Wanna see something cool #2

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,802
Almost three years since the last post; I was thinking of starting a "Something Cool" thread but decided to look to see if someone else had done so before. Turned out this thread was started three years ago. I know I'm resurrecting an old thread but I saw this and thought it was just an absolutely cool build.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,802
OK, someone moved this into a new thread of its own. The original thread was back in 2018. If you find something cool; post it here. I'm always seeing something cool and have posted a lot of them on the "Something Weird" thread. Perhaps this deserves a thread of its own.
 

twister007

Joined Feb 29, 2012
50
OK, someone moved this into a new thread of its own. The original thread was back in 2018. If you find something cool; post it here. I'm always seeing something cool and have posted a lot of them on the "Something Weird" thread. Perhaps this deserves a thread of its own.
Wow! That kid had a lot of skills making the molds and parts!
 

strantor

Joined Oct 3, 2010
5,505
Why aren't the ducts pointing straight down? There better be a good reason for that because it's driving me crazy thinking there's not.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,802
Why aren't the ducts pointing straight down? There better be a good reason for that because it's driving me crazy thinking there's not.
If all four ducts were pointed straight down there would be no stability. Like balancing a broom stick on a ball. Having the ducts stretch out like a tripod (actually like a quad-pod) you gain stability. On a quad copter you have the motors and blades out at the perimeter of the copter. But if you could put the motors inboard you move the center of gravity closer to the center. Your copter would be even more stable. Using the ducted fans with the motors centrally mounted and the exhaust (thrust) ports outboard he gained much more stability. Learning to fly it and balance it is a part of the engineering and testing he must have put into the project.

I thought it was really cool how he built, tested and accomplished his goal. I almost posted it on "And now for something weird", but it's not "Weird" it's "Cool".
 

wayneh

Joined Sep 9, 2010
17,018
I thought this was accomplished by diverting power to one quadrant or another? Regular quadcopters don't have their propellers set at random angles do they?
I think - but don't know - that the key difference is rotational torque of the motors on a drone. Changing one motor torque (rpm) causes the entire drone to rotate. That control method is missing when thrust is coming from rocket motors. The motors of a drone can point straight down but that doesn't work for rocket thrusters.
 

ZCochran98

Joined Jul 24, 2018
131
I think - but don't know - that the key difference is rotational torque of the motors on a drone. Changing one motor torque (rpm) causes the entire drone to rotate. That control method is missing when thrust is coming from rocket motors. The motors of a drone can point straight down but that doesn't work for rocket thrusters.
Precisely. The rotors on a drone, when all spinning at the same speed, theoretically generate the same torque but in opposite directions so net angular momentum is zero. By speeding up/slowing down certain propellers, you can maintain the net angular momentum as zero, but also tilt the drone, which then focuses a small fraction of the thrust outward to allow for lateral motion. If you want to turn, you change the combination of slowed propellers so net angular momentum is no longer zero, causing it to spin.

As @wayneh and others have said, you don't have this same rotational stability when you have thrusters, so you need to angle them to prevent unwanted rotations or sliding. If you look at rocket boosters, the nozzles are tilted slightly, which is intended to prevent the rocket from spinning too much or going any other direction other than "up." The angle of them can be adjusted for calibration (which is part of the issues with some rockets, if the sensors are, say, misconnected with swapped but identical-appearing cables it can cause the guidance system to flip the rocket around and slam into the ground.)
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,802
Yaw (Pitch, Roll, Yaw are the three of six motions possible) is when an aircraft points its nose left or right. In fixed wing aircraft yaw is controlled by the rudder. In a helicopter yaw is controlled by the tail rotor and is partially caused by changes in torque of the main rotor.

In a quad copter yaw is controlled by torque. Two motors spin clockwise while the other two spin counterclockwise. To maintain a given altitude while yawing two motors are increased and simultaneously the other two are decreased, resulting in maintaining altitude while yawing to one side or the other. If all four motors spin the same direction then yaw control would not be possible. I didn't see the Ducted Fan Quad (DFQ) make any yaw maneuvers. It SHOULD be possible with two left hand spinning motors and two right hand spinning motors but I don't know that this guy did that. Given that some of the vectoring tubes were not pointed directly downward I would assume the vector stabilization was controlled by angling the downward tubes. I also didn't see any mechanism for rotating the tubes to change vector. But like all things experimental, first step is to prove the concept. He did that. Next he will have to address maneuverability. And from what I saw he did have some difficulty with stability as well. Counter rotating fans will help with yaw control. I'm sure he's figured out much of the problems.
 

strantor

Joined Oct 3, 2010
5,505
Precisely. The rotors on a drone, when all spinning at the same speed, theoretically generate the same torque but in opposite directions so net angular momentum is zero.
Ok, there's the explanation. That makes sense.
Thank you.

I get it now. We can talk about something else cool now, instead of strantor's drone noobness.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,802
Another young cool drummer. And I appreciate he's wearing hearing protection. That's the reason why I had to give it up.
 
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