VX1: 154.5 mph 5s Quad

By Phanny P on May 10, 2017

3 1,015  15 

June 9, 2017: Got much better Mobius Mini video today. FPV video is not in perfect sync... Hits 150 mph around 1:04 in the video.

June 8, 2016: Had another 150+mph run (153.2 mph) on a 5s lipo, and hit 132.2 mph on a 4s (video on 4s will come later). Both runs had a Mobius Mini strapped underneath the VX1(rigged with a mirror that's too small) so it's a bit odd. Links to 5s verification:

This is the first of the VX series of frame projects. More info: https://downanddirtydrones.com/portfolio/
A lot of engineering, physics, calculations, trials, concepts, crashes, time, etc. went into developing this frame: https://downanddirtydrones.com/drone-physics/

Contrary to how this build looks, it is not at all awkward to fly. In fact, this is now my favorite frame to fly (now that I put the camera angle at 40°)!

Just broke the speed record and hit an average of 244.5 kmh (152 mph) with a 5s! However, score board goes by max ground speed which was 154.5 mph

PLEASE READ - NOTES ON THE SPEED RECORD:

Note 1: OSD speed is in kmh. A list of the speeds recorded, direction, and time in the video:

212 kmh (131.7mph) West to East 0:31
230 kmh (142.9mph) East to West 0:47
240 kmh (149.1mph) West to East 1:06
248 kmh (154.1mph) East to West 1:21
241 kmh (149.8mph) West to East 1:34
HOWEVER - GOING FOR AS MUCH AS I CAN GET: Blackbox/gps log says 69.06 m/s which is 154.5 MPH
Blackbox Log File: https://drive.google.com/file/d/0Bw5AmHq7h72NQU1tamt5VkljUzA/view?usp=sharing
GPS Log File: https://drive.google.com/file/d/0Bw5AmHq7h72NaEdxRnRTa21lOEU/view?usp=sharing

To rule out any wind (which was calm), I took the highest reading from each direction and averaged them to get 152 mph.

Note 2: Flight took place around 8pm on May 26, 2017 and winds were 5mph max: https://www.wunderground.com/history/airport/KPTK/2017/5/26/DailyHistory.html?req_city=New+Hudson&req_state=MI&req_statename=Michigan&reqdb.zip=48165&reqdb.magic=1&reqdb.wmo=99999

Note 3: Very poor OSD reception/quality. The Eachine DVR records a black screen if there is any interference.

Note 4: After much research, I have found out that GPS is the most accurate way to determine speed. A summary of my findings: https://downanddirtydrones.com/gps-vs-radar-gun/

Note 5: Flight ended in a small crash - I thought I had turned on angle mode, removed my googles, pulled back on the stick to land it and realized too late I was still in acro.

Photos

Part List

Frame

Down and Dirty Drones
Downanddirtydrones.com
See Site

Flight Controller

BetaflightF3 AIO Flight Controller (144 builds)
Rccrazed.com
$42.99

ESCs

4 x Super RacerBee 30A BLHELI_S (Now Dshot Ready!) (2 builds)
Pitchrollyaw.net
$43.96

Motors

4 x Cobra Motor Black CP2207 2450kv (2 builds)
Store.excelrc.com
$91.96

Propellers

RK5051 Triprop Smoke (Set of 4) (3 builds)
Pirofliprc.com
$3.99

FPV Camera

Crazepony 700TVL Wide Angle FPV Camera 700TVL 3.6mm Lens NTSC for QAV250 (3 builds)
Amazon.com
$15.99

FPV Transmitter

AKK X1 40CH 25mW/200mW/600mW Switchable FPV Transmitter with Push Button and Digital Display (9 builds)
Amazon.com
$18.99

Antenna

Anbee FPV 5.8Ghz Circular Polarized Clover Leaf Antenna High Gain Aerial Set w/RP-SMA Female Plug (4 builds)
Amazon.com
$8.98

Receiver

Lemon Rx DSMX Compatible Diversity Satellite (DSM2 backward compatible but must use DSMX compatible primary receiver) LM0037 (29 builds)
Amazon.com
$13.09

Batteries

SMC Extreme 1400mah 4S Racing Battery - True Spec Extreme (12 builds)
Racedayquads.com
$29.95

Misc Parts

Tarot Dia 10MM 3K Carbon Fiber Tube Boom 280MM TL68B22 For FY680 Quadcopter Hexacopter Multi Rotor (3 builds)
Amazon.com
$7.39

Misc Parts

MIDWEST PRODUCTS 5742... CARBON FIBER STRIP,.057x.177 ( (3 builds)
Propshophobbies.com
$6.99

