Hi,

I'm new to the rc scene and wanted to get into quadcopters.

I've been tinkering around with some compact quadcopter designs and wanted to make a little one that had horizontally folding propellers so that I could store the whole setup in a small box/container.

After doing a lot of looking around I realized there was nothing like that for quadcopters. That lead me to think about using rc helicopter blade setups since the two blades are individually connected to the hub (is that what you call it?).  

I was thinking of using these helicopter blade/hub combinations for the 4 motors on an rc quadcopter.

I could fold the blades inward after using the quadcopter and then easily store it.

See attached image for details.

My main question is:

1) would this cause to much vibration in the propeller setup? (Since it's no longer a solid piece but made of of two blades individually connected)

2) Is there something about helicopter blades in particular that make them unsuitable for quadcopters?

Thank you for any help with this,

-Josh (image of what I mean below)

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You'd need some way of adjusting the tracking of each blade like when setting a heli up (but times 4 so pretty time consuming) and balance might be a little harder to achieve.

Why not just a folding quadcopter? There's a few designs around, mine: http://diydrones.com/profiles/blogs/epp-foam-folding-h-frame-quad and Murray's: http://diydrones.com/profiles/blogs/folding-quadcopter-for-the-holi... amongst others.

In short, main problems:

1) Helicopter blades are less efficient than fixed pitch props.

2) Shooting for a typical 10-12" prop size is difficult. The biggest tail blades commonly available are 105mm, resulting a roughly 9" disk.  The shortest main blades commonly available are 205mm, resulting in a roughly 18" disk.

3) Helicopter blades are much heavier than fixed pitch props, making control via variable speed difficult.

Hi R_Lefebvre, thank you for the input.

1) Why are helicopter blades less efficient? I did I cursory search online but could not find a good explanation...

2) I'm going for a small quadcopter (about 10-11 cm in diameter / 5 - 5.5 cm in radius for one propeller) 

    a) you mentioned that the heli tail blades are about 10.5 cm (radius?) max so I supposed I could easily find heli tail blades with 5 cm (radius) ?

3) Yes, I suppose that makes sense. More inertia would make it difficult to change speeds quickly... why are heli blades heavier? Is is just the setup (gears, hub...etc) or the blades themselves?

Lastly, are there any quadcopter propellers that are not one single piece? That is, can I get individual quadcopter blades (as is normal for rc helicopters)? 

Thank you for you help, your input is really valuable to me.

-Josh

Hi Graham,

when you say 'tracking' what exactly do you mean? 

I apologize in advance for a lot of newbie questions :) I'm very new to this...

Yes, I've looked at your design before I even joined diydrones and I like the concept. 

I want to do something similar - using characteristics from your design but also folding the props....

Hi Josh,

I have unsuccessfully mucked with 450 helicopters over the last 12 months and recently got into multi copters out of frustration. I must say MCs are much more user friendly. The very nature of how a heli head works is complex eg blade balance, tracking (whereby each blade is in exactly the same plane), blade angle according to throttle position etc etc. All these things must be in accord for a successful flight.

With a MC using fixed pitch blades all this is no longer required apart from blade balancing. Rather than setting up an intricate prop folding mechanism that is only going to assist with carrying/storage and of dubious flight value, why not investigate a quick release method to remove the props.

A heli blade is based on a flying wing planform, some lift is generated by this shape, using it to generate "thrust" is an inefficient use of the design.  Quality ones are made from carbon fibre, mid range are fibreglass and cheap ones are plastic over wood but they all have one thing in common.... internal lead weights. In a 2 blade setup each blade must weigh exactly the same and also have the same midpoint balance, hence the weights.

Blade tracking means to ensure each blade is in the same plane when the assembly is rotated. This is usually a variable pitch issue. Going to fixed pitch (just like a regular propellor) should not have a tracking issue IF your hub/grip assembly is made symmetrical. Also in this case, it would mean that all 4 assemblies are in the same plane to each other.

There has been development in this area... and a more than one here post regarding things like it.

