Hacker News Reader

Comment by 8note | Hacker News Reader

How do you keep the propellers from cutting people up? Does the parachute also tangle up the prop?

Most (if not all?), like the SafeAir line from ParaZero [0] physically power off the drone before deployment to eliminate both factors as risks. This also allows them to handle flyaway situations effectively, making them useful even when you're not flying over a crowd.

Really the biggest problem is they aren't cheap, costing more than the drone themselves.

0: https://parazero.com/products/safeair-for-dji-mavic/

You can get propeller guards like so[1] to avoid them damaging something (or the blades themselves being damaged).

[1] https://m.dji.com/product/mini-2-360-propeller-guard

They aren’t sharp. Doesn’t seem like a realistic concern tbh.

Being hit in the eye with a flying object spinning at high speeds...how much would it matter how sharp the blades are?

This comment thread is about someone adding a parachute to their drone if they lose power, so it doesn’t fall on someone.

The propellers would not be spinning, and the object would be gently gliding down.

The start of the thread was about either losing power or losing control.

The GP dismissal of the danger of the propellors sounded suspiciously like the guy on YT who just got fined $182k by the FAA, who argued that the first offense for hitting someone in the head should be a $20 fine.

The drone’s blades would likely still be spinning during a parachute descent... albeit at lower revolutions per minute. I’d imagine drones operate like a helicopter: in the event of an engine failure, the helicopter goes into “autorotation” in which the now unpowered rotor blades move due to the air going through the blades as the helicopter descends, thus braking the fall. However, if drones have locking rotors, then in that case the blades would not be rotating during a parachute descent.

Regardless of whether the blades are locked or spinning at lower RPMs, still better than powered drones falling from the sky!

this is a reasonable hypothesis, but quadcopters don't work this way. the propellers are usually not large enough to meaningfully slow the descent of the aircraft. also, quads are not stable the way a helicopter with one large rotor is. a drone is likely to tumble when the power is cut.

Fair point. Didn’t mean to imply that the rotors would meaningfully slow descent. Just meant to say that, parachute or not, the rotors could still be moving while unpowered. It’s more of a technicality since the slow rotation of the tiny blades would probably be towards the bottom of the list of safety concerns, parachute or not.

Danger: Engage safety squints.

Having driven someone to the ER from a drone accident, just because they're not "sharp" doesn't mean they won't cut straight through your arms, hands, or wrist if you touch them while they're landing. When the blades are going at ~10k RPM, it doesn't matter that they're made of plastic or whatever.

I used to work for a drone company. I made sure to go watch the mechanical testing for prop safety. One of the test objects was a chicken leg, and the prop cut through more than 2mm of bone. The props can do some serious damage!

I don't know what, if any, approaches are implemented but one solution is that you can design a safety feature in the motor control to turn off the motor if it detects blockage.

Reply on news.ycombinator.com