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The moment a clutch begins to engage...

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The moment a clutch begins to engage...

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Old 03-02-2015, 06:24 PM
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Default The moment a clutch begins to engage...Added Ramp - CENTAX STYLE

It's been a few years now and there's still something that's cloudy and elusive about the moment a clutch engages. There are so many factors in play that I admit that it's all theory and reaches into the depths of molecular science. Like most things that depend on friction, a micron off and it hasnt engaged, so we are talking a very small and instantaneous force between the clutch shoe not engaging and it beginning to engage.

Here are some of the factors that I can think of:
  • The acceleration of the clutch shoe engaging against the bell - ( Spring / gap / Throw weights )
  • The amount of friction created as it engages - ( Shoe type / Bell coating / End Play )
  • The power of the engine, the tuning and pipe, making the power band - (Accelerating the flywheel / Heavier throws versus light / Spring types / Tension )
  • Slip, do I want an aggressive clutch or one that slips a little - ( Shoes / Bells / Gap / Throw Weights )
  • Ramp angle - ( Throw Attack, Throw weight, Throw Weight position)
  • Inertia - (Steel versus Alu bells)
  • Aggressiveness, Mounting hinged throws in reverse with trailing edge forward will. (Throw Weights mounted leading, not trailing)
    TBC - Harder spring, the more power required to throw the shoe
    TBC - More aggressive clutch setup, lose about 25 seconds of run time I will have to figure this one out at a later time.

Indeed there are instructions, these are baselines and the actual operation of a clutch seems straight forward, is it really that simple? Considering belts can stretch, temps can change and engine power, the transmission's gearing and track can be a consideration.

Summary (Real world info provided by racers):
  • Longer Softer Spring with larger gap, allowing enough slip with throttle feathered, staying engaged in medium paced corners. This seems a good setup for fluid tracks with high speed infield cornering to help prevent unsettling of car during turns keeping the clutch engaged and not disengaging mid corner and weight transferring away from fronts. Risks are it can unwind if clutch not correctly shimmed and setup. Throw weights, shoe and bell. - TBC (Courtesy - lil-bump)
  • Reversed throws / Longer Stiffer Spring with larger gap - With leading the clutch will be more agressive. A clutch wil also be more agressive when a strong spring is mounted and a a larger gap is used. TBC - (Courtesy - Roelof)
  • To create more or less force during engagement of a clutch, the primary clutch (not other) factors are the throw weights and the spring tension. These two opposing forces can be fine tuned by changing the gap providing the "linear" spring does not fully compress prior to engagement. I have measured tests off and on clutch for spring compression and there is a difference of .2mm in my findings, why I havent worked out. The changes in radius and forces are in the order of 2-4% where a grub screw in the throws can increase forces up in the order of 20%.
    (Courtesy for Centrifugal forces - RBakker)
  • AVS pointed out that the gap does effect the forces, as the 3% change in force occurs, the engine is compensating and continues accelerating the flywheel. The spring will have a lot to do with the amount the shoe accelerates. If using a lighter spring the additional force of the increase in radius, plus the increase in gap will accelerate the movement of the clutch shoe. If the spring is stiffer, the resisting forces of the spring will reduce the clutch shoe's acceleration or, prevent engagement all together. The weight of the throws and spring tension remains a major factor in the gap effect.
    (Courtesy for Gap effects - (AVS
  • IC-racer proposed a torque converter, there's a pic in the link to a small one, its likely too heavy a solution, one could propose an electromagnetic clutch in future too, with eletronic ingnition. We by default keep it simple and fast... Might run out of fuel too. It was nice to be thinking outside the box though! Courtesy - ic-rcacer


Terminology:

