Must launch from garage roof - suggestions?

[sdunwell]

The single most effective method to prevent a fly away is to check that the heading shown on the map display agrees with the actual orientation of the AC.

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If they don't agree that means the AC, for whatever reason, has the wrong heading value and erratic flight and/or flyaway is likely. One need not attempt to determine if launching from a table, raised arm, etc. will move the AC out of any geomagnetic distortion. Just check that the orientations are the same.

in general, doesn't rebar absorb and eventually align with the prevailing mag field? Local distortions caused by cars moving about inside a garage?

 

[BudWalker]

in general, doesn't rebar absorb and eventually align with the prevailing mag field? Local distortions caused by cars moving about inside a garage?

I suppose it's possible for the rebar to become slightly magnetized - a "hard iron" effect. But, the rebar will still bend and distort the geomagnetic field - the "soft iron" effect. Both effects will cause the geomagnetic field to be distorted at most points around the rebar. It's just a question of the distance required for those effects to be negligible.

Attempting to determine if, where and by how much the geomagnetic field is distorted without actually measuring it is almost impossible. Better to let the I2 tell you what it thinks the heading is.

 

[JimBinDallas]

I have also discovered that being within 80 feet of my Tesla or Prius Prime was guaranteed to send the compass crazy. Apparently the magnetic structure in the motors has quite a reach.

 

[davidjmurray]

The single most effective method to prevent a fly away is to check that the heading shown on the map display agrees with the actual orientation of the AC.

Bud: Your input misses the issue raised in the original post (I think). Sometimes the I2 refuses to take off because its control software determines that there's a compass error, and the only way to get around this condition is to either successfully recalibrate the compass, or to power down, move the drone, and try powering up again. So that's not a condition you want to run into on a job, especially if you don't have the flexibility to change where you take off from, and if you know that the environment is likely to trigger a compass error. And, unfortunately, concrete roofs are one such setting where this often happens. So the OP isn't asking how to know if there's a real compass calibration problem, or how to avoid a fly away. He's asking if there's anything he can do to prevent the roof top environment from triggering a compass error. The problem is usually caused by metal reinforcement material within the concrete.

The reason you don't want to recalibrate your compass when nearby objects are causing the problem, is that you want your compass to be properly calibrated for the environment through which your drone is flying, and those nearby objects, such as the metal in the roof, won't be relevant once you take off and get any distance away. If you were to successfully recalibrate your compass while standing on the metal-containing roof, the calibration would become incorrect once the drone leaves the immediate vicinity of the roof.

sdunwell: I have successfully overcome rooftop compass errors using a plastic folding table as mentioned above. But it has also failed me. Hopefully you'll be able to do a site visit ahead of the shoot date to evaluate conditions. If you can't make it work from the roof, here's something else I've done: A couple of times I needed to operate my drone from a tiny roof top "widow's walk" due to required piloting site lines. There was no room to launch or land the drone from up there (there was not even room for an assistant to help with hand release/catch). So, we kept the drone on the ground, in a location visible to me from the roof top. My assistant, standing at ground level, turned on the drone. I, standing on the roof, turned on the RC, and remotely controlled the drone's take off and landing. We had two other helpers at ground level to ensure public safety during takeoff landing. Piloting the drone from above like that is certainly interesting...you have to compensate for the strange perspective, especially when landing. Good luck!

 

[sdunwell]

Bud: Your input misses the issue raised in the original post (I think). Sometimes the I2 refuses to take off because its control software determines that there's a compass error, and the only way to get around this condition is to either successfully recalibrate the compass, or to power down, move the drone, and try powering up again. So that's not a condition you want to run into on a job, especially if you don't have the flexibility to change where you take off from, and if you know that the environment is likely to trigger a compass error. And, unfortunately, concrete roofs are one such setting where this often happens. So the OP isn't asking how to know if there's a real compass calibration problem, or how to avoid a fly away. He's asking if there's anything he can do to prevent the roof top environment from triggering a compass error. The problem is usually caused by metal reinforcement material within the concrete.

The reason you don't want to recalibrate your compass when nearby objects are causing the problem, is that you want your compass to be properly calibrated for the environment through which your drone is flying, and those nearby objects, such as the metal in the roof, won't be relevant once you take off and get any distance away. If you were to successfully recalibrate your compass while standing on the metal-containing roof, the calibration would become incorrect once the drone leaves the immediate vicinity of the roof.

sdunwell: I have successfully overcome rooftop compass errors using a plastic folding table as mentioned above. But it has also failed me. Hopefully you'll be able to do a site visit ahead of the shoot date to evaluate conditions. If you can't make it work from the roof, here's something else I've done: A couple of times I needed to operate my drone from a tiny roof top "widow's walk" due to required piloting site lines. There was no room to launch or land the drone from up there (there was not even room for an assistant to help with hand release/catch). So, we kept the drone on the ground, in a location visible to me from the roof top. My assistant, standing at ground level, turned on the drone. I, standing on the roof, turned on the RC, and remotely controlled the drone's take off and landing. We had two other helpers at ground level to ensure public safety during takeoff landing. Piloting the drone from above like that is certainly interesting...you have to compensate for the strange perspective, especially when landing. Good luck!

