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!
