Page 2:  Assembling the Chassis

While writing about this build, I am going to concentrate on the differences between this and the last chassis in the TRF line I built (the TRF 414M) and also the standard TRF 415 (which I've never built but have studied).

The original TRF 415 carried over the same suspension as the TRF 414M, but if you look closely at the picture on the left you'll see "58331" molded on the sprue for the lower suspension arms.  This reversible arm suspension system began with the TB Evolution IV chassis in July of 2004, 5 months after the original TRF 415 but 4 months before the TRF 415MS which first brought it into the TRF line.  The rest of the TRF 415 variants continued with these parts as did many other chassis including the TRF 416.  The 49346 Lightweight Suspension Set allowed this suspension to be installed on an original TRF 415 or TB Evolution III.  The other information on the sprue reveals that these parts are molded in carbon fiber reinforced Nylon (polyamide) manufactured in November of 2005.  Since the TRF MSX was released in December of that year, I probably have one from the very first production batch (or maybe there is only one batch for limited edition models).

On the right you can see an exploded and assembled view of the parts for the rear suspension arms.  These arms have 3 ball joint holes on the edge of one side, and the 2 on the opposite side are offset to be between them.  This allows a total of 5 shock attachment positions by flipping the arms.  There are also 4 different plastic balls for anti-sway bar attachment molded into the arms, although this chassis uses blue 5mm aluminum balls for both shock and sway bar attachment.  The set screw inserted perpendicular to the arm sets the down travel stop where it contacts the chassis plate.  The arms pivot on titanium coated hinge pins, and aluminum spacers are used to control the fit and the precise wheelbase.  One useful building tip to keep in mind is that carbon filled plastic is much stiffer and more brittle than standard PA, so it is a good idea to tap the threads before inserting any screws to prevent cracking.

The suspension mounting system shown on the left was first introduced with the 58299 TB Evolution III chassis in 2002.  This system originally consisted of blocks labeled X, A, B, C, D, and E which each varied slightly (0.75mm) in width.  Mounting your suspension arms using two of the same width blocks resulted in no suspension arm toe, while using two different blocks resulted in 0.5° of toe per letter of difference up to a maximum of 2.5° with the original version.  Changing both blocks at the same resulted in a 0.75mm change in track width.  It's a very versatile system.  The TRF 415 introduced the second generation of these blocks which each include a "1" in front of the letter, as well as expanding the list of options with 1XA-1XD.  These blocks are 1mm lower than the original blocks.  The "X" can be thought of as a negative sign so the order of width from narrowest to widest is 1XD, 1XC, 1XB, 1XA, 1X, 1A, 1B, 1C, 1D, and 1E for a total variation of 6.75mm.  For those of you who care about the math, consider this.  If the difference in width is 0.75mm per letter, then that's 0.375mm per side.  The length of a hinge pin is 46mm, but the difference between ball centers is 43mm.  Doing some quick trigonometry: tan^-1 (0.375/43) = 0.5°.  Nice job Tamiya.

The picture on the right shows the rear suspension installation which uses blocks 1XD and 1B resulting in a rear toe of 3° (there is no additional toe in the uprights).  It is pretty easy to see that the hinge pins are not parallel in the picture.  The original TRF 415 had 2.5° of rear toe, 0.5° in the mounts and 2° more in the uprights (the same uprights used on the TRF 414M).

The two-piece pulleys are pretty annoying.  The retaining ring has to be glued to the main pulley very carefully to avoid getting glue into the teeth and messing up the smooth travel of the belt.  The TRF 414M used an aluminum pulley with staked retainers.  The front and rear pulleys have the same number of teeth (35T compared to 32T on the TRF 414M), but the rear pulley (pictured lower) is set up for a ball differential while the front pulley (pictured upper) is set up for a one-way.  The ball differential shown at the right uses 8 balls instead of the 10 used on the TRF 414.  The drive cups shown for the TRF 415 MSX have a much wider slot than those from the TRF 415.  More on the reason for that later.  See those black plastic rings on the left side of the exploded view?  Those have eccentric holes for the diff bearings and are used to adjust the belt tension.  More on that later as well.

Here's the completed rear ball differential with the eccentric bearing holders installed over the drive cups.  On the right you can also see the white belt which is a low friction version which was new to the TRF 415MS and carried forward into the MSX.  The picture also shows four upper bulkheads which are new to the TRF 415MSX (only two are actually used on the rear.  These trap the diff bearings and allow easy removal of the diff for maintentance without removing the rest of the bulkhead.

On the left you can see that the rear bulkheads have been installed over the top of the suspension mounts.  The slots for the center pulley shaft are built into the bulkheads, and the left hand bulkhead also houses the motor mount.  Now the rear differential can be installed into the rear bulkheads along with the upper caps as shown on the right.

