NASA Chooses Helicopter for Mars Drone

mars-_helicopter_final15-640x353NASA is now planning on using a UAV in addition to the Rover in order to explore Mars.  The reasons are very simple, and parallel the desire to use UAV’s on earth.  Having a camera in the air, instead of being stuck on the ground, allows for better perspective to see details of the terrain.  And also, avoids the problem that rovers have with negotiating difficult terrain.

But what is particularly interesting with this story, is that they have decided to use a coaxial helicopter instead of a quadcopter.  Why?  Multirotors on earth, already have enough trouble with stabilization due to the need to accelerate and decelerate the propellers to control their flight.  While small quadcopters do fly very well, as they get bigger, and the rotors get bigger, stabilization gets harder.  This is because the rotor inertia increases exponentially with diameter.  It takes much more energy to change the speed of a large rotor than it does smaller ones.  This is why you do not see very large multirotors flying very dynamically.

mars-helicopter-jpl1

On Mars, the problem is even worse.  Due to the thin atmosphere, the rotor must be very large to be able to generate enough lift to fly. It would require a very large and heavy rotor to achieve lift, and the power required to change their speed quickly enough for flight control, would be much too large and heavy to fly.

Helicopters do not have this problem, because they use a swash plate to actuate variable pitch on each blade for flight control.  The motors do not need to be large enough to accelerate the rotors quickly for roll and pitch control.  So you can have a tiny motor spinning a large rotor in the thin Martian atmosphere.  Roll and Pitch control is achieved by cyclic pitch.  Yaw control of a coaxial helicopter is achieved via motor torque, and thrust can be controlled either by variable collective pitch on the rotors, or increasing the rotor speed.  I expect they used the former in this case, for the same reasons why fixed pitch props don’t work for pitch and roll control.  All of this also explains why large UAV helicopters fly so much better than large multirotor drones.

mars 161

One interesting thing to point out, is that all of this also holds true for UAV’s flying at high altitudes on earth with thin air.  Multirotors will suffer much more than Helicopters will.  We have flown UAV’s in Colorado, both multirotors and helicopters.  The multirotors required installation of larger diameter propellers to achieve enough lift, in our case, changing from 10″ props to 12″. This negatively impacts the flight control, as the propellers are noticeably heavier.  The helicopter however, simply required a change to the motor controller to run the rotor slightly faster to make up for the thinner air.

This 37 minute presentation video goes into deep detail on the system:


Source: NOVAerial Robotics

8 comments

  1. Anyone else notice on the graphic, the rotors are pitched to rotate in the same direction, as opposed to counter-rotating? A coaxial helicopter, to counter the torque, must by definition use counter-rotating blades.

      1. Nut, look, the engineer is looking straight at it in the video! If I had made a mistake of that proportions I would say – “Oh, that’s not correct.” The rotators are a the wrong pitch realtive to one another!” or something ot the effect 🙂

    1. Good catch! I did too! But I guess, I always give a second chance to the engineer-fothe-moment to explain. Maybe there is something I do not understand? But no. If there is, there should be some explanation of why this would be different.

  2. Will the rotors have solar cells on their face, if not, why not? Seems like they could then be tilted to collect maximum light when landed and recharging.

  3. NASA will try to sell to the public they are on Mars and using prop-driven drones. Many will buy it.

    There’s a sucker born every minute.

  4. Full scale collective pitch coaxial helicopters such as the Kamov KA-32 yaw by increasing collective pitch on one rotor and decreasing it on the other and they are almost certainly using the same system here.

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