I'm wondering what some of you more experienced pilots have found regarding the quadcopter frame designs for FPV freestyle/racing quads.

It's seems that a rectangular design was quite popular early on, but more and more frames are designed as a square, where all 4 motors are equal distance from each other.

Have you found that this creates a more stable platform?  My assumption is that (especially for freestyle) that the square design would flip and roll similarly, and on all axes, but the rectangular design would be just a bit slower for a flip (front/back) than a roll (left/right) - just based on basic physics.   If a quad is longer front to back, the front and back edges would need to travel farther and faster to perform a flip than a square frame.

Just looking for your thoughts to satisfy my idle curiosity.

Thanks!!!

Originally in a mini quad, width (left to right) are normally longer than the length (front to back) due to popular frame designs and how mass is distributed, mainly along roll axis because of the "cage".

Now more and more frames have a "tower" style design where the mass are mainly located right in the centre of the frame therefore it makes sense to match the frame width and length.

Different length and width do make a difference to how a quad react to rolls and flips (faster/slower), however this can be compensated (kind of) in PID, that's why you normally see higher PID numbers in Pitch axis than Roll axis on a rectangular frame (non-square).

I remember we had a debate a year or two before on whether or not we should apply custom motor mixer to frames that are non-rectangular, and my thought is we don't need to worry about it, as we can achieve the same thing with PID tuning. https://oscarliang.com/custom-motor-outp...uadcopter/

Another trend is becoming popular - quadXL (X-config Long) where motor distance is longer on pitch axis. This is due to two reasons:
- we no longer care about props obscuring fpv feed/hd footage because of higher camera angles
- Supposedly this config behaves better on racetrack on sharp turns thanks to better thrust-mass distribution

(14-Nov-2016, 04:50 PM)Oscar Wrote: Different length and width do make a difference to how a quad react to rolls and flips (faster/slower), however this can be compensated (kind of) in PID, that's why you normally see higher PID numbers in Pitch axis than Roll axis on a rectangular frame (non-square).

(14-Nov-2016, 05:43 PM)KonradS Wrote: Another trend is becoming popular - quadXL (X-config Long) where motor distance is longer on pitch axis. This is due to two reasons:
- we no longer care about props obscuring fpv feed/hd footage because of higher camera angles
- Supposedly this config behaves better on racetrack on sharp turns thanks to better thrust-mass distribution

Interesting indeed.  Again - just morbid curiosity - and thanks.  I started to go and read some scholarly articles on general quadrotor aerodynamics and flight characteristics - and then my head exploded.  I was thinking of working out a way to build some custom CNC'd carbon fiber frames, but now I think my money (and time) will be much better spent building and flying rather than pursuing a PhD in FPV.

(14-Nov-2016, 09:51 PM)illushinz Wrote: Interesting indeed.  Again - just morbid curiosity - and thanks.  I started to go and read some scholarly articles on general quadrotor aerodynamics and flight characteristics - and then my head exploded.  I was thinking of working out a way to build some custom CNC'd carbon fiber frames, but now I think my money (and time) will be much better spent building and flying rather than pursuing a PhD in FPV.

Imho aerodynamics play the biggest part in a quad's behaviour.

Differences between roll/pitch axis (because of weight distribution or motor layout) are very small with today's powerful, responsive motors and escs.

(15-Nov-2016, 12:30 PM)fftunes Wrote: Imho aerodynamics play the biggest part in a quad's behaviour.

Differences between roll/pitch axis (because of weight distribution or motor layout) are very small with today's powerful, responsive motors and escs.

Which makes me wonder about the physical design. I don't know why I'm just a "why" guy, but it's always cool to try and understand what's going on at the physical/physics level.

With crafts so small and light, would modifications to the frames actually have any noticeable impact on flight characteristics?
If we were able to truly compare two otherwise identical crafts, one with a basic carbon fiber frame, and one more like a Husban x4 style, would there be a measurable difference in any metrics? Acceleration, top speed, maneuverability, flight time, etc? Probably nearly impossible to test scientifically, but fun to think and talk about.

Maybe streamlining the frame does make a difference?

http://intofpv.com/t-the-stigg-top-speed-run

(15-Nov-2016, 01:14 PM)illushinz Wrote: ...but fun to think and talk about.

Yes!

