How would you design a cyclocopter?

[TFerenc]

How do you set up assymetric pitching?

The pitching axis should be pitching crankshaft (calotte storage) with four pins bearing, turned off 90 deg. to the base. It should work like the crankshaft in the piston motor, but moving the pitching arms accordingly. In fact the 2jujube7’s present solution has a fixed pitching axis - however we have to make a geared axis later on to drive the SUAV.

 

[2jujube7]

I was having some trouble with the strength and durability of the 3D printed airfoils, so I came up with a process to make them out of XPS (pink) foam. Although the airfoil is many times weaker than a 3D printed one, its also 9ish times lighter. After doing some math, I calculated that it should be able to take the centrifugal forces. I'm not sure what the impact of the aerodynamic forces will be, but I've read that they are minor so I'm just ignoring them for now. I'm pretty sure that they'll bend a little, but it shouldn't be enough to significantly effect the thrust. If it does, I'll just throw in a pultruded carbon fiber tube as a spar. For those of you wondering, the airfoil shape is just cut out of the foam, then one side is covered in packing tape (the side on the outside of the rotation), and finally I'm gluing an end cap to the airfoil so that the bearings can screw in.

I also started screwing the bearings into the 3D printed parts instead of designing in weak 3mm diameter 3D printed shafts that the bearings press fit on.



(Ignore the wrinkles on the airfoil from the tape being poorly applied, that airfoil was a test to see if the glue used to put on the end cap would melt the foam)

 

[2jujube7]

I did a thrust test a few days ago, and I got up to 112g thrust at 50% throttle. I need around 120g thrust to do a tethered flight, and 150g or so for a free flight.

Here's what I'm thinking about for the basic setup. I'm just going to do a 2 rotor tethered hover at first, and after I get it flying sufficiently I'll start working on a 4 rotor untethered flight.

 

[Piotrsko]

Instead of tape, why not do a paper covering, your choice of adhesive? Would be stronger and less wrinkles, probably just a bit heavier.

 

[2jujube7]

Instead of tape, why not do a paper covering, your choice of adhesive? Would be stronger and less wrinkles, probably just a bit heavier.

When spinning around, weight really matters because of the centrifugal forces. The tape works well at the current speeds/forces, is smooth, is easy to apply, and has a good strength to weight ratio. If I need more strength, I'd probably find a really light carbon fiber spar and stick it in somehow.

 

[2jujube7]

This week I successfully reached 170g thrust with the cyclorotor after messing around with the transmission a little. For context, the whole setup weighs 131g so it has a sufficient T/W for me to start working on a cyclocopter. Plus, the 170g thrust test was not to failure, so there is probably still more thrust if I need it. I'm going to change around a few parts such as some vector attachments, but in general it's ready to hover.

(This picture of the overall copter is a week or so old, it doesn't have the new idler and motor plate)

 

[NickRehm]

Really curious how it sounds with the belt drive? Build is looking absolutely amazing

 

[2jujube7]

Really curious how it sounds with the belt drive? Build is looking absolutely amazing

This is the video where I reached 170g thrust:

The belt drive is a lot quieter than the gears I've used in the past; the gears didn't have any lubrication on them so they clattered a lot. The pulleys are fully 3d printed though, so they aren't the smoothest running.

 

[2jujube7]

Working on a new idea. It should reduce airfoil bowing and let me run it at higher speeds, along with an increase in strength by making the vector links straighter

 

[Piotrsko]

If the airfoil is bowing, lack of rigidity is that issue. Other than unloading the center via the ends the added complexity probably won't gain you much. You were running carbon spars, right?

 

[2jujube7]

If the airfoil is bowing, lack of rigidity is that issue. Other than unloading the center via the ends the added complexity probably won't gain you much. You were running carbon spars, right?

