Mini 4WD Madness! Part 3: Building a Body Mass Damper

It’s been some time since my last Mini 4WD-themed post. As of writing this Japan Cup 2016 is around the corner, but this time around you had to register by downloading some app and I missed the deadline. Besides, I don’t spend enough time tweaking my machines to have any confidence tackling the crazy Vertical Changer for one.

Anyway here in Japan, official races have been incorporating elements such as jumps and banks for the past few years, making the layouts of tracks more three-dimensional than before. As a result, speed isn’t the only important criteria, and poorly set-up machines no matter how fast would go off course and retire. To reduce the rebound after a landing, mass dampers are installed. Due to their weight, they have the disadvantage of slowing a machine down, but the increased stability they confer is incredibly vital.

While Tamiya has a wide range of mass dampers in various shapes and designs, some creative folks have come up with even more diverse, effective designs. Among the hardcore in Japan, they have somewhat nonsensical names which I won’t go into detail since they don’t seem to make sense. However the common characteristic among them is the increased actuation range compared to stock dampers which are usually weights sliding up and down a fixed pole or swing with small arcs.

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One of the easiest designs is the hanging damper, where a pair of reinforcement plates mounted on either the front or rear reach across the length of the machine and has sliding weights mounted on the sides. Depending on the complexity of the design, you could either make the whole thing sit on top of the body, or cut the body so that it sits on top of the assembly instead, making it look more integrated with the machine as a whole.

Here I will show how I built my body mass damper which has the body attached on top so that it moves along with the damper. This design is for the AR Chassis where you will need 3 straight reinforcing plates, at least 2 X Chassis rear roller stays, a mass damper set with round weights, spacers and screws of assorted lengths. For convenience, you may also use a pair of throwaway pliers (ones you don’t mind damaging for cutting up the plates), diamond-tipped files and to speed things up, an electric router with a diamond cutting tool attachment.

Depending on its width, the chassis can get in the way of the straight plates. I believe that it would be even more difficult to build a damper for the wider MA chassis while the narrow Super II Chassis may require fewer parts. Hence, part of the plates will have to be cut depending on your layout and chassis.

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In this case, I used carbon fibre plates which are stronger and lighter compared to FRP plates with the same design. Due to my incompetence/inexperience, the thinner sections on mine are weaker than they should as I damaged the surfaces with my cutting tool. The sections were removed to avoid the counter gear and motor areas of the chassis. Cuts were first made using an electric router, then filed smooth.

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2 X Chassis rear stays were cut up as shown above. On the upper one, the left and right pieces are used while on the bottom, the centre piece is kept, and its edges filed smooth. The centre piece on the bottom is for keeping the straight plates parallel to each other and prevent the assembly from becoming lopsided like a parallelogram under lateral forces.

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For added structural strength I cut up an FRP multi roller stay and mounted it at the rear like so. It turn out this part might not be needed after all.

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You have a lot of freedom in building the damper. Here a straight plate was used to extend the sides, and two screws were used on each side to prevent the dampers from twisting to the sides. As the hanging damper experiences a lot of vibration, I used lock nuts throughout.

Since taking these pictures I tweaked the layout a bit to move the weights up front as close to the front wheels as possible, and swapped the lower extensions so that the weights don’t go past the line traced by the front and rear roller mounting positions to keep within official regulations.

Flat head screws were used on the side extensions, and recessed holes were made so that the underside is smooth. The lengths of the screws were chosen to get the weights as low as possible. A sponge was applied on the underside of the centre plate for cushioning. The protruding screw ends are for mounting the body on top.

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The holes in the straight plates can be worn out over time where the damper is mounted to the chassis. To prevent this, brass eyelets can be glued to the holes. However, they are not sold and do not come with newer cars so I decided to improvise and cut up some aluminium pipes as a replacement.

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Springs are used to keep the damper in position. Rubber tubing was used as a stopper for mounting the body to the damper.

As there is no hard and fast rule to the design, there are many variations and I am unsure which one is the most effective. As far as I can tell, in 2016 there is a trend of mounting the damper in front instead.

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