Mini Racing Quad Frame Design - Opinions

[Snarls]

Hi all, I've decided that my next multirotor build will be a mini racing quad. I may purchase a carbon fiber frame, but traditionally I design and cut my own frames out of plywood. The issue is that I have no idea what makes a good racing frame, and I need your opinions.

Here are my current observations:
Most frames I've seen seem to try and cram everything into as little space as possible, which is completely reasonable. The racing quads tend to also be H shaped frames while classic X frames are more "acro" quads. The fpv camera gets the front row seat while action cameras tend to be mounted right on top, on a vibration isolated platform. The arm booms are only long enough to provide prop clearance.

Are my observations correct? Is there a reason that the arms are slightly angled out in the H configuration? Should I think about angled mounts for the motors and FPV camera?

Overall I'm just looking for favorable aspects of a mini racing quad frame in an effort to help me think of a design. I will probably be doing more fast paced FPV exploring than full speed racing.

Thanks!

 

[x0054]

I don't understand why people insist on making racing quads H shaped and Acro quads X shaped. Acro quads are designed to be light and to go very fast. Right? Well, those are the kinds of characteristics you want out of a racing quad, no? Of course, not having ever actually raced, I can't be sure, but it strikes me that for racing a quad like Twitchity Acro with his FPV POD would be very fast. For fast exploration I am very partial to my Foldy design. In both cases I think that the X shape gives you better speed, though not by much I suppose. In general, for ultimate speed you probably want to do an aerodynamic shape, like the TBS Hex.

 

[Ocean]

For racing I would recommend tilted motors (if possible) and almost definitely tilted camera, otherwise you will be looking at the ground all the time!

I think people use the H-Quad design to fit all the extra things for FPV and a GoPro as well. A X frame would be faster, but if you want to fit a gopro on then H might be the only way to go.

 

[cranialrectosis]

The H frame is used to carry a heavy camera like a Mobius or GoPro. In a racing quad 30 grams is a ton.

If you want to win races, skip the GoPro or put it on your hat. Mustang is running a Twitchity Acro Quad (X-Shaped quad) with an FPV pod. Nothing is even close to him when he races. He typically has the smallest, lightest craft.

He often laps the competition.

If you want to film the winner of the race, get an H quad and put a GoPro and a 2200mAh lipo on it. If you want to win the race, strip off the extra weight, fly with a 1000mAh or 1300mAh 45-90C lipo and go X quad for the agility.

 

[x0054]

I just got the HD camera module from Hubsan H107C It's about 3 grams, and it shoots and supposed to output video out. The video recording is meh, but good enough. I haven't checked the analog delay yet. Also the 808 #16 records and send analog out. Mine comes in at 23 grams with video TX and battery in the 808 cam, but the without the battery and the housing it's about 12-15 grams, depending on the lens you use. The D lens is a little heavier. I measured a roughly 100ms delay, but the same TX with Sony 600TLV I get about a 85ms-90ms delay, so I figure it's about a wash 15ms delay for the ability to record. But I don't race, so maybe the 15ms would make a difference.

I really like the new frame Mustang is building. It's also X based with tilted motors, which is pretty cool! I am not sure about the 3D printed frame, but the design is pretty cool. I think the X is the way to go because you get the smallest cross-section in a fast foreword flight.

 

[Cyberdactyl]

IMHO why the rectangular boxes with flat plate booms are so overwhelmingly popular can be answered in five words: They are easy to build

But, the counter to that is they are robust.

However, as we all can see, the aerodynamics are close to the most dreadful shape asked to fly. ALL fixed motor multirotors have to tilt their z-axis over to move perpendicular to God's g. As that happens, the shape of the popular mini rectangular boxes work against themselves by exposing more and more surface area to the oncoming air. The same goes with their flat plate booms. Not only does the flat plate constantly have to work against the thrust column, but as the z-axis tilts forward, the plates deflect the oncoming air upwards, attempting to drive the mini into the ground. So the motors are asked to work against the fundamentally poor aerodynamics of design as the craft is asked to go faster and faster.

 

[cranialrectosis]

IMHO why the rectangular boxes with flat plate booms are so overwhelmingly popular can be answered in five words: They are easy to build

But, the counter to that is they are robust.

However, as we all can see, the aerodynamics are close to the most dreadful shape asked to fly. ALL fixed motor multirotors have to tilt their z-axis over to move perpendicular to God's g. As that happens, the shape of the popular mini rectangular boxes work against themselves by exposing more and more surface area to the oncoming air. The same goes with their flat plate booms. Not only does the flat plate constantly have to work against the thrust column, but as the z-axis tilts forward, the plates deflect the oncoming air upwards, attempting to drive the mini into the ground. So the motors are asked to work against the fundamentally poor aerodynamics of design as the craft is asked to go faster and faster.

