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In my rush to build the machine, I just stuffed the servo plugs into the receiver slot I thought correct, and if it worked, I was
happy. And when I needed to fix something, I just ripped stuff apart and then struggled to get the connectors back
in the correct slot. It's so much easier to just take the time to label them - #1, #2, etc so that the next time
you can re-build things quickly.
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The two big considerations about routing the wiring, is that:
you dont want the wires too tightly or loosely stretched
you need to secure the wires, but not too tightly
Here are some photos of my installation to give you some ideas. You can curl the wires - that works pretty darn good
when there is a lot of slack - you can reduce the length of the wire by about 1/3 this way.
For securing the wires to the airframe, I used zipties, but the thing that's actually in contact w/ the wire is a little
piece of that double-sided velcro - I put the loop side against the wire, and the hook side helps to keep it in place under
the ziptie. This gives some flexibility and looseness that I hope will help minimize the vibration damage that seems to be
just a part of a helicopter.
The wires from the HH gyro are loose, but not too loose, and I tried to keep the same loose but not too loose approach that with all the wires.
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These pix show my setup as of 22Feb09. The receiver is underneath the battery tray. Above you can clearly see the wire ties with the velcro
piece holding the wires at the 2 locations. On the left side, I wanted the throttle wire from the ESC to have some separate clearance,
especially from the power wire coming out of the bottom of the BEC.
I felt that this setup is better than the previous layout, mostly in the bouncing up and down the machine was doing. It still does a little,
but I tend to think of it more as floating up and down pretty slowly.
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There are lots of folks who have written about CCPM (aka Cyclic Collective Pitch Mixing) - just google "rc heli ccpm" and you'll have some good reading.
I just wanted to add, for the total newbie, a few words about Cyclic and Collective Pitch.
Helicopters stay in the air according to the physics of aerodynamics - the aerodynamics of the rotating blades. But your ability to control
where the heli flys to depends on the physics of gyroscopes. This is actually the part that I find most interesting. The "Cyclic" in CCPM, refers
to your ability to cause the rotor disc to tip in a direction of your choosing. If you tip the rotor disc forward, the heli will try to fall out of the sky
to the front. If you tip it to the right, the heli will try to fall out of the sky to the right. How does this operate? How is it that you can
cause this thing that is spinning like a daemon to tip a little to the right or the left?
If you remember back to maybee gradeschool or junior hi, when you played with gyroscopes? you got that little thing spinning and it would stand
upright. If you pushed it with your finger, it might fall over, but it would fall in a direction that was different from how you pushed it.
This is called gyroscopic precession. (Wikipedia has a great article about precession - "torque-induced" is what is happening in a heli) But
basically, the spinning object (rotor disc) tips in a direction that is 90 deg *later* than the force applied. In other words, if you want the
rotor disc to tip forward, push the top of the rotor shaft to the left - gyroscopic precession will cause the disc to tip forward for you. I dunno - I just
think this is *so* cool! Here is physics at work for you, in living color.
The mechanism is setup in the heli, so that, via the flybar, the pitch of each blade is individually adjusted so as to effectively "push" on the rotor mast
at the appropriate time, so as to allow physics to do its thing and tip the disc in the direction you want. And that is the cyclic.
The collective pitch is about affecting the pitch of both (all) blades simultaneously in the same way, to cause the machine to rise or fall in
the air.
CCPM is kinda cool in it's idea of the floating swash plate - it allows the swash plate itself to support *both* functions - the cyclic by how it
is tipped, and the collective by how high or low it is on the mast.
And I just wanted to point out that my description of gyroscopes and physics and all that is really at the most elementary level possible - what's
actually going on is substantially more complicated, sophisticated and subtle - something to look into on those long winter evenings.
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There are so many things on the heli and in this sport that rotate: the servos rotate, the transmitter sticks can move in circles,
the gears, blades, swash, etc. So I found myself thinking in terms of o'clock, rather than some percent number or some other arbitrary idea.
For example, it's really convenient to think about the transmitter sticks in clocks - you have mid-stick, and from there you go some direction,
so for the cyclic stick, you'd move to 3 o'clock to go right, 9 o'clock to go left.
For the servos, midpoint might be at 6 o'clock or 9 o'clock, and for the gyros, those really dinky adjustment screws might go
from 7 o'clock to 5 o'clock, so you can keep track when you're trying to figure out what is the right setting by noting: 7:no 8:no 9:ok
10:good 11:ok 12:no - is pretty clear.
just a thought...