Flywheel Collet - The tapered collar that compresses and grips onto the crank shaft and must be tapered to suit the flywheel and cannot protrude to prevent the clutch nut from binding the flywheel to the crank.
Fly weights / Clutch Throws - The 3 or 4 hinged or unhinged components of the clutch that ramp against the flywheel and/or clutch plates dish to push the clutch plate forward.
Clutch Nut - This nut binds the flywheel to the crank, and has a threaded end that the clutch spring retainer screws onto to increase of decrease spring tension.
Clutch Plate - The plate that pushes the shoe against the bell, it is mounted behind the spring cup and is rigid enough to distribute the force on the shoe evenly.
Clutch Spring - The spring that controls the tension applied to the clutch plate. They can be conventional springs or some can be a series of conical high tensile steel rings.
Spring Cup - The component that combines the clutch plate and shoefor the clutch spring to sit in and to apply tension to the plate/
Clutch Spring retainer - The threaded adjustable retainer that applies tension to the clutch spring
Thrust Bearing - A flat bearing that allows a clutch to slip at the point of engagement.
Thrust bearing retainer - A tubular insert with a retaining end to it that mounts to the end of the crank. It retains the thrust bearing, shims and bearing and keeps the clutch from falling apart. Various length retainers can be used in conjunction with the fly wheel collet lengths to set the overall position of the clutch.

Clutch Gap - The total distance between the clutch shoe at rest, and the Clutch bell hard against the thrust-bearing. We can assume this value is FREEPLAY + ENDPLAY (See below)

Gap Freeplay = The distance between the shoe and the bell shimmed at the lower bearing when clutch bell is pushed close toward the shoe. It should be a value equal to (GAP - ENDPLAY). One can assume this is the amount of free spin the engine has before it comes into contact with the bell.
(NOTE: I dont know what the correct term for this is but sounds good in respect to ENDPLAY)

Endplay - this is the amount the bell can float before the clutch shoe can engage fully be pressing against the thrust bearing retainer. ENDFPLAY allows the throwing shoe to slip a little while it conquers the inertia of the BELL and GEARS and prevents binding of the thrust-bearing through heat expansion, clutches do get hot.


Forward Clutch - The conventional style where the ramp for the throws are on the flywheel
Reverse Clutch - Where the ramp for the throws are on the clutch plate and not the flywheel
Forward & Reverse Clutch - Where the throws are tapered on both sides and ramp exists on flywheel and plate.

Leading throw - When throws open leading the pin in rotation - Aggressive
Trailing throw - When throws open trailing the pin in rotation - Smooth

Dusting - When the surface of clutch shoe breaks down causing clutch shoe dust to form. (assumed to soft a shoe for the aggressiveness and power applied)
Glazing - When the clutch shoe glazes (assumed slipping) causing a shiny surface to appear on the shoe.
Stretching - When the holes in the shoe to stretch (assuming to much grip and too much inertia)
Deformation - When the clutch shoe deforms and warps (Assuming to much force or heat)


Any comments, suggestions, additions would be appreciated.

h


NOTE: Disclaimer:
Clutch bag - Not to be confused with anything RC related. Although this is an absolute must and a critical component to a happy marriage and RC experience. Must also be colour and style matched with shoe's, also not of the RC clutch type!
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Last edited by blis; 04-05-2018 at 04:49 PM.
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Old 03-03-2015, 12:37 AM
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Hey brother,

You need a FINCH SPEC clutch. You and the bloody clutch. Only jokes Harry.
Ring me if you like I'll talk clutches with you for as long as you like.

GC
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Old 03-04-2015, 04:18 AM
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Originally Posted by blis View Post
Any comments, suggestions, additions would be appreciated.

h
You think to much.....
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Old 03-04-2015, 05:14 AM
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I assume that these are considerations for the top end racers...I'm happy if the clutch engages at the point in the power band that I want and doesn't dust the shoe

Will watch this thread with interest.
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Old 03-04-2015, 07:06 AM
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Originally Posted by jtrmx250 View Post
I assume that these are considerations for the top end racers...I'm happy if the clutch engages at the point in the power band that I want and doesn't dust the shoe

Will watch this thread with interest.
Ok, Dusting, so I assume that if you are using a high bite shoe and there's very little slip it may do similar to marbling soft tyres. Would engagement be better just prior to the power band? So it's a good example of the questions as to why and where the variables play. Aluminium bells, versus steel bells and inertia could be factored in too. I often look at the holes in the shoe to see if they have stretched and if Im stressing it.
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Old 03-04-2015, 07:08 AM
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Originally Posted by M7H View Post
You think to much.....
Not enough to get my head around a clutch!
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Old 03-04-2015, 09:49 AM
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To me over the years I've found a few clutch setups that work for me in differing traction levels and don't really think too much more about it. I know what's acceptable and what is past its best when maintaining the clutch and really that's about it!

