Overlapping Props

[ringolong]

Hey guys, I am building an new quad and I was hoping to use 17 inch props, but I am at 800mm, and it is maxed out for 15 inch props. I thought about setting two of the motors higher than the other two so the props would not hit each other.

I think I read that this could cause vibrations. Anyone know?

Still trying to decide on 3510 350kv or 4216 310kv motors. I am leaning towards the 4216 with 15 inch props if I cant use 17 inch props. I think the 3510 is good for 13 inch props.

Still a ways to go, but here is a picture with 12 inch props.

 

[HDtallrider]

Looks like it's gonna be a good looking quad! I noticed something that might help you on two fronts. A quad will fly better when it's wheelbase is "square". In other words the dimensions from motor to motor front to back and side to side are all the same. the other benefit is you will have the clearance for your larger props. On your build you can achieve this by extending the rear arms until the distance between the rear motors is the same as the distance between the front 2 motors. That should then make the distance from front to back motors that same dimension. You will probably be at 850mm or more but CF doesn't weigh much. This is why Reptile frames fly better than Dead Cat. That's gonna be one bad ass quad!!

 

[ringolong]

Thanks HDtallrider. Seems simple enough to just extend the back ones if I need to. I still wonder how overlapping props would perform. Have you ever overlapped any before?

 

[GJH105775]

It would make stabilization a lot harder for the FC, but it is possible. Probably can't get 3 blade props.

 

[HDtallrider]

Thanks HDtallrider. Seems simple enough to just extend the back ones if I need to. I still wonder how overlapping props would perform. Have you ever overlapped any before?

I haven't overlapped any but when I think of octocopters it could work. For example, if you mounted the front motors facing down and the rear motors facing up I don't see why that wouldn't work. The props are going opposite rotations like the octo's.
Personally I would extend the rear arms or shorten the front ones to stabilize the quad. I'm too chicken and not savvy enough to program the FC to compensate. An alternative to replacing your rear arm is these;

http://www.phoenixflightgear.com/Phoenix-Flight-Gear-CarbonGear-Motor-Extension-Plate_p_73.html

I used a 4pk of these on a build I wanted to use larger motors and props without changing the arms. They are 2 3/8' center to center. Work great and would be less hassle than making a new arm.

 

[Jackson]

A quad will fly better when it's wheelbase is "square". In other words the dimensions from motor to motor front to back and side to side are all the same

I don't know what you mean by 'better' but many very popular quads are NOT square. The most obvious example is the often copied TBS Discovery.

A few others.

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[HDtallrider]

I agree with your point,Jackson, particularly with racing quads. Designing in a planned amount of instability greatly enhances agility. Just like fighter jets are purposefully designed that way. They rely on computers to maintain the flight of an airplane that normally would be unable to get off the ground. That is an extreme example. I was voicing my experience with "square" dimensions and their comparatively natural stability. The Dead Cat design can, for example, be accommodated by programming the FC. Programming and I don't get along. Not even a little bit. I rely on FCB's and ESC's that are virtually plug and play. Folks like you seem to take to this stuff like ducks to water. I rely on mechanical means, which I do understand, to achieve solid flight characteristics on my builds.
I may not have done a very good job of explaining to ringalong. I am always impressed and a bit envious of you and others that take these programming adjustments in stride as just another run of the mill part of the game. I have to think of "analog" solutions. LOL

 

[holtneil]

Hi I second what HDtallrider is saying, the dead cat has flight problems unless you edit the program to tell the FCB the front motors are out compared to the rear, even tho racing frames are not square the motor set up on the FCB is still square or H which is close to Square in the maths set up of the FCB
As for over lapping props your be ok just dont over lap more than 20% it will fly well it has been done before, there are multirotor called Y6 which has 3 motors up the right way and directly under them another 3 motors upside down and they do not have any lift problems at all they fly very well , I did read of a guy who has done over lapping props due to frame size the 2 rear motors mounted higher than the front 2 , He did not have any problems that he reported in the write up

 

[holtneil]

Have a look at this it was done by a guy called 13brv3 it has 50% over lap on the props

 

[HDtallrider]

Have a look at this it was done by a guy called 13brv3 it has 50% over lap on the props
View attachment 950

Wow! Do you know why he has 2 pieces of noodle facing up and 2 facing down? Do you think he's tweaking the airflow? I bet he's a huge hit at air meets!

 

[holtneil]

Sorry cant answer that I know he made this a fair while back , He knows his stuff

 

[HDtallrider]

Thanks. Just curious.

 

[Jackson]

even tho racing frames are not square the motor set up on the FCB is still square or H which is close to Square in the maths set up of the FCB

HUH? I see, so now it's not square, but close to square? Which is obviously NOT the same thing.

the dead cat has flight problems unless you edit the program

And... So what does that have to do with it being NOT square?

