RcTek : Brake Cam Modification

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This article offers a suggestion for a modification that can be made to the brake cams on remote controlled model cars. Although the diagrams used show a brake assembly for a large scale car, the principle will be applicable to most cars.
Section Contents Model Car Handling Model Car Engines 2 Speed Transmissions Model Car Differentials Bearing Information Fixings & Fasteners Centax Clutches Radio Control Gearing Charts Conversion Charts	Standard Brake Cams The brakes on remote controlled model cars usually involve some sort of cam to actually apply pressure to the brake disk. As a cost effective measure, most of these brake cams are made by machining a flat onto a round cylinder, an example of which can be seen to the right.   The Modification The purpose of this article is to introduce the reasons why you would want to modify the shape of your brake cam(s) on your model car. The image of the brake cam to the right has had the edge that contacts the back of the brake pads rounded off to improve the action of the brake assembly it would be fitted to. Please note that only the side that contacts the brake pads need to be modified.   Why? The reason why you would want to modify your brake cam(s) can be seen by studying the animated images shown below to either side, which show a typical cam and brake/disk set-up from a large scale model car. Please note that in the images below the size of the cam has been considerably enlarged for clarity. Playing the animated image to the left shows a standard brake set-up in which you can see that the movement of the cam in moving the brake pads (white) to apply pressure on the brake disc (yellow). Playing the animated image to the right shows a modified brake set-up where the cam moves the brake pads in the same way. There are a few benefits of using a modified cam, which are in the way in which this movement is generated and the resultant contact area of the cam. If you have played both the animations you will notice that different coloured lines appear at the end. It is the relative positions of these lines that form the basis of the following explanations.   Progressive Action In the images above the red lines that appear at the end of the animation show the amount of rotation of the cam in moving the brake pads to contact the disk. With the modified cam, the amount of rotation can be around double that of the unmodified one, which gives a much more powerful and progressive action to the brake. This will give the brake an amount of 'feel' and is due to effectively shortening the length of the lever that the cam represents.   Contact Point & Contact Area The blue lines on the images above show the distance of the contact point of the cam on the brake pads. The modified cam has a contact area much nearer to the centre of the brake pad and therefore puts more equal pressure on the assembly. The contact area of the modified brake cam is also better than the unmodified one due to its round shape, which will more easily release and not tend to mark the back of the brake pad.   Important Note As modifying the cam in the way suggested in this article radically alters how the cam works, it is important that the profile of any pair of cams that work together on opposite sides of the car are the same. Failure to do this can lead to problems in getting both wheels to brake by the same amount, the results of which will be a car that moves off to one side under braking. Summary Depending on the configuration of your model car, this modification can be a worthwhile one that results in substantially improved brakes. Be careful before modifying any parts of your car, you may render such parts useless by removing too much material. Related Information Large Scale Car Brake Lever Modifications Further Information If you have any comments or suggestions about this or any of the other R/C car content on the RcTek site, please feel free to ask them on our On-line Forum Home  Technical Information  FAQ  Tips & Tricks  Car Information  Site Map  Forum  Links Unless stated otherwise all images and content are Copyright (c) RcTek 2000/2001