A clutch can be difficult to get your head fully around for beginners but once you get the fundamentals right and can build a clutch ACCURATELY then I feel there is little more the average Joe needs to worry about.

As the others I'll watch this thread with interest!
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Old 03-04-2015, 10:59 AM
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Originally Posted by dan_vector View Post
To me over the years I've found a few clutch setups that work for me in differing traction levels and don't really think too much more about it. I know what's acceptable and what is past its best when maintaining the clutch and really that's about it!

A clutch can be difficult to get your head fully around for beginners but once you get the fundamentals right and can build a clutch ACCURATELY then I feel there is little more the average Joe needs to worry about.

As the others I'll watch this thread with interest!
What I've found about how I like my clutch to react is that I like a clutch that has low-mid speed sensitivity. meaning that my clutch will stay engaged just below the mid-throttle range (ie carousel portion of the track) and it stills has the ability to lock-up 100% (without bogging the engine or breaking the tires loose) on the exit of the carousel onto the straight section. This is why a clutch setting relies so much on the track conditions and track layout.
What I've found that with a slightly softer spring setting and a bigger clutch gap helps achieve this. A longer spring is also more desirable.
The best clutch in my mind is a clutch that is the most drivable in all locations of the track (slow and mid). Any decent clutch will engage at 3/4 to full throttle.
In my opinion a clutch shoe that has just the right amount of slip is also better with drivability, fuel mileage and engine temps.
With all this being said; I still sometimes struggle finding the perfect clutch engagement. Maybe the perfect clutch is a Unicorn... if you find it PLEASE give it my address. I think its because I'm always searching for a better clutch s


Pass you soon...
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Old 03-04-2015, 02:22 PM
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I didn't start nitro racing until 2 years ago. At the beginning, it was just so difficult to get the right clutch and went through many hardships with all sorts of problems. Part of the reasons was that I thought too much and focused on things that I was doing right and that I ignored other important things. And every time I asked the others, all had different ways to set up their clutch and I got confused big time.
Lil bump said he keeps searching for perfect clutch set up but I think, like dan said, understanding the fundamentals and not messing up with that too much should come first. I found that setting up preload, gap and endplay in the ballpark should get you going for the time being. Focusing on those too much, I lost focus on the other things like checking bell, flatness of the preasure plate, checking fly shoes, making sure the bell doesn't touch the shoe when set up, checking ball bearings, etc,. Well obviously lots of you guys have way passed that stage I know. But I wanted to point out in novice's perspective
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Old 03-04-2015, 04:27 PM
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Originally Posted by lil-bump View Post
What I've found about how I like my clutch to react is that I like a clutch that has low-mid speed sensitivity. meaning that my clutch will stay engaged just below the mid-throttle range (ie carousel portion of the track) and it stills has the ability to lock-up 100% (without bogging the engine or breaking the tires loose) on the exit of the carousel onto the straight section. This is why a clutch setting relies so much on the track conditions and track layout.
What I've found that with a slightly softer spring setting and a bigger clutch gap helps achieve this. A longer spring is also more desirable.
The best clutch in my mind is a clutch that is the most drivable in all locations of the track (slow and mid). Any decent clutch will engage at 3/4 to full throttle.
In my opinion a clutch shoe that has just the right amount of slip is also better with drivability, fuel mileage and engine temps.
With all this being said; I still sometimes struggle finding the perfect clutch engagement. Maybe the perfect clutch is a Unicorn... if you find it PLEASE give it my address. I think its because I'm always searching for a better clutch setup.


Pass you soon...


Pass you soon...

Hey, nice input....Tks, I added to summary and Ill keep updating the post with everyones input!!

