did the calibration after letting the Phantom "cool down" for 5 hours.. and started the calibration withing 1 minute of plugging the batter in and connecting to my computer. It seems as it heats up that is where the problem start to manifest so in my mind it makes sense to do the calibration when an typical operation temperature rather than cold. I havent tried it yet, but the cold IMU adv. Cal didnt seem to help at all.

Doug Fletcher

I can get this too. Upon powering on, I might be 6 feet up. Then when landing, I'm 15 feet up (On the ground). I've been told not to worry though, as these numbers are more estimates, then precision figures. So I'm not worried lol.

 

[doug86]

I too have started to notice that the altitude readout when on the ground is often well above zero. Today, even turning off the Phantom completely and then starting it back up while it was on the ground (at about 20' above sea level), it reads altitude of +20' or more. And, as I fly around, the discrepancy seems to grow. I came home and was reading this thread, and then it occurred to me that I'm flying in winter, and the phantom just came from my warm home.

I don't know exactly how temperature can or does affect the internal barometer, but I suspect that if I left it out in this cold East Coast weather for an hour before powering up, this issue would go away.

I'm surprised that DJI hasn't created a software solution that allows you to just say "you're on the ground right now" to the NAZA. IF we can reset the home point, how hard would it be to reset the ground level to current barometer reading?

 

[JezzaInSingapore]

I too have started to notice that the altitude readout when on the ground is often well above zero. Today, even turning off the Phantom completely and then starting it back up while it was on the ground (at about 20' above sea level), it reads altitude of +20' or more. And, as I fly around, the discrepancy seems to grow. I came home and was reading this thread, and then it occurred to me that I'm flying in winter, and the phantom just came from my warm home.

I don't know exactly how temperature can or does affect the internal barometer, but I suspect that if I left it out in this cold East Coast weather for an hour before powering up, this issue would go away.

I'm surprised that DJI hasn't created a software solution that allows you to just say "you're on the ground right now" to the NAZA. IF we can reset the home point, how hard would it be to reset the ground level to current barometer reading?

I suspect the barometer is calibrated to 29.92 inches / mercury at 15C, known as a standard day. Sticking it on the ground and telling it "zero" would fix. Less temperature = higher

 

[N017RW]

Basically that's what it does. Current pressure is assigned '0 altitude' upon take-off.

BTW this thread is 1.5 years old