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HelicopterMain Discussion › 120 or 140 CCPM
12-01-2007 12:13 PM  10 years agoPost 41
synodontis

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United Kingdom

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Absolutely agreed John, linear servos will not solve the problem. Also has it not occurred to you Matt that at fixed collective the balls on the swash trace out the surface of sphere, which consequently means curved planes, how does a linear servo help with that?

When I asked around about CCPM they did mention about linear servos would fix the problem, but personally I think they mention that because people can't be bothered to think about it and just follow on from what other people have been saying.

Also it's a mere triviality to convert a normal servo to linear because all you are doing is converting radial motion to linear motion, and this would generally mean the use of a cog and a slide bar with teeth.

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12-01-2007 06:11 PM  10 years agoPost 42
GimbalFan (RIP)

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Big Coppitt Key, FL

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this would generally mean the use of a cog and a slide bar with teeth.
I can see the ads now:

"You've got rack & pinion steering on your Porsche...
Now -- Rack & Pinion Servos for your Helis!"

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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12-01-2007 06:43 PM  10 years agoPost 43
RappyTappy

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North Denver, Colorado

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Anybody ever crash a 140 swash and bent those arms so it had to be replaced. That my big fear of the 140, I've never had to replace a swash even from the most hardest of crashes(three total destructions to be exact) but it looks like 140 swashes may take become a replacement part sometimes. I highly doubt that 140 is the end all be all, take a look at Szabo Jr, he flies the lowest most precise flying 3D out there and he's using T600N and Aurora with 120.

As far as 120 versus 140, it doesn't matter to me except the 140 swash looks more vulnerable to damage in the event of the inevitable. The main interaction I see and what drives me mad is when pumping the pitch and the swash wobbles on its own, that is eliminated through radio and good servos and not through how the balls are arranged on the swash.

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12-01-2007 06:59 PM  10 years agoPost 44
Portblock

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Van Nuys, CA

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Here is a 140 swash that doesnt have extentions on it, so its a little less vunerable in a crash.

Oh, and that bolt sticking out the other end of the ball, I was just checking to see what thread size it was.

The voices in my head can beat up the voices in your head.

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12-01-2007 07:46 PM  10 years agoPost 45
wlfk

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uk

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Presumably a disadvantage of 140° CCPM is that the pitch servo now has to work harder than the aileron servos?

If you don't use servos with plenty of oomph to spare, might you get unwanted pitch interactions as the aileron servos will respond faster than the pitch servo?

Presumably the pitch servo will wear faster than the other 2?

K

A bit like a kite, but 500 times more expensive

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12-01-2007 07:54 PM  10 years agoPost 46
GimbalFan (RIP)

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1) Yes, while doing elevator functions anyway.

2) Yes, but that can be remedied with a good tx & some skillful programming.

3) Possibly, but not by any great significant amount. Remember that in the course of a wide range of maneuvers, the aileron servos also end up doing a lot of work that the elev servo has little or no part in.

Best solution -- always use servos with far more torque than required for the particular application. It's cheap insurance against in-flight servo failure and they generally hold up much better in a crash.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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12-01-2007 08:12 PM  10 years agoPost 47
wlfk

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uk

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Compare flying straight and level then adding full collective, to flying inverted, then adding full collective.

I would imagine that the forces on the servos would be quite different in each case, so you couldn't program it out on the TX because the TX doesn't know what the heli's doing.

K

A bit like a kite, but 500 times more expensive

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12-01-2007 08:19 PM  10 years agoPost 48
GimbalFan (RIP)

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Why would that put any different loading on the three servos? Seems to me that with symmetrical airfoil blades and a symmetrical +/- collective pitch setup, the loading on the servos would be the same either way, just in the opposite direction.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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12-01-2007 08:21 PM  10 years agoPost 49
wlfk

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uk

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I was assuming that at least some of the flight forces would be transmitted to the servos - is this not the case for sym. blades?

In case it wasn't clear, by 'full collective' I meant pushing the stick up - which if you're inverted would take you down, with gravity as an aid (ergo lower forces on the blades).

K

A bit like a kite, but 500 times more expensive

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12-01-2007 08:23 PM  10 years agoPost 50
GimbalFan (RIP)

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Big Coppitt Key, FL

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I was assuming that at least some of the flight forces would be transmitted to the servos - is this not the case for sym. blades?
I believe the forces transmitted in the scenario you describe would be nearly identical, but opposite.
by 'full collective' I meant pushing the stick up
Even like that I don't see how there'd be any significant difference in the individual servo loadings (and therefore wear). Besides, you're not EVER gonna spend a whole lotta time at max up collective while inverted, eh?

