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Cleo Robotics Demonstrates Uniquely Clever Ducted Fan Drone (ieee.org)
118 points by jonbaer on Feb 13, 2018 | hide | past | web | favorite | 35 comments

Unless the fit of the casing parts is atrocious, there appears to be a slit right above the grey ring the camera is mounted in.

Due to the shape, and it's location it's quite possible that internal shutters or ducts can be configured so as to allow partially disrupting the coanda effect on either side by selectively allowing air to exit through the slit. Possibly, but not necessarily ducted in from the fans high pressure zone.

This would likely cause a rather strong vectoring of the thrust as it would also almost certainly lower the lift on the detached side due to interactions with the fans.

If that isn't how its done, I'm quite positive it can be done in this way. I'll be happy to be named inventor in any thusly aquired patent and collect a very modest licensing fee, if only that would be how the world works...

My wild bet: The two rotors are not coaxial. It is a very narrow bicopter (if the two rotors are not actually on the same axis and contrarotating then you get 3 degrees of freedom)

Throwing my idea out there: What if the to propellers are synched. Depending on desired direction, they are "un-synched" ever so slightly. This causes additional thrust on one side of the "duct".

ATH Zurich have a single prop craft that uses just a single channel high speed motor control to stabilise and steer it: https://www.youtube.com/watch?v=P3fM6VwXXFM

I wonder if this maybe has two contra rotating single blade props that they can control quickly enough to be able to speed them up for half a revolution to generate asymmetric thrust to provide pitch and roll?

Pictures show 2*3 blades (well, one three bladed and two blades of a similar layout, with one obscured)

But it could still be based on the same idea: if the blades are not flexing in the same way under acceleration, any asymmetry might do it, if it can be properly controlled.

Which brings us to how I thought this thing does pitch/roll until I noticed that I just got hung up on a difference between a prototype in the picture and a later iteration in the video: contrarotating propellers will influence each other when blades meet, creating nonuniform efficiency over the duration of a rotation. Three peaks and three troughs, like the legs of miniscule of pressure differential. I don't know where the peaks would be relative to the meeting points, but given the general fickleness of aerodynamics thrust of contrarotating propellers just can't be perfectly even all around the rotation. But that's still three-symmetric. It could become a control option when overlapped it with e.g. an n-symmetric grid where n is not a multiple of three, even if not a good one (mixing it with yaw would be a wobbly mess). The prototype picture shows five arms which is how I got the idea, but in the video it seems to be six/three, so this candidate is out (unless the specifically made a misleading dummy for the video, which I don't think, even though the video is cut in a way that it might be).

I believe varying the speeds of the props will only give you yaw right/left. In one of the shots in the video you can see it moving sideways.

Perhaps the attitude of each fan blade rotates independently. To angle the drone, say, forwards, the fan blades might angle flat when they're at the forward position, every cycle, and angle tilted at the backwards position?

Seems expensive and tricky though.

"An Underactuated Propeller for Attitude Control in Micro Air Vehicles"

Paper is not free but video conveys the idea well: https://www.youtube.com/watch?v=KZe7l5_LfoA

Likely with clever two-material molding you could do away with the hinge and it would look similar to the prototype shown in the article.

That is very clever, but the article says that this drone "introduce[s] control surfaces into the airstream to change the direction of the airflow and create a thrust vectoring effect." My guess is tiny spoilers around the inside of the duct to cause separation of the flow in one quadrant of the duct, allowing the Coanda effect to draw the stream in the opposite direction.

For those interested in details, the papers are linked from the project page: http://www.modlabupenn.org/2014/10/23/underactuated-rotor/.

> The main motor directly drives the propeller hub, which is itself connected to the propeller blades by two inclined hinges. The hinge geometry couples blade lead-and-lag oscillations to a change in blade pitch. Instead of only driving the motor with a steady torque, we add a sinusoidal component in phase with the rotation of the rotor to induce a cyclic pitch variation. The amplitude and phase of this control signal determines the magnitude and direction of the vehicle response.

Oh, that's clever. Very nice. Tough to design, cheap to manufacture in quantity.

That's how helicopters work, and it requires complicated mechanical linkages. Read the wiki article about swashplates for an introduction.

Yep, that’s how helicopters work, using a swash plate to change the rotor pitch every revolution.

It could all be done with weight shifting:


Maybe shifting the battery?

I can't remember the details but as you shift weight and begin moving laterally, when you pick up lateral speed it interferes with the ducting effect or enhances it in some way can counter reacts against the movement, giving dynamic stability.

For what it's worth, the article says it isn't done with movable weights.

I don't know a lot enough about aerodynamics or airflow to be sure, but could they be moving pieces of plastic on the inside of the donut to block some of the airflow on one side to make it bank in that direction?

> Cleo, meanwhile, boasts a useful battery life in the 12-15 minute range

For some definition of useful. Batteries really are the worst thing ever. We got dense energy from oil so early, and then nada.

If there is a charger at each desk only 5 minutes of battery is needed.

> With fewer motors than conventional quadrotors, it promises to be more efficient as well [...]

I doubt that, because in "stacked propellers" configuration the second propeller gets very turbulent air, causing extra noise and vibration, i.e. loss of efficiency.

Could you flex the shape of the inner donut somehow to change the vortex?

Yes. There is this company [1] trying to use a similar concept (ejectors) to build a « motorbike hovercraft ». I haven’t heard about them for a while. They have patents on the concept [2]

[1] www.aerofex.com [2] http://www.google.ch/patents/WO2011126535A2?cl=en

EDIT: link to patent.

This. The simplest way to guide would be with a flexible membrane in between the two rotors that contained some sort of electrofluidic bladder

+1. This is what I was thinking but I'm not a a MechE. Would it work?

I'm not a mechanical engineer either :p

Very interesting. I wondered when someone would try to mesh coaxial rotors [0] with quadcopter use cases.

To make a real co-axial vehicle, you'll need to handle changes in the 3 translational axes (forward/backward, strafe left/right and up/down) as well as the rotational axes. Despite being a complicated movement, it's pretty well understood and Kamov has been making coaxial helicopters for many years.

My best guess based on the video is that there are two contra-rotating fixed pitch props in the middle. This gives you up/down and by varying the speed of the props gives you yaw right/left. A couple of clever ducts forward, aft, left and right on the duct give you stability forward/backwards and left/right.

I look forward to actually learning how they did it. It certainly looks cool.

0 https://en.wikipedia.org/wiki/Coaxial_rotors

You only need four degrees of freedom to control an air vehicle in gravity (upward thrust and roll/pitch/yaw). You could still use internal ducting (as you suggest) to do that, but it'd probably be easier and more effective to have little flaps that deploy into the airstream under the rotors to divert the airflow.

Would it be practical to use a gyroscope to control one axis of rotation in a "drone" like this?

That is a cool idea, if you can get really light and efficient mechanical gyro.

A boring solution will be fins operated by micro servo/

Coanda effect? Some little jets somewhere to entrain the flow?

Yep, perhaps just coanda effect with control surfaces on the bottom. Sort of like what the AESIR guys did:


Anyone seen any tip driven motors in drones ? I found one test but not much detail, http://ieeexplore.ieee.org/abstract/document/8101907/

Did anybody else notice that this is a flying saucer?

With a little control autonomy, it's the throwable flying map-ball bots from Prometheus.

they could just deform the shape of parts of the duct, altering lift generated on one side or the other.

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