Un-Folding a Quadcopter to Increase Efficiency - Part 1

I've recently had a fascination with tailsitter VL aircraft VL stands for vertical takeoff and landing and tail sitter just means they take off and land on their tails before pitching over into an airplane with wings I love the Simplicity of tail sitters because you just pitch the whole body over to change flight modes with all that Wing area potentially facing the wind in Hover they can suffer from lack of Control Authority which makes them harder to fly this little guy tries to remedy this by using four Motors like a quadcopter to get more control and some biplane wings for lift and forward flight this definitely works and is plenty controllable but then you have all this extra stuff creating drag and forward flight plus a bip plane design like this actually isn't that efficient despite twice the wing area if only there was a way to take a highly stable and controllable platform like a quadcopter and somehow unfold it into a single large efficient wing for forward flight oh yeah let me show you how I built this thing I started out in cadland with the intention of being able to 3D print print the entire airframe my primary goal was to create a very high aspect ratio wing for forward flight aspect ratio is just the geometric ratio of the wingspan to the wing cord since a large portion of a Wing's drag is produced by induced effects from the tips a high aspect ratio Wing gives more total lifting area for proportionally smaller wing tip drag penalty in an extreme case a wing with infinite aspect ratio has no drag losses from wing tips because it doesn't have any this is why gliders typically have very long skinny Wings to increase efficiency in addition to high aspect ratio I obviously needed a strong and reliable folding mechanism generally it's a bad idea to have a discontinuous Wings Spar let alone one intended to fold since the lift forces while in flight are doing their best to fold the wing on their own too much lift and too little wing strength causes catastrophic buckling of the wing which is not ideal so clearly this joint needed to be strong it also needed a high strength actuator to allow it to fold on command without back driving under the forces of flight eventually I settled on using this high torque linear your actuator which is allegedly good for 40 lbs of pulling strength I 3D printed some test parts and assembled this mockup to test the concept the linear actuator is fixed to the folding Wing segment and pushes and pulls on a little offset linkage connected to the inboard Wing segment this causes the two pieces to rotate inside the joint pieces are just a few small bearings and a carbon Rod to serve as the axis of rotation what you're seeing as the result of tons of Designing and iterating to get such a strong joint with as little mechanical slop as possible if if I couldn't get this part right the rest of the project would never get off the ground literally but luckily I was pretty happy with the strength and overall actuation so it was time to focus on some other Design Elements I Siz this thing to use standard drone motors with a four cell lipo battery for power the two at the tip will have smaller propellers with higher pitch optimized for forward flight I'll be sure to spin them to oppose the wing tip vortices after being inspired by a certain someone's experiments with wing tip mounted Motors be sure to go check out my buddy cabin's video where he explores this idea to improve efficiency in much greater detail for the inboard Motors I decided to mount them on the trailing Edge utilizing the existing 3D printed Wing joint pieces for the folding mechanism these will have larger propellers optimized for hover efficiency and then I can just shut them off and fold the props back while in forward flight to further reduce drag all the parts in red will be printed using regular pla filament since they serve a structural purpose but the parts in white are purely for aerodynamics and don't need to be as strong so I printed those parts using lightweight pla filament this was my first time 3D printing an airplane with this material so it took a few tries to get the settings dialed in one thing I did to the design was add a tiny slit down the middle so that it can be printed in one continuous layer line without this the foaming pla gets all stringy during print retractions with it I get perfect Wing parts right off the printer that don't need any postprocessing with all the parts printed it was finally time for assembly of the airframe all the parts slide over the main Wings spars which are five and 10 mm carbon tubes each 500 mm long each of the three wing sections is built around these sparse sizes so the final wingspan is just over 1.5 M with an aspic ratio of about 12 the red pla Parts use some set screws to lock onto the spars and the lightweight pla Parts in between are just naturally pinned in place now since the Wings Main structure comes from those carbon spars The Fragile lightweight pla Parts don't need to be that strong but I still anticipate them taking a beating during my flight testing so I went ahead and gave them a thin layer of fiberglass this included the left and right outboard Wing pieces as well as the center fuselage section this process only added about 80 g to the total weight and I think it was well worth it just look at how much tougher the fiberglass pieces [Applause] are next I mounted the wing tip Motors and routed the wiring through the wings I also buried a Servo in there before the fiberglassing to actuate the control surfaces for forward flight I made sure to carefully route the wires through the joint and secure them with the zip tie so that the wing could still freely fold so satisfying and after lots of soldering and routing wires off camera the build was nearly complete under the hood I've got my open source flight controller dream flight running the show this takes care of all the control mixing and Wing folding logic while providing stabilization so with all that taken care of let's go take it outside for its first test [Music] hover with the wing folded up it's