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Old 07-06-2013, 01:12 AM   #1
Atomic Skull
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Default Moving in the ball vs reprogramming the servo arm deflection.

Would reprogramming the rudder servo to have reduced defection work better than moving the ball in? The goal of moving in the ball is increased control resolution which comes at the expense of rudder speed. It seems to me that reprogramming the servo's deflection range would increase resolution without sacrificing speed.
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Old 07-06-2013, 01:34 AM   #2
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Default Moving in the ball vs reprogramming the servo arm deflection.

It is really a balancing point. There is also a trade off in torque. Moving the ball in decreases mechanical gain which will allow you to increase electronic gain.
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Old 07-06-2013, 10:45 AM   #3
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Not sure which you're referring to, exactly, by "reprogramming the servo's deflection range would increase resolution without sacrificing speed".

The servo's resolution is fixed. Adjusting stuff on the radio/FBL will never increase the servos resolution. Let's assume the servo has 360 rotation steps for 180 of rotation, 1 step = 1/2.

So if you simply reduce your servo travel, with the ball out far on the horn, you will have:

- Low resolution (to exaggerate, say your used servo travel is only 50 steps). At some point, you will start getting "grainy" tail response, where even small servo changes start approaching wag.
- High speed
- Low torque/force

With high speed and low force, if your tail takes very little force to change pitch while spooled up (or if your servo just has a lot of torque), you will get very quick response.

If you move the ball in closer on the horn, you will have:

- High resolution (again, to exaggerate, maybe your used servo travel is 200 steps)
- Low speed
- High torque/force

The servo can now make finer adjustments to your tail pitch. You will sacrifice response speed on paper, but if your tail requires a lot of force to change pitch, or if your servo is light on torque, you can actually get quicker real-world response. It has more force available to actually make the pitch slider move quickly.

As gothicbunny concisely said, it's a trade-off, there is a happy medium to be found. Some heli's list suggested servo-ball distances. Some FBL systems will also suggest that your FBL tail endpoints be between a certain range, to help ensure that the required amount of servo response plays nicely with their control loops.
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Old 07-06-2013, 05:05 PM   #4
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Originally Posted by RedOctobyr View Post

The servo's resolution is fixed. Adjusting stuff on the radio/FBL will never increase the servos resolution.
That's not what I meant. Some servos like Hyperions and some Hitecs are programmable. You can change things like deadband and deflection by hooking the servo up to a programming box.
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Old 07-06-2013, 05:21 PM   #5
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Sorry, I misunderstood

At some point, you will run into the limits of what the potentiometers can distinguish, for tiny movements (related to the # of degrees per increment of rotation). But I don't know whether the servos are already at that limit with a full range of travel.
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Old 07-06-2013, 05:31 PM   #6
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Limiting servo's won't gain resolution, It just sets a limit inside the servo electronics, the same way you set limits in a FBL controller. Like stated above Servo resolution is based on the quality of the Pot and the electronics. Ya get what you pay for.

Now that said, going in on the ball Can make it appear to have better resolution because the ball acctualy travels less per servo 'tick' But yes, speed is affected, lowered, but Tq is increased
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Old 07-06-2013, 07:15 PM   #7
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Quote:
Originally Posted by RedOctobyr View Post
Not sure which you're referring to, exactly, by "reprogramming the servo's deflection range would increase resolution without sacrificing speed".

The servo's resolution is fixed. Adjusting stuff on the radio/FBL will never increase the servos resolution. Let's assume the servo has 360 rotation steps for 180 of rotation, 1 step = 1/2.

So if you simply reduce your servo travel, with the ball out far on the horn, you will have:

- Low resolution (to exaggerate, say your used servo travel is only 50 steps). At some point, you will start getting "grainy" tail response, where even small servo changes start approaching wag.
- High speed
- Low torque/force

With high speed and low force, if your tail takes very little force to change pitch while spooled up (or if your servo just has a lot of torque), you will get very quick response.

If you move the ball in closer on the horn, you will have:

- High resolution (again, to exaggerate, maybe your used servo travel is 200 steps)
- Low speed
- High torque/force

The servo can now make finer adjustments to your tail pitch. You will sacrifice response speed on paper, but if your tail requires a lot of force to change pitch, or if your servo is light on torque, you can actually get quicker real-world response. It has more force available to actually make the pitch slider move quickly.

As gothicbunny concisely said, it's a trade-off, there is a happy medium to be found. Some heli's list suggested servo-ball distances. Some FBL systems will also suggest that your FBL tail endpoints be between a certain range, to help ensure that the required amount of servo response plays nicely with their control loops.
Nicely explained!

Rick
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Old 07-06-2013, 08:52 PM   #8
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Default Moving in the ball vs reprogramming the servo arm deflection.

I wanted to add that you don't want to move the ball in too far or you begin to lose linearity of travel near the ends. Generally you will want no more than 45 degrees travel from center in either direction since this is the point where sine starts to become greater than cosine or some such jibber jabber.
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Old 07-07-2013, 06:51 PM   #9
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Quote:
Originally Posted by gothicbunny View Post
I wanted to add that you don't want to move the ball in too far or you begin to lose linearity of travel near the ends. Generally you will want no more than 45 degrees travel from center in either direction since this is the point where sine starts to become greater than cosine or some such jibber jabber.
That's probably why most servos default to 45 degrees deflection from center.
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Old 07-07-2013, 08:51 PM   #10
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I move the ball towards the fulcrum (in) to reduce travel
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