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wanna see what everyone here thinks happend to my control of a plane w/ expo set wron

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Old 06-03-2014, 09:37 AM
  #26
Charlie P.
 
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Nothing speaks better for progress than technology when it fights you. Like computers: the darned things only do what you told them to do, not what you meant.

Haven't had the pleasure of flying with gyros but the little 3-axis accelerometers on the AS3X models are pretty incredible.
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Old 06-03-2014, 11:08 AM
  #27
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Quote:
Originally Posted by Bozarth View Post
Ackermann Effect is a moot point, since our control systems experience countering effects. at both ends of the control system (in typical configurations). ie. The expo movement of the pushrod from a round servo wheel would be an issue except for the fact that this pushrod now pushes on a control horn attached to a control surface that arcs around a hinge ling...which removes the Ackermann effect all by it self. We still have a proportional movement of the control surface. Not always a 1:1 ratio proportionality, but nonetheless proportional (1:2,,1:2.5,,1:5,,etce)
Excellent point and one I did not consider and should have but with further consideration wouldn't the canceling effect only completely apply if the angle between the hinge line and the pushrod attachment to the control horn was the same as the angle described between the pushrod attachment to the servo wheel and the center of rotation. Also would the movement be proportional if the distances (arc radius) described above were different? Off the top, I wouldn't think so. Probably shouldn't continue this as it is not on topic to the thread, I was just asking as I kinda thought the primary function of expo was to counteract Ackermann, about which I was wrong.
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Old 06-03-2014, 08:19 PM
  #28
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I fly the plane without any expo then decide if it needs it or not. It's not something you can just randomly install before maiden. I usually end up with 25% to 40% depending on the plane. Some need it and some don't. Like Shawn I think people put too much throw in there new planes. I use a degree meter and all new planes start out with about 12 degrees except for 3-D planes, then it's 28 to 30 degrees. All my planes have as much rudder as I can get and never get any expo in the rudder. I don't use expo in any trainer type of plane but that's just a choice thing.
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Old 06-03-2014, 11:31 PM
  #29
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Quote:
Originally Posted by dspeers View Post
...Also would the movement be proportional if the distances (arc radius) described above were different?
The movement would still be proportional. 10% movement of the stick would generate 10% movement of the servo. 50% movement of the stick would generate 50% movement of the servo. Changing the either the servo horn radius or the control horn radius would simply change the actual movement of the control surface. They do not have to be the same. All of this assumes zero expo and a stardard setup. Pull-Pull systems installed geometrically incorrect bring some of these issues back to life.

Expo would be something like "10% movement of the stick would generate 3% movement of the servo" and "50% of stick movement would generate 35% movement of the servo." The servo movement % would now quickly need to catch up, or more mathematically speaking, it would need to "exponentially" increase to reach 100% by the time the stick reached 100%.

Fun stuff!

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Old 06-04-2014, 05:59 AM
  #30
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On the subject of expo... personally I don't use it on every plane.. some need none, some need a bit, and once in a blue moon one needs a 55 gal. drum full. Many years back I'd got a 47" Scott Stoops designed Extra(?) from 3DHS. A new line of aggressive performers they'd come out with. So got it built, going through setup, and noticed the recommended expo settings. Elev or rudder had a recommended expo setting of 78% WHAT!!??? Hahahaha!!! .. must be a typo... I managed to get in touch with Scott. Was no typo. He explained it, it made sense.. what I could understand, still a bit skeptical but went with his suggestions. That was the BEST 3D flyer of its size I've flown yet. Good stuff.... don't think I've used a 78% expo since..
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Old 06-04-2014, 06:38 AM
  #31
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Too much expo just gives you an On/Off/On feeling to the sticks (IMHO). I like some - have several models with none at all. The most I have is 45% on my little 15" 30mm ducted fan GP Sabre jet. VERY sensitive to elevator and ailerons and there is no practical way to change the mechanical linkage.

Years back (young folks roll eyes at this time) we had double or triple rates. Now I never use low rates and instead set 20 or 25% exponential to give a flatter centered stick position.
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