What's up with one ways?

What's up with one ways?
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What's up with one ways? - 7/11/2003 10:01:51 AM

Spiro

Posts: 335
Joined: 4/14/2003
From: Mesa, AZ, USA
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I was wondering if someone could explain to me why a one way bearing is a necessary / good thing?

I will be the first to admit I have no experience with the flight characteristics of the electric LMH. All of my background comes from flying their nitro powered cousin. In the nitro world when I back off the throttle the blades try to �over run� the engine and the engine breaking effect will slow them down in a hurry. This, of course, causes the tail to swing about if I or the gyro do not control it properly.

In my simple world of ignorance this seems entirely analogous to how I have read people describing the same event in the electric world. Yet nobody talks about how great and or necessary one way bearings are with the nitro heli. Further, it would seem to me when you reduce or increase the throttle you would want the blades to spin up and down quickly. The longer the rpm change requires to take place the mushier/sloppier/greater delay in the vertical control authority. Aerobatics and inverted flight aside, the delay caused by having to spin up and down fixed pitch main rotors is one of the strongest arguments for collective pitch machines, and on that I would have to agree with them.

People have also mentioned how one way bearings are not required with brushless electric motors which do not �cog�. I have a firm grasp of the cogging idea, but I do not see how a cog effect free motor would behave any different under a transient speed reduction. It seems to me the rotor would still be locked into phase with the speed control and the �back torque� effect would be identical. If this were not the case, with all of the inertia in the rotor disk it seems to me that a throttle change from say 3/4 to 1/2 would take several seconds to spool down. Such an abrupt change would also cause a no torque effect on the main shaft, if indeed a cog free brushless setup allowed the rotor to overrun the speed control on speed decreases. If this were the case, I can only imagine that a large uncommanded pirouette would start and persist for the entire duration of the time that the main shaft was under no torque but the tail rotor was still being driven.

Please enlighten me as to what is going on. I am clearly ignorant in several key areas here�

Further questions I am left wondering about are:

Why does a one way bearing improve flight quality/performance?
Wouldn�t M/R authority be significantly reduce by not being able to quickly lower RPM?
Why would a �cog free� brushless setup not require one?
Why would a piston engine setup not require one?

Don�t get me wrong here. I have read all sorts of posts where people talk about how great their flight quality is after the one way install, how smooth hover became, how the tail became more controllable. I don�t doubt all of these people. They have seen the results with their own eyes and I have not. There must be something to what they are saying. I just am scratching my head as to why.

Thanks in advance,
Spiro

one way - 7/11/2003 2:23:39 PM

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From: Eatoville, WA, USA
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I have flown both tyoes in my concept srt which is collective but has no one way bearing, and adding it made all the difference in the world , I think more than anything it just smoothed out the throttle control, and allowed the blades to unwined smoother when backing off the throttle, before the clutch disengaed, the one way bearing does lock instantly when the gas is applied so you lose no power or have any slipping, the blades will free swing so you can do auto rotates, with out, the head speed would just slow down to fast from the engine drag and it would drop like a rock, I think that the benifit to the lmh would be smoother thottle con trol and on a flame out it would come down slower,and on hovering you would not have such a big swing in head speed as with a direct drive, up and down throttling, and you elimanate the over speeding remember this is not a clutch, it is a locking device,it only takes 1/4 of a degree ot 1 tooth on the main gear to be locked solid, in either direction, there is no mushy feeling to it,and you tend to be able to back off the gas with out the oops to much and have to give more gas to recover. I have toyed with adding it to mine, to see if it would help with the constant throttling on a windy day, not a dumd question but great food for thought,

(in reply to Spiro)

What's up with one ways? - 7/11/2003 9:28:04 PM

Spiro

Posts: 335
Joined: 4/14/2003
From: Mesa, AZ, USA
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Fastlash,

Thanks for the information. I have a couple of questions for you.

Forgive my ignorance but is the concept srt a glow powered heli? I was not able to find any information about the SRT model online. Your message talks about engines and flameouts, so I would assume glow power. This certainly addresses my questions regarding how applicable the one way bearings would be to the glow powered LMH.

