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All Forums >> RC Airplanes >> RC Jets >> RE: Jets Over Kentucky Part II (Crash)
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RE: Jets Over Kentucky Part II (Crash) - 7/28/2012 3:54 AM   
Boomerang1



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quote:

By the way, that was the most realistic flat spin crash I have ever seen


Absolutely! I was waiting for the pilot to punch out! - John.

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RE: Jets Over Kentucky Part II (Crash) - 7/28/2012 6:19 AM   
essyou35


 

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Status: offline 		Re: servo jitter, I have some high end high tecs that do the same thing. I can tell you that they generate a lot of heat doing that.

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RE: Jets Over Kentucky Part II (Crash) - 7/28/2012 7:51 AM   
sysiek



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Status: online 		Hi please post mine maiden with f-22 on Saturday and the thanks.

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RE: Jets Over Kentucky Part II (Crash) - 7/28/2012 3:32 PM   
P. Richards



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Status: offline 		After I finish with the Series I usually start with the individual flight videos, Part III is finished with a tribute to Lewis Patton's
last flights with the A-7, it will be uploaded early Thursday Morning so stay tuned,
I am also working on the DVD which will be available at Best In The West and other Jet events...

P. Richards aka SwatTeam

< Message edited by P. Richards -- 8/2/2012 3:40 PM >

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RE: Jets Over Kentucky Part II (Crash) - 7/28/2012 11:30 PM   
mr_matt



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ORIGINAL: rhklenke

A servo is a feedback control system. That is, a part of the output (the servo position) is fed back into the input (the motor control polarity and voltage). If you get the conditions right, *any* feedback control system can oscillate. Since the high-end JR servos are designed for tight centering (narrow dead-band and high gain), if you put them into a system that has low initial force (like a balanced surface, or nearly so), but high inertia (like a big stabilator), you're very likely to get oscillation.

As long as the oscillation is damped (i.e., it is of a constant, or non-increasing amplitude), and it stops as soon as force is applied or you command a surface movement, you're fine. If your surface is oscillating and when you push on it, it continues or gets worse, then you have a servo problem.

Bob


Great post Bob. In you work have you seen any servos that let you adjust any gain settings? I have only seen deadband adjustments on hitec. I thought maybe you have used dynamixel or futaba at your work and you have exposure to the latest stuff. Thanks

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RE: Jets Over Kentucky Part II (Crash) - 7/29/2012 1:08 AM   
rbxbear44


 

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quote:

ORIGINAL: mr_matt


quote:

ORIGINAL: rhklenke

A servo is a feedback control system. That is, a part of the output (the servo position) is fed back into the input (the motor control polarity and voltage). If you get the conditions right, *any* feedback control system can oscillate. Since the high-end JR servos are designed for tight centering (narrow dead-band and high gain), if you put them into a system that has low initial force (like a balanced surface, or nearly so), but high inertia (like a big stabilator), you're very likely to get oscillation.

As long as the oscillation is damped (i.e., it is of a constant, or non-increasing amplitude), and it stops as soon as force is applied or you command a surface movement, you're fine. If your surface is oscillating and when you push on it, it continues or gets worse, then you have a servo problem.

Bob


Great post Bob. In you work have you seen any servos that let you adjust any gain settings? I have only seen deadband adjustments on hitec. I thought maybe you have used dynamixel or futaba at your work and you have exposure to the latest stuff. Thanks


+1 here on that...great intel Bob!

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RE: Jets Over Kentucky Part II (Crash) - 7/29/2012 2:12 AM   
rhklenke



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quote:

ORIGINAL: mr_matt


Great post Bob. In you work have you seen any servos that let you adjust any gain settings? I have only seen deadband adjustments on hitec. I thought maybe you have used dynamixel or futaba at your work and you have exposure to the latest stuff. Thanks


Matt,

Thanks. I don't have any real experience with tunable servos. Our work is generally from the autopilot on up. Being computer engineers vs. aero and controls types, we use off-the-shelf aircraft (or modified aircraft) and servos and we build our own autopilot hardware and software optimized for the application at hand.

We mainly use JR servos and our experience has been that if you use the right size, you can assume that they go where they are commanded to go and stay there. (with the occasional unloaded oscillations being discussed...)

Bob

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RE: Jets Over Kentucky Part II (Crash) - 8/2/2012 4:24 AM   
Instructor



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Status: offline 		Hi Bob,

I have been told not to balance a full flying stab just for that reason. I was told to add a little weight to the leading edge of each stab to help in reduceing the load to the servo. Do not balance to the point where the stab is in neutrtal if you remove the linkage. The digital servo keep looking for the neutral position trying to overcome the weight in the stab.......


Larry

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