Misc Parts

HYPERION HPMESH3FG... WIRE MESH GUARD 3mmX1m F.GRN
Propshophobbies.com
$3.99

Misc Parts

Micro uBlox M8N GPS GLONASS W/ (18x18mm) (6 builds)
Readytoflyquads.com
$16.00

Misc Parts

MagiDeal Pack of 4 Carbon Fiber Tube 8*6mm 330mm DIY Vanished Surface Tail Tube (4 builds)
Amazon.com
$13.99

Misc Parts

Braided Carbon Fiber Round Tubing ~ 1.75" ID x 24"
Dragonplate.com
See Site
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Discussion

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MTR-FPV   Jun 04, 2017  

Video and need either radar gun or 10hz or lower gps to prove that speed. Please provide so we can document.

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Phanny P   Jun 06, 2017 

Just to cover EVERYTHING and put to bed any doubts about my background, etc., here is a quick rundown of the process I used to derive the formulas used in the calculations. I will end up polishing this off (and put it on my website) but I would like to at least put out a rough version (very rough):
When a quad is moving through the air, we only have 2 opposing forces to consider when determining top speed: thrust and the drag. We will get to gravity later (this is simply taken care of by trig). Top speed is attained when our drag force is equal to our thrust. However, this isn't so easy since we know that our drag force will exponentially increase with velocity AND our thrust will linearly decrease with velocity. Now look at the terminal velocity equation. This equation is the equation we need, however, we need to rearrange this in a way that is understandable to illustrate what is being done before getting into the initial value ODE (ordinary differential equation) iterations. If you remember, F=ma. the mg term in the terminal v equation is a force (since gravity is in terms of acceleration). We can replace mg with Ft (thrust force) since both are expressed in Newtons. Thrust is measured in grams, but we need kg so this is a simple division by 1000 and to get our Ft in Newtons (required by the equation using dimensional analysis), we multiply our thrust (expressed as a mass in kg) by 9.81m/s2 (not needed right now since we are going to work with terms only for the time being). If we take our new equation and solve for Ft, we see that the right side of the equation = 1/2 Cd p v^2 A. This is actually the equation to determine drag of an object in a fluid medium. So now we have our equation that equates Ft to Fd (drag). Solving for v (which is what we want to know) brings us back to the original eqn. We could simply plug in numbers here but this wouldn't be accurate since we need to take into account that the forces involved are both dependent on velocity. To solve this accurately, we can calculate our initial Ft (which is max at t=0). From here, we can determine our velocity, acceleration, etc. over multiple time intervals (usually short - I think I used .001s). Also for each iteration, we use the calculated velocity to determine our new Ft value which is simply the ratio of v/(pitch speed) - note that pitch speed depends on the voltage drop. Iterations are carried out until we see little or no more acceleration. Also note that Cd is a guesstimate at first. Once you fly and get top speed, you can dial this in. Also take note of voltage at top speed so you can calculate an accurate pitch speed. It was through these calculations that I was able to determine what factors affect speed the most.

Phanny P   Jun 07, 2017 

I can't believe it took me this long to realize this (and throttle position is even overlayed on the video) I actually only went wot when I (thought) I was level, not during the dives but in reality I was climbing, not level.

showintellpro   May 15, 2017  

Yeah.. This is an interesting design.
I'm curious.. You said this was not designed for speed, but it ended up that way, what was the original intent?
Based on the motor set up, I'd imagine it could max out speed without increasing camera tilt and each motor should be at best efficiency (not compensating for craft angle/weight distribution).

Phanny P   May 15, 2017 
1

I have a bad way of wording things sometimes... It was meant to be fast, but I had the camera (accidentally) set more for a speed run type quad. It is hardly flyable the way the camera was which made it exclusive to flying it as a speed run quad only (I was probably hitting 80-90mph to maintain altitude by the time I pitched low enough to see the ground). I did fix the angle and might fly it tomorrow. And, yes you are right - camera angle won't have any effect on speed.
Main intent is to see the flight characteristics compared to the VXS (https://rotorbuilds.com/build/4104) design which has the arms angled and gives a more efficient cross section at tamer speeds.
Lots of ideas - never enough time to get them across as clear as I like. I appreciate the questions so I can get a chance to clear up my ideas/intent!

metropolis   May 11, 2017  

Niiiiiiice job man! :D

Phanny P   May 11, 2017 

Thanks! Too bad the same couldn't be said about the video - gotta change out the prodvr. Any static and it records a black/blue screen. Also going to add a diversity rx to my ev800 this weekend :)

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