Jim & Bud & David et al - thanks for this helpful discussion. I really appreciate it. ..I will pre-test with the card table & see what the compass says. ..Steve

 

[mmarian]

Philz and mmarian and dobmatt...this is really helpful. The plastic card table sounds good. In my own experience (I2 and Mavic 2P); CompassCal has been required several times in places with no evident ferrous material....such as a field of dirt or gravel. Maybe other pilots can report their experiences launching from concrete parking garages. Thank you.

If you get the amber light flashing and warning on the screen check your compass value under the sensor status manu. If it is in green area try to take off and just hover a few meters above your take off point. The compass might "recover" and you might get the green light instead of amber. Be prepared to go into Atti and land if something goes funny. In most cases, from my experience at least the green light comes back in air and you can then go and fly the mission with peace in your mind.

 

[BudWalker]

Bud: Your input misses the issue raised in the original post (I think). Sometimes the I2 refuses to take off because its control software determines that there's a compass error, and the only way to get around this condition is to either successfully recalibrate the compass, or to power down, move the drone, and try powering up again. So that's not a condition you want to run into on a job, especially if you don't have the flexibility to change where you take off from, and if you know that the environment is likely to trigger a compass error. And, unfortunately, concrete roofs are one such setting where this often happens. So the OP isn't asking how to know if there's a real compass calibration problem, or how to avoid a fly away. He's asking if there's anything he can do to prevent the roof top environment from triggering a compass error. The problem is usually caused by metal reinforcement material within the concrete.

The reason you don't want to recalibrate your compass when nearby objects are causing the problem, is that you want your compass to be properly calibrated for the environment through which your drone is flying, and those nearby objects, such as the metal in the roof, won't be relevant once you take off and get any distance away. If you were to successfully recalibrate your compass while standing on the metal-containing roof, the calibration would become incorrect once the drone leaves the immediate vicinity of the roof.

sdunwell: I have successfully overcome rooftop compass errors using a plastic folding table as mentioned above. But it has also failed me. Hopefully you'll be able to do a site visit ahead of the shoot date to evaluate conditions. If you can't make it work from the roof, here's something else I've done: A couple of times I needed to operate my drone from a tiny roof top "widow's walk" due to required piloting site lines. There was no room to launch or land the drone from up there (there was not even room for an assistant to help with hand release/catch). So, we kept the drone on the ground, in a location visible to me from the roof top. My assistant, standing at ground level, turned on the drone. I, standing on the roof, turned on the RC, and remotely controlled the drone's take off and landing. We had two other helpers at ground level to ensure public safety during takeoff landing. Piloting the drone from above like that is certainly interesting...you have to compensate for the strange perspective, especially when landing. Good luck!

In the end the OP is still going to have to decide if the I2 is far enough from any ferrous material for safe flight. Checking for orientation consistency is the best way to know if it's safe to launch. Many fly aways have occurred with the Go App showing acceptable interference levels (in the green) with the motors being allowed to start. The orientation check will prevent this.

I agree that calibrating at the launch site isn't the answer. But, for a different reason. Calibration is only about measuring the AC's internal magnetic properties. Except for field strength any external magnetic properties can not be measured or compensated for. If the launch site is geomagnetically distorted enough to cause a fly away then no calibration at that site or anywhere else will change that.

The controversy about whether it's a good idea to re-calibrate at every launch is, IMHO, moot. It's not necessary since the calibration is only measuring the internal magnetic field which doesn't change with location. But, it doesn't hurt either since calibrating where you shouldn't will lead to the "calibration failed, move to a different location" message. If it makes the pilot feel secure then go for it.

 

[sdunwell]

Successful outcome update on I2. Hollow-core door placed over plastic sawhorses, making a 3x6 ft airport for take-off. Landing on the garage roof adjacent (concrete w/re-bar). Repeat 15 times over 2month period to get all views needed. Each power-up preflight OK with compass. Almost every landing onto concrete followed by "compass calibrate required" flag, which was ignored. Power off, change batteries, put back on the little table, compass good, back into the air. All OK. Similar results with Mavic 2Pro, on the table, or on a 4ft aluminum ladder with a 2 ft square plywood piece bolted on the top (brass bolt) for airport. In addition, each flight required a FAA authorization to exceed LAANC altitude. All requests granted except one (no reason given), usually within 48 hrs. Very built-up urban location, next to a 700 ft glass-steel tower. Panoramic photo technique discussed in a separate post. ...Many many thanks to all who commented and advised me on this.

 

[Dobmatt]

Successful outcome update on I2. Hollow-core door placed over plastic sawhorses, making a 3x6 ft airport for take-off. Landing on the garage roof adjacent (concrete w/re-bar). Repeat 15 times over 2month period to get all views needed. Each power-up preflight OK with compass. Almost every landing onto concrete followed by "compass calibrate required" flag, which was ignored. Power off, change batteries, put back on the little table, compass good, back into the air. All OK. Similar results with Mavic 2Pro, on the table, or on a 4ft aluminum ladder with a 2 ft square plywood piece bolted on the top (brass bolt) for airport. In addition, each flight required a FAA authorization to exceed LAANC altitude. All requests granted except one (no reason given), usually within 48 hrs. Very built-up urban location, next to a 700 ft glass-steel tower. Panoramic photo technique discussed in a separate post. ...Many many thanks to all who commented and advised me on this.

Thanks for sharing. It confirms my experience as well ...

 

[sdunwell]

Yes - your comments were very helpful. Each power-up is a separate instance, with any previous compass issues discarded and forgotten. Saw horses approx 3 ft above the concrete deck.