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CSU Chico Tilt Rotor Flying Machine, (Airframe and Electronics, 2 of 3).

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Patrick

Thu Mar 29 2012, 09:02PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Steve Conner wrote ...

OK, but my point is: Let's say your vehicle acquires a pitch error. Maybe a gust of wind tips the nose up. How will the control system correct it?

I fail to see why tilting both rotor fans to counter the unwannted pitch up, wont work. isnt this what the v-22 does? or does the V-22 use variable pitch to increase effective collective.

Steve Conner

Fri Mar 30 2012, 07:19AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Well, the problem is: If you made the thrust vector of the fans pass through the centre of gravity, then there won't be any pitching moment no matter how you tilt them. And if you didn't, then you'll have other serious stability problems. Either it won't hover or it won't convert.

I don't know for sure, but I guess the V22's rotors both have cyclic pitch control like a helicopter. The blades vary pitch in time with the rotation, allowing the thrust vector to be placed anywhere you want.

For example, if a helicopter wants to move forward: The cyclic pitch control causes the rear half of the rotor to produce more thrust than the front. This moves the thrust vector aft of the CG, causing the nose to pitch down. The thrust vector now has a component rearwards as well as downwards, and the chopper moves forward.

A multicopter works in exactly the same way, modulating power to its four small rotors to move the thrust vector around as required. Except with only two fans, you can't move it fore and aft.

Electroholic

Fri Mar 30 2012, 01:03PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

I think if the CoG hangs below the tilting axis, then everything works.

Patrick

Fri Mar 30 2012, 03:44PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Electroholic wrote ...

I think if the CoG hangs below the tilting axis, then everything works.

yeah i think so, then its like a pendulum, and i think it becomes a first order stability problem. I think. I noticed a slight dihedral on the kkmulticopter's fans in that video. That (and having the CoG low) should give some restoring force to large scale stability (favoring controlability) , while still allowing small signal instability (Still allowing maneuverability).

Patrick

Mon Apr 16 2012, 10:47PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

ok CF and GF are cut out and curing, progress so far:

Seen here the dry layers,

3 layers of FG, plain weave, 73 grams dry. Quasiisotopic, should be about 0.030" thick.
5 layers of CF, 2x2 twill weave, 156 grams dry. Quasiisiotropic, should be about .055" thick.

total dry wheight is 229 grams. untrimmed.

Now we see if im talented enuff to screw it all up by adding to much epoxy!

Patrick

Wed Apr 18 2012, 03:52AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

it weighs in at 400 grams, + a few mods im adding, but subtracting their weight from my other budget mass items.so its all going well. Its super strong and light. only a few pultruded peices and balsa need to be added.

Seen here curing, then it will be sheared down to the white line. Next time ill use 4 layers of CF instead of 5, and then embed the balsa between two layer of two CF, still being quasiisotropic.What you see is the Gen 2 airframe.

Patrick

Mon Apr 23 2012, 11:06PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Ive got this forum posting. which raises the issues already discussed on our threads here.

tilt rotor, RC forums.

Patrick

Sun May 06 2012, 06:11AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Weights:

MS Kinect : 144 g
Airframe w/o Tail : 197 g
4 cell lipo: 250 g
Left Wing : 320 g
Right wing : 320 g
main boards : 60 g
ESC's w/ reciever : 170 g
Gyros, accel's : 40 g
servo tray : 120 g
------------------------------
total mass : 1,621 g

Patrick

Tue Jun 12 2012, 10:20PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

IT WORKS!!!

it does fly, however, its unstable in the pitch axis. (As someone predicted [Steve Connor]) i will try to increase the vertical moment arm from 1.2 inches, to about 3 inches. Hopefully that will give gravity more influence on the pitch.

i would like to be able to calculate things out, instead of guessing. But at the moment the measurements, math, and physics elude me...

I have video and many pics, but ive got to edit it all down to reasonable file types and sizes...more posts to come!

AndrewM

Wed Jun 13 2012, 01:57AM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362

Patrick wrote ...

it does fly, however, its unstable in the pitch axis. (As someone predicted [Steve Connor]) i will try to increase the vertical moment arm from 1.2 inches, to about 3 inches. Hopefully that will give gravity more influence on the pitch.

I think you are still failing to understand Steve's comment.

Have you tried drawing a force diagram? I am interested to see if you can locate the restoring moment you assume exists.

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