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Underactuated Rotor for Simple Micro Air Vehicles

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Re: Underactuated Rotor for Simple Micro Air Vehicles

#31

Post by lotsofmangos »

wiredfool wrote: post #16
command_tab wrote: post #2

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.

Sure it would work. It only needs a variable clutch on a standard engine and the motion on the blades is very slight and mostly balanced, so the torque difference should be pretty manageable.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#32

Post by TaylorAlexander »

prbuckley wrote: post #27
erobbins wrote: post #25

Earlier quoted context omitted.

It won't scale because of inertia. Rapidly changing the speed/torque of a large combustion engine is nearly impossible. It's a great solution for reducing mechanical complexity in mini/micro sized UAVs, though.

I don't think scaling this up is a question of inertia it is more a question of weither a material exists that can be used in those flexural joints with much higher loads. This is a material science question. A material may exist that has the right combination of flex, strength and lets also not forget durability. I am a mechanical engineer and crack propagation and cycle fatigue would be a major concern for a joint…

The joints looked like simple pivots, not flex joints. See how the blade is attached at a 45 degree angle? I think it just pivots there.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#33

Post by TaylorAlexander »

erobbins wrote: post #25
TaylorAlexander wrote: post #20

Earlier quoted context omitted.

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 sys…

It won't scale because of inertia. Rapidly changing the speed/torque of a large combustion engine is nearly impossible. It's a great solution for reducing mechanical complexity in mini/micro sized UAVs, though.

You can use an electric motor. We can easily make extremely high power electric motors (see: CNC machines and Diesel trains), and power storage will continue to improve.

The added cost of batteries at even today's prices could be worth it for the decreased mechanical complexity of the rest.

If all we need to do is change the torque of an electric motor, that can be done essentially instantaneously even at high power levels.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#34

Post by TaylorAlexander »

ajuc wrote: post #18
command_tab wrote: post #2

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.

You're not worried about speeding up the blades, just changing the torque on the drive system. The inertia of the blades actually helps you here.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#35

Post by TaylorAlexander »

FrankenPC wrote: post #11
command_tab wrote: post #2

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.

The parts will cycle back and forth exactly as much as they would in a traditional helicopter, and there are fewer comparatively small parts. It would likely be stronger and more fatigue resistant than current methods of controlling blade pitch. We can program the motor to change torque as smoothly as we want.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#36

Post by TaylorAlexander »

lucaspiller wrote: post #21
TaylorAlexander wrote: post #19

Earlier quoted context omitted.

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.

That sounds cool, do you have any links to your projects?

Thanks! Currently I'm working on delivering Flutter Wireless, which is at www.FlutterWireless.com.

The 3D printed robots will be for some tutorials we will be launching. Other than that, I've been continually procrastinating about making a website for my personal projects, but I have a lot. If you dig through my youtube account at the original link, I have some other project videos there.

Notable ones are: The robot I made when I was in High School: https://www.youtube.com/watch?v=8FJu1eL_dYs&list=UUxTluifYa_...

An app to interface with some cheap helicopter joysticks (and not shown - I could fly the heli with an app on my phone). https://www.youtube.com/watch?v=gq2x3DVq7gs&list=UUxTluifYa_...

Lighting a campfire with thermite: https://www.youtube.com/watch?v=7pu-R_IHirE&list=UUxTluifYa_...

A demo sketch I made for 3D printers: https://www.youtube.com/watch?v=KEH7Ji4a3Ss&list=UUxTluifYa_...

The time I was on G4 TechTV: https://www.youtube.com/watch?v=J2R-TlBomnQ&list=UUxTluifYa_...

My stuff on thingiverse. http://www.thingiverse.com/tlalexander/designs

Not currently represented online are some of the robots I have made, the Tesla Coil I made when I was in High School, and the gas powered hovercraft I made in 8th grade. :)

Re: Underactuated Rotor for Simple Micro Air Vehicles

#37

Post by TaylorAlexander »

brk wrote: post #26
aosmith wrote: post #8

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

Seriously, why? Injection molding has far lower cost, higher quality, and you're talking about things that are very cheap and easy to ship. What does 3D printing bring to this?

Injection molding is on the order of 10,000x more expensive if you only need a single part.

I'm currently on a quest to design highly functional robots that can be made with just a 3D printer and a minimum of external parts - so far only bearings, motors, drive belts, batteries and electronics are the non-printed parts needed. I make everything so that it fits together by interlocking or with minimal use of some coarse printed fasteners.

Since nothing needs to be bought from the store that won't be useful if the design changes, it is trivial to iterate and build a newer version.

My hope is that with developers worldwide working on improvements, injection molded versions of the parts would become obsolete before the mold was even cut.

When it comes to manufacturing, 3D printing is a whole different ballgame. No other manufacturing technique can make so many complex parts without human intervention. This means it opens up all new possibilities for how we manufacture things - like continuous iteration of shipping hardware.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#38

Post by TaylorAlexander »

lucaspiller wrote: post #21
TaylorAlexander wrote: post #19

Earlier quoted context omitted.

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.

That sounds cool, do you have any links to your projects?

Oh, I forgot I have a portfolio of machine parts online now too. http://www.tlalexander.com/files/portfolio.pdf

Re: Underactuated Rotor for Simple Micro Air Vehicles

#39

Post by lambda »

TaylorAlexander wrote: post #33
erobbins wrote: post #25

Earlier quoted context omitted.

It won't scale because of inertia. Rapidly changing the speed/torque of a large combustion engine is nearly impossible. It's a great solution for reducing mechanical complexity in mini/micro sized UAVs, though.

You can use an electric motor. We can easily make extremely high power electric motors (see: CNC machines and Diesel trains), and power storage will continue to improve. The added cost of batteries at even today's prices could be worth it for the decreased mechanical complexity of the rest. If all we need to do is change the torque of an electric motor, that can be done essentially instantaneously even at high power…

> power storage will continue to improve

Power storage may continue to improve, but it will take a long time before you hit the energy density of fossil fuels; the difference between batteries and fossil fuels is something like a factor of 10 (actually greater than that, but electric motors are more efficient so let's say 10 for the sake of argument), and it's improving much more slowly than Moore's Law, doubling maybe once every 10 years. That means if those trends continue (and there's no guarantee they will), you're looking at 30-40 years before the energy density allows electric helicopters to be competitive with fossil fuel powered.

For cars, energy density isn't quite as important, as the weight of the car is not the dominant factor in its efficiency (it does have an effect, but the aerodynamics, engine efficiency, transmission efficiency, tires, etc. all make a big difference too). But for a helicopter, every pound you add to the batteries is another pound you have to lift, so energy density of your power source is quite important.

So, if trends hold on battery technologies, it will come about eventually; but I would put money more on the decades timeline than the years timeline.

Re: Underactuated Rotor for Simple Micro Air Vehicles

#40

Post by jacobolus »

lotsofmangos wrote: post #30
brk wrote: post #26

Earlier quoted context omitted.

Seriously, why? Injection molding has far lower cost, higher quality, and you're talking about things that are very cheap and easy to ship. What does 3D printing bring to this?

1m square deskspace requirements and fast tooling in software, rather than thousands of pounds and new metal every time you want to change a detail. Injection moulding is only lower cost when you want to buy something that is already mass manufactured or millions of identical things. Up to about 10,000 units, 3d printing is cheaper.

At-home 3d-printing uses shitty materials and has terrible precision. If you don’t want to go all the way up to making expensive metal tooling and doing injection molding, you can sill get much better results from CNCing some material and then using resin casting than using a 3d printer: http://lcamtuf.coredump.cx/gcnc/
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