Assuming the quad can do what we want it to do, i think it comes down to these 2 things:

• power/weight ratio
  
• aerodynamic drag
  

But the fun part starts when you are thinking about actual flying scenarios. Do i want to fly forward? Or only upward? Float inverted?
My latest 2 quads were pretty interesting for that matter: close to equal power, weight and size, but one was an H-frame, the other an X-frame. And guess what? I think the biggest difference is aerodynamics.

PS: Maybe you seen my 'devilbug' build thread in the miniquad folder. That one is pretty much an aerodynamics experiment, to test wether the quad feels the same while having moOore power.

(15-Nov-2016, 06:55 PM)illushinz Wrote: Maybe streamlining the frame does make a difference?

Yes of course, if you want to get most out of your power this is the way. However, i don't want to fly with 90° camera angle so basically it would ideally be streamlined at your personally preferred angle. But what i find more interesting than lowest-possible-drag are the spoiler- or wing-effects.

(15-Nov-2016, 07:01 PM)fftunes Wrote: My latest 2 quads were pretty interesting for that matter: close to equal power, weight and size, but one was an H-frame, the other an X-frame. And guess what? I think the biggest difference is aerodynamics.

So which was more aerodynamic?

(15-Nov-2016, 07:01 PM)fftunes Wrote: Yes of course, if you want to get most out of your power this is the way. However, i don't want to fly with 90° camera angle so basically it would ideally be streamlined at your personally preferred angle. But what i find more interesting than lowest-possible-drag are the spoiler- or wing-effects.

So - Essentially incorporating a wing or spoiler effect into the design of the frame...  Hmm...

Airflow would just need to increase across the top of the frame and the arms.  The arms might really be the trick, having to deal with the directional difference between static airflow and rotor wash.

Oooh - or aerofoil shaped arms with bottom mounted motors.....  

I think a pilot's skill in tuning and flying far outweigh advantages that might be gained by improving aerodynamics. Having said that, it's not a bad thing to improve the aerodynamics of a quad. I am just a little bit surprised that more attention seems to be paid to the arms of a quad as opposed to the "box" that holds all of the components. That Stigg mentioned above still has this huge box sitting on the nice, thin, streamlined arms. I don't know why "pod" designs haven't become more prevelent. Seems like more could be gained by streamlining the body as opposed to the limbs (my 2 cents).

(15-Nov-2016, 08:26 PM)sloscotty Wrote: I think a pilot's skill in tuning and flying far outweigh advantages that might be gained by improving aerodynamics. Having said that, it's not a bad thing to improve the aerodynamics of a quad. I am just a little bit surprised that more attention seems to be paid to the arms of a quad as opposed to the "box" that holds all of the components. That Stigg mentioned above still has this huge box sitting on the nice, thin, streamlined arms. I don't know why "pod" designs haven't become more prevelent. Seems like more could be gained by streamlining the body as opposed to the limbs (my 2 cents).

Excellent point, and exactly why I wondered about having a 'body' like a husban. Even just a streamlined 'cap' would be cool.

(15-Nov-2016, 08:26 PM)sloscotty Wrote: I think a pilot's skill in tuning and flying far outweigh advantages that might be gained by improving aerodynamics.  Having said that, it's not a bad thing to improve the aerodynamics of a quad.  I am just a little bit surprised that more attention seems to be paid to the arms of a quad as opposed to the "box" that holds all of the components.  That Stigg mentioned above still has this huge box sitting on the nice, thin, streamlined arms.  I don't know why "pod" designs haven't become more prevelent.  Seems like more could be gained by streamlining the body as opposed to the limbs (my 2 cents).

Aerodynamics don't have that much of an impact on tight turns. Mostly on straight lines.

Stigg is designed to reduce drag created by propellers hitting the arms, thus making more space for all those Watts pushed trough the motor. IMO you are right about pods - putting one on this design would make it even more effective

That stigg above is a good example of what i would not want on my quads...

Yes the arms have lowest possible drag on the props' airstream - but at the same time they create drag in forward flight (maybe even in a way it could disturb yaw control due to asymetric design), even worse imho they could create additional lift in fff when we actually want to fly low.

Every plane will act as a kind of wall, or guider of some sort, depending on the direction/angle we fly.

I remember ctzsnooze saying he put airfoils on his alien's arms, and that flying felt completely different afterwards...