How would you design a cyclocopter?

[LitterBug]

Where are the pedals? I think of pedals when I see Cyclo..... ;-)

 

[NickRehm]

Looks great! Just one comment: I recommend putting the pitching axis of the blades at the quarter-chord to reduce the required force to pitch the blades. The center of pressure is loosely located there (despite some weird cyclo aerodynamics at play) meaning the net moment about it when pitching is very low--making it easier to actuate

 

[2jujube7]

Where are the pedals? I think of pedals when I see Cyclo..... ;-)

Not on this one. This is going to be a little ~300-400mm wingspan one, so I'm going to find a mouse and put him in a running exercise wheel to power it.

 

[2jujube7]

Looks great! Just one comment: I recommend putting the pitching axis of the blades at the quarter-chord to reduce the required force to pitch the blades. The center of pressure is loosely located there (despite some weird cyclo aerodynamics at play) meaning the net moment about it when pitching is very low--making it easier to actuate

I agree that moving the pitching axis of the blades back a little would be beneficial. The trouble is that it still needs to be forewords of the CG because the airfoils use centrifugal force to push against the outside ring and vector themselves. I can still move it back a good amount though, and I think I'll do that.

 

[2jujube7]

Adjusted it a little, here's a screenshot with a CG mark. It has an extremely aerodynamically optimized free-handed spline airfoil.

 

[Scotto]

Hey I was thinking about this again and I wanted to try to visualize it. I love this little program. I've spent way too much time on little virtual mechanisms but its a lot of fun.
Linkage App

@2jujube7 it looks like your creation would have full proportional control up, down, forward, back with neutral being actually neutral. That would be awesome for a lighter than air vehicle picking up payloads.

 

[2jujube7]

@2jujube7 it looks like your creation would have full proportional control up, down, forward, back with neutral being actually neutral. That would be awesome for a lighter than air vehicle picking up payloads.

Haha, not sure it's my creation at this point, I've been borrowing heavily from other's attempts. Let's call it reverse engineering.

I put it on a scale yesterday to measure the thrust and I got none. I think it might be time for a complete redesign...

 

[2jujube7]

I recently started over and took inspiration from @Rcjetflyer2 's cyclocopter article. I CADed it out this week and started 3D printing it. This design is SO much less complex than the previous design I was trying to make, so it is printing very quickly.

Above is the new design, below is the old one for comparison:


I did have a thought though: Voith-Schneider propeller. I did some research, and it seems like it's been pretty developed (well enough for commercial use in boats). I can't see any reason why it's not being used in aviation as a cyclorotor, except that it's patented. Is that just it?

 

[Scotto]

Im guessing this isnt used in manned flight because each rotor blade is being loaded, unloaded, loaded the other direction, and unloaded again each rotation. That would put a lot of stress on something big and aluminum, flexing back and forth. And to fight that it gets heavy. But small stuff like this I could see it having advantages over a normal quadcopter. But its that "fast, cheap, or quality. Pick two" thing however that goes.
Good luck on version 2! Hey just turn version 1 90 degrees and build a tug boat around it

 

[2jujube7]

It's been a good month since the last update, and the overall design hasn't changed much. I've just been working out little bugs that are causing me lots of troubles. Ex. the bearings have been slipping out from the 3d printed parts, parts are sliding off of the shaft/bearing connectors, I got a new motor that had screw holes on the end with the shaft to reduce new vibrations so I redesigned the mount, then I drove a screw back in too far so I shorted it and had to go back to the old one. Lots o' little things like that. On the positive side, I was able to generate 50g thrust before it fell apart. I did some weighing and found that i'll need around 200g thrust in order to make it fly, so i'm around 1/4 of the way there! Here's a YouTube link of the first thrust test.

 

[JasonK]

It's been a good month since the last update, and the overall design hasn't changed much. I've just been working out little bugs that are causing me lots of troubles. Ex. the bearings have been slipping out from the 3d printed parts, parts are sliding off of the shaft/bearing connectors, I got a new motor that had screw holes on the end with the shaft to reduce new vibrations so I redesigned the mount, then I drove a screw back in too far so I shorted it and had to go back to the old one. Lots o' little things like that. On the positive side, I was able to generate 50g thrust before it fell apart. I did some weighing and found that i'll need around 200g thrust in order to make it fly, so i'm around 1/4 of the way there! Here's a YouTube link of the first thrust test.

maybe I am missing something in your photo, but it looks like you have a fixed offset for center of the angle control bit. That seems like it would work better to be able to move that anywhere in an area around that point (so thrust can be vectored in any direction and any amount of thrust, vs having to rotate the thrust and be required to change the motor speed to change the amount of thrust).

 

[quorneng]

2jujube7
Just a point but a symmetrical wing section works equally well either way up so it could produce lift on both the top and bottom arcs if the incidence is correct. Or am I missing something?

 

[Piotrsko]

I agree with @quorneng on the fully symmetrical airfoil, even more so with a minimal pitching moment.

Perhaps too much incidence on your offset device? Most of what I use stalls at 10 degrees positive and 3 degrees is pushing it for drag polars. Swag engineering says perhaps less than 1/4" off center? The diagram is inconclusive.

Are you lubing your pivots?