And the solution is.......?

 

[Cyberdactyl]

Well. . you seen my attempt. I have the form drag of the main frame/cage, more or less the same in all axis'. I have the booms vertical so when the z-axis tilts forward the booms deflect the oncoming air down provides a token amount of deflection lift. But the real plus is, as the z-axis becomes closer to horizontal, the vertical booms align with the direction of flight. In reality, I have to say, my skill isn't to the point of tilting forward more than 60 degrees for more than a few seconds at a time because the camera is looking into the ground, even when I preset it to look up 30 degrees or so.

Now, as I have said, the mountings of my motors are nowhere as robust as those mounted on a plate. However, my mini was a first attempt to see how the configuration would fly. It flies very good, and is very fast. With the cardcam and Vtx on board, (no DVR) I am getting in the low 50's mph on 3S and has an AUW around 710g with a 1300 3S using 0645s. But I am using those rather beastly Rctimer 2600KV 28mm x 22mm motors.

Mine is only one attempt at breaking the rectangular box mindset. But the caveat is, it definitely moves up a notch from the rectangular boxes in building difficulty. The TBS Gemini is still a higher jump in frame complexity. But I really believe a much more aerodynamic FPV mini with the complexity somewhere between the rectangular box and mine is coming from someone soon. The recent idea of tilting of the motors gives me confidence people are at least thinking about aerodynamics now.

 

[cranialrectosis]

You need a mini-version with 6" rotors...

 

[FinalGlideAus]

H quads are used because they can fit in the components easily and more importantly they are pretty bullet proof in crashes (so long as you have a decent design). You can't race a broken quad and most X quads are very slender, being only one crash away from being out of the days racing. If I had a choice I would race an X quad but who wants to bring multiple quads when they race. The stakes aren't that high yet. Mustangs 3D printed quad is a great little design but one crash and he's out. If there is not at least some crashes then the course is far too simple of a design. My Blackout mini H is about 10 months old now and all I have broken is a top plate and anyone who knows me knows I don't take it easy on my frames.

The biggest difference between an X quad and a H quad in a race is the X quad doesn't have a whole heap of weight distributed out along the pitch axis which in turn gives fantastic handling in both axis as well as much faster yaw response. The difference in drag at the speeds we are currently racing is minor. I'll start buying into that argument when we are cruising at 160km/h plus. Oh and my Blackout rectangular box with only 5 inch propellers has been recorded at just a fraction over 75mph.

One other thing, and I hate to be picky about it but it just erks me when others get credit for some things..... I am reading plenty of of stuff about these X quads with FPV gear on them and who's idea it was for the FPV POD. Please give credit where credit is due. Soma came up with the idea originally. Oh and Soma came up with the Cutdown 6x4.5 and worked with Feng at HQ Prop to make them as well. He has quite a brilliant I must say.

https://vimeo.com/96810013

 

[cranialrectosis]

Soma rocks. His was the first FPV pod for a mini-X-Quad I ever saw.

His build videos for the WarpQuad helped me step up my game by light years.

I don't think Mustang plans on the Orange Scream (love it, Mustang) being his only option for the day. I do like how he is pushing the envelope with the tilted mounts. He made an FPV pod for a Polakium that had a servo so you could tilt the FPV camera on the fly.

I like how an X flies better than an H for exactly those reasons. Now I am playing with a mini-Tricopter and I gotta admit, I am a fan!

Check out a mini tricopter FGA. Compare that to the quads. I would love to see how you tune it.

 

[Mustang7302]

The H layout mini quads are the most common because they were the most durable as the mini niche caught on. Then people started seeing how much power you can still drive off a five or six inch prop, and racing was born. Just how serious and fast you want to go, will change many of the choices you make from the "usual" mini setup.

If you want to win races, skip the GoPro or put it on your hat. Mustang is running a Twitchity Acro Quad (X-Shaped quad) with an FPV pod. Nothing is even close to him when he races. He typically has the smallest, lightest craft.

He often laps the competition.

If you want to film the winner of the race, get an H quad and put a GoPro and a 2200mAh lipo on it. If you want to win the race, strip off the extra weight, fly with a 1000mAh or 1300mAh 45-90C lipo and go X quad for the agility.

You said it better than I could. I will just leave this here:

And this for good measure:

You can't race a broken quad and most X quads are very slender, being only one crash away from being out of the days racing. If I had a choice I would race an X quad but who wants to bring multiple quads when they race. The stakes aren't that high yet. Mustangs 3D printed quad is a great little design but one crash and he's out. If there is not at least some crashes then the course is far too simple of a design. My Blackout mini H is about 10 months old now and all I have broken is a top plate and anyone who knows me knows I don't take it easy on my frames.