effectively just a quadcopter with a really weird looking frame it flies exactly the same and has some pretty good Control Authority note how despite the high aspect ratio Wing we designed only a third of it will face the wind in any direction now that it's folded up this makes it much more controllable in the wind one thing I did to increase y Control Authority was mix in a bit of control service deflection since the outer Motors are partially blowing over them normally ya for a quadcopter just uses the torque of the motors but with such a large frame this can be sluggish utilizing the existing control services for forward flight was basically free Control Authority nice this may have looked easy getting it the hover but behind the scenes there was plenty of tuning to account for the weird asymmetric motor configuration I'd be a liar if I said this process went smoothly I don't know what that was feel like this would have been a lot worse without the fiberglass you may have noticed I mentioned folding props in the design but didn't use them during those first couple of hovering flights the reason is that for the life of me I can't find anyone who sells counter rotating folding props so we'll need to build some I took these regular props and cut them diagonally across their Hub then I filed out a square Groove and drilled a hole through the remaining Hub pieces for the center Hub the sponsor of this video PCB way hooked me up I designed the Hub to be machined in aluminum uploaded my file to the website and placed in order in a matter of minutes the part showed up in less than 2 weeks and I was really pleased with the quality for such a quick turnaround these hubs can now be mounted on the motor shafts and some M3 Hardware will hold the modified prop blades on so now I've got that counter rotating set of props I need for hover but then they can fold back to reduce drag and forward flight when I shut these motors off thanks PC for helping me out and sponsoring this video make sure to check their website out Linked In the description they do everything from CNC Machining and laser cutting to pcbs and 3D printing now that we've got hover locked in it's time to start thinking about forward flight I rigged up this test harness and loaded up some code from my last video where I prototyped some smooth tail sitter transitions with a bicopter wing go check that video out on my channel for a better explanation of the flight controller code changes needed to pull the V transition off it's surprisingly not as simple as just pitching over 90° who knew in Hover variable motor RPM is used to control and stabilize the whole vehicle when I flip a switch on my radio to begin transitioning into airplane mode the wings begin unfolding as they unfold the whole thing slowly pitches over and the control surfaces begin moving to stabilize forward flight once the wings are fully unfolded the inboard motor shut off and it's basically just a flying wing with elevon control that's the idea at least now we need to go start flight testing I packed everything up and found a large field to go fly at coming in at just about 3 lb this thing wouldn't necessarily be a floaty flyer in forward flight and would certainly need plenty of room to fly [Music] around when testing a transitioning VTO like this it's best to start from a known flyable configuration and slowly work your way into the next configuration so what I'm doing is only transitioning partway into forward flight if anything starts going wrong or feels weird during the transition I can always fall back on my hover flight mode that's been tuned [Music] [Applause] [Music] already I spent some time easing into forward flight with varying amounts of success some attempts went very smoothly and others seemingly increased the weight of my pants whoa whoa oh my God in this flight you can see some nasty oscillations starting to form so all I did was switch back into hover and it quickly recovered who despite some of the scares I had a fun time feeling out how this thing Handles in the sky after a little bit of adjusting at the field I was finally comfortable enough to do a complete lap or two while half transitioned into forward flight as Tiny oscillations started to form I was able to manually prevent them from growing but going any further toward forward flight still proved to be too dangerous without risking crashing so clearly there's still more tuning and adjusting to be done on the flight controller side whoa It's so scary it's terrifying it looks so cool though I know exactly what kind of changes I need to make after getting this experience flying at the field so now it's time to go back home with what we learned and make them happen that's why I'm going to pause this video and pick it back up in the next one I think I can can get this to work but I just need a little bit more time to work through the issues this is an incredibly complex project with a lot of time invested in it and a crash St a careless flight testing would be painful to say the least so if you want to see this design fully unfolded cruising around with some detailed measurements of efficiency be sure to subscribe so you don't miss it if that's not enough for you feel free to check out my patreon where I've been sharing regular behind the scenes updates as I work on this project you can also get early access to all the 3D print files over there before I release them to the public when this project is finished now time to finish making this thing fly see you in the next video [Music] cheers

Channel: Nicholas Rehm

Views: 550,148

Keywords: vtol drone, unique drone design, folding wing vtol, pterodynamics transwing, pterdynamics vtol, pterodynamics xp-4, spinning drone paradox, building a drone, vertical takeoff and landing, drone efficiency, what is aspect ratio, vtol tailsitter, quadrotor biplane vtol, educational engineering, spinning drone efficiency, efficient hovering drone, vtol drone forward flight, rc vtol airplane, new drone design, radio controlled vtol, 3d printed vtol, 3d printed drone design

Id: gZQEOjyjwhc

Length: 10min 57sec (657 seconds)

Published: Fri Nov 24 2023