Passive thrust vectoring with anti vibration mounts.

 

 Have constructed an enclosed ‘H’ frame carbon/Kevlar quad with soft mount front and rear arms for vibration reduction. Initially yaw was awful as the arms tilted in the wrong direction and opposed any motor torque so I had to stiffen the mounts to prevent yaw reversal. Now I have reversed the motors in the code and the tilt actually helps the yaw. The mounts on the video are very soft, just to help demonstrate the movement but I think they were bottoming out.

Am quite pleased with the lack of vibration showing on the camera.

Apart from the motor reverse all parameters are completely stock. Will tweak them when I get some time.

 

Vince

Views: 3718

Comment by Joshua Ott on January 29, 2013 at 5:13pm

Like I said before, you really make quick work of things. This is very intriguing work!

Comment by Gary McCray on January 29, 2013 at 6:28pm

Very interesting Vince, you can definitely see the tilt aiding the Yaw.

But I do notice that there is a noticeable hysteresis lag in the whole system that could translate into lag in responsiveness in pitch and roll as well.

Manually that might not be much of a problem and might even be an advantage in smoothing things out.

My concern is that in the automatic modes it might be possible that the existing sense and response loops could end up fighting each other possibly resulting in oscillations or worse continuously increasing oscillations.

Just a thought, may not be a problem at all.

I will be very interested to see how it loiters.

Comment by Dale on January 29, 2013 at 8:39pm

How do the motors sound so cool and quiet?  Is it the isolation from the arm mounts?  Or are they big heavy motors and they look like pretty low kv?

Comment by Max Yeo on January 29, 2013 at 9:39pm

how your passive thrust vectoring works ??? 


Developer
Comment by leonardthall on January 30, 2013 at 12:59am

LOL, very nice job. Glad you got the code working. I think this is very cool :)

Comment by Vince Hogg on January 30, 2013 at 3:13am

To turn the quad, one motor on each arm will speed up and the other one will slow down. This uneven lift causes it to tilt. The one behind the camera is of course doing the opposite.

It might not look like much ‘vectoring’ but when it was in the wrong direction it was overcoming the normal yaw control, so I guess it is at least doubling the yaw effect.

The motors are not very big, just low Kv – 530, so turn much slower than normal so you need bigger props for the same lift. Its quite efficient, hovering at 14A – not bad for 2.1kg. The video is from a gopro in the case so its a bit muffled. I have one from another camera and it sounds like a Lancaster bomber.

 

This tilt effect is only noticeable with yaw, (and is exaggerated in the vid because I used extra soft mounts). It seems firm in roll and pitch. Hopefully I will get some tuning and flying done today (but its very windy).

 

Thanks for the pointers Leonard. I suspect most quads flex a bit and some may see better yaw rates with reversed motors. I may try and get a vibe reading today.

Comment by Michael Utz on January 30, 2013 at 3:18am

can you publish some pictures from the mount?

Comment by Vince Hogg on January 30, 2013 at 3:52am


Developer
Comment by leonardthall on January 30, 2013 at 4:13am

I suspect that you are correct. It depends on the geometry of the frame but some copters may flex the other way too. This is very interesting :)

I have been thinking about a similar concept as your fuselage. How flexible is the central fuselage?

Comment by Vince Hogg on January 30, 2013 at 4:30am

The single layer kevlar shell was very floppy on its own. I was hoping to have the carbon battery floor removable but to give sufficient tortional strength it needed gluing. Now it is absoultly rigid end to end but makes it a bit fiddley to install stuff. Now I know it works I will loose some ali from the brackets.

Mk II is forming in my head.

 

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