When you're racing, crashes are much much harder. The Twitch X has taken some incredible beatings and having only broken a pile of props (as seen above). The new 3D printed from wont be nearly as durable and I am very aware of one good crash taking me out of commission. To that end I have an idea of where the weak points are, worked out being able to swap parts without too much headache, and will carry extra parts. There is also pilot discretion of not doing anything dumber than necessary as the race/brackets progress.

 

[FinalGlideAus]

Yes I like Mustangs design a lot. The challenge is to make it a bit more durable. There is always some hurdle to overcome . It's interesting because I plan to tilt the motors on one of my quads but not because it will lower the drag. It is because I am limited to how much camera tilt I can get from the frame. I can get about 30 deg but want another 10 deg and the motors tilted will get that for me. Then the issue is to make sure the handling isn't screwed up.

Back to the tilted motors to reduce drag debate for a second. Please do this with your quad. Tilt your quad to about 45-50 deg. That is about the angle that a decent powered quad sits at during high speed flight. Then look at how much profile drag it has i.e. look at it from the front as though it was flying straight at your face with a 45-50 deg tilt. Now take off 10 deg angle. The profile drag hasn't reduced much at all has it. That 10 deg is the difference a 10 deg motor tilt will make to a quad. Now drag is is not linear. Of course as we start to reach very high cruise speeds it will effect us more but right now it really makes little difference.

 

[FinalGlideAus]

The H layout mini quads are the most common because they were the most durable as the mini niche caught on. Then people started seeing how much power you can still drive off a five or six inch prop, and racing was born. Just how serious and fast you want to go, will change many of the choices you make from the "usual" mini setup.



You said it better than I could. I will just leave this here:

And this for good measure:

When you're racing, crashes are much much harder. The Twitch X has taken some incredible beatings and having only broken a pile of props (as seen above). The new 3D printed from wont be nearly as durable and I am very aware of one good crash taking me out of commission. To that end I have an idea of where the weak points are, worked out being able to swap parts without too much headache, and will carry extra parts. There is also pilot discretion of not doing anything dumber than necessary as the race/brackets progress.

Yup those X quads really hammer don't they . Pity they won't allow 4s and 6" props. My Franken-Warp was designed just for that type of racing.

Where is the track in that video or are you just doing laps? The tracks we set up here are around and under trees and things and are a lot more technical.

 

[FinalGlideAus]

Oh and I'd love to try out a tricopter but as usual I am struggling to keep up with what I have on my plate as it is. Yeah I know, white man's problems

 

[Mustang7302]

Drag was not even a consideration I had when designing the tilted motors of this new frame. As you can see in the video, I had an issue where wide open throttle at full pitch would make the quad climb in the air almost as fast as it was covering ground. In the racing, I try to keep a reasonably low altitude and there was just too much power lost for directional thrust to lift. I was faced with learning to fly in manual mode (which I did) or figure out how to get more pitch authority past 45 degrees of attack.

With the motors tilted 15* forward it will allow them to bite at a 60* angle of attack, while the camera sits at a 25* angle of attack as it looks up 20*, all the while limited by auto-level mode's 45* angle of attack.

 

[Mustang7302]

Yup those X quads really hammer don't they . Pity they won't allow 4s and 6" props. My Franken-Warp was designed just for that type of racing.

Where is the track in that video or are you just doing laps? The tracks we set up here are around and under trees and things and are a lot more technical.

There will be an unlimited/open class. I am still pondering if I will make some changes to that setup and run it on 4S, or if I will *gasp* retire it for a Y6 Tri in the open class.

The track there is just the parameter of the open field. There are a couple of gate/pylons to go through to make sure you're not cutting corners. Nothing too technical about it really, which makes reaching silly speeds safer/easier. There has been talks of making a more technical course setup, which includes flying under things, which is intended to level the playing field. But even running on these kinds of setups, it just means I carry less throttle on average.

 

[FinalGlideAus]

Wow you still fly auto level with that! I'm impressed you are going that fast. Fighting the FC all time will slow you down. You may find even more speed by going to rate mode and letting the poor motors get a more constant thrust for forward flight. Good job anyway by showing them who's boss

 

[Snarls]

Wow, quite a discussion has started here. It's a topic I thought was overlooked and I guess I was right. Lots of ideas to take into consideration when I start designing my own frame. Ideas about angled arms, motors, and x style configuration have got me thinking about what I want in a frame of my own. Let's just hope I'll have the skill to build it myself!

 

[FinalGlideAus]

Yes there's quite a bit to it Snarls. Mustang, if you are only doing that type of course then a 3D printed frame is perfect as there is little chance of crashing. Go out there and grab first with both hands I say