The Champion That Wasn’t: Kyosho 1987 Worlds Optima Mid LWB Custom

[Anthroxoid 190]

Phew, what a long title. Sorry for that. 
 

The original Optima Mid was IMHO the best 4WD RC buggy ever released in the mid-80s. Yeah, the Schumacher CAT beat it for first place, arguably superior in a few key aspects of modern buggy design as well as having a phenomenal driver at the helm. 
 

When Kyosho released the Optima Mid to the masses the kit was more affordable and obtainable, maintainable, and durable in most aspects aside from perhaps direct front A-arm strikes due to the crash back system that the CAT utilized—a clever application of o-rings set to fold the front suspension rearward and then allow it to rebound into running order after a collision. This feature along with the longer wheelbase of the Schumacher, perhaps in addition to the CVDs utilized by the Schumacher CAT prototype, and even the ball differentials set it all a bit farther skewed towards a truly skilled builder and serious racer. Despite these features the Optima Mids got sold well and remain to many the first “modern” 4WD buggy that many of us got our hands on. 
 

Kyosho recently released its 60th Anniversary 1987 World’s edition of the Optima Mid prototype that lost to Cecil’s Shumacher masterpiece. The ‘87 Mid is a glorious kit on its own, utilizing carbon components and gunmetal anodization for all of its aluminum structural components and a saw-off Optima Pro body (sans undertray) under the emerging standard of large rear wing. What would happen if we took as many aspects that gave the Schumacher CAT the dirt track advantage over the four Mid prototypes that raced against the CAT and applied them to this lovely, Kyosho anniversary kit?

It all begins with a very small box, tightly packaged with parts bags like a modern Associated or Losi racing buggy’s volumetric efficiency of production and distribution. There’s no blister packaging to be seen in static glory here but there is a fantastic kit contained within. It contains the prime ingredients to build a champion that never existed. 

—Xoid

[Saito2 7654]

Great start to a build thread. This is the kind of response I was hoping to get for my somewhat dead "What made a a good 4wd buggy" thread. I really like comparing the technical aspects of these old race designs to see what made them tick and how they compared to one another. My Tamiya obsession aside,  given the choice of the Schumacher, Yokomo or Kyosho Mid BITD, I would have chose the Mid. It was a great, well built, solid kit that you could get parts for here in the States. Looking forward to your progress.

[BuggyDad 5904]

Looking forward to this. 

One of the tinkering projects I had in mind myself was to make my own carbon LWB chassis plates for my Mid. I see the LWB belt and a lexan cover for it are readily available. Interested to know what else is required? I suspect on its simplest level it could be achieved with just these parts although I think I read they changed some other stuff beyond just the wheelbase? 

[Anthroxoid 190]

8 hours ago, Saito2 said:

Great start to a build thread. This is the kind of response I was hoping to get for my somewhat dead "What made a a good 4wd buggy" thread. I really like comparing the technical aspects of these old race designs to see what made them tick and how they compared to one another. My Tamiya obsession aside,  given the choice of the Schumacher, Yokomo or Kyosho Mid BITD, I would have chose the Mid. It was a great, well built, solid kit that you could get parts for here in the States. Looking forward to your progress.

Thanks! I probably hadn’t been a member of these fora when you posted that thread but I’ll look at it because it sounds like your conversation will likely give me insights beyond my own observations.
 

6 hours ago, BuggyDad said:

Looking forward to this. 

One of the tinkering projects I had in mind myself was to make my own carbon LWB chassis plates for my Mid. I see the LWB belt and a lexan cover for it are readily available. Interested to know what else is required? I suspect on its simplest level it could be achieved with just these parts although I think I read they changed some other stuff beyond just the wheelbase? 

Check out the parts over at RCmart or Kyosho America. You’re correct in that if all you want is LWB and the option to layout major components like a modern buggy then the carbon plate LWB offerings will work. There are small placement changes between the vintage Mid and ReRe Mid’s chassis holes but anybody here could fit one to the other assuming that they had a drill and countersink. 

Got the bench cleared off in ritualistic fashion last night so the build begins today.