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Again, there are lots of great sites out there that talk about the mechanical aspects of servo setup. I just wanted to add my 2cents
and provide possibly a little different insight.
Underlying all of the ideas about setup is the implied notion that the effect of all of these controls is linear. That moving the stick from
the center to the edge will produce the same amount of change for each millimeter of movement, and that each millimeter of movement of the
servo will produce the same change in the affected part.
But this is not the case - certainly not in the servos, and I didnt really find anyone talking about this particular aspect of setup.
When you install a servo, you have those crazy control arms, with lots of holes on them, and you can put your ball end on any one of the holes.
So which hole do you choose - and why?
OK - well, my opinion is that you should select a hole that is far enough from the center that the total end-to-end movement of the ball joint
will cover about 1/6th of a circle, or about 60 deg. of rotation (i.e., from 5 o'clock to 7 o'clock). And of course, try to organize things so that
this 60 deg. more or less corresponds to the middle of the total throw of the servo.
The reason for this is that, assuming you'll set things up so that the midpoint of the throw is about the midpoint of the control surface you're
trying to affect, then about 30 deg. from midpoint will be the maximum movement of the servo arm, and this 30 deg. represents the first 1/3 of
the arc to 90 deg. In this first 30 deg, the difference between the effect (i.e., the amount of movement created) of the first degree's
movement and the effect of the 30th degree's movement will be quite small. If you were to set things up so that the servo moved for 1/3 of a
circle - 120 deg., then you can see that the linear affect of the first degree's movement is *substantially* greater than the linear affect of
the 60th degree's movement.
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Here is a little graphic to depict the problem i'm talking about. It shows the 120 deg and 60 deg sweeps, and the linear movement between
0 and 5deg, between 25 and 30 deg. and between 55 and 60 deg.
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Anyway - hopefully you get the idea. I'm just trying to keep things reasonably linear - that seems like a good thing to do. When you allow
the total servo travel to go beyond the 60 deg total travel, you increase the non-linear effect your control movements will have - a sort of
built-in expo, which is probably not a problem, but it's good to understand that it's there.
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Here is an area where I struggled quite a while before I discovered the magic.
I had bought the bigger heli, but it wasnt RTF - I had to actually install some new gyros and get everything working correctly.
And it was fun and challenging. But basically I reached a point where I felt stymied - I finally (using the Rev function on my transmitter)
had the servos working so that left-right worked correctly, front-back worked correctly, but up-down looked the same as front-back - the
swash would tip forward. I could move this mis-behavior to the other servos, but regardless of how I set things up, one of the 3 axes would
always misbehave.
So after some further looking (in my Futaba transmitter), I found the "Swash AFR". (AFR = Adjustable Function Rate.) Anyway - in the SWSH setup
in the transmitter, I can declare how much each servo should move (and which direction) in response to the stick. I found that moving
the E (elevator) pseudo-channel in the opposite direction my problem was solved. I.E., I changed it from +50% to -50%, and the swash became
a perfectly behaving citizen.
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This seemed to me to be another one of those taken-for-granted deals - sure - *of course* you check/setup your heli's C/G - right? Well, not
me, not for a while anyway. And then it took 2 tries to get it right.
The thing is, you need to have the machine *completely* setup, just as if you were about to go for a little flight - with the blades
extended correctly, the canopy on, battery in place etc.
*Then* you can tweak the C/G - and I dont know how big of a deal it actually is - it seems that perfection is not really necessary
but generally you're trying to get it to hang level when you dangle it from the rotors - in my picture below, I'm just holding it by the flybar
wires - the skids should be fairly level, or possibly in favor of being a little nose heavy. Try to move stuff around that you have control
over to make it nice, rather than add weights somewhere.
You probably have noticed that it's somewhat nose-heavy. I actually flew it this way just fine. But it *does* still look a little nose-heavy
to me.
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Blade balancing is *not* a dark art, there are lots of great sites online with pictures and exhaustive explanations about balancing blades.
So I wont go into that. All I feel the need to say is - don't be afraid to balance the blades! If they're off, and likely they will be if
you're installing new blades after your first crash, and you decide to what the heck, just go ahead and fly it, well, you'll see quickly enough
how big of a deal unbalanced blades actually are.
I found this site that has a good discussion about balance in general:
http://3dflight.org/books/balancing-your-helicopter-incredibly-smooth-flight
I'm still in a mode of trying to keep my expenses to things I think are absolutely necessary, so I'm still OK with my little kludge of a
blade balncing tool - I know I could do a better job w/ a real balancer, but this seems to do a good enough job for now.
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