By having flown both types in your SRT, do you mean both gas and electric or with and without the one way bearing. Obviously, from your helpful insights, you have flown with and without the one way bearing. I was just wondering if you had gone both electric and gas with the Concept SRT as well.

Finally, I was wondering if you had a glow or electric LMH. I would be interested to hear your appraisal of a one way bearing for either version of the LMH, should your wallet become suddenly to heavy and you decide to get one

Thanks again for the information,

Spiro

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bearing - 7/13/2003 6:01:05 AM

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Spiro the srt is a 30 size glow and was last made I think in 1992 by Kyosho, it was a direct drive via a clutch , and I updated it with the one way bearing, It did require a different feel for throttling, not bad just different, once I got the feel for it I would not go back to the old set up, see what you did now, I got to try it on my lmh, lmh is glow and so is my old concept srt is
glow,

< Message edited by fastlash -- Jul 13 2003 6:35AM >

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What's up with one ways? - 7/14/2003 11:57:37 PM

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From: Surrey, BC, CANADA
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I have installed the one way on my corona and can tell you it makes a world of difference! The one way reduces the abruptness of the heli wanting to drop when power is reduced. Due to the fact that (through the gearing) the main rotor is essentally connected directly to the motor - the motor acts like a rotor brake, as when power is reduced the motor respondes instantly. The "cogging" effect is the magnets in the motor. So if you go from 75% throttle to 50 % throttle the main rotor does the same thing, and the heli drops like a rock. With the one way, the rotors spin down at their own speed - reducing the sudden drop due to the slower motor. Also there is less of a torque change - due to the one way slowing the rotors less - so you don't get a drastic tail swing. BTW - the speed control only controls the motor not the main rotor.

Hope this helps!

Marc

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bearing - 7/15/2003 12:12:51 AM

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Hey skyhawknut what would I need to do to add this to my 110 glow LMH

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What's up with one ways? - 7/15/2003 12:24:56 AM

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From: Webster, MA, USA
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Hi Skyhawknut:

I've asked this question here on this forum three times, and never got an answer:

Does the "cogging" occur in ALL motors ... or just in brushed motors ... Or just in SOME brushed motors???

I also wonder if the cogging occurs in brushless motors, especially Mega and Astro Flight??

I have a Hacker C40 in my Corona, and there is NO "braking" or cogging effect as the motor decelerates ... just a nice smooth inertial slowdown of the drive train.

Just came to mind, ... it may have something to do with the ESC program. too?!?

I'm, curious, as I am sure Spiro is, and others too, I'd guess.

Thanks for the help and Happy Choptering,

Russ

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What's up with one ways? - 7/15/2003 1:52:52 AM

Spiro

Posts: 335
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From: Mesa, AZ, USA
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Mini Boy,

I can definitely confirm the cogging for all brushed motors I have ever held in my own hands. I am actually quite curious how you could build a motor, brushless or otherwise, without this effect.

The mystery to me is how any brushless motor, like your hacker, could get away without experiencing the same flight qualities. As far as I can see, while the speed control is putting out a cyclic power curve to the motor windings, the rotor (motor rotor) will still be locked in phase with the speed control regardless of how little cogging there is with the power off. I am not saying it can't and doesn't happen. I am just saying I don't understand the principle behind it.

Your idea about the ESC programming is a possibility I had not considered before. What kind of ESC do you have?

Thanks again,
Spiro

(in reply to Spiro)

What's up with one ways? - 7/15/2003 4:09:59 AM

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The "cogging" effect happens in all brushed motors - some more than others. If you take a brushed motor and turn it by hand, you will feel it stick then move a little. That is the armature passing each magnet. In a brushless it is opposite - the motor is mounted on the spinning shaft and the esc tells which set of windins to turn on. In other words in a brushed motor the spinning motion is self induced and it's not in a brushless. I'm not very good at explaining electrical things but check out this link:
[url]www.aveox.com/articles.html[/url]

Marc

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What's up with one ways? - 7/15/2003 4:12:48 AM

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You could get a much simpler and better explanation over at e-zone - that's where all the electric guys hang out!

