A large scale Variable Pitch Tilt Quadrotor implementation.

                                

 

                               A  large scale Variable Pitch Tilt Quadrotor implementation.

  

 

Here is a description of a Variable Pitch Blade Quadrotor build with some unique features. It is a large Quad, and can be quickly split into 2 halves, enabling easy packing into a carry case for simple transport. The ‘Upper’ half of the quad contains all the electronics, IMU, Autopilot, Payload control electronics, etc. The lower half carries the battery packs and the payload. The upper and lower halves slot together and are affixed by means of 4 captive spring release screws. The payload similarly mounts to the underside of the lower body half. The entire Quad can then be separated into an upper and lower body half, and payload. 

 

Each motor has a standard ESC ( not any fancy hi-speed update type…) mounted beneath the motor. This keeps the 3phase motor leads very short, ensuring little electrical noise radiation from said leads.. Beneath each ESC is a small CPU module which receives a serial command from the Autopilot. This serial command contains the desired motor speed, the blade pitch angle, and the rotor tilt angle for Yaw control. This small CPU module generate the relevant PWM signal to the blade pitch servo, the rotor tilt servo, and to the ESC, while monitoring the motor RPM, ensuring constant motor speed, as commanded.

 The upper half of the Quad has 2 Variable pitch, variable Tilt, same direction rotating rotors. The lower half has only two variable pitch same direction rotating rotors fitted. The motors are operated at commanded constant speed, and lift is varied by blade pitch, giving much faster control of individual blade lift for stabilization. This is a problem with conventional control by motor speed variation, as the rotor blades become larger in diameter. The inertial mass of the rotor increases, and it becomes increasingly more difficult to rapidly change rotor RPM, both to enable horizontal stabilization, and to control Yaw.

 The Tilt rotors are both fitted to the upper half of the Quad, with the rotors spinning in the same direction. This ensures that when the rotors are tilted ( always in the same direction) to control Yaw, Gyroscopic Precession is equal and opposite across the two rotors, thereby canceling out. Gyroscopic Precession also begins to play a bigger role in larger diameter rotors, when the tilt rotor concept is employed.

 The construction is almost complete. So far all simulations and math shows we should have around 2.5kg lift per rotor head, with an all up Quad weight of 5.5kg, inc 2 of 6cell, 6000mAH batteries, leaving around 2kg for payload. We should get around 15 to 18minutes flying time.

 If it looks like it came out of the ALIGN Factory, it did not…I used parts from the Trex600 series chopper, the tail rotor pitch assy, etc, as well as tail boom, stays, and a few more bits and pieces…The composite parts were all modeled in 3D CAD, and molds made for them. All the custom Aluminium parts were likewise modeled and CNC machined.

 Basic Specs:

Dimension from blade tip to blade tip – 2100mm

All up weight – 5.5KG, inc batteries, 3.4kg exc batteries.

Blades – Trex 450 style.

Variable pitch on all 4 blades.

Variable Rotor Tilt on 2 blades.

Max payload mass – 2Kg.

Estimated flight time with 1.5kg payload – 18minutes

Autopilot – NamPilot

 

 

I hope to fly it real soon now….!!

Just running out of space for all the aircraft here!, Guppy, Hornbill, Kiwit, all the 60 trainers, ……Need some sky-hooks!

 

Regards

Joe

‘The NamPilot’

 

Two unfinished body Halves:

 

 

 

Cutting out lightening Holes on the CNC:

 

  

 

2 halves with IMU:

 

 

 

Lightened Central Hub Assembly: (with unpainted autopilot cover)

 

 

 Lightened Central Hub Assembly:

  

 

 

 

CNC Machining of Motor Arms:

 

 

 The Pitch Tilt Arm:

 

 

 

The Variable Pitch Motor Assembly:

 

 

 

 

The Variable Pitch and Rotor Tilt Assembly:

 

 

 

Partial frames fitted Together: (floor squares are 300mm X 300mm)

 

 

Frames in Transport Mode:

 

 

 

 

 

Views: 18044

Comment by Johann Van Niekerk on January 5, 2012 at 9:41am

?

