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On 1 May 2009 16:58:26 -0400, Warp <war### [at] tag povrayorg> wrote:
>Stephen <mcavoysAT@aoldotcom> wrote:
>> The focal blur is overdone :)
>
> It's funny how some people complain about focal blur being too strong
>in some renderings, even though it really happens in real photos...
>
It is, isn't it?
> I suppose reality is unrealistic. ;)
Well just you tell Godot that you're fed up waiting. :-)
--
Regards
Stephen
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Warp wrote:
> Stephen <mcavoysAT@aoldotcom> wrote:
>> The focal blur is overdone :)
>
> It's funny how some people complain about focal blur being too strong
> in some renderings, even though it really happens in real photos...
>
> I suppose reality is unrealistic. ;)
http://xkcd.com/331/
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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I have this one:
http://www.walkera-helicopters.co.za/media/43B.jpg
After a long time I was able to hover and control it pretty well facing away
from me, but getting your head around keeping it stable while facing towards
you or left or right is too hard at the moment.
Maybe I should get one of those ones like yours with the opposite rotating
rotors, I hear they are much easier to fly?
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scott <sco### [at] scottcom> wrote:
> http://www.walkera-helicopters.co.za/media/43B.jpg
Looking at that, I assume that altitude is not controlled in the same
way as in a real helicopter, ie. by changing the angle of attack of the
rotor blades. Instead, I assume that in this case it's done by changing
the speed of rotation?
Also in a real helicopter pitching and rolling is done by changing the
angle of attack of the blades differently at different positions, but
here I assume it's done with those small blades. Yawing is probably done
in the same way in both.
--
- Warp
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> Looking at that, I assume that altitude is not controlled in the same
> way as in a real helicopter, ie. by changing the angle of attack of the
> rotor blades. Instead, I assume that in this case it's done by changing
> the speed of rotation?
Yes, this is common with (almost) all 4-channel helicopters, the altitude is
controlled by the speed of the rotor, not the angle of the blades.
> Also in a real helicopter pitching and rolling is done by changing the
> angle of attack of the blades differently at different positions,
Actually in the model here it works the same as a real helicopter, the swash
plate is tilted forward and backwards or left and right by two servos (the
red circular part with the attachments to the vertical rods), then the black
plastic part sits on top and rotates with the rotor. As it rotates it
pushes levers to change the angle of attack of the blades.
The difference to a real helicopter is that the model doesn't have any way
to adjust the average pitch over a rotation, amongst other things this means
you can't generate negative lift, which is needed to fly upside down.
There are more sophisticated models with 5 and 6 channels that work exactly
the same way as real helicopters, and of course then allow upside down
flight.
> but here I assume it's done with those small blades.
No that's just a stabilizer bar and it spins with the main rotor, offset by
90 degrees. It is connected in a certain way to help cancel out any
external forces on the rotor. In small models it is pretty much essential
to allow them to be controlled by humans!
> Yawing is probably done
> in the same way in both.
Yes.
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Orchid XP v8 wrote:
>
> http://xkcd.com/331/
>
Do you have a mental catalog of every XKCD in existence? :)
--
~Mike
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scott wrote:
> I have this one:
>
> http://www.walkera-helicopters.co.za/media/43B.jpg
>
> After a long time I was able to hover and control it pretty well facing
> away from me, but getting your head around keeping it stable while
> facing towards you or left or right is too hard at the moment.
> Maybe I should get one of those ones like yours with the opposite
> rotating rotors, I hear they are much easier to fly?
Counter-rotating is more stable in the air. The one thing that annoys me
about mine, though is the precession it seems to exhibit when hovering.
But, it does seem easy to fly, and it is very stable. I've not had a
chance to fly a collective pitch bird, though. So I can't say whether
it's easier or not.
Thing is, if you're disoriented when the helicopter is facing certain
directions, counter-rotating rotors won't do you any good :)
The one I have also has a gyro built into it's control board, so as far
as yaw goes, it's rock-solid.
--
~Mike
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Warp wrote:
>> http://www.walkera-helicopters.co.za/media/43B.jpg
>
> Looking at that, I assume that altitude is not controlled in the same
> way as in a real helicopter, ie. by changing the angle of attack of the
> rotor blades. Instead, I assume that in this case it's done by changing
> the speed of rotation?
I read scott's reply before adding my own ... :)
Right. Actually just by looking at this model I guessed wrong. It looked
like a collective pitch, but apparently not. But for cyclic, even on my
tiny model, it works the same as it's full-sized cousins. The blades do
vary through their rotation
> Also in a real helicopter pitching and rolling is done by changing the
> angle of attack of the blades differently at different positions, but
> here I assume it's done with those small blades. Yawing is probably done
> in the same way in both.
>
The small blades (the flybar), as explained act as a stabilizer. They're
weighted and will act on the pitch of the main rotor blades to keep the
helicopter stable in the air, mostly because they are so light, they're
easily affected by outside forces. I'm not exactly sure how the flybar
works, though... I know the position of the weights affect stability,
and the speed at which the helicopter reacts to the control inputs, but
that's my limit.
--
~Mike
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>> http://xkcd.com/331/
>
> Do you have a mental catalog of every XKCD in existence? :)
No, just the amusing ones. ;-)
http://lmgtfy.com/?q=photoshop+site%3Axkcd.com
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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It took me about 2 weeks of 30-45 mins per evening to even get off the
ground in a stable manner :-) I can now make it go pretty much where I want
within +/- 30cm in each axis so long as it's facing away from me. Sometimes
I try to turn it slightly but then I can't control it and either crash or
bring it quickly back in line.
> Counter-rotating is more stable in the air. The one thing that annoys me
> about mine, though is the precession it seems to exhibit when hovering.
> But, it does seem easy to fly, and it is very stable. I've not had a
> chance to fly a collective pitch bird, though. So I can't say whether it's
> easier or not.
>
> Thing is, if you're disoriented when the helicopter is facing certain
> directions, counter-rotating rotors won't do you any good :)
I have a cheap little 3-channel Chinook one that someone got me for
Christmas, I can fly that fine because it's so stable and can't move
anywhere fast. With my 4-channel one you need to be continually working the
controls to keep it steady, and I just can't do that when it's not pointing
directly away from me. Maybe I should reduce the sensitivity of the
controls, that might make it easier, I haven't played with it for a while
now.
> The one I have also has a gyro built into it's control board, so as far as
> yaw goes, it's rock-solid.
Apparently mine does too, but it tends to drift over a 15 minute session
just out of reach of the trim on the transmitter. Turning the helicopter
off and back on again seems to reset it correctly though.
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