- 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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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'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.