How High can a DJI Mavic Drone Go??

[Major Lee]

It seems that they can go quite high, in fact, Mt Everest high!

 

[ZachariasX]

21 minutes ago, Major Lee said:

Mt Everest high!

…if the weather is right.

But the juice you can pull from batteries these days is truly insane. In RC cars they currently can pull up to 60 hp from those small batteries. Makes your car go 220+ mph…

[wheelsup_cavu]

8 hours ago, ZachariasX said:

Makes your car go 220+ mph…

Scale speed or true speed?

 

Wheels

[ZachariasX]

4 hours ago, wheelsup_cavu said:

Scale speed or true speed?

 

Wheels

True speed.

See here as reference:

It‘s insane what you can do with just stock cars and you just up their power with off the shelf motors and batteries. It‘s the battery the limits your motor. The motor on itself will just increase power until it gets on fire.

Power requirements for speed scale to the cube vs. the speed gained. Same as in aircraft. Funny, almost none of the guys running cars know that, it helps choosing the gearing and answers a question like „why am I getting slower? I should be faster with a larger pinion!“

Same with real cars:

If an Audi RS4 needs 14 hp to sustain 100 km/h, then for 200 km/h it will need:

2^3 * 14 = 112 [hp]

and to go 300 km/h (3 times as fast as 100 km/h) it will need

3^3 * 14 = 378 [hp].

In the real world, this matches about exactly with its performance read by telemetry and its top speed. (At least when I had such a car at hand.)

As we obviously do get limited in rpm of the motor (past 50‘000 it gets dodgy…), what we have to do is increase power draw (Amps) from the battery. If you can do that, depends on the type of battery.

In the good old days of NiCd cells and „The Fall Guy“ on TV, in my RC flying club there was one (several times world champion though) who had electric gliders that could climb vertically. Most impressive. I put the most insane and expensive motor in my little RC and paired it with the batteries I had, 7 cell NiCd. The results were „meh“ to the degree of almost permanent discuragement. Minor gains from a 540 type silver can motor, but not much more. How come?

Answer: internal resistance of the battery cells. This is what makes the drone go to the top of mount everst.

Knowing the formula U = R * I, I can calculate the power draw to produce, say 1 Volt of voltage drop.

A fully charged NiMH battery has about 70 milliOhms internal resistance, increasing with discharge (as with any battery). Hence

1 V = 0.07 Ohms * X A

X A = 1 V / 0.07 Ohm

X = 14 A.

This means, I will run my standard 6 cell NiMH (6 * 1.4 V = 7.4 V) pulling 14 Amps and then the Voltage will be 7.4 V - 1 V = 6.4 V. 

I will produce 6.4 V * 14 A = 89.6 Watts.

The RC guy mentioned needed to pack about 40 cells in his plane to be able to draw about 500 W (~89.6 / 7 * 40) to have his plane go vertical.

Enter LiPo batteries.

Their internal resistance is about 1 mOhm at full charge for a very good LiPo pack. Looking at the formula above, I can see directly that for the same drop in voltage, I get 70 (!) times the power, meaning in the example above that when I put load on the very same system used above to get a voltage drop of 1 V, I get 6272 W! Now compare that power to the 40 Cell NiCd example. Of course in the real world, 2 cell LiPo will not tolerate continuous 6 kW (but in that order) discharge, but this max discharge rate (a multiple of the capacity, labelled „C“) is where all the fraud in selling batteries is.

You can see now that while running the system with no load (no propeller) there is no difference between using a NiCd or a LiPo battery. Both batteries will easily provide enough power to spin the motor at max rpm, where it just tops out. But as soon as you put load on it, things change monumentally.

In essence, you don‘t need new motors to make things fly to the top of Mount Everest. A new battery will do.

However. 

There is the efficiency of the motor. Old brushed motors have some 80% efficiency. If I fire them up with 100 W, then they are heated with 20 W, which is not that much. If I fire the same motor with 1000 W, then I suddenly need to dissipate 200 W, which is a lot in a small motor. Also, I am missing the heat in propulsion, hence I have only 800 W on the shaft from the 1000 W I put in.

Take brushless and I get 98% efficiency. Firing in 1000 W I not only get 180 more Watts usable power, I only have 20 W to dissipate as heat!

Battery tech is the most underrated achievement in the last decades. Motors are almost no issue.

 

Raz in the vid posted above is a prominent figure in the speedrunning world. He knows what he is doing. Totally crazy stuff.

[Boo]

Incredible to see how busy it is. Like Snowdon on a summer's day.  I presume the lower base stations get the most most traffic and many of those dont go on to actually summit. 

[ZachariasX]

1 hour ago, Boo said:

many of those dont go on to actually summit. 

Why would you go there when not trying to go up? given the deah numbers, a lot of folks try to go up.

This is not mountaineering, this is sick.

[Boo]

2 hours ago, ZachariasX said:

Why would you go there when not trying to go up? given the deah numbers, a lot of folks try to go up.

This is not mountaineering, this is sick.

Hmmm - does somewhat take away that feeling of a great adventure. I presume theres a Maccy Ds on route or at least a Starbiucks? 

[ZachariasX]

3 hours ago, Boo said:

I presume theres a Maccy Ds on route or at least a Starbiucks? 

There was a TV show in Switzerland called „Verstehen Sie Spass?“ (basically it translates into „you have a sense of humor?“ but in its essence it is untranslatable into Shakespeares language, as only people lacking a true sense of humor can come up with such a syntax), an analogue of the Show „Surprise, Surprise“ or „Candid Camera“. Messner annonced climbing the Matterhorn along with some other climbers. The show producers thought of that as a great occasion to punk him and then had a helicopter bring up the kiosk right toward the end of the climbing route by flying in from the Italian side of the mountain, hence the climbers never saw a Helicopter.

Messner was monumentally pissed. Even when the kiosk guy told him that every morning would carry all daily newspapers up on the summit to have them ready for the climbers that would come later, he didntn‘t realize getting punked. The further statement that on every mountaintop, there would be a kiosk later on, that was too horrifying for Messner to come to his senses, something Messner admitted later on. He only „got the joke“ once they flew in the Showrunner. There are no subtitles which makes it less painful to watch.

But now we have Kiosks on Mount Everest. Sort of.

Edited August 2 by ZachariasX

[Boo]

I worked for several years as an instructor in the Lake in the UK. I would always get peed off at "tourists" ruining my solitude. Took me several years of growing up before I came to realise that I was also likely ruining their solitude as well. 

In the end we took to very early morning expeditions. Im found that Im a lot more tolerant of people still struggling up when Im coming down 🙂 

Helvellyn on a bike was the favorite. Its was a bloody long way long grind up on a no sus Carerra but worth it to see the look on the walkers faces who all assumed you's come via Striding Edge. SAdly, I think those routes are so popular now so as not to be a mystery. 🙂 

 

[Chief_Mouser]

3 hours ago, Boo said:

In the end we took to very early morning expeditions. Im found that Im a lot more tolerant of people still struggling up when Im coming down 🙂 

Same here. Did Jack's Rake and the Langdale Pikes from a four o'clock start one Easter Saturday. Had the place to myself and was well on the way back down and feeling well smug as the hordes of Langdale campers were struggling up between 10 and 11. Picked up the missus and went off to Beatrix Potter's house and the Tower Bank Inn as regular tourists for the rest of the day. 🍻

Edited August 3 by Chief_Mouser