I want to calculate the maximum speed and hence range of my drone. To do this I'll need to use it's drag coefficient to work out the terminal velocity. Luckily the drone is dome shaped so I was thinking could I just approximate the whole thing as a sphere and use that drag coefficient?. Doesn't need to be super exact, this isn't NASA, I just need a rough estimate for my business adviser tomorrow. Pic related.
I want to calculate the maximum speed and hence range of my drone...
If this doesn't get any replies (as usual) I'd also like to know why is it that nobody can ever answer my basic aerodynamics questions but whenever someone makes a thread asking for spacetime to be explained there's always 50 replies from Minkowski "experts"? Where are the Prandtl experts?
It's actually rather tricky to find accurately. On top of just drag, you also need to work out the propeller dynamics, taking the advance ratio into consideration (here: web.mit.edu
estimating it as full sphere sounds a little too generous for less than half a sphere rotated sideways with 4 props sticking out
a sphere is around 0,5
a cylinder is around 1
if I were you I'd take the middle with 0,75
Oh, and also, if you truly want to be accurate you also have to take motor dynamics into consideration as well. At high power settings and tilt angles, these propellers "unload" somewhat as airspeed and advance ratio increases, causing motor RPM to rise even further. The motors produce less torque and shaft power at higher RPMs, so finding the dynamic RPM itself is a challenge.
> laminar flow over the propeller
Yeah this is way out of your scope
meant to say cube
Ok I'll go with 0.75.
Easier to draw.
I have another dilemma. The slower it travels the longer it stays in the air, but how far it travels is proportional to speed and time therefore there must be some specific speed where it travels the furthest distance.
I have a simple equation that can do that. I'd share it, but last time I did Veeky Forums just berated me with their autistic ballsacks, so you can all go fuck yourselves
>I have another dilemma
dude, that's a rudimentary technical question solvable even with basic hobbyist knowledge
are you by any chance working in the sales department of your company?
For hover I estimated 80% efficiency, you're saying this advance ratio business will push that down even further at high speed? At what speed will it start to matter? Drones aren't very fast remember.
Ok what's the answer then captain genius.
Yes I work in sales. Why do you think i'm pitching this to a business meeting tomorrow?
The equation is here on wikipedia
I dont think drag is even that significant.
Most power loss for quadcopter drones should be from fighting gravity and fighting the other props.
Oh and terminal velocity...usually is unpowered flight. I think its just called maximum speed.
This isn't about power loss it's about max speed. Anyway I'm gonna try 0.75 and see what I get. I hope it's at least 20 miles or I'm done for.
*20 mile range
1. Terminal velocity is for unpowered flight
2. That drag coefficient is way too low for propellers anyway
3. Unless you're planning on dropping your drone from a tall building you should stop caring about drag.
Can you just post a link to your robot?
>Yes I work in sales. Why do you think i'm pitching this to a business meeting tomorrow?
some honest career advice
actually knowing the product you're selling to an atleast semi-professional degree is one of the things which sets you apart from other people in your career field
it's what gets you raises and promotions
if you still have a job after tomorrow, you should start with some extensive research, one that goes beyond looking up formulas on wikipedia and plugging in numbers
also compiling a specification sheet one day before you need to pitch it is setting yourself up for failure from the get go
plot power draw against absolute speed
the optimum should become very obvious
also terminal velocity does not apply to this, at all
forget ever considering it
I would just mount a pitot tube, floor the throttle and measure the max speed.
>For hover I estimated 80% efficiency
Efficiency of the motors? That's probably a bit optimistic, depending on how aggressive your prop selection is.
>you're saying this advance ratio business will push that down even further at high speed?
Actually it will more likely go up a bit, but again this depends on the prop. At normal operating RPM, power output and power draw of an electric motor decline as load decreases and RPM increases.
Anyways, I was speaking most narrowly in terms of top speed at full throttle. I've flown simulators that hold thrust constant (regardless of advance ratio) and use drag only, and they're all wrong, with either ridiculously high top speeds, ridiculously poor acceleration or beach-ball aerodynamics. The propellers really DO dominate the aerodynamics of a quadcopter.
>At what speed will it start to matter?
Oh, 20 MPH I suppose, for a typical quad? It's sort of arbitrary. It's not very significant at moderate speeds and tilt angles, but as you push to higher speeds and more aggressive tilt angles it becomes very significant. Hell, just look at the camera angles on some of these racing quads, that should tell you a lot about how pitched-over these things are going around a track.
>Drones aren't very fast remember.
No, not compared to airplanes. And if you're trying to find maximum range instead of actual outright maximum speed, you'll probably going to be at reduced (near-hover) throttle anyways, not balls-out; so tilt angle might not be significant enough to fuss over advance ratio.
always do the bare minimum to get your money anything more is wagecucking
build it and see t. engi
This. If you really want a quick and dirty answer. Weight the drone before and after flight at various speeds. That should give you a rough idea, though it will change depending on how much fuel you have left in the tank.
But hey, you don't have much time so tick tock.
HOLY FUCK, IT'S THE "MUH MAGNUS OPUS" GUY
if you need money you should just sell tickets to this business meeting of yours. the looks on their faces when you present your """research""" will be priceless.
you're going to get laughed out of the building.
>MAGNUS OPUS" GUY
I'm not Norwegian, no
Ok guys I got 52 mph, seems legit.
>always do the bare minimum
in case you haven't noticed
desperately scribbling together a spec sheet last minute with the help of a botswanian typesetting trade journal is way below bare minimum, even for a shitty sales clerk stuck in a mental deadend like yourself
some people have lives outside of work you know.
>"user! that sales pitch you gave yesterday was bullshit, it said the drone has a top speed of 52mph, but the client reported it not even reaching 25mph!"
>"b-but mr goldenstein, I calculated it all by myself, the m-math was l-legit!"
>"I don't care, this will have consequences!"
>"p-please no, mr goldstein, if I don't keep this job I'll l-lose my wife and my 2 kids"
>"make one more mistake and you're fired"
>"yes, of course sir, t-thank you sir"
>atleast I'm not one of those wagecucks
Who the fuck is gonna fly a drone at 52 mph? Some hipster will probably use it to film a pro-immigrant documentary because he can't be bothered to hold a camera. No-one will ever find out.
>Who the fuck is gonna fly a drone at 52 mph?
>No-one will ever find out
living hand-to-mouth because you're scraping by on pilot light makes you a literal wagecuck
but the irony of the situation seems to be lost on you
this aint my problem. if you want to get fired because you are shit then be my guest.
It's not a racing drone. Look man this is just a fucking requirement, to get the design approved there must be a spec sheet, doesn't mean it will ever have to perform like that exactly. Have you ever driven your car at 160 mph? No? well that's it's max speed in the spec but guess what if you did that speed your engine would quickly melt. Barely anyone is gonna drive over 100 so it doesn't need to be exact. Leave me alone.
This is goy: the board. lick massa bossman's ass that's Veeky Forums's motto alright
Finally, IT'S A FUCKING DRONE! A TOY! Guys acting like I'm building a space shuttle or some shit. Like who cares if it's not perfectly to spec? That's what you get for buying cheap toy shit.
>Have you ever driven your car at 160 mph? No? well that's it's max speed in the spec but guess what if you did that speed your engine would quickly melt
top fucking kek
>spouting uneducated bullshit
>lying out your ass on relevant documents
>doing an overall shitty job
>thinking you're justified in doing a shitty job because "muh wagecucks"
you really do belong in sales
Do you even have a job kid?