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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Eureka!!! Linear servo motion!!!!!
03-12-2014 02:42 AM  6 years ago
icanfly

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ontario

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in the tx negative expo values, tomayto toemaatoe, six or 6,

positive expo yielding a curve bending downwards works to soften my dfc just fine, in the op tdr(?) heli the output is linear from the servo taking commands from something. Either or, so there, it's pretty good, you're looking for maximum efficiency, something about a number of wheels and gears always equals a multiple of two times the first and final gears, may apply. You want numbers or pretty looking helis? that is a question.

do your brains hurt?
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03-12-2014 05:04 AM  6 years ago
HeimD

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HeimD: when flying straight and level in the wind, the FBL makes corrections without the sticks moving. There are other moves where the sticks are still in at least one dimension and the FBL makes corrections.

If the expo matters to the FBL, putting it in the radio won't help in these use cases.
Those tiny little corrections are done around center and not at the extreme ends of servo throw. EXPO doesn't matter in that situation.
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03-12-2014 09:21 AM  6 years ago
ChristianM

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In order for rack and pinion to work, you have to have special s/w in the FBL.
Thus, if you now use a linear servo, the FBL unit needs to know not to do that extra math.
If you have the VBar Pro then you can turn off that extra math / linearization by deselecting the "Geometry correction" under the Swash expert parameter tab in the setup wizard. So no need for new software.

Having said that, for this application (straight line speed) I do not think it will make much difference with the geometry correction.
This is engineering genius at its best.
I agree. Jan makes exquisite helis. Drool
Also, Jan is a perfectionist so he would not put out anything half arsed with respect the control and performance of his helis.

Christian
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03-12-2014 04:07 PM  6 years ago
Four Stroker

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Thank you. Someone finally answered my question. Why doesn't one of you ASK JAN what FBL unit he is using and what he did about linearization corrections.
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03-12-2014 04:16 PM  6 years ago
HeimD

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Thank you. Someone finally answered my question. Why doesn't one of you ASK JAN what FBL unit he is using and what he did about linearization corrections.
Does he even answer emails from the unwashed public? He might just tell you it's proprietary info anyway. LOL
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03-12-2014 04:28 PM  6 years ago
ChristianM

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For the TDR Jan recommends the VBar. He even supplies a setup file for the VBar specifically for the TDR. I would expect the same for this heli.

Christian
Burn fuel, be happy
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03-12-2014 05:16 PM  6 years ago
rexxigpilot

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Many on here, even some smart folks, are missing the whole purpose of the linear servo design developed by Jan Henseleit. It's advantage is not in the fact that it provides linear motion since, as many have already pointed out, there are other non-liner motions in the linkage system and swash, and a linear servo motion can easily be created electronically in the TX or even FBL. The reason Jan's design is a better design is due to linear torque!

A standard servo wheel and link has full servo torque only when the link is at 90° to the wheel (sin(90°) = 1). When the wheel has turned 60° the torque acting to push or pull the link is only 50% the servo's torque (90°-60° = 30°, sin(30°) = 0.50).

Maintaining high servo torque to the blade grips is very important with a high speed machine where the aerodynamic forces are very high on the control surfaces.
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03-12-2014 05:49 PM  6 years ago
Four Stroker

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"He even supplies a setup file for the VBar specifically for the TDR."

Then when this file shows up for the new heli, it will be obvious what he did with the linearization corrections.

I liked linear rack servos back in the day. Some had the additional advantage that they turned the pot 180 degrees. They perhaps unwittingly provided vibration isolation as well.
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03-12-2014 06:23 PM  6 years ago
JKos

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Redondo Beach, CA

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A standard servo wheel and link has full servo torque only when the link is at 90° to the wheel (sin(90°) = 1). When the wheel has turned 60° the torque acting to push or pull the link is only 50% the servo's torque (90°-60° = 30°, sin(30°) = 0.50).
Not quite. Torque is not applied to the link. Force is applied to the link. The servo can actually supply the least force to the link at the 90° point. As the servo rotates away from 90°, it can actually apply more force to the link.

The servo's maximum torque is always the same but the effective distance (moment arm) decreases as the wheel rotates away from 90° thus the maximum force actually increases. In fact, mathematically the force goes to infinity with a zero angle.

- John
RR rules!
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03-12-2014 06:29 PM  6 years ago
whoamis

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Still correct, JKos... :-)oops, bounced it!
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03-13-2014 04:26 PM  6 years ago
rexxigpilot

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Yep, you're correct John. The moment arm does decrease so force goes up. I was thinking of a rigid link system where the force opposing the servo wheel motion had a longer moment arm, thus apply more torque against the servo.
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03-14-2014 05:48 PM  6 years ago
Justin Stuart (RIP)

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Plano, Texas

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But interposing a belt between the elevator servo and the swashplate? What if the belt stretches? Seems like asking for trouble. It looks cool and all, but I don't think I trust a belt for such a critical application. But the good thing about the rack and pinion setup on the aileron servos is that in a crash, the servo probably survives intact.Avant RC
Scorpion Power Systems
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03-14-2014 05:55 PM  6 years ago
icanfly

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ontario

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and, if a servo arm were the same distance as the swash ball to the main shaft the servo arc would be identical to the swash rotational arc thus achieving linear action.

Could it have been a combination of keeping the profile narrow as well as maintaining linearity without long ass servo arms?
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03-14-2014 08:08 PM  6 years ago
Sam2b

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Advantage: likely more precise for high-speed flying (i.e. at IRCHA). At high speed, the flybarless units are working hard to keep the heli from pitching up or down. I'm not referring to max travel/moment of the servo "arm." A linear servo may enhance the stability performance, and even in 3D. Just my educated guess._Sam B_
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03-14-2014 08:18 PM  6 years ago
Sam2b

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solved with negative expo.
Bingo.
Good luck getting it exact. You don't just add arbitrary negative expo and call it "solved."

What is your procedure for measuring movement after using negative expo to achieve exact linear travel with a non-linear servo? Otherwise you have the potential to have the same problem on the opposite way, or not actually solve the problem at all.
_Sam B_
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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Eureka!!! Linear servo motion!!!!!
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