 

[2jujube7]

maybe I am missing something in your photo, but it looks like you have a fixed offset for center of the angle control bit. That seems like it would work better to be able to move that anywhere in an area around that point (so thrust can be vectored in any direction and any amount of thrust, vs having to rotate the thrust and be required to change the motor speed to change the amount of thrust).

You are not missing something. My previous edition had the 2D vectoring arrangement that allows it to change magnitude and direction. However, it was very complicated, large, and locked up when I tried to move it. This current (should I call it rotary?) vectoring mechanism is "reverse engineered" aka copied from Rcjetflyer2, and it's super simple to hook up with just a single servo/linkage. That lets me just work on the parts that actually generate thrust, instead of just the linkage that's only needed when it makes enough thrust to fly. The last design (it's back a little farther on this thread) had the 2D vectoring arrangement, and I was spending much of the design/debugging time on getting it to not lock up (I was very unsuccessful at this). Perhaps I'll try to come up with a better 2D way when I get this working better.

2jujube7
Just a point but a symmetrical wing section works equally well either way up so it could produce lift on both the top and bottom arcs if the incidence is correct. Or am I missing something?

Yes. A symmetrical airfoil would generate more lift, be more efficient, and overall just work better. I'm just sticking with a rough Clark Y airfoil shape in order to have the flat bottom that's easy to 3D print without the hassle of dealing with supports or post processing sanding.

On second thought, I'm actually getting thrust out of the cyclocopter now so I should probably make them symmetrical soon to see how much of a difference it makes. I made the flat-bottomed Clark-Ys when I was still trying to figure out how to get the thing to not fly apart when I used it, so it might be time for a change.

Perhaps too much incidence on your offset device? Most of what I use stalls at 10 degrees positive and 3 degrees is pushing it for drag polars

This is a valid point. I'm pretty sure that I read somewhere that a 45 degree angle of attack was the most efficient pitch to generate thrust, but I would have read that a good 4 months ago when I was doing a bunch of research, so I could be mistaken. I'm going to be printing out different parts to allow different AoAs of the Airfoils, and I'll be thrust/power testing them to find the most efficient set-up.

 

[quorneng]

2jujube7
you started this journey with the concept that a cyclocopter could be aerodynamically more efficient.
I appreciate you are still in the experimental stage but you should always keep in mind the power (Watts) that you are using.
Static thrust is measured in g/W. Obviously your design needs to be compared to the most efficient way of creating 'helicopter' thrust which is a 2 blade rotor.
Depending on how close you are to that sort of performance rotor may determine whether a cyclocopter is just another 'idea' rather than a practical alternative.

As far as printing aerofoils go have you tried printing in two parts like this and then simply gluing them together. Note the filament direction is still along the length of the wing. Done like this you can print any wing section shape you like.
Oops! Sorry forgot to add the attachment

 

[NickRehm]

That thrust test video of it running looks great @2jujube7! You're probably getting 1.5-2x more thrust than what you read on the scale, though, since a lot of the air is not directly hitting the scale. When we tested the cyclos in the lab, we had a special mount for them that rigidly attached to the scale, with the rotor cantilevered off the edge of the table

I took my old 500g cyclo out and got it flying again with updated flight control code yesterday. Had a little mishap with the right cyclorotor when some hardware came loose, but a new bolt and some locktite has it back in the air. Thinking of doing a proper video in the near future showing some better flight footage and explanations of the mechanics/aerodynamics...

 

[Scotto]

Cool! Good work. At first I thought 2 servos to be able to change the magnitude would be better but I totally agree that it is just added comlexity and weight you dont need. I bet its great on ships and itd be cool on an airship, but not for this. Although it could make it super easy to find your optimum AoA or incidence(?) if you could go from 3 degrees to 50 without taking anything apart just sitting on a test stand scale with a watt meter. Optimum might change with different airfoils. And rpms maybe.
One other thing I noticed is the blue linkages in your cad drawings are separate pieces. Ask @Rcjetflyer2 first but I was assuming that was all one piece like your green piece next to it on his machine. I could be wrong.

 

[NickRehm]

One other thing I noticed is the blue linkages in your cad drawings are separate pieces. Ask @Rcjetflyer2 first but I was assuming that was all one piece like your green piece next to it on his machine. I could be wrong.

The geometry does not stay perfectly 'square' all the way around the rotation, actually ends up looking a little elliptical,. So the independent control linkages are definitely required

 

[Piotrsko]

Stupid question: why not attach it to the scale, then measure weight/thrust directly? It will require subtraction however.

 

[2jujube7]

Scotto here's a screen shot of the weird blue non-squareness. It's not very much, but its still significant enough to need a separate rotating piece for each connection. It adds complexity and weight, and is a little annoying to work with by have 4 different parts to change each time it needs and print them out, but its not too bad of a problem. Not much you can do about it...

quorneng I have not tried printing them like that yet. It would also probably add to the strength, as the bottom layers while printing would turn into a spar once It's glued together That is a very good idea that I should probably try soon.

Rcjetflyer2 Thanks for the tip about the thrust, that's helpful to know and a somewhat big thing to overlook. I'll have to set up an actual stand up at some point and see how much more I need to go.