Tamiya TRF419X Project

Page 1: Chassis Assembly

TRF kits come in pretty small, unadorned boxes because they do not include a body, wheels, tires, or electronics. Even with the small size of the box, it is about half empty inside.

You can see that there are hardly any plastic parts trees here. Usually that happens for a very simple chassis, but this is not simple. Most of the parts are metal or carbon and are contained within the labeled hardware bags.

The build starts with the carbon fiber (CFRP) chassis plate and the anodized aluminum rear bulkheads. This model uses all hex hardware, and most of the bolts are countersunk to sit flush with the bottom of the chassis. The left hand picture also shows the rear-forward suspension mounts which partially control the rear toe angle. These parts (05g) in combination with rear-aft mount 1E and the stock 0° uprights result in 3° toe angle. In the right hand picture I've also added the supports for the rear pulley and spur gear. Note that everything is carbon or metal at this point.

The rear differential uses the first plastic parts. The housing appears to be glass reinforced. You might be surprised that the internal gears are plastic, but these run quiet and wear slowly and are plenty strong for a touring car. They are white but they are not Delrin. They seem to be something much stiffer. The cross shafts are metal, possibly titanium. This is a sealed differential and the kit comes with the clear shock fluid (900cSt kinematic viscosity) to use for filling. The outdrives appear to be aluminum. The completed diff is shown on the right. The teeth surrounding the outdrive are eccentric indexes. The whole diff can be rotated to move the diff back and tighten the belt.

The aluminum caps are used to enclose the bearings which mount the differential and also contain the ball joints which support the upper suspension arms. They are shown mounted on the right with the shorter rear belt installed.

The spur gear is 64 pitch (tiny teeth) and uses 116 teeth. Smaller 113T and 111T versions are available for more top speed. A pulley is located on either side of the spur to drive the front and rear belts in parallel.

The front uses a solid spool instead of a differential so assembly is much simpler. The spool just bolts to the front pulley as shown on the left. Note the toothed cams for tension adjustment just like the rear. The completed front bulkhead assembly is shown on the right.

Here's an overall view showing the completed front and rear bulkheads with both belts installed and tensioned. Belts have a lot of rolling resistance compared to gears, but they sure are smooth and quiet and, best of all, have zero backlash. The pockets milled into the chassis plate are to provide clearance for the motor and make it as low as possible.

Now we can install the dual bellcrank steering which is all aluminum and equipped with ball bearings. This is an extremely well made steering system with virtually no slop. On the right you can see that the upper carbon chassis brace has been installed. This significantly increases the stiffness of the whole chassis. It also supports an idler bearing for the long belt which helps to reduce slap.

Now the lower glass filled plastic suspension arms can be installed. The rear is shown on the left and the toe angle can be seen. There is no toe on the front arms. The aluminum suspension mounts capture the ball joints which support the arms.

The rear uprights are also plastic and support aluminum CVD axles. Because the inboard dogbone end mates with an aluminum drive cup, a Delrin slider sits over the pin to prevent it from digging into the drive cup. This results in very smooth action with no slop. The upper suspension arms are turnbuckles which allow easy adjustment of camber angle.

The front knuckles and C-hubs are also glass filled plastic. The front axles uses a dual cardan design which allows for increased steering angle without jitter. On the right you can see the completed front suspension with the upper arms and steering links attached.

This picture shows the completed front and rear suspension installed on the chassis. A close look will reveal the stabilizer bars installed also in both the front and rear.

TRF shocks are always a thing of beauty and these are no exception. These shocks have very short travel, but that doesn't change the number of parts. The shock body, both end caps, and spring perches are all aluminum. The piston head and rod guide rings are Delrin for smooth action. The picture on the left compares a completed shock to an exploded view. The shocks are the same at all four corners. They are shown installed on the right which completes the suspension entirely. Note the thick carbon shock towers.

The kit comes with a couple of front and a single center ballast weight which I installed as shown on the left. On the right I've installed the foam front bumper which will help protect the body. Note that even the bumper support is made from carbon fiber and also supports the front body posts.

This rubber sheet cushions the battery. Unlike most Tamiya kits, this one is intended to use a rectangular Li-Po race pack. I quite hate the method for securing the battery though. The slots shown are for adhesive glass tape which much be replaced every time. I don't really see what this buys you in a race setting. I just use a duct tape strap I made.

On the left the last few parts have been installed including the carbon steering servo holder and the antenna tube. The kit thankfully comes with a high torque servo saver, but I also added an aluminum horn. On the right all the electronics have been installed. I used a Hobbywing sensored brushless motor and ESC with a blue Protek steering servo. Note that even the wheel hexes and lock nuts are blue anodized.

As a final detail, I installed this hard, clear adhesive sheet to the bottom of the chassis. It will serve to protect the carbon from minor scrapes and gouges.

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