Comment by Ian Lee on January 5, 2012 at 10:11am

Outstanding!  I love the snap together design even without the tilt function.


Developer
Comment by Rob_Lefebvre on January 5, 2012 at 10:16am

Nice!

 

Do the 450 main blades fit right into the 600 tail blade grips?

Comment by Tobias Krieger on January 5, 2012 at 11:03am

Simply said, two thumbs up! 

Comment by Stuart Norton on January 5, 2012 at 12:36pm

That looks beautiful, but I don't understand how the tilt works. Can you help? Thanks, stu

Comment by Steve on January 5, 2012 at 12:48pm

Hope to see it flying. I have seen many attempt this and not get too far.

Comment by Alex Roup on January 5, 2012 at 12:50pm

I'm very interested to see this fly!  

I've thought of building a variable pitch quad as a means to improving the actuation bandwidth of the rotor thrust, as you mentioned.  I had assumed I'd drive the props via driveshafts from a motor or motors in the center of the airframe in order to reduce the rotational inertia of the airframe.  If a single central motor and drive gear were used, it would allow interleaving rotor disks, with possible efficiency benefits.  The cost versus this arrangement would be increased complexity and fragility.

Do you intend to use differential prop pitch for yaw control as well as the tilt control?

What is the intended mission for the quad?  Is it an anti-poaching surveillance platform like the fixed wing aircraft you posted about a while back?  What unique capabilities does it provide for that mission?

All in all, it looks very well engineered and executed!

Comment by Gisela & Joe Noci on January 5, 2012 at 12:57pm

@ Robert - The 450 blades fit with about a 1.5mm gap - I made slotted Teflon Spacers to snug the blades up nicely.

@Steve  - I hope so to! We have succeeded with many other planes ( see my other posts) but this is a first on a Quad! However, google MIT - Variable Pitch Quadrotor and watch the video....

 

@Stuart _ if you look at the 3rd and forth pictures from the end of my blog - the one 4th from the end shows a Variable pitch only motor mount - the Quad Tube ( that connects motor mount to frame) is shown connecting directly to the motor mount, ie a rigid connection. The rotor tilt arm has a bearing that fits inside the end of the Quad tube, so can pivot around the tubes axis. The larger servo you see then controls that pivot motion. Does that help?

Comment by Stuart Norton on January 5, 2012 at 1:18pm

Thanks, but sorry I didn't explain myself. I understand the mechanism, but was struggling to understand the flight method. I presume you'll tilt the rotors, and the non-tilting rotors on the nose and tail will control pitch, while the tilted rotors will be yaw/roll (if not 90 degrees tilt). Is that right? Thanks

Comment by Gisela & Joe Noci on January 5, 2012 at 1:53pm

Stuart,

All four rotors have variable pitch control. The upper half of the quad has the North/South rotors which also have the rotor tilt mechanism. The East/West rotors are only variable pitch.

The North and South rotors rotate clockwise, the East/West, anti-clock. The North/South rotors control the airframe horizontal pitch, by applying different blade pitch angles to North compared to South Rotor. Likewise, the East/West rotors control the horizontal Roll.   The North /South rotors when tilted control the airframe Yaw, as follows- To Yaw such that the airframe rotates clockwise around its vertical axis, the North rotor is tilted to the East, while the Southern rotor is tilted to the west, and vise-versa. When hovering, a 2degree rotor tilt on this Quad will give a yaw rate of around 80deg per second, so not much tilt is required. A huge advantage on this type of control is the fact that the control loops are well seperated and do not overlap much in cross coupled effects, unlike the high degere of coupling in a conventional control by varying only motor speeds. In such a system, motor RPM control yaw, and roll and pitch and lift, so all these have to be balanced against each other , each with PID control loops fighting for domination....

Cheers

joe

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