Kyosho Turbo Optima Project

Page 1: Building the Chassis

The Turbo Optima box is not super exciting on the outside. In is a fairly plain black box with a photograph of the product. On the inside, however, things are quite a bit better. Here we see the gorgeous gold anodized parts presented in blister packs along with some of the special parts like the pulleys and belt.

The parts inside the box are sorted as shown. There are series of loose plastic parts trees and also a set of 6 sequentially labeled bags of hardware and specialty parts. Step 1 begins with the parts for the differentials. Each step shows the parts required for that step so you can find and arrange them ahead of time. Kyosho instructions are very well done and clear with excellent graphics. The first step also includes the hex keys and some nice black grease.

The front and rear differential internals are identical with metal gears, but externally the rear incorporates a spur gear. This is a sealed diff unit so you can load it up with grease or oil as you choose.

The differential housing is plastic and supports ball bearings. The tiny cog you see is an idler support for the belt. Not shown is an another metal internal gear driving the differential. Shown on the right is the completed rear differential. The protruding shaft drives the smaller gear and will support the slipper clutch.

Now we get to break out those incredible gold parts. Note that large size of the bearings. The parts you see here are from Bag B and include the undertray and motor shroud. The small bottle is thread lock. The first thing to install is the front suspension bulkhead.

These long channels protect the belt and also serve to separate the front and rear gearboxes. There is still play in the joint at the front which allows the front gearbox to be slid to tension the belt. The right hand image shows a part which was bagged separately, apparently as a last minute replacement for the upper belt guard. I studied it thoroughly for quite some time and can't find any difference between it and the one that came stock in the box. It is possible that a couple of tiny screw holes in the back have gotten smaller, perhaps to make the screws grip more tightly.

These parts are for the rear gearbox and form the major part of the structure of the back of the chassis. The curved part with holes is the motor shroud and presumably the vents are for cooling. The large flat plate is the motor mount and right hand rear gearbox attachment. The pin you can see sticking out of it does not spin, it is a support for an idler gear.

Now the undertray has been installed along with the longitudinal chassis rails. The rails are intended to carry all the load (in fact the Javelin doesn't even have the undertray) and the tray is there to keep debris out. Protective undertrays tend to be polycarbonate, so the fact that this one is formed aluminum is impressive.

Time to open Bag C which contains gold supports for the front bulkhead, steering, and suspension support parts. The first thing to build is the front skid plate as shown. This protects the underside of the front gearbox and serves to lift the chassis over any obstacle that makes it between the tires. However, the front bumper will later extend even under this, protecting it from scratches. The slots you see in the bottom are to slide the whole front end to adjust belt tension.

Here the skid plate has been installed along with the side supports for the front gearbox. You can also see the upper suspension arm supports if you look closely. The front sway bar pivots right at the front of the chassis.

The slipper clutch is pretty conventional although it may have been a bit of a novelty at the time. It uses a slipper pad (essentially a brake disc) on either side of the spur gear. The slipped plate is keyed to the flats on the shaft, but the gear is not. This allows the gear to spin freely unless there is enough clamping across the pads to produce adequate friction to transmit torque into the plates. The compression spring used to adjust preload is actually installed on the opposite side of the gearbox which I like because it reduces how far the adjustment nut needs to hang out from the chassis.

Bag D contains the parts for the front suspension and both shock towers. I've built some links which will be used as upper suspension arms and steering tie rods. The rod ends are plastic but feel strong.

Here I've installed the front and rear shock towers which each consist of flat anodized aluminum plate complete with holes and countersinks. A close look at the rear shock tower will reveal a note near one of the holes which says "MAX 12mm". Presumably this is because using a longer screw here would cause it to poke inside the gearbox and foul the differential. The shock supports are just cantilevered screws which is not my favorite. I would much prefer they were in double shear, but I'm sure this is adequate for the weight of the buggy.

Now I've installed the lower suspension arms which are single piece plastic molded parts with a significant amount of diagonal bracing. The upper arms are just rods which means the lower arms need to carry all the thrust and braking forces. In the left hand image you also get a clear view of the installed slipper clutch.

The steering is fun to build. The system uses C-hubs to support the steering knuckles and kingpins. The bearings and drive cups and housed within the knuckles. The knuckles are metal and appear to be die castings. The right hand image shows them installed. They aren't gold like the rest of the aluminum parts, but they still stand out from the black plastic.

