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# A crash course on indoor flying robots

Learn the physics behind how quadrotors fly and find out how they can by themselves without human help. Created by MIT+K12.

## Want to join the conversation?

• If the quadrotors fly up by pushing air downward, how is it possible for them to fly upside down like at ""?
• Glad you picked that up in the video! What we didn't tell you was that the quadrotor flying upside-down is actually a variable-pitch version, i.e. the blades themselves change pitch (they are actuated by a servo) so that even though the motor is only spinning in one direction, the direction and magnitude of the thrust can be changed very quickly. Here's the full video explaining the variable-pitch quadrotor and some neat things it can do: http://www.youtube.com/watch?v=VIkqqVr_u9U
• This guy (Alexinparis) took apart his Nintendo Wii remote to get cheap parts (gyroscopes, accelerometers) to build a tri-copter under \$100. The code is open source and you can read instructions on how to build your own.
• What is C++ code?
• At , to determine the quadrotor position, what is the "slightly more complicated math" that they are talking about?
• As the video showed, assuming you have a camera whose view is parallel to a wall of a cubic room (lets say define this wall as the x axis), they can obtain the height (the z axis) and x coordinate. Using a camera on parallel to the ceiling would give the x and y coordinates of the quadcopter, the information of height is lost. Therefore, from both the views, the position of the quadcopter (x,y,z coordinates) can be accurately obtained. However, its generally very hard to get a camera exactly parallel to a wall/an axis, and generally a projection of the 3rd axis slips into the image. So, to find out the accurate position, they use a technique called Direct Linear Transformation (DLT), which solves for the actual x,y,z coordinates, from the two camera projections of the room. This, I believe, is the 'slightly more complicated math' they are referring to.
• Where can you get quadrators?

it has quadrotors less than \$100 to over \$250.
(1 vote)
• Do more propellers equal higher lift? Also do more motors make it go faster?
• Simple answer - Yes. Well it all depends on how much thrust each one must provide. For example: a 6lb quadcopter with 4 motors, each weighing 1lb: comes out to 10lbs total. Times by 2, the number of pounds of thrust you'll want is 20lb. Which divided amongst 4 motors would be:
5lb thrust per motor.
With 5 motors, total weight is 11lb. Times by 2 is 22. Divided into 5 motors, you'll need:
22/5 - 4.4 lb thrust per motor.
It really depends on the weight of everything. Do the calculations yourself.
Sorry if too complicated.
• Ok, so if you have variable-pitch propeller, are the RPMs constant? For example, a traditional prop gains or loses altitude as based on a variable speed motor, with a fixed pitch, so is the inverse true?
• Yes, with variable pitch propellers, you can also control your altitude by changing the pitch of your propellers, although this is not efficient because your motors are still rotating at the same RPM and drawing as much power
• At how do they make it stop perfectly on the battery changing machine without falling, does it have like a camcorder on the front of it or something?