In response to the requests for information regarding Centax type clutches, we have put together the following article that explains the way they work and what parts are involved. The name Centax is used by Serpent Model Cars and is used throughout this article as it has become synonymous with this type of clutch.
This is the second part of an article about the centaxial clutches used by many of the top remote controlled model car manufacturers. This part of the article hopefully explains how this type of clutch works. The First Part of the article introduced all of the various parts of a centax type clutch and the Third Part of the article provides further information and a few tips.
Please note that I only have knowledge of the Serpent and PB Racing products, so cannot cover all possible variations of this type of clutch.
How the Centax Clutch Works
As mentioned in the First Part of this article, Centax type clutches operate (just like any other clutch used in remote controlled model cars) by converting the centrifugal force that the speed of the flywheel generates into a movement that connects the driving force from the engine to the transmission. The image shown below right below shows a cross-sectional view of a typical Centax type clutch assembly. All of the parts were identified in the First Part of this article.
Basically the clutch works in this manner;
The flywheel is spun round by the engine and the flyweights (yellow) are then subjected to centrifugal force and try to move outwards.
Because of the tapered sides of the flywheel, the flyweights move up the sides of the tapers, which makes them move in a diagonal direction (both vertically and horizontally).
It is this movement that forces the clutch shoe (green) against the clutch bell (grey).
This principle will be better understood by the studying the animation to the left, in which some of the parts have been removed for clarity.
When Played, the animation shows how the centrifugal force (that the speed of the engine generates) causes the flyweights (yellow) to slide up the ramps on the inside of the flywheel and force the clutch shoe (green) sideways.
The description above left out the involvement of the spring (red). The purpose of the spring and its associated adjusting nut (pink) is to provide a means to control how and when the clutch shoes engage. The spring presses against the flyweights and provides resistance against them moving. If you tighten up the adjusting nut you compress (preload) the spring. It then requires more centrifugal force from the spinning flywheel to overcome the resistance of the spring to allow the flyweights to move. Conversely, if you loosen off the adjusting nut there will be less preload on the spring and less centrifugal force will be required to overcome the resistance of the spring.
When the engine speed decreases, the amount of centrifugal force also decreases to the point where force of the spring is able to return the flyweights and clutch shoe to their former position, therefore disengaging the drive to the transmission. This is helped on the Serpent clutch by the inclusion of the Spring/O-ring around the flyweights, which is shown in the First Part of this article.
The spring/adjuster is not the only adjustment that can be made to how the clutch operate though. As the clutch works by the flyweights pushing the clutch shoe sideways, the amount of free play (end float) also affects when the clutch engages.
The whole assembly pushes against the retaining screw in the end of the crankshaft, so if it were further away, it would have to move a greater distance before it engaged. Conversely, if it were closer to the flywheel, it would take less movement from the flyweights to engage the clutch.
Adjusting this end float can be done in a number of ways, the PB Racing solution is shown on the right and uses a threaded adapter. Simply tightening or loosening the nut allows the end float to be adjusted without any disassembly.
The same adjustment can be made to the Serpent clutch using some shims (part #1093) like those that are pictured on the left. Many people do not use these, they alter the end float by adding and removing the shims from behind the flywheel. This long winded method is used, presumably, because there are few instructions on how to use them.
As there are two different methods of adjusting the engagement of the clutch, you can use them both to achieve different effects. A larger end float measurement gives more movement and also will yield in a harsher engagement, as there is time for a significant increase in the momentum of the flyweight/clutch shoe assembly.
Summary
As stated at the beginning of this article, there are many different versions of this type of clutch available on the model car market and we cannot cover all possible variations. The information given explains the theory and principles behind the centaxial clutch and so should have informed you as to how they all work irrespective of any design differences. For further information regarding this type of clutch see part three of this article.
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