I'm using solid (XPS aka pink) foam airfoils right now. Although it's not strong at all, it only weighs 1g so the centrifugal forces don't bend it that much. I've been thinking about incorporating carbon spars, but it would make manufacturing more complex and I don't actually think I need it. The airfoil doesn't bow that much right now, I was just trying to develop a way to increase the strength for future bigger versions. I'll just cross that bridge when I come to it and probably put spars in.

The end plates that connect to the middle of the airfoil turn out to have too much slop, so I'm going back to a modified version of the original idea that I've already tested.

 

[2jujube7]

Hmmm... I actually made a thrust stand this weekend, and It ran up to 310g thrust. (with 130g rotor weight) Turns out that @Rcjetflyer2 was right, the previous airflow testing got me around 220g max thrust so it was short by around 40%. I ordered more bearings and they'll be here soon, so I'll be putting together a dual rotor tethered hover cyclocopter soon.

 

[NickRehm]

310g thrust is absolutely awesome, can't wait to see the tethered tests

 

[2jujube7]

A sneak peak of what might fly tomorrow...

 

[2jujube7]

It flies!!!! A little unsteady, but that's to be expected when it's not in trim and there's no flight controller. I'll be able to post a video tomorrow.

 

[2jujube7]

 

[NickRehm]

I've been very inspired by @2jujube7 's success 3D printing his belt-drive cyclorotor, so I've started designing my own to be fully-3D printed--minus bearings, shafts, and blades of course. Blades are foamboard with 2mm carbon spar, sanded to a rough 0012 profile by hand.

Using a lumineer rx22206 2350kv motor geared down 4:1, I'm getting above 300g thrust (still need to make a proper attachment for my scale to properly measure thrust...) at less than 5a current draw on a 3s. Pretty good so far, minus it exploding at about 60% throttle haha. There's a surprising amount of force on the endplates. Updates already made and on the printer for the next version. I think I will be further increasing the gearing ratio so I can run it on 4s.
The end goal is mini-quad-sized quad cyclo that doesn't take an eternity to build like some of the original prototypes at my old lab...

In the meantime, enjoy Texas A&M's latest cyclo:

 

[2jujube7]

I've been very inspired by @2jujube7 's success 3D printing his belt-drive cyclorotor, so I've started designing my own to be fully-3D printed--minus bearings, shafts, and blades of course. Blades are foamboard with 2mm carbon spar, sanded to a rough 0012 profile by hand.

Great to see! The only thing I'd say is to increase the airfoil size to something like an 0020, the larger thickness should make it more efficient. if you can't do that with foamboard, I'd recommend XPS foam; Its been great because its stiff and light enough that I don't need a spar.

What's the wingspan and weight/blade weight?

A few updates
-Increased gearing ratio to 6:1, produces around 20% less thrust at a given throttle setting, but makes the motor cool enough so that it doesn't heat up the plastic motor mount and warp it.
-Added a SG90 servo, so it can now vector thrust +/- 20 degrees or so
-I just got a shipment of carbon fiber rods so be prepared for another flying version soon; the rods for the frame will weight 66% less than my aluminum rods

 

[Piotrsko]

0020 isn't a scaled up 0012 there are camber and streamlining differences and the nose is almost gottengen like.

I am also thinking this isn't really a 0012 since I bet the nose is too blunt. Wicked, nasty and unpredictable stall on 0012 that I wouldn't want on the nose going up side.

However, if like you indicate, you're just pushing air out of the way, airfoil is immaterial.

 

[NickRehm]

My airfoil thickness was solely a function of foamboard without paper thickness because I needed something quick haha. Thicker would definitely help with reducing stall on the blades due to the 'virtual camber' effect

Each blade weighs about 2g or so (my scale sucks) with a 2mm spar through the length, and the whole rotor with motor and servo is about 115g--I still have some weight reduction to do on the 3DP parts. Blades are 110mm x 26mm and the rotor diameter from blade pitch axis to blade pitch axis is 150mm. I thought I was doing good on current draw, but just did a spool up to 90% throttle and my motor was HOT, even though my cheapo amazon special current meter was only reading about 12 amps. The motor is rated for 30+... probably a bad current meter?