- Blackbox Log File: https://drive.google.com/file/d/0Bw5AmHq7h72NNC1TRHE3bEl3Zkk/view?usp=sharing
- Decoded GPS Log File: https://drive.google.com/file/d/0Bw5AmHq7h72NMWpSYWhEOC1EOFE/view?usp=sharing
- GPS Log Graph: https://drive.google.com/file/d/0Bw5AmHq7h72NdUkxS0liUzQwTTg/view?usp=sharing

- Blackbox Log Link https://drive.google.com/file/d/0Bw5AmHq7h72NNEUwSkVOMzA4UkE/view?usp=sharing
- Decoded Blackbox GPS Data https://drive.google.com/file/d/0Bw5AmHq7h72NLUlXYkFiX0F5bXM/view?usp=sharing (see graph in the pictures section)
- Mobius Mini video with FPV video (rather confusing to watch...):

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°)!*

**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.

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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).

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!

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

It has already been reviewed, verified, and documented. You need to read the description: you will find links to the GPS log, the blackbox log, and article on why/how radar gun is less accurate than GPS (yes I wrote the article, but bias is handled via half a dozen references on the same subject). GPS log is actually generated from blackbox. GPS sampling rate has absolutely ZERO to do with speed accuracy: GPS velocity reading is not calculated by displacement change, it's calculated using doppler. So in this case, sampling rate will only improve resolution, not accuracy. I'm my own worst critic and went through a lot of measures on the research and made sure evidence was as bulletproof as I could make it. But if you think about it, no one will know for sure - MAYBE I did speed up the video, edit the osd reading, forge the GPS positions/velocity/altitude samples, and forge the 450,000+ blackbox samples - all that and manage to make them all synchronize with each other. However, no one will ever know the truth :)

The validation of this would be to do this in parallel to the ground and not in 100' dives. Gravity itself can increase your speed by 30%. 154mph is roughly 68.8meters per second. If I subtract 9.8meters per second gravity you would get roughly 59 meters per second which is 131mph which is roughly what x-foot got running 5s x-foot 2207 2600kv motors got 132mph.

If you graph out the altitude and speed from the GPS log, you will see that the 4th pass had level flight about 7-8 seconds long where top speed was reached about 3.8 seconds in. Regardless, subtracting 9.8m/s doesn't make sense (any engineer will tell you this.) Gravity is measured in meters per second per second which is an acceleration - not a velocity.

What kind of math is that? Nasa would like to live in that world where gravity is set to a constant velocity, lol. The P is right on the graph- max speed at level flight and equations are good - covered in great detail. Nobody else has done this that I'm aware of. If you sit here and pretend some sort of authority, then act like it and know what you're talking about. Otherwise you just hurt your credibility.

Gravity is not a constant velocity but is used in the equation when calculating the speed of a dive which is terminal velocity of the diving object plus the thrust.Use the terminal velocity formula, v = the square root of ((2

mg)/(ρAC)).m = mass of the falling object.

g = the acceleration due to gravity. ...

ρ = the density of the fluid the object is falling through.

A = the projected area of the object. ...

C = the drag coefficient.

He also stated all dives where a 100' dive. It has been proven that a aircraft maintaining level flight at max speed is slower than the same aircraft diving at max speed. We can argue all day what the true actual calculated speed is but it does not mean anything if it isn't a level acceleration to top speed which is what the standard is. I can dive any aircraft and level it for 2 or 4 seconds to grab a speed before drag slows it back down. But to accelerate in a straight as possible parallel to the ground is the accepted way to get top speed. If I where to go and take my 145mph complete parallel quad and dive it like you did I would be roughly 181mph and the majority of the people would not accept my record. My suggestion is go run it parallel to the ground from slow to max and it will be a valid run.

Evidence is actually better than I thought -

the quad was actually in a climb (for 7 full seconds) during which it obtained max speed 3.8 seconds into this climb. (please refer to the uploaded image).The graph shows velocity and altitude as recorded by the GPS log (they are in sync). You should be able to see from the terminal velocity equation that you can't just add/subtract gravity as though it is a velocity. This equation is only a part of the puzzle - to fully understand it all and see why a dive has little to no effect. I unfortunately climbed sharply after all my other passes. As you know, you have to work in the thrust into the calculations - in order to do this, you have to determine the force generated by drag. Since drag force is dependent on velocity, AND velocity is dependent on acceleration, AND thrust dependent on velocity, you can see that taking the terminal velocity equation falls short (the calculations have to be solved with diff eq's/calc/numerical methods). I have also used these calculations in rocketry so this isn't anything new to me. Term V eqn alone falls short.Not sure if I covered everything, but the rest of it all is on the website. I'll also put the equations used in the pictures section. Not trying to get an attitude here, but it is rather irritating (especially when the graph is so clear). All I'm looking for is a fun learning experience and also share the things I have researched and tested. As far as I am concerned, it's good to be challenged and I expected it to happen, but not to this extent!Look it is like this. These are the things I had to prove to get the right to say I went 145mph. There is just a lot about your build that is very similar to others that went only 132mph. They had to prove just like I had. I have looked thru your data and GPS data and as long as your m8n is setup right your pull 4 started off as a drop then leveled out for a few seconds. It was the shortest dive. I have my theory of why you have hit the speed you have hit but it isn't a motor issue but more a limitation in ESC properties is why your lower kv motors did better than others that used 6s.

How similar was their set up? Cd, CG/CT alignment, and cross section make a huge difference. The spreadsheet on my website is available to download and it is a great way to see how these things affect each other. It was originally used for rocketry - basically the same setup but was a little easier for quads since weight stays the same (no propellant loss) and thrust for quads decreases linearly with speed (rocket motors have a non linear change in impulse). Speeds calculated were with 5mph of what I hit on 4s and 5s (I didn't believe the 5s calculation until I flew with it).

Did you ever try getting onto the leader board on fpvlabs? That was the only board I knew of before today. Challenging claims has to be done since there is no set of rules on how to go about verifying a claim. I don't agree with the fact that all these claims are based on ground speed. I waited specifically for a calm day, etc. to make sure I could get as accurate of an air speed as possible. When all is said and done, the only "official" record is the one for the fastest quad climb in which Guinness was there to verify. Until we can have Guinness come out for us (yeah right), we are left to documenting these things as best we can. I also think GPS logs should be required since GPS (and radar guns) can still toss up a false reading. With a log, it is easy to spot as it is a quick spike in the data. I have experienced this once last week when I landed and my osd said "max speed: 252"kph. I knew off the bat that it was a glitch and upon reviewing the video, I saw that speed pop up for a fraction of a second when I was taking off (I was actually around 10-15kph). It was the only time it happened in roughly 100 flights.

The M8N was set up using configuration settings from iNav which is nothing more than what Betaflight has EXCEPT that it sets it to use the Airborne<4g dynamic platform model. This will be the new default for BF but I have to do a bit more coding to allow other models to be enabled before we release it.

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.

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.