Do u use a softer or harder clutch shoe in this configuration and do you run a steel or alu bell, throw weights added or throws drilled out for lighter?

PS: Tks for the input Snuvet, so true about neglecting other issues!

Last edited by blis; 03-04-2015 at 04:41 PM.
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Old 03-04-2015, 05:02 PM
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To those that think Im getting too deep into it, I'll let out a little secret that I learned when at the worlds, it might get your thinking caps on too.

The top runners, both Alexander Hagberg and Dominik Reiner (sp) didnt have crazy aggressive clutches on their cars. Alexander specially had a very soft setup (versus stiff srping and aggressive).

The infield was tricky, there were two sections where a 2 speed came into play and engaging at the wrong time and the perils of running off line would be punishing. In amazement as I was watching Dominik's solo practice, he was manipulating his 2 speed engagement with the initial level of acceleration and as I watched and listened, my jaw dropped lower and lower in amazement at the control the world's best drivers have.

Add to that the smoothness and control that Alexander demonstrated in the turns, the way he rotated the car at the apex, all lead me to believe that a punchy clutch on a track like HugeRC wasn't in our best interests.

Taking that on board, as Dan knows, the atmosphere was electric, (no pun intended) and without a good foundation and in depth knowledge of clutches and the plethora of variables to tune and adapt to the conditions and at the time, my son would stabbed me with a tuning screwdriver if I did! I thought it might take a few racing minds to get into the specifics of how and why...

To any new racers that want to submit tips and advice, please do, this thread will hopefully bring out the many subtle techniques and methods we need to adapt to varying conditions.

Thanks
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Old 03-05-2015, 07:07 AM
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Originally Posted by blis View Post
Hey, nice input....Tks, I added to summary and Ill keep updating the post with everyones input!!

Do u use a softer or harder clutch shoe in this configuration and do you run a steel or alu bell, throw weights added or throws drilled out for lighter?

PS: Tks for the input Snuvet, so true about neglecting other issues!
I always try to keep my clutch components the same. I only use the shepherd spring with the Serpent sedan clutch, Yellow shoe, steel bell, standard weights. I've found that these components work together well. The Serpent spring works too it just does not last as long as the shepherd spring The only time I've used weighted clutch weights is when I ran the Serpent black shoe and aluminum bell. This configuration gives tons of pop but it not as smooth as the yellow shoe setup. I do have a complete Dynamis clutch it's works pretty good. It's about 20% more aggressive than my standard yellow clutch setup but for some reason I lose about 25 seconds of run time when I use this clutch. I will have to figure this one out at a later time.
This season I will the aluminum bell with my base setup. Paolo M uses a aluminum bell with the yellow shoe. But some things that work great for Paolo do not work for me.
I do agree with the statement It's better to have a good working knowledge of how a centax clutch works and try to keep your variables down to a minimum.


Pass you soon
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Old 03-05-2015, 07:23 AM
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On the Natrix I too use the standard weights, yellow shoe and steel bell. I've played with other setups but find the standard kit the most consistent. I use the standard kit spring without issues.

I do add grub screws to the weights and tighten the spring lots for extra snap in high traction and did so at the worlds.. Interesting to hear your points about Hagbergs and Greiners clutches.. Perhaps we were going the wrong direction Harry!! However huge rc track is unique and normal logic didn't apply there so perhaps should be side lined for this discussion?
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Old 03-05-2015, 07:51 AM
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clutch set up were related to the engine setting,especialy LSD.
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Old 03-05-2015, 08:38 AM
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Originally Posted by kyosho malaysia View Post
clutch set up were related to the engine setting,especialy LSD.

Maybe a factor. Centex style clutches just have to think of centrifugal force. The lighter of weight of clutch shoes the earlier it engages and strength it engages. You can physically see it on test bench when breaking in your engine. Average folks 1/3 of throttle is start to engage. I like to see it engage as soon as possible when you crack the throttle. The more rpm, the aggressive it is. All come down the style of driving. Everyone is different. Diagnosis of wear parts tell you, dust, glazing, cracks(lack of friction), should tell you whats happening.
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