Town of Paradise Valley enlists drone as inspector

SB 1449 sets new statewide guidelines for unmanned aircraft usages similar to the one pictured here. (File photo)

One of the most dangerous parts of an inspector’s duties is performing a roof nail inspection.

Walking on a sloped surface often covered in saw dust can result in slips and falls. The classical solution used by fat guys and old guys was to poke at the roof sheathing with a 2” x 4” from below. Now there is a technological solution and that is an unmanned aerial vehicle or drone.

There are a couple of things a drone operator must know when flying in Arizona. Flights of drones are limited to line of sight and 400 feet elevation. Because the control system of the drone is much like that of a video game it is all too easy to get caught up in flying the drone simply by looking at the video screen. This could lead one to fly beyond where the drone is visible to the operator.

On the most professional model of drones the altitude is a programmable number that can be set during initialization. 400 feet is quite high anyway. And, Arizona law prohibits drone flights over nature preserves.
There are a number of options that should be considered in selecting a drone. The three most significant are stability, collision avoidance and camera resolution.

Stability is achieved in hobbyist models by a gyroscope that will return the drone to a level position. In more professional models this stability is achieved by communication with Global Positioning Satellites. The advantage of this system is that it not only knows what level it is, but it also knows the starting point of the flight. This can be a good feature that will return the drone to the starting point as the battery life erodes.

Collision avoidance is achieved on the hobbyist models, if at all, by a ring around the blades. This works well enough if the drone flies into a hard vertical surface like a building. Not so well if it flies into a tree or bush. This collision avoidance is handled quite differently on the professional model. It is done by some combination of stereo vision and infrared sensors.  This not only detects and avoids buildings but also vegetation.

Most importantly is camera resolution. If the drone is going to be used as a substitute for the inspector’s eyes, the camera resolution should be as good as is available. Models are available that have a 20 megapixel capability and can take 4K video at 60 frames per second. So not only can you see as well as being on the roof but it can record the visual image either as a video or as a still photograph.

Multi-tasking is always a good thing. So not only can the drone be used for roof nail inspections, it can assist with fire investigations and with wash mapping. It may be of use to police departments also.

Of course any tool is not without limitations. Even though the professional model drones are quite stable in moderate winds, either high winds or gusty winds can present issues. This is especially true when operating close to a building or to a building component like a parapet or chimney.

Because the communication with the drone is by radio, there may be times when the signal experiences interference.  Professional model drones attempt to overcome this by operating on multiple frequencies and transferring seamlessly between them.

The drone also communicates with the GPS satellites. Generally it won’t allow operation without being in contact with at least 10 different satellites and it prefers a dozen or more. But again there are circumstances where that communication can be interfered with. As long as the 10 satellite minimum is maintained, the drone should operate normally.

Then there is the physical limitation of sight. The gimbal on the drone can pivot between horizontal and vertically down with a simple switch on the control panel.

But it cannot rotate above the horizontal so fire investigations can be limited as looking at the ceiling or the underside of the roof isn’t possible.

But even with these limitations a drone can be a useful tool to lessen inspector risk and increase inspector efficiency.

Editor’s note: Mr. Lee is the building inspector for the Town of Paradise Valley

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