If square was somehow the ideal as he stated all quads would be square, it's obvious they are not. Some of the best frame makers out there have chosen to NOT be square, your arguments are spurious and have nothing to do with his statement.

 

[holtneil]

I have sent him an email to ask him

 

[holtneil]

Hi Jackson its to do with the maths of the FCB it sees it as a square even tho the frame is not ,forget the frame look at where the motors are , the arms are the same size and angle front and back
dead cat has 2 arms longer and at a different angle this is what makes it fly strange ,but after you edit the FCB and tell it where the motors are it flies right
The frame shape has to do with what they are doing with it like the FPV flip frame its to carry a camera and for prop not to be in the shot

 

[GJH105775]

Hi Jackson its to do with the maths of the FCB it sees it as a square even tho the frame is not ,forget the frame look at where the motors are , the arms are the same size and angle front and back
dead cat has 2 arms longer and at a different angle this is what makes it fly strange ,but after you edit the FCB and tell it where the motors are it flies right
The frame shape has to do with what they are doing with it like the FPV flip frame its to carry a camera and for prop no to be in the shot

As far as stabilization goes the FCB does not care where on the quad it is relative to the motors as long as the motors are where they should be relative to each other. The flight controller should be mounted on the COG when using auto level as it has a slight effect on I values.

Appendix F from the KK manual

 

[HDtallrider]

I think I can clarify part of this. I had a discussion about drones with my brother-in-law who is a Boeing engineer. I was asking him about different quad designs I was interested in. He stated that the + and X quads(square) are the most stable in flight because no matter what the axis, DURING HOVER, they pivot on a precise center point with equal authority. As forward speed increases there are forces acting on the quad that move that pivot point and it becomes slightly better in roll than pitch. He and I then got into the reptile style frame with spread front arms and swept rear arms with equal distance between the motors. Because of the longer body and swept rear arms this now increased pitch authority to better match the roll authority from the spread front arms.
On the little racers, which I briefly considered,his view was the "I" configuration was the ideal for agility and has the ability to be biased toward a desired axis with minor adjustments in arm length and angle(sweep). Then you can program the FC to take advantage of the set up and also keep it flying with micro second adjustments. This is kinda what ringalong has on a larger scale.
As far as the square and H being treated similar by the FCB, I know less than zip.
I hope I didn't add more confusion, but this is what I build and fly by. Others are free to build and fly whatever they wish. I've seen videos of hat boxes and cigar boxes and bicycle rims flying. That's what makes this hobby great. I am convinced of that. " Y peace Y"

 

[HDtallrider]

Oooops. Got outa synch again.

 

[GJH105775]

I think I can clarify part of this. I had a discussion about drones with my brother-in-law who is a Boeing engineer. I was asking him about different quad designs I was interested in. He stated that the + and X quads(square) are the most stable in flight because no matter what the axis, DURING HOVER, they pivot on a precise center point with equal authority. As forward speed increases there are forces acting on the quad that move that pivot point and it becomes slightly better in roll than pitch. He and I then got into the reptile style frame with spread front arms and swept rear arms with equal distance between the motors. Because of the longer body and swept rear arms this now increased pitch authority to better match the roll authority from the spread front arms.
On the little racers, which I briefly considered,his view was the "I" configuration was the ideal for agility and has the ability to be biased toward a desired axis with minor adjustments in arm length and angle(sweep). Then you can program the FC to take advantage of the set up and also keep it flying with micro second adjustments. This is kinda what ringalong has on a larger scale.
As far as the square and H being treated similar by the FCB, I know less than zip.
I hope I didn't add more confusion, but this is what I build and fly by. Others are free to build and fly whatever they wish. I've seen videos of hat boxes and cigar boxes and bicycle rims flying. That's what makes this hobby great. I am convinced of that. " Y peace Y"

As long as the balance is the same and the motors are all in the same place it does not matter how you get them there. So a U shaped frame, an X frame or an H frame will be treated the same. I agree 100% that generally having each motor the same distance is optimal for stability and simplicity. Though you could add different power motors, or use different motor configurations to get flight characteristics you want such as increased YAW without having to sacrifice pitch and roll.

 

[HDtallrider]

As long as the balance is the same and the motors are all in the same place it does not matter how you get them there. So a U shaped frame, an X frame or an H frame will be treated the same. I agree 100% that generally having each motor the same distance is optimal for stability and simplisity. Though you could add different power motors, or use different motor configurations to get flight characteristics you want.

Agreed. I was addressing the kind of quads most common to our hobby and ONLY the mechanics of how the different designs accomplish their goals. NOT the electronics or the mixing of different props and motors. Nothing exotic. Just regular ol' quads.