iQuad Tilt-Rotor Quadcopter (v2) Flight Testing

After more than a year of design and development, I've built version 2 of the iQuad custom tilt-rotor quadcopter which is capable of achieving high forward speed by tilting its rotors forward in flight. After several days of flight testing and tuning, I was able to achieve stable hover and incredibly fast forward flight. Near the middle of the video, you can see the iQuad hitting a top speed of 53.3 miles per hour on the third flight of the day! This was achieved with a 40 degree forward tilt of the rotors.

 

For stability control, I'm using an APM 2.5+ and a modified version of the 3.0.1 arducopter firmware. Big thanks to R_Lefebvre and Gary McCray for convincing me to switch to the 3.0 version and other suggestions. To support tilt-rotors, I created a new body configuration, which adds servo control and does the proper mixing of the pitch, roll and yaw inputs depending on rotor tilt. I also added logging for the tilt input and servo angles, which was very helpful for debugging some initial stability problems. For the final phase of the project, I'm planning to add four wings that will wrap around the metal arms (and maybe some tail-fins), to allow a full transition to forward flight.

 

Here's another video of me having some fun with the iQuad. Near the middle of the video you can see the iQuad hovering in place while tilting forward/back.

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Comment by Ilya R. on November 30, 2013 at 10:49pm

Gary, that's an interesting point... I was actually trying to decide whether to use a symmetric or an asymmetric airfoil, and one the things I was concerned about with an asymmetric airfoil is that I'd always have to tilt the rotors slightly forward during hover, and the amount of tilt necessary would vary depending on thrust.

I wasn't thinking of using the asymmetric airfoil as a way to control tilt in forward flight, but you're absolutely right, it should be possible to control yaw and roll simultaneously by speeding up the rotors on one side or the other. However, I'm not sure whether this would be a good thing -- it may cause a lot of unintended consequences like the differential tilt (which seemed like a good idea at the time).

I need to think about this some more, although my first instinct is to get rid of all the possible complications by going with a symmetric airfoil.

I do like the idea of a rudder/fin for the same reason you mentioned. You can probably tell from the video that the quad wasn't necessarily flying in the direction that I was pointing the nose in, which is kind of scary at the speeds it was going.


Developer
Comment by leonardthall on December 1, 2013 at 3:59am

Nice job Ilya!!!

Comment by Stan Clayton on December 1, 2013 at 10:20am

"I was actually trying to decide whether to use a symmetric or an asymmetric airfoil, and one the things I was concerned about with an asymmetric airfoil is that I'd always have to tilt the rotors slightly forward during hover"

Conversely, if you use a symmetrical airfoil you will always have to have some tilt-up in forward flight at a cost in efficiency. I guess it all boils down to where you plan to spend the majority of your flight time: in hover mode or forward flight.

Comment by Scott Ramirez on December 1, 2013 at 2:44pm

I wonder if you can link the forward tilt to the accelerometer such that the tilt is not enabled until after a predetermined amount of forward momentum has been established.  The idea being that the quad having first established forward movement and the quad having become tilted forward10 or 15 degrees to help with prop wash.

A few ideas you probably have already gone through.  Love the quad!  Keep up the great work!

 

Comment by Scott Ramirez on December 1, 2013 at 2:47pm

Also,  Have you considered raising the rear blades?

Comment by Ilya R. on December 1, 2013 at 7:47pm

Stan, I think tilting up slightly may actually be better because the whole quad can act as a lifting body. Most flight time probably in forward flight, but stability is my main concern (over flight time). Luckily my design makes swapping the arms pretty easy, so I might actually try with both symmetric and asymmetric wings and see which works better.

Scott, I think raising the rear would help, but it would probably have to be substantially higher to make a difference. Plus, I'm already kind of locked into a design with the front and back being in a line. The propwash doesn't seem to be a huge deal after I shifted the CG slightly forward. I was thinking in the future I could also try using slightly smaller props on the front motors.

Comment by mP1 on December 2, 2013 at 4:51am

Is there any reason why one doesnt simply put a prop or edf on the back and have it push the copter about with the facing down props doing the lifting ?

Comment by Rob_Lefebvre on December 2, 2013 at 12:00pm

mP1:

My off-the-cuff opinion on that would be that it's less efficient to fly that way, and will also produce higher vibration.  These rigid propeller systems are not well designed for high speed flight with an airflow perpendicular to the propeller disk.


Moderator
Comment by Bill Piedra on December 28, 2013 at 4:27pm

Fantastic job on the tilt rotor.  I'm working on something similar.  I'm curious as to where you got the shaft bearings and motor mounts, and the size of the shaft the motors are mounted too.  They almost look like stainless steel, but I'm guessing they're aluminum.  I'm curious as to why not carbon fiber tubes for the shafts.  

Comment by Ilya R. on January 5, 2014 at 8:41pm

I got most of the stuff from servocity. The shafts are 5/8", aluminum. Carbon fiber would work, but probably not save a lot of weight. Most of the added weight is in the tilt mechanism, landing gear, motor mounts, etc... The tubes are surprisingly light (about 15 grams each).

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