This side view of the rear drive cups illustrates the belt tensioning method.  The bearings are mounted in eccentric plastic mounts.  By this I mean that the inner hole for the bearing does not share the same center as the outer ring of the mount; it is offset.  There is a tab at the bottom of the mount which fits into one of fourteen scalloped slots on the bulkhead.  By rotating the bearing bolder to choose which of these slots the tab fits into, the bearing can effectively be moved forward or backward, tightening or loosening the fit of the belt.  These parts were new for the original TRF 415 and are unique to the 415 series, although a very similar system was used later putting the complex scallops on the plastic bearing holder instead of the bulkhead.

Note that the further you rotate the eccentric bearing holders from center, the greater the component of movement is vertical instead of horizontal.

The little horseshoe shaped parts shown on the left are stamped 49381 which means they were new for this model.  The plastic is identified as glass filled POM (Polyoxymethylene), a very unusual polymer for Tamiya.  This is a very strong, very hard plastic which makes sense given the application.  They are used on the dogbone ends of the axles as shown on the right.  More on the reasons why further below.  The CVD style universals changed slightly for the TRF 415MS and are carried forward here.  The rear axles are steel and the front are aluminum (both 46mm), presumably because the front one-way eliminates all braking from the front wheels so they can use lighter, weaker axles.

The TRF 414M used a combination of 5mm and 6mm balls, with the 5mm ball cups coming from the TA04.  The updated 5mm ball cups shown at left are stamped 58261 which is the TA04 PRO chassis.  They are supposed to be made from a lower friction material which will last longer.  The right hand picture shows an exploded view of the camber links assembled from these cups combined with a turnbuckle.  The aluminum uprights shown are standard on the TRF 415MSX replacing the plastic parts of the MS.  Note that the aluminum uprights have no built-in toe angle while the older plastic parts included 1° of rear toe.

Now the rear hub assembly can be added to the rest of the rear suspension as shown.  The threaded screw pin from the TRF 415MS has been replaced with a hinge pin secured with a set screw on the MSX.  This avoids having to tap anything into the hard plastic of the lower suspension arms.  While I understand the desire to eliminate the older E-clip secured design, the MSX solution is much superior to the threaded screw pin which was only used in a couple of models.

Here we can finally see the purpose of those horseshoe shaped parts on the ends of the axle dogbones.  The slot in the drive cup is there because the dogbone needs to be able slide in and out of the cup as the suspension moves up and down.  The classic problem is that high contact stresses between the pin and the slot gradually dent the drive cup.  Once the dent is present, the dogbone can no longer slide freely and the efficiency of the suspension is compromised.  By putting the plastic bit between the pin and the slot, the contact stress can be absorbed by the more resilient plastic and distributed to a wider area in the slot.  In the event the plastic is ever damaged, it can be easily and cheaply replaced to keep everything operating smoothly.  This clever solution requires a wider slot in the drive cup so it can't easily be swapped into older models.  This basic design (with updated materials) is still used on Tamiya's high end chassis today.

Whereas the TRF 414M came with three different spur gear options, the TRF 415 line comes with a single 102T 0.4mod gear.  The MS version added the carbon reinforcing plate.  The spur gear shaft is directly coupled to the rear pulley but uses a one-way to drive the front.  The center pulleys have 16 teeth for an overall belt ratio of 35:16 = 2.1875:1.

Here's the completed center shaft assembly.  The TRF 415MS version used the same shaft design, but it had to be assembled in-situ by passing the shaft through the bulkheads.  The MSX version can be assembled outside the chassis and inserted as a unit, then held in place by the upper brace shown on the right.  This is a major maintenance improvement. 

   

The front aft suspension mount is installed upside down with 3mm spacers to make room for the belt to pass beneath it.  The original TRF 415 and the 415MS used a specialized bridge mount for the same purpose, but this achieves the same thing without any unique parts.  The steering posts are also installed at this point which have less standoff built into them (compared to TRF 415) resulting in lower steering cranks.  The TRF 415MSXX changed to a totally different steering system, so these posts appear to be used only on this model.

Normally both front suspension mounts would be the same width resulting in parallel hinge pins, but in this case the combination of a 1XB and 1B suspension mount means there is -2° of front arm sweep.  Conventional wisdom suggests this is a bad idea, so I don't know why this chassis is configured this way.  The TRF 415 and 415MS used no sweep angle and, interestingly, the 415MSXX went back to a bridge mount also with no sweep.

The steering cranks on the TRF 415MSX are the same as on the previous versions, but the bridge has been moved on top of the cranks instead of beneath them since the cranks themselves are now installed lower.  The cranks appear to be the same parts from the TRF 414M but with the longer one swapped to the right instead of the left.  The new front bulkheads are installed in the same step.  The TRF 415MSXX changed to a completely different steering crank setup.

Here are the parts for the front one-way which seem unchanged from the baseline TRF 415, but the method of installation into the bulkheads using removable caps is new to the MSX.  Now the belts are all fully encapsulated in the chassis.

These steering knuckles are made from carbon filled Nylon and are stamped as coming from 58331 (TB Evo IV) which is consistent with the rest of the suspension.  These were not used on the original TRF 415 (which used the parts from the 414M) but started with the 415 MS.