 

[toyolien 5908]

Looking forward to this one. I'm about to start a Mid myself. The Mid and the CAT XLS were the first two buggies I ever saw racing....

[Big Jon 686]

Glad that you’re posting this build, my brother!

I’m hoping that you’ll give us some comparison shots next to your CAT and Optimas…

[Anthroxoid 190]

Some thoughts as a preface to this build: First and foremost is that it was far too expensive to perform on multiple ‘87 kits or even base Oprima Mid ReRes but it sure has been fun gathering parts from across the world to pull it off and I’m still waiting on rear CVDs, some aluminum parts from Yeah Racing, and hunting for a wheel set that I think will end up being both runner and displayworthy parts. 
 

We start here:

This lineage was too tempting to not include as a reflection on progress with belt-driven champions and shaft-driven bashers alike. The stash prior to deployment:

what a pile of stuff!

Here’s a brief walkthrough of the drawing board thus far. The Long Wheel Base conversion kit in “classic” (not “racing”) flavor for the 2022 Optima Mid is the most immediately obvious inclusion of aftermarket changes. I’ll follow with some comparisons of weight and dimensions though suffice to say it solves the layout and component protection issues that the base Optima Mids suffer from in allowing the builder the peace of mind in having every component extremely well protected by the 3mm, 3K carbon plate. It is extremely rigid and fits perfectly inside of a LWB Turbo Oprima Mid Custom undertray as Exo Design seem to have simply copied the profile of the original aftermarket parts from Kyosho and others.

This adds 20mm to the wheelbase, and there’s an equally important improvement option aside from straightaway stability in that the builder can choose to mount battery to one side of the belt casing and Servo/ESC opposite. This lowers the CoG quite significantly due to the height of the belt race. The kit does include carbon plates to build up battery mounts for the traditional rear, horizontal layout in case you decide to stretch your Optima Mid and plan to compete in Vintage races where adhering to heavy, period-accurate motors and batteries may be mandated. 

Some observations of what weight penalty you pay for the layout options and strength offered by running a giant carbon fiber plate as your bottom chassis plate:

Note the lovely dado milled out of the factory carbon/FRP chassis to aid in guiding the belt. This decision gives me shivers as it creates a horrible fracture line for stress concentrations to handily shatter the bottom plate. If you keep your ‘87 Mid stock, or migrate this chassis to a regular Mid I’d recommend the addition of a full undertray as well as standing thst undertray off of the carbon plate via thin servo tape, or similar cushioned, double-sided adhesive. I could see a single belly slap on a carpet track snapping that thing right down the groove. Oof. 

One more thought on the LWB chassis and how it will mate with the lovely Optima Pro body has me a little vexed. I purchased a LWB complete Turbo Optima Mid Custom body set from Penguin. That included the body, undertray, rear wing, and even the original lexan gear cover that the Mids were shipped with. Curiously enough the undertray fits almost perfectly inside of the Optima Pro’s more streamlined chines than those of the body that it’s intended to run under. I wonder if this will create alignment issues that’ll interfere with this ideal chamfering upward towards the sidewalls of the body; this is a wonderful feature for getting over junk in the track or your own back yard:

Finally, for those wondering about wheels and tires I’d chosen several different colors of wheels from RC Mart and had even imported some Schumacher pin spikes in 2.2” to go on these, however I could’ve sworn that I’d also acquired regular Optima Mid wheels in silver for wearing Marwan’s period accurate OT66 tires or IMHO an even superior loose track offering in using Tamiya’s hybrid pin spike set from the Egress and Avante BS. I am NOT a fan of the ugly mixed carpet/clay narrow tires that Kyosho supplies with their Re-Re Optima Mids. They work fine, and you can see my own 2022 Mid wearing them in the first image due to a fatherly, protective (OK, let’s call hoarding hoarding) instinct with regard to keeping Marwan’s OT66 tires NiP. I’m off to find an appropriate set so that I can drive the hundred bucks’ worth of Egress tires on this machine and save the 2.2” combos for my other Mids for bashing since the tires cost far less than either Tamiya’s hybrid pins or importing tires from Kuwait.

Oi!