Again, using over-spec'd servos solves a lot of these sorts of problems in helis used for hard 3D.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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12-01-2007 08:50 PM  10 years agoPost 51
wlfk

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Even like that I don't see how there'd be any significant difference in the individual servo loadings (and therefore wear).
OK - rather than arguing full collective, let's argue a transition from stable altitude to a climb, accelerating out at 1g. So the disk-loading is 2g times the mass of the heli.

The inverted copter doing the same maneuver will be almost weightless - no disk loading.

Assuming there is some relationship between disk loading and servo load, then you would expect to see significantly different servo loads in the 2 conditions.
Besides, you're not EVER gonna spend a whole lotta time at max UP collective while inverted, eh?
No, but the changes would be at the transitions, not in the steady state. e.g. you can feel a lift start to move, but once it's reached a steady speed, you weigh the same whether it's going up or down.

K

A bit like a kite, but 500 times more expensive

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12-01-2007 08:56 PM  10 years agoPost 52
GimbalFan (RIP)

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Assuming there is some relationship between disk loading and servo load, then you would expect to see significantly different servo loads in the 2 conditions.
Sure, but probably not to the degree that you're thinking, and the significance of any differences would be markedly reduced by using over-spec'd servos.

It would be interesting to see if anyone reading this has had occasion to repair or service a set of servos, and observed any differences in wear between the elevator servo and the two aileron servos. I'll guess (again) that the loading and therefore wear differences are quite minor over the long run.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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12-02-2007 10:54 PM  10 years agoPost 53
MrMel

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Gotland

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I have two identical helis (Stratus:es), one with 120 degree and one with 140 degree swash.

120 degree:
Interaction, Interaction, interaction, regardless how good you get it, its always "a little".

140 degree:
Rainbows, tictocs, loops goes like on rails, I mean it, you can drink coffee while flying, and it will stay straight on the line.
However, Piroflips and other piromoves doesnt get as "smooth" as on my 120 degree swash Stratus.

Which one, Well,.... hard to say.... both have its + and -
so I keep both

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12-02-2007 11:04 PM  10 years agoPost 54
GimbalFan (RIP)

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Very interesting. Why dat be, dooya think?

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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12-03-2007 01:35 AM  10 years agoPost 55
Yug

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UK. Herts

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ChristianM - explained the issues perfectly. However, even if the system is setup geometrically and mathematically perfect, the next big problem lies in the servo performance which, from the perspective of being able to apply a cyclic input at some vector becomes non linear when considering the unequal workload for a given dynamic cyclic input. As you increase the power and speed of these servos, things get smoothed out somewhat but perfection is virtually impossible to achieve. This is where flybarless steps in, because the gyros will endevour to provide the required input no matter what imperfections exist in the control system.

Vegetable rights and Peace

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12-03-2007 01:46 AM  10 years agoPost 56
GimbalFan (RIP)

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Big Coppitt Key, FL

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Would you agree then that using over-spec'd servos on the swash is always a good idea?

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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12-03-2007 01:53 AM  10 years agoPost 57
Yug

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Yes. BUT only in more demanding flying styles. One gets to know how ones heli behaves with whatever inputs, so the appropriate corrections can be made. However, if you then factor in dynamic wind conditions like ground eddies and rapid changes in wind direction, then it's down to the pilot no matter what. It just makes it easier if the heli responds more directly to the given inputs.

Vegetable rights and Peace

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12-03-2007 01:58 AM  10 years agoPost 58
GimbalFan (RIP)

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Big Coppitt Key, FL

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140 degree: Rainbows, tictocs, loops goes like on rails, I mean it, you can drink coffee while flying, and it will stay straight on the line. However, Piroflips and other piromoves doesnt get as "smooth" as on my 120 degree swash Stratus.
What do you suppose could explain MrMel's above assessment?

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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12-03-2007 02:11 AM  10 years agoPost 59
Yug

rrMaster

UK. Herts

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Cyclic inputs on rainbows are small and it's more down to thumbs being synced and making the appropriate corrections.
140 degree on tictocs - depends on orientation but forces are evened up or 4 point tictocs as previously discussed. 120 degree is less symmetrical as is also the case with loops depending on size.
For piroflip and other piromanouvers, the cyclic inputs are averaged which would suggest little difference between 120 or 140 but this depends on how the thumbs are tuned because 140 and 120 pose different aileron and elevator responses, possibly leading to less smooth figures.

Vegetable rights and Peace

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12-03-2007 07:37 AM  10 years agoPost 60
MrMel

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Gotland

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Cyclic inputs on rainbows are small and it's more down to thumbs being synced and making the appropriate corrections
I disagree, have you tried both 120/140 on the same machine?
Im not talking about ONE rainbow, im talking about doing 10 rainbows in a row, from full leveled stop each time.

Its day and night, all pure elev or ail input on the 140 is WAY easier. It really goes like on rails.

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HelicopterMain Discussion › 120 or 140 CCPM
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