Replies to This Discussion

3D RoboticsPermalink Reply by Chris Anderson on July 30, 2011 at 7:57am

Do you mean yaw? If so, you do it by speeding up the counter rotating props while you slow down the forward rotating ones, or vice versa.

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Permalink Reply by Ajit Krisshna on July 30, 2011 at 9:42am

Hi,

 

Thanks for the quick response! Would you care to elaborate on that? I really don't understand the dynamics of what you're saying

 

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Permalink Reply by hikkakaru on August 8, 2011 at 12:23pm

 

Ajit, in the above diagram you can see that two of the props turn clockwise, two of them turn counter-clockwise. In order to spin the quadrotor flat against the plane that it's on (yaw) , the two pairs of same-spinning motors are sped up, while the opposite pair is sped down. To reverse the spin all you do is reverse the order.

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Permalink Reply by Ajit Krisshna on August 8, 2011 at 10:10pm

Oh! It's like that! I get it now! Thanks a lot man, seriously!!

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Permalink Reply by Allen Babb on September 22, 2011 at 9:57am

Take note that accelerating the motors has a greater effect than simply setting the pairs at different speeds, so the quad will turn faster while the motors are changing their speeds, and will turn slower when the motors have a constant speed.

 

...At least that's what my knowledge of physics tells me.

 

 

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Permalink Reply by Ajit Krisshna on September 23, 2011 at 1:49am

oh okay, thanks for the information! 

 

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Permalink Reply by Greg Fletcher on September 23, 2011 at 8:40am

Yes Allen, you are right, but the conservation of angular momentum effects are small compared to the constant torque from the motors pushing the props though the air. How do you explain the fact that a quad can rotate indefinitely if you want it to. 

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Permalink Reply by Allen Babb on September 23, 2011 at 1:57pm

That comes from setting the motor pairs at a different speeds, like having the CCW motors moving faster than the CW motors.

 

The reason this works is because of the fact that the motors are still applying work to the propeller to keep it spinning. If the motors did not, the propeller and motor would eventually slow down due to air drag.

 

Finally, because the motors are continually working on the prop's, they continually apply a torque on the frame, which allows us to rotate the quad indefinitely (Thank Newton).

 

For aggressive maneuvers, the angular momentum effects may have more of an impact on the flight dynamics than the steady state torque... although I haven't gotten to verify that with my own testing just yet.

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Permalink Reply by teja on September 17, 2011 at 11:16pm

so are you guys done with it?

 

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Permalink Reply by Ajit Krisshna on September 18, 2011 at 12:32am

No man, not yet! Lots of work to do!

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Permalink Reply by Allen Babb on September 22, 2011 at 9:57am

Hope your not trying to build everything from scratch, that'll take forever. Lol.

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Permalink Reply by Ajit Krisshna on September 23, 2011 at 1:52am

No, not really. We bought the frame, and one of the things we want to do from scratch is build our own autopilot system, and image processing algorithms. Any idea how much time that will take? What do you suggest we do? I mean, we want to gain as much experience from this project as we can.

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