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Underactuated Rotor for Simple Micro Air Vehicles

modlabupenn.org

11–20 of 84 posts

Re: Underactuated Rotor for Simple Micro Air Vehicles

#11

This thing is so nimble in the air yet has a fraction of the complexity of a regular helicopter. I wonder if this method will scale up to "full size"?

That's what I was thinking. That would require electrical motor control of the blades. Maybe turbine generator for power source. I would imagine this kind of pulsing would cause severe fatigue on the parts if they scale up too large.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#12
post #5

This is so clever! Turning mechanical control problems into informational control problems is critical to the ubiquity of micro air vehicles.

There is a lot of potential in solving mechanical problems with information systems, rather than using complicated mechanical solutions. For instance, hydraulic automatic transmissions and differential.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#15

This thing is so nimble in the air yet has a fraction of the complexity of a regular helicopter. I wonder if this method will scale up to "full size"?

Electric motors remove a lot of the complexity in powered-lift flying machines. As soon as your power/endurance requirements demand a combustion engine, you also have to manage the complexity of a piston engine or turbine (jet) engine.

This means either including a crankshaft and optionally a system of gears to route the rotational power along the axes you want the rotation in, or ducting the output of a jet turbine in some way that drives the rotors. In addition, there are different limitations with regards to the time required for a given change in RPM as compared to an electrical motor.

My impression is that a lot of the complexity in conventional helicopters (and flying machines in general) stems from the limitations of combustion engines. There's a reason that you very rarely see vectored thrust in conventional airplanes, for example.

Of course, if batteries and electric motors become sufficiently powerful, this changes the dynamic and it will become possible to design electric aircraft that re-evaluate the traditional design restrictions. This is one of the reasons that the rapid progress of electric cars is so exciting.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#16

This thing is so nimble in the air yet has a fraction of the complexity of a regular helicopter. I wonder if this method will scale up to "full size"?

Probably not, for the same reason that a quadcopter doesn't really scale to full size. The inertia effects of larger rotors make changing the speed of the rotors within a rotation much harder.

With full sized helis, it takes a long time to spin up the rotors to speed before the pitch is changed to take off.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#18

This thing is so nimble in the air yet has a fraction of the complexity of a regular helicopter. I wonder if this method will scale up to "full size"?

Big rotor = big moment of inertia = more energy lost on accelerating it and slowing it down each time. At some point it's better to rotate it at constant velocity and change pitch independently.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#19
post #8

Now if we could just start printing these parts at home...

I did printed helicopter blades three years ago: https://www.youtube.com/watch?v=qXlUSWrVzys

These other components look printable too. Right now I am making 3D printable robots that don't need any non-printed parts aside from motors, bearings, and drive belts (and batteries and electronics).

So these definitely should be printable at home.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#20

This thing is so nimble in the air yet has a fraction of the complexity of a regular helicopter. I wonder if this method will scale up to "full size"?

Probably not, for the same reason that a quadcopter doesn't really scale to full size. The inertia effects of larger rotors make changing the speed of the rotors within a rotation much harder. With full sized helis, it takes a long time to spin up the rotors to speed before the pitch is changed to take off.

Well the critical difference here is that changing blade speed is not needed or desired. They just need to change blade torque, which would apparently immediately cause a change in blade pitch.

I don't see a specific reason why this wouldn't scale. I do wonder what changes in load do to the system though. If it can't handle changing loads without messing up the blade dynamics, it would only work for fixed payload systems like camera platforms.

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