From above you can just barely see how the steering works. The dual bellcranks are under the upper belt guard and supported only at the bottom. The servo saver is built into the left hand crank. The right hand image shows the steering tie rods attached and the sway bar links as well.

Bag E has the parts for the rear suspension which don't look like much because the main parts are plastic and on separate trees. Note the complicated geometry of the sway bar.

The lower oblong holes in the rear uprights are for inserts which can be swapped out to change the rear toe angle. By default the 2º toe is used but parts are included for 1º and 0º. The rear sway bar has also been attached here.

This plate is not carbon fiber but it looks pleasantly like it. This upper plate stiffens the chassis and provides a mounting surface for the receiver and ESC. The receiver sits on top and will be hidden by the driver. The ESC adheres underneath. The "wings" you see protruding are supports for the Velcro^® straps which hold the battery.

Finally we get to build those beautiful shocks with the parts from Bag F. There are quite a lot of O-rings and other miscellaneous little parts here. Even the springs are gold! Among the parts are those needed to build the tools shown at the right which will assist with assembly. The rectangular slot in the wrench fits over the head end lug, and the Glaive shaped tool fits over the rod end gland. With both tools you can effectively tighten the ends of the cylinder.

The aluminum parts of the shock consist of only two parts because the head end plug is integral to the cylinder which must everything must be inserted from the rod end. Note how much longer the rear shocks are than the front. The picture on the right shows one completed shock next to an exploded view making it clear just how many parts there are. I count 18 parts per shock. The part you didn't see is the almost invisible gasket sitting just beneath the rod end gland. The front piston heads have 2 holes and the rear have 3. Each is retained by 2 E-clips. There are also a pair of O-rings and a couple of rod guides inside each gland. Both front and rear shocks have a spacer on the outside to limit compressed length, and the front shock also has an internal spacer to limit extended length. The threaded collar on the outside of the cylinder is used to adjust spring preload (which controls ride height) and contains another O-ring to add some friction to it doesn't vibrate an unthread while driving. The shocks use very thin 7.5wt oil.

With the shocks installed, the chassis is nearly done. Other than the electronics, it might not be obvious what is still missing at this point.

Time to install the rather substantial front bumper which will protect the front tires from direct impact. It is well anchored to the chassis and isn't coming loose any time soon.

With the rolling chassis done, I can get started on the electronics. A light buggy like this doesn't need a fancy or high powered steering servo, but the model is just so pretty that I wanted something special. I knew Savox servos use a nice orange aluminum case which I was hoping would match the anodizing, but it didn't quite. I bought a sheet of gold foil as shown on the left and used it to wrap the metal part of the servo. To do this, I had to take the servo apart, wrap the center portion, then put it back together. The result on shown on the right which looks pretty great if I do say so myself.

Much to my chagrin, it turns out you pretty much can't see the servo case once it is installed in the chassis. Oh well, at least I know it is in there. (Hard to justify that high dollar, titanium gear servo though.) On the right you can see the power system I got for this model. I wanted a genuine Kyosho Le Mans system, but updated for modern times like the buggy. This is a sensored brushless motor and controller. Let's see what's inside.

Regardless of how this motor might perform, it looks great with the shiny petal can and chrome label. This is a 15.5T motor which is the hottest recommended for this model. On the right you can see the motor installed along with the stock 25 tooth, 48 pitch pinion. The model will accept a wide range of pinions from 16T - 31T. The spur is the only plastic gear in the model. Note that I'm not that bad at adjusting gear mesh, I just haven't done it yet.

Look at this tiny, chrome silver controller! I really like how small it is, and the size is convenient because there isn't much room on this chassis for electronics. I'm not sure how they did it back in the day with a mechanical speed controller. I used to servo tape to stick it to the bottom of the chassis plate and soldered on my standard XT60 connector.

I had to cut each wire carefully to size and solder so that they wouldn't interfere with anything. This chassis is really designed for a brushed motor with wires coming out the end rather than a brushless motor which has them coming out the side, so there isn't much room available. I ran the sensor wire under the shock tower. The final picture shows the rolling chassis with wheels, tires, and a hard battery pack installed. At this point it can be driven.

Update:

For my replacement Turbo Optima after the fire, I got some gold aluminum wheels and applied the white lettering on the tires via sticker (which I hadn't noticed existed the first time). I don't think the stickers will stand up to actual driving though, so I got an extra set of tires and I will use the original white wheels with those tires when running the model.

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