MkII H frame quad now flying.
Frame weighs about 60g less than Mk1 with much more room and accessibility to the nose sections. The arm O rings mounts are more firm than the Mk1 but vibration levels about the same. All RAW x,y,z accel vib about +- 1.5. Its possible to fly without reversed motors but the YAW rate is still much better with them reversed. As the arms are enclosed there is no problem if an O ring brakes and it has been flown with two missing on the same side.
I am now working on an internal nose gopro gimbal.
Comments
The MK1 Blog
http://diydrones.com/profiles/blogs/passive-thrust-vectoring-with-a...
Why?
Thats a fair question.
We started messing with quads just after Christmas with a cheapo Chinese frame. I fancied the low Kv motors for efficiency and they seemed a good price, however I think their lower RPM puts the vibration frequency in a worse band and large props produce greater amplitude if not perfect. This all added up to a quad that couldn’t be tuned very well and flew like pants. Also it appears we were one of the first to use these motors which had design issues, detailed here-
http://diydrones.ning.com/forum/topics/530kv-4008-motors-with-large...
Partly due to the above problem and a scattering of other issues I got quite used to recovering the quad from the chicken run covered in s**t. Its not easy cleaning poo out of all those wires.
So some problems to solve.
Being a lazy bugger I didn’t like the idea of balancing the motors with tiny buts if tape, and then having to do it again after the next crash (I do balance the props). Also I wanted a ‘wipe clean’ design. Not that I was planning to crash again.
I started experimenting with ways to isolate the vibrating bits.
http://diydrones.ning.com/profiles/blogs/quadcopter-anti-vibration-...
I think the mass of the battery could be a great source of anti-vibration inertia but most frames have them dangling or loosely strapped (and perhaps making matters worse). I decided to have the battery clamped firmly above to the APM using a lid with sponge to push it down.
So, I then built the Mk1 from Carbon/Kevlar. It was vacuum bagged over a foam core like many things I build, and used the same O ring tube supports as the test rig.
The Vibration levels were fantastic and I was able to tune up very high. RATE P .25 RATE D .014 . Didnt find the limit – would probably go higher. I mounted a gopro directly on the frame and there is very little noticeable vibration (but auto missions are a little twitchy – roll on 2.9.2)
It flew very nicely – from long auto missions to acro flips.
The MK1 frame had lots of space but the ends were difficult to access after I glued in the battery floor for stiffness, and it didn’t stand close visual inspection.
I wanted MKII to be lighter, slightly bigger and have much better access, front and back. I was also worried about the O rings snapping and the motor arm coming off, however it did make it home several times with one snapped. MKII needed to have the tubes surrounded to have better survivability from snapped rings.
Antonie-
The O ring system it much more ‘tweakable’ for experimentation. You can try different lengths, thicknesses and materials. Its still evolving.
Hey guys, looking ta the design, please indulge me. Instead of having the rods, alluminium and o-rings - would it not be an option to have the motor mouting rods through a tube with latex foam inner. The outer tube laminated to the fuselage. I suppose you'll have to find a way to maintain the motor orientation....Your design opens a lot of oppertunities. Thanks for sharing.
Hi Leo, would you mind sharing some fuselage dimensions. Have you had a look at the vibration in the APM logs - is it worth the effort?
How is the mapping twin boom carbon drone coming along. Have you started mapping yet?
Antonie
Vince,
Awesome design for the fuselage, I really really like it. Well done!
I can't imagine this is the lightest configuration... what does creating a shell buy you? even a half inch sq CF tube should be adequate to tie everything together and you can still do a fair amount of vibe reduction. what were the drivers behind creating this fairing?
The fuselage shell was vacuum bagged around a foam core. The foam was then dug out after the fuselage lid was cut off. The wind effect was similar to the X-frame. We were considering mounting the ESCs on the inside with heatsinks to keep it streamlined, but we considered against it because of RF noise and cooling.
She is big and a beaut - I love it. The space is awesome. Like a C130 with rotors. I like the look. Did you vacuum bag it around a foam core. How did you do the shape?
Good job. Do you see an drag effect, wind effect?
Antonie
That is very different. A+ for originality.
To be sure your arm mounting could use some tweaking but like all things different, the solution will make itself clear soon enough.
I think integrated molded vehicles will eventually replace the 'plate and tube' types. Improvements in our fabrication process will get us there. The basis for such already exists. We just need to find the easiest and fastest way to mold, trim, and integrate assembly of parts.
Outstanding effort!
-=Doug
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