How do you rig a drone so it will crash into a tree and not literally explode into a hundred pieces? How do you waterproof it to survive flying in the snow and rain, race after race?
These are especially important questions when you’re making FPV, or First Person View, racing drones, which exist to race at high speeds and perform dizzying acrobatics. These vehicles don’t play it safe — they crash. A lot! FPV pilots get used to picking up the pieces at the end of every race. Needless to say, they need frequent repairs and even more new components.
I’ve been making and flying FPV drones for about three years. I wrote an earlier post about designing the Über Design Ü180 multi rotor — an FPV drone that prioritizes usability without compromising on performance. Since then, rugged product design techniques have become a priority when designing a successful and appealing drone frame.
These vehicles don’t play it safe — they crash. A lot. FPV pilots get used to picking up the pieces at the end of every race.
Along with a focus on usability, drone design and general product design share the challenge of ruggedization. Product design engineers are always optimizing for a variety of different variables, including strength and water resistance. Of course most consumer product designers don’t have to worry about use cases where a device will be slamming into trees or walls over and over again, but we do need to consider some hostile environments. It’s a good hobby for a mechanical engineer as there are learnings in both directions.
How Do You Optimize a Racing Drone for Strength?
Whether for simplicity of repair and construction or cost, the electronics in a typical multirotor are sometimes exposed and vulnerable to the elements and to damage upon impact. The drone world is somewhat of a Wild West, with lots of makers at all different expertise levels contributing solutions to this widespread problem.
FPV drone frames range from unadorned and barebones to fully enclosed and super-strong — with many alternatives in between. Generally, frames are comprised of carbon fiber plates that are bolted together as in the Impulse RC frame, pictured above. To increase strength, there are more brute-force approaches, such as using thicker carbon-fiber or custom machined aluminum which isn’t always great for racing when you want the vehicles to be as light as possible.
Some have tried to solve the strength issue by creating thermoformed polycarbonate shells. These look like bulbous three-dimensional shapes (see the Kraken, pictured above), and their gradual curves and unibody design can be stronger and lighter than multiple plates that are pieced together. This particular approach works well to protect vehicles used for drone combat, where two drones duel inside a netted area and whoever’s left flying at the end wins. While durability is the key to success here, the expansive surface area of these frames generate too much air resistance for regular racing. This is a rugged solution for a very specific problem.
The drone world is somewhat of a Wild West, with lots of makers at all different expertise levels contributing solutions to this widespread problem.
Then there is the Drone Racing League, or DRL, the most successful racing league right now, after working with ESPN to push FPV racing into primetime. Their pilots have teams of technicians building and repairing drones for them, with hundreds of drones at their disposal for filming and racing. The Racer 3, their main racing platform, uses an injection-molded polycarbonate shell and carbon fiber plate to protect custom electronics, HD cameras, and radios, and a lot of lights crash after crash. The cost of injection-molded tooling usually precludes casual designers from employing molded plastic parts in their designs, but uniquely suits the higher volumes that DRL sees to maintain their fleet of racers.
There are also more exotic solutions such as the Aerodyne Nimbus 195, which relies on a fully carbon fiber, fully sealed monocoque shell. “Monocoque” means the frame is all one piece instead of multiple, connected parts — being one piece makes it much stronger. (This strategy is also used with race car and fighter jet frames.)
With the monocoque, all electronic components are placed inside the drone’s enclosed body and protected from the environment. There’s a video of a truck driving over the Nimbus (pictured above), and it comes out unscathed, with nary a crack! The Nimbus also boasts an IP54 water ingress protection rating, which effectively means splash protection in case it falls into the snow or into a puddle. This type of design requires expertise, experience, and a great deal of time to make.
How Do You Waterproof A Racing Drone?
Waterproofing drones is a little trickier. Although some of the solutions for strength and durability inherently protect the drone from water ingress, they can be costly to produce or difficult to disassemble.
The simplest way that pilots have found to prevent water from shorting out sensitive electronics is plain old electrical tape or heat-shrink tubing. A few wraps of the ubiquitous, semi stretchy black tape will do a decent job of preventing light rain or dirt from getting to the electronics.
The simplest way that pilots have found to prevent water from shorting out sensitive electronics is plain old electrical tape or heat-shrink tubing.
Heat-shrink can be used for a more polished look and those with a hot glue lining (marine grade heat-shrink) can even protect against water or dust ingress. Many pilots also use special self-fusing silicone tape. Originally developed for the military, these stretchy strips of silicone can wrap around exposed electronics and wires to seal them entirely. After minutes, the tape fuses to itself and forms a strong physical and electronic barrier. Removal is easy; the pilot can just cut the tape off and reapply after repairs are made.
Sometimes it’s not always easy or practical to wrap tape around a board and that’s where conformal coating comes in. Like nail polish, you paint it over any exposed electronics and after drying, it provides a protective barrier against dust and fluids. Although they are easy to apply, they don’t protect exposed connectors like USB and can even render them useless if the conformal coating flows into the connector. They can also be challenging to remove without special solvents.
More extreme solutions revolve around mechanically barring water or dust from entering, usually by means of a hermetically sealed enclosure. Here, seal design and casework that can provide adequate sealing force are key. My alma mater, Rutgers University, has developed the Naviator (pictured above), a drone that is able to transition between aerial flight and subaquatic movement. The flight and motor controllers are completely sealed, allowing it to dive underwater and maneuver using the same propellers it uses to fly with. This opens up the possibility of using drones more effectively for surveying and imaging over water, defense and security, or environmental cleanup.
Of course, you can always use a pottant, a rubbery material that is essentially cast and cured around electronics. Since most hobbyists don’t do this, hot glue works in a pinch, although you can’t guarantee that it will look good in the end.
Freedom To Fly
Designing a FPV racing drone to successfully survive crashes in both dry and wet environments is no small feat. As with any product, using the right materials and design principles is just the start. Balancing those factors with cost and usability is often the difference between a frustrating repair day inside and a relaxing race day, flying high outside.
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