—Xoid

 

[BuggyDad 5904]

Excited for this build. Why do you get a significantly lower CoG with the battery alongside electronics layout vs the transverse battery behind electronics layout? I thought all parts would be at the same height either way? 

[Anthroxoid 190]

6 hours ago, BuggyDad said:

Excited for this build. Why do you get a significantly lower CoG with the battery alongside electronics layout vs the transverse battery behind electronics layout? I thought all parts would be at the same height either way? 

The belt race for a Mid goes over the top of the chassis, not under it as with a 1987 Schumacher innovation (the CAT XLS shows this clearly—the belt runs under the chassis and is protected by the undertray) so this requires mounting the battery up on blocks with the Optima Mids and it’s above the chassis in order to clear over the entire lower belt race and its protective dust cover. Landing your power source on the lower deck drops the battery a fat quarter of an inch. If you were set on LiPo but still wanted classic battery positioning then investing in a flat 2S would help mitigate some of this change, however doing so while also clamping the battery flat to deck would be even more ideal. There’s nothing that we can do about getting the gear train and motor lowered down into a laydown arrangement short of making a different rear transmission and I feel at this point it’d lose the heart of what made the Optima Mid the Optima Mid. It runs small spurs, a second set of counter gears to further reduce gear ratio and then takes power off of the rear differential and loops it to the front differential casing for full-time 4WD. 
 

My friend @Big Jon pointed out that the 2016-era Losi 22-4 may have been the pinnacle of mainstream belt-driven 4WD buggies as designers struggled with mass distribution and motors’ rotating mass effects to a moving (and often flying) vehicle, though it was a complicated 3-belt system with multiple requirements for tensioning and extensive teardown necessary for routine maintenance. The modern Schumacher CATs are 4WD thoroughbreds and didn’t go to such odd extremes in search of balance. The L1 Evo and L1R bury the motor forward and let into the chassis for extreme low CG, utilize minimal gearing and instead of having a slipper or center diff part out freewheeling power to the loosest tire or front end, they can instead opt to keep the front wheels always absorbing the full allotment of horsepower and torque that your motor can give while allowing looser slipping in the rear ball diffs. This is more akin to migrating into a FWD solution but is user tunable quite easily for different traction scenarios. If you were driving on ball bearings you might want to have that rear end slip quite a lot to reign in fishtailing, then something inbetween you’d let the rears keep pushing in order to dial in your rear drift. That’s a bit of an oversimplification but with belts the tunability took a long time to develop—much, much longer than harnessing the efficiency of belt driven systems as the latter here was immediately obvious of chain and shaft of the time.
 

The Optimas (all of them) never had this option for easily customizing power differential. The user could over or under drive one end of the vehicle on loose dirt creating a similar effect by say having the front end pulling harder than the rear on loose surfaces but it’d be a distaster on your belt drive to try this on high grip as the belt teeth would need to jump or just start burning your ball diffs with a lot of slip in the rear, whichever link in the chain fails first though simply put you’d be maintaining your buggy as much as driving it. I intend to keep my ‘87 Worlds Optima Mid Custom balanced with ball differential finesse, and to let the slipper clutch protect these belt teeth from being shorn off too easily. I can foresee the need to rollback the front ball diff to a packed gear setup if the Optima ball diffs won’t tight well enough or take too much fiddling between drives when asking them to absorb brushless power. 
 

—XOID

[Anthroxoid 190]

Here’s a tiny update with more to come this evening:

I had a small window to crack open the kit so took a dive in at what I consider the hardest things in RC: ball diffs. These Kyosho adaptations are lovely and the quality control is very good. The need to CA on the rear flange of the belt tracks leaves a funny taste in the mouth but some very steady application of medium CA, assembly of the diff cases, then resting them glued-face down on the silicone mat makes for a clean build. 

I’m not sure about you guys but ever since my very first RC car—a Tamiya Fox—it’s been customary to futz around with tires before building the kits. I dunno if it was Mould release fumes coming out of the freshly opened kit boxes or just knowing that they needed to be seen put together ASAP to ***** grippiness, but tires still go on first.

The chances that I may end up using these weird, creamy, mint green Ultima wheels on