HERE is a post of Youngblood's variable pitch quad. One motor, 4 servos, 4 heli tail assemblies.

HERE is a post of an overgrown version of your idea.

To proceed, I would obtain some fixed pitch helicopter head assemblies. Even these are manipulated by a swashplate on the working helicopter. Something in the Blade 120SR range is cheap and plentiful. You could also go with any of the coaxial copter heads to experiment with.

For example, the 120SR head section below:

The blades fold as in your diagram/idea but notice the amount of other stuff used in the assembly. You don't need all that for a quad but will have to supply the hub/blade grip assembly to mount the blades and the method of securing the hub/grip to the motor shaft.

It only gets more complex as the heli gets bigger...

The 450 3D, a variable pitch heli, has even more stuff around the hub/grip area. Again, if you want to experiment, go with fixed pitch parts. There are fewer parts for dampening the grips. All the vari-pitch blades fold in the method you mention.

You might be able to cheaply obtain some 100 to 250 size hub/grips as these helis are falling out of popularity and support from the manufacturers. You can find all the manufacturers parts diagrams online and free to download. This will give you an idea if you can adapt an existing part rather than try to build totally from scratch. Simple is better.

Most important! Don't let anyone tell you it cannot or should not be done. Try it out, build it, learn from it. You just might discover a new way to do something and show all us 'experts' a new thing. On the other hand, if it turns out to be a total disaster, let us know that too. The value of the experience and being able relate it to others is great also.

Just don't mortgage the house to do it. ;)

Think on!

-=Doug

Doug,

Thanks for your last paragraph, it brought me back to ground and reminded me why most of us are in this hobby.

At the moment I'm working on an idea to install a tricopter into a 450 scale MD500 shell, why, because I think I can.

So Josh, don't stop because of my negative comments.

Respect,

Dennis

That MD500 Tri sounds like fun with a possible futuristic 'Avatar'-type look if worked that way.

I am sketching and fiddling with ideas around my DJI F550 Hex build at the moment...while collecting parts for a Clone Trex 450 build (with the intent of going APM Heli)...and also a F450 clone build for knocking around (KK FC)...and a 'Flying Man', 'Dead Cat', 'Alien' clone quad (have chassis) for FPV.

That should be quiet enough multi-rotors for a while.

Oh and I am scanning/restoring some ancient R/C plans...and... wait...I have too many interests perhaps for one lifetime.

-=Doug

Thanks everyone :)

I've decided to go with a single blade design.  So my quadcopter will have 1 blade on each rotor. This allows me to fold the arms into the belly of the quad easily and does not require a propeller folding mechanism.  I've found several people online (youtube) that have made single blade quadcopters that worked fine.  I am really interested to test the efficiency of a single blade quadcopter!

I'll have to custom manufacture the blades though - since I can't find much in the way of single quadcopter blades anywhere online.....

-Josh

I am trying to do the reverse. It has been 4 years since the initial discussion, and today's 200 - 250 sized helicopters use a direct drive tail and main motor is easily converted to direct drive. So, my 200 sized heli is basically a multi rotor system. No gears no belts. And today's heli blades are at the same price point as quadcopter blades, and they weight the same for the same size. It is sort of convergence evolution. And there is no flybar any where any more. And quads use folding props all the time just like helis do. The only thing left to do is to install the better engineered quad propellers on helicopters. The only advantage of heli is higher efficiency due to concentrated motor. Quad motors is like installing 4 full sets of engines with carburetors/exhausts. Heli is like adding cylinder volumes to a single set of engine, and of course that saves weight, paving market for mass consumer deployment with the sub 250 gram FAA registration waiver.

A quad with folding props have exactly 12 moving parts(4 motors plus 8 blades), and that is also the number of moving parts for today's direct drive, fixed pitch helicopters (2 motors plus 2 servos plus swashplate plus rotor hub plus 2 blades plus 4 linkages). Today is a converged world. The only advantage of quads is the quick flips for city building diving for making adrenaline-rushing fpv videos. 

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