Hey all,

Has anyone used Variable pitch propellors on their quadcopter?? I'm thinking about using them on my new project and was wondering if anyone had any experience with them or could let me know if its a dead end or if its even done??

Any help would be greatly appreciated :)

Thankyou,

Harry 

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It adds quite a bit of additional mechanical complexity, and ultimately the only material advantage is a higher forward speed capability (the ability to increase the blade section AoA at higher rates of inflow).

Here's a paper from some MIT guys who did some research, but it was focused on control response.  If you have a mission profile where ultimate transient handling response is your goal, i.e. precision flying in a very turbulent aerodynamic environment, it might make sense to pursue.  If you don't find this paper to be daunting, and don't mind treading down your own technical path, then go for it. 

The electric multicopter's primary advantage is mechanical simplicity.  If you really think being able to change the pitch of the blade in flight suits your goals better, and if you don't want to embark on your own course of invention (with all the trials and tribulations that entails), then trying a conventional single rotor helicopter might be a better idea.

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Yeah, I actually just had a mechanical failure on my heli yesterday.  The tail pitch slider broke, and I lost rudder control.  Thanks to the excellent APM stabilization, I was able to mostly save it from doom.

This is the same part you'd use in a VP Quad.  I can't imagine having 4 of these things on a quad, waiting to fail...

That's basically what we're up against.  A VP quad increases the number of failure points maybe 10X a basic quad.  So you better have a really good reason for wanting to do it.

Inverted flight and all the 3D fun it brings. ;-)

Yeah  this is my main concern as well :S

I need it to be quick and also need it to eventually carry a load, i Thought that if it was variable pitch then when a load was applied it could be able to increase the RPM and blade angle to lift the load, making it theoretically possible to be more efficient then if i had to design it with a fixed pitch props. Im going to start off with fixed pitch and as i gain experience and practice and knowledge will convert to variable pitch as it is designed to be developed this way.

Thankyou :)

Harry

Thanks so much for that Brad, going to have a good look through it now, really appreciate it :) But yeah for what i need it to do i think i will eventually need it to be variable pitch but thats a way off yet, just going one step at a time :)

Harry

Brad, Just read through it and it was extremely helpful, thanks a lot :) 

From reading it i can see that its exactly what I'm going to need and have contacted a few of the people in the references for more information and resources, thanks a bunch for that :)

Harry 

You're most welcome.  Virtually all of my research has been into very large scale electric multicopters, to the extent of probing the viability of manned flight (years before "the Germans" successful publicity stunt).  There will come a point in scale where variable pitch becomes more compelling, and not for reasons you're probably considering.

The primary design attribute for lifting efficiency is disk loading.  If you make the total disk swept area large enough (somewhere between 2-3 lbs/ft^2), then rotational the inertia becomes too large to manage without a ridiculous number of thrust units, given:  Ir = m*r^2  (my current manned prototype has 36)

Also as scale goes up, so too does your operating regime Re.  Beware of the 100K Re examples which use thin airfoils - they won't have the wide AoA range most desirable for variable pitch use.  Am I suggesting you're going to end up making your own blades?  Yes, or your FM won't be nearly what it ought to be.

Large Scale Electric Multicopters Thread

In other words, welcome to the "biting off more (aerodynamically) than you can chew" club.  :-)

Thats awesome, would be very interesting :)

I'm working on an autonomous submarine to mao ocean floor and creeks swell as have torpedo capabilities and the quadcopter is just a secondary thought to be able to carry the sub and deploy it, I know its a huge task and probably am biting off more then i can chew but i have lots of technical support and a lot of really tallented individuals helping. 

ANd yes we will probably end up making our own blades, we have full access to commercial 3D printing  swell as carbon fibre, kevlar an fibre glass contraction. Would you have a link or some information for the type of fil i should be looking at making? (Im only really familiar with NACA 0012 foils as my qualifications are marine based)

Thanks :)

Harry

I worked on this project under Mark Cutler, I was his undergraduate hardware guy. If you have any specific questions about the hardware setup, let me know. I spent my summer working on that quad. Ultimately we found that your performance is going to be limited by vibration. The variable pitch mechanisms we used all had a certain speed where they would essentially vibrate themselves to death and thus bottlenecked the performance. Look at page 7 of the paper that Brad posted above.

Just to note, they tried using helicopter tail rotors before I joined the project. Apparently it shook itself to death. 

Thanks mike, 

Do have a few questions, what did you use for the flight planner/code? i cant find out if the arducopter flight planner and code of the ardupilot Mega works with variable pitch or how to make it work with variable pitch?? Would you know anything about that or know someone who does?

ANd im using main blade rotor heads but yeah i think no matter what you use there will be a vibration problem :s

your help would be greatly appreciated :)

Harry

Harry, 

In terms of flight planner and code, I believe that the quad was using this board with 'custom' code on it. One thing you have to remember is that it was flown indoors using a VICON system for position and velocity data. There was definitely some MATLAB interface, and the actual flying was done with a python script. Iver used the APM stuff for a few months now, but I don't think it is setup for variable pitch. You may have to modify the arduino's code yourself to integrate that--Im sure someone on the forum will know how to do that--I'm not a programming guru unfortunately. I think that the APM definitely has the potential though. 

From a control-law standpoint, I remember that variable pitch alone was very difficult to use to stabilize the quad even with all the VICON gear and simulations to tune the gains properly. Ultimately they used pitch for large attitude corrections and motor RPM for small corrections-- I havent read through the full paper above, but it probably talks about that. I would actually recommend trying to fly it using just motor control first (fixing the pitch of the blades) before you step into the variable pitch world. 

If you look back on the MIT ACL youtube channel, some of the other 'uberquad' videos showed some of the old mechanics and old footage of flying. 

Mike

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