4 ms·

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

by zan2434 12y ago

fasteddie31003 12y ago
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.
- lumpypua 12y ago
  The mechanical solutions are always really interesting and clever, but digital systems are much more flexible. Really cool video on the mechanical ignition timing control in a delorean to control emissions. Explanation of ignition advance at the end: https://www.youtube.com/watch?v=ge1GwepqtK0 https://www.youtube.com/watch?v=ge1GwepqtK0
swah 12y ago
I have no idea what you're talking about.
- Cushman 12y ago
  "The linkage to change the pitch of this rotating blade is way too complex! Can we simplify it somehow?" "How about we just add a simple device that associates the pitch of the blade with the torque, and let a computer figure out how to spin the motor to get the pitch we want? No linkage!" Yeah, that is dang clever.
  - mrfusion 12y ago
    I'm still not getting it. Wouldn't the pitch of the two sides be the same so how would that be useful? How do you control the pitch of two blades with a single motor?
    - lnanek2 12y ago
      Didn't you read the article and watch the video? There is a sinusoidal signal added (i.e. up and down) that matches the rotation of the blades and controls the hinges on the blades. So the signal can be high when the blade is on one side of the vehicle then low when the blade is on the other side. Or vice-a-versa if the control system wants to go the other way. Both blades tilt the desired direction when they are on the desired side of the vehicle. The video is quite good and shows the blades hinging different directions on different sides when the signal is applied.
    - mhb 12y ago
      There are two motors.
      - robotresearcher 12y ago
        The second motor and rotor provides vertical thrust and torque compensation only. It spins the opposite direction to the upper rotor. It does not steer the vehicle.
    - jzwinck 12y ago
      Look at the hinge picture. See how the two hinge pins are parallel? Now imagine the blades turning 180 degrees. The hinge pins will now be at the "opposite" angle to before, despite that the blades are symmetrical so identical at 180 degrees to 0 degrees. So at 0 degrees, increasing torque will, say, increase pitch of the "right-hand" blade while decreasing pitch of the "left-hand" one. But at 180 degrees it will be the opposite. This has the presumably beneficial effect of allowing the craft to climb by simply increasing rotor speed steadily (it will "wobble" a bit but in a spiral fashion which will let it climb without too much inefficiency). Put another way, this means that increasing torque at 0 degrees but decreasing it at 180 degrees allows an asymmetrical pitch to be maintained at a rotational speed which can be seen as constant (over the long term). In other words, your intuition falls down because the mechanism is not as symmetrical as your brain wants it to be at first glance. Symmetry is an intuitive and attractive for mechanical systems, but it is actually limiting in many cases, and this is a great example.
jahnu 12y ago
How do they determine blade position?
- phkahler 12y ago
  >> How do they determine blade position? I assume you mean the motor rotation angle. It's probably not a brush motor, but a 3-phase synchronous motor. That means instead of having a commutator to apply the voltage to the coils, a computer switches some FETs to apply the voltage. In the simplest case, the rotor is assumed to follow the applied voltage waveforms. In a more typical system, the rotor position is estimated from the applied phase voltages and measured currents (usually via PLL or a sliding mode observer). If you mean "how do they determine the blade pitch?" then the answer is that they don't need to. The controller - weather that's a computer with inertial sensors, or a person watching it - will just manipulate the amount of torque variation until it gets the response that it wants from the copter. Much like you don't actually need feedback of your cars gas pedal position so long as you have vehicle speed feedback.

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

by zan2434 12y ago

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

fasteddie31003 12y ago

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.

lumpypua 12y ago
The mechanical solutions are always really interesting and clever, but digital systems are much more flexible. Really cool video on the mechanical ignition timing control in a delorean to control emissions. Explanation of ignition advance at the end: https://www.youtube.com/watch?v=ge1GwepqtK0 https://www.youtube.com/watch?v=ge1GwepqtK0

swah 12y ago

I have no idea what you're talking about.

Cushman 12y ago
"The linkage to change the pitch of this rotating blade is way too complex! Can we simplify it somehow?" "How about we just add a simple device that associates the pitch of the blade with the torque, and let a computer figure out how to spin the motor to get the pitch we want? No linkage!" Yeah, that is dang clever.
- mrfusion 12y ago
  I'm still not getting it. Wouldn't the pitch of the two sides be the same so how would that be useful? How do you control the pitch of two blades with a single motor?
  - lnanek2 12y ago
    Didn't you read the article and watch the video? There is a sinusoidal signal added (i.e. up and down) that matches the rotation of the blades and controls the hinges on the blades. So the signal can be high when the blade is on one side of the vehicle then low when the blade is on the other side. Or vice-a-versa if the control system wants to go the other way. Both blades tilt the desired direction when they are on the desired side of the vehicle. The video is quite good and shows the blades hinging different directions on different sides when the signal is applied.
  - mhb 12y ago
    There are two motors.
    - robotresearcher 12y ago
      The second motor and rotor provides vertical thrust and torque compensation only. It spins the opposite direction to the upper rotor. It does not steer the vehicle.
  - jzwinck 12y ago
    Look at the hinge picture. See how the two hinge pins are parallel? Now imagine the blades turning 180 degrees. The hinge pins will now be at the "opposite" angle to before, despite that the blades are symmetrical so identical at 180 degrees to 0 degrees. So at 0 degrees, increasing torque will, say, increase pitch of the "right-hand" blade while decreasing pitch of the "left-hand" one. But at 180 degrees it will be the opposite. This has the presumably beneficial effect of allowing the craft to climb by simply increasing rotor speed steadily (it will "wobble" a bit but in a spiral fashion which will let it climb without too much inefficiency). Put another way, this means that increasing torque at 0 degrees but decreasing it at 180 degrees allows an asymmetrical pitch to be maintained at a rotational speed which can be seen as constant (over the long term). In other words, your intuition falls down because the mechanism is not as symmetrical as your brain wants it to be at first glance. Symmetry is an intuitive and attractive for mechanical systems, but it is actually limiting in many cases, and this is a great example.

jahnu 12y ago

How do they determine blade position?

phkahler 12y ago
>> How do they determine blade position? I assume you mean the motor rotation angle. It's probably not a brush motor, but a 3-phase synchronous motor. That means instead of having a commutator to apply the voltage to the coils, a computer switches some FETs to apply the voltage. In the simplest case, the rotor is assumed to follow the applied voltage waveforms. In a more typical system, the rotor position is estimated from the applied phase voltages and measured currents (usually via PLL or a sliding mode observer). If you mean "how do they determine the blade pitch?" then the answer is that they don't need to. The controller - weather that's a computer with inertial sensors, or a person watching it - will just manipulate the amount of torque variation until it gets the response that it wants from the copter. Much like you don't actually need feedback of your cars gas pedal position so long as you have vehicle speed feedback.