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What's up with one ways? - 7/15/2003 5:09:37 AM

Posts: 432
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From: Webster, MA, USA
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Spiro /Skyhawknut:

First, I am NOT an expert on brushless motors, so please don't think thay I'm an authority on the subject. And, in fact, I'm an absolute newbie to the E-R/C world, although it is is SOoo exiting since it is a "cutting edge" time in the history of R/C.

I spend at least 4 hours daily reading through the hundreds of threads on these forums, to say nothing of the 2 million links. The latest I just read was about a DIRECT DRIVE brushless motor from our ingenious friends in Deutchland which is the most unbelievable thread I've ever read.

What you must realize is that we are all on the threshold of a whole new ballgame in the R/C power business, and in a year, it will be another BETTER variation of the same game.

When I got involved with an electric heli, AND as a beginner, I read, watched and listened to the advice I was given, And got a Hacker powered /Hacker ESC Corona with the MG servos, Futaba GY-240 gyro, 2600NiMh packs and a good charger. Since I got the machine built and flying, I have never had to get onto these forums and ask 100 questions about why this doesn't work with that, or how come my motor is so hot that I can't touch it, or how come my Pegasus ESC melted(EDIT .. Sorry, I meant Phoenix), or how come I've got glitches that cost me more in crashes than I paid for the heli!! Believe it or not, although about $30.00 in repair parts, NEVER a bent tail boom?!?!! (I have two unused spares!) I took advantage of all the research and experimentation that others had spent thousands of hours on.

Brushed motors are SPARK GENERATORS, like you use to light your gas barbeque grill! They are inefficient at best, but work well to start your car or truck. They make lots of electrical noise that R/C receivers really dislike a lot. Suppose your washing machine or refridgerator had a brushed motor in it ... do you think you'd get 15 to 20 years out of it? Just so you know, fridges, washers and dryers have brushless motors. They are not a new invention.

O.K. ... I'm going off on tangents( as I do so well)!

Spiro, the brushless motors (at least Hackers, and I'm not so sure of others) don't have magnets, and from what I understand (and here again I hope someone comes along to correct me if I'm wrong) are not even D.C. motors ... rather they are three phase A.C. motors (in a sense) as they can have their timing changed by the pulse program of the ESC. You can pretty much make them run any way you want, by letting the ESC know what you are trying to do!! ... And trust me, my hacker and ESC are like SILK!!! .... NO "COGGING"!!!

My lobsters are boiling over, gotta run!!

Russ

< Message edited by Mini Boy -- Jul 15 2003 12:18AM >

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What's up with one ways? - 7/15/2003 7:23:04 AM

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UMMMM.....................Even a brushless motor needs a magnet

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What's up with one ways? - 7/15/2003 8:26:38 AM

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From: El Paso, TX - USA
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Brushless motors have no magnets... how the hell is that gonna work

A brushless needs magnets exactly as the bushed does BUT... the brushed one has them fixed and the coils rotate and need to change direction of the magnetic field - therefore we have brushes.

The brushless one on the other hand rotates the magnets and has fixed coils. Therefore we have the special ESC which has to change the current through the coils to make the motor spin.

So far

Michael

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What's up with one ways? - 7/15/2003 8:44:19 AM

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From: Central, MI, USA
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This is a wag but I think a brushless motor could indeed operate without magnets. Since a magnetic force is created in the static coils, it would only need a ferrous substance to act on -- not necessarily a magnet. No?

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What's up with one ways? - 7/15/2003 4:46:06 PM

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Just to be pedantic but brushless are three phase DC, not AC. It's true that the three coil circuits are energized in turn (based on where the controller sesnse the stator to be) but the voltage applied is either 0V or +motor volts. But never -motor volts so it's not AC but phased DC.

And of course brushless have magnets. It's