The C-hubs are glass filled instead of carbon filled (less strong but more resilient) and are also stamped with 58331.  The kit comes with two sets of hubs and the manual setup section says they are for using either 2° or 4° camber angle.  It took me forever to figure out what the actual difference was, partly because the manual is wrong about how it describes them.  If you look closely at the picture on the right, I've inserted the lower hinge pins and you can see that they are not parallel to the hubs (I've lined up the hubs with the grid on my cutting mat to make it more obvious).  The pin in the upper part stamped "4L" is at a greater angle than the pin in the lower part stamped "2L".  This tends to tip the hubs slightly backward in the lower suspension arms resulting in a caster angle, not a camber angle.  The camber is adjusted by changing the length of the upper links as usual.

These exploded views show how the axle is assembled into the knuckle (left), and the knuckle installed into the hub via the kingpins (right).  This is all consistent with the 58331 suspension system.  Those clamping 12mm hexes are new to the TRF 415, replacing the parts from the 414 which were retained with o-rings.

Now we can complete the front suspension my installing the steering into the lower suspension arms with hinge pins and fixing with the upper camber links.  The completed front suspension is shown on the right with the steering links also connected.

The original TRF 415 and the MS included 3 different stiffnesses of anti-sway bars, but the reduction to only a single option was one of the few downgrades to the MSX.  The smaller yellow bar is for the front suspension and the red is for the rear.  In general, red represents the softest option and yellow is medium.  When a blue option is available, that's the stiffest.  The sway bars on the TRF 414M were not very effective because of the loose way in which they were mounted to the chassis.  The 415 kept the same bars and mounting method, but this was somewhat improved for the MSX with the addition of stopper collars (the annular disks in the picture above).  More on these in the installed photos below.

Here the anti-sway bars have been installed.  The blue stoppers sit between the plastic brackets which create the pivot points on the bulkheads.  These stoppers keep the sway bar centered and prevent it from sliding side to side during motion.  Note that the front sway bar has changed shape.  The front sway bars beginning with the TRF 414 and through the 415MS had two bends on each side, but the newer front bar for the MSX has only a single bend on each side like the rear bar.

The glorious TRF shocks are largely unchanged from the 414M except that the threaded shock perch changed from two pieces to one piece with the 415 and then added an internal o-ring (shown in the exploded view above) with the 415MS.  Why?  The TRF 414 used plastic spacers to change the preload on the shocks.  The 414M added two-piece threaded rings instead.  The advantage of having two parts is that they could be jammed together tightly after adjustment to prevent them from rotating during the vibrations and impacts of driving.  The 415 made this simpler with only a single ring, but now it was susceptible to unwanted movement.  The 415MS solved this problem by using a longer ring with an internal o-ring groove.  The o-ring interferes slightly with the threads and adds friction.  This provides enough resistance to prevent unwanted movement while still allowing easy adjustment.  The same design is still in use today.

These photos show the parts for the rear shock assembly (left) and their completed installation (right).  There are five possible shock attachment locations.  The outer holes are for the body posts.

These photos show the parts for the front shock assembly (left) and their completed installation (right).  There are four possible shock attachment locations.

The shock towers changed part numbers with each model update (415MSX is different than 415MS is different than 415).  It wasn't obvious at first glance what changed or why, so I prepared the pictures above comparing them (front tower on the left, rear on the right).  Red is 415, blue is 415MS, and green is 415MSX (and MSXX).  The TRF415 version had some overlapping holes at the lower edges which is a really bad idea structurally, but these holes were unused and there is no indication in the manual as to what they might be intended for.  The MS eliminated these holes and added an extra shock position option (rear) as well as lowering the position of the body posts (rear).  The MSX further lowered both the body post holes (rear) and the shock mounting locations.  The center holes on the front 415 tower, which were never used for anything and have no identifiable purpose (except a theoretical and non-existent center body post, were also eliminated.

The upper deck is another part which changed for the TRF 415MSX.  The 415 and 415MS had a much longer upper deck and also a pair of carbon stiffeners which were completely eliminated from the MSX because they would have restricted the newly accessible maintenance access to the differentials.  Interestingly, even though the lower chassis is new for the MSX, it retains the holes for the stiffener posts which are unused.  Perhaps this is to make it backwards compatible with the MS.  A rolling belt tensioner is also installed on top of the upper deck at this point.

I don't like displaying models without any motor in them, but I also didn't see any reason to spend a bunch of money on a motor which would never be used so I just put a standard silver can in here as a placeholder.  This model did not come with a pinion gear so I added my own 39T pinion which is in the middle of the usable range (23T-50T).  In combination with the belt ratio this gives us a final drive ratio of 35:16 x 102:39 = 5.72:1.

I also threw in a cheap servo to hold the steering in place.  This model uses aluminum servo mounts and a high torque servo saver.  The servo mounts are shorter brackets new for the TRF 415MSX.

The bumper mount and body posts have been the same all the way back to the TRF 414, but the undercut shape of the foam bumper is new to the TRF 415 line.