Thread: Stuff that is like Holy Crap!

Originally Posted by rush2049

It is hard to tell the speed of an object on film. I based my guess on the ascension rate of the drone on the cloud cover and the drones ability to go past them.

A guess ... I suppose any guess is okay ...

I don't see the drone making it to cloud cover at all. I don't think this thing gets anywhere close to supersonic. No sonic boom, no real point of reference. A fast little beast no doubt, but speed of sound? ... no

... something like "86 mph"

Quadmovr drone is so fast it makes other drones look like they’re standing still | News | Geek.com

quadmovr's blog - RC Groups

Originally Posted by Amador +JP2+

A guess ... I suppose any guess is okay ...

I don't see the drone making it to cloud cover at all. I don't think this thing gets anywhere close to supersonic. No sonic boom, no real point of reference. A fast little beast no doubt, but speed of sound? ... no

... something like "86 mph"

Quadmovr drone is so fast it makes other drones look like they’re standing still | News | Geek.com

quadmovr's blog - RC Groups

I totally agree.

This is nowhere near as fast as watching a fastball fly across home plate. I'd venture a guess and say it's sub 80mph

Definitely impressive. But still clearly far away from Mach 1. Lets do some Math here:

First we can estimate the inherent ultimate speed limit of the setup. We are lucky, the title has every info we need for this. He use 4 cells Lipo battery with a 2000KV motor with 4.5 inch pitch propeller. Math goes:

RPM = 4 * 3.7 * 2000 = 29600
SpeedLimit = RPM * .0254 * 4.5 = 56.4 m/s or 203 km/h or 126 mph or 1/6 the speed of sound

Past this speed, the propeller no longer provides thrust, so the only way to go faster is by going down with the help of gravity.

Now lets estimate the speed from the video itself. Saddly there is no still shot so we can't derive the speed from the image itself. There is one particular horizontal flyby at approx 0:18 that we can use to derive the speed by analysing the doppler effect.

From a spetrum analyser I estimate the frequencys of the whining pitch going WeeeeeOnnnnnnn! going from about 750 Hz to 650 Hz.
Math :

f0 = (f1 + f2)/2
deltaF= f0 - f1
deltaV = deltaF * c / f0

Gives us an horizontal flyby speed of approximately 24.5 m/s or 88 km/h or 55 mph


MythBusted

Originally Posted by Antotabo

Gives us an horizontal flyby speed of approximately 24.5 m/s or 88 km/h or 55 mph


MythBusted

That's consistent with what the speedometer read also.

Holy Crap 1.2