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Old Feb 07, 2015, 06:59 PM
AvB
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Pipe dream ... a "Gearbox Servo"?

A bunch of us were chatting about the challenges of balancing control authority in DS planes ... wanting good roll rate authority at landing speeds in big heavy planes with heavy tips, vs the need to cut the rate right back for high speed DS. So the final setup is always a compromise - you could always use more low speed authority and you'd could also like to use more of the servo resolution at top speed low rates.

Will D dreamed up the idea of a "geared servo". Wouldn't it be great if you could flip a switch and instead of changing the servo rates in the transmitter, it changed a gear ratio in the servo. So you launch on normal "high range gear", set up with generous throws, then on dive-in you switch to "low range gear" where the servo motor is still working at full rotation and giving max resolution, but the gearbox is giving say 30% rotation of the arm, compared to high range.

Or maybe as a bolt-on accessory that fits to the main servo?

Imagine if you could get one at 12mm thickness for DS aileron servos e.g for K130 etc.

A pipe dream most likely? I wonder if other DS disciplines could use geared servos?

Thought it was worth "putting it out there".
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Old Feb 07, 2015, 10:50 PM
U down with EPP? Ya u know me
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I think Alan's hydraulic servos did exactly what you describe and more.
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Old Feb 08, 2015, 01:52 AM
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Wellington, New Zealand
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interesting idea. While not quite the same, i have been playing around with an OpenTX EEPE file for in-flight adjustable rates system.
I also wondered about OpenTX doing the job of digital servo programmers but being able to in-flight adjust the centering and/or throws in mid-flight. The difference being no loss of resolution.
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Old Feb 08, 2015, 05:12 AM
AvB
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Aaron, is there a link to something about the hydraulic servo?? I missed that.
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Old Feb 08, 2015, 05:24 AM
Where is the inspiration
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Moira
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After thinking about it more I have realised that its not travel for power, its speed for power, so if we geared the servo down, we would loose speed and gain torque.

If we had a faster servo to bigin with it would be ok, but alot of our servo choices are already traiding speed for torque, so to drop that down again and loose efficiency in the extra gear train too makes this quite a challange that may not be worth it.

Some of the lads here fly MKS DS 65 K in their D40 and Stabs, but they are notably slow when the model is in launch / land and even slow DS, it only when the model gets going that the pilots get confidence.

But again maybe that is proof that it could work? do we mind a slower servo when the model is in the 250+ range?

(Maybe some of these thoughts should have been filtered)
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Old Feb 08, 2015, 10:02 AM
U down with EPP? Ya u know me
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Alan has it all figured out and has tried to get Hitec to license his incredible servo designs. Magnetic encoders, regenerative braking, clutches, ultra-low power consumption, hydraulic drive to name a few of his advancements. The servo industry seems to prefer selling servos that underperform and easily fail so he has not been able to get all his tech into mass production.

So far though, Hitec has released standard servos with his brushless motors and controller circuit. These servos use very little power yet are super fast and extremely high torque. They also benefit from regenerative braking.

Here is the link:

http://hitecrcd.com/products/servos/...-servo/product

The Alan servos are only available in standard size for now. With luck, Hitec will release smaller servos with the licensed technology. If they do make smaller servos with Alan's circuitry then Hitec would be the undisputed leader for high performance servos. Every aspect of RC benefits.
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Old Feb 08, 2015, 12:07 PM
Objects in mirror are losing
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I'm confused.
Low rates don't increase the size of the steps they just reduce the number of steps.
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Old Feb 09, 2015, 03:09 AM
Where is the inspiration
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Moira
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Quote:
Originally Posted by 1000MPH View Post
I'm confused.
Low rates don't increase the size of the steps they just reduce the number of steps.
When you drop rates, you have less resolution for the same amount of stick.
As as the model goes faster, it takes less displacement, but potentially more power.

So we want a servo that when you change "Rates" or "gear" you get more power to the output, and improved resolution per mm of throw.

But as said before I beleve this will come at the sacrifice of speed, that may or may not be a problem.

We are also more interested in a maximum of 13 mm thick servo with this tech.

How difficult would it be be to make a gear box that can be added onto servos to do this?
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Old Feb 09, 2015, 09:10 PM
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The problem is, you're not just talking about a "gear box" in the sense of a
box full of gears with a fixed ratio, but a gear changer.
Think about what that takes in any other application. Changing gears smoothly,
without jumping or gnashing the teeth not a trivial task.
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Old Feb 09, 2015, 09:45 PM
AvB
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Australia, QLD, Woody Point
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Yes, definitely agree. Hard to imagine it not causing centering problems.

Maybe a CV system? Infinite ratio, conical spline?
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Old Feb 09, 2015, 11:10 PM
U down with EPP? Ya u know me
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Not only that but to get all servos to change gears at the same time or you have oddball control.
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Old Feb 09, 2015, 11:29 PM
AvB
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And ... the gears could be under a lot of load or being shaken about while the shifter is changing ...

However I'm sure there would be a way around the problem ... the limitation being whether the market justifies the R&D.
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Old Feb 09, 2015, 11:57 PM
Objects in mirror are losing
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Mechanical Principles (1930) by Ralph Steiner [4min selection] (4 min 13 sec)
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Old Feb 10, 2015, 02:12 PM
the occasional flyer
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Rexburg, ID
Joined Jul 2008
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oops. already said..
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Old Feb 11, 2015, 02:59 AM
Where is the inspiration
wdeighton's Avatar
Moira
Joined Feb 2006
865 Posts
If the gearing is done in the servo the centers should remin.
Some cars have a duel cluch system where the next gear is already preselected. if we only have 2 gears, this means we should never get crunching (But I hear you fitting a clutch in a servo will make it massive.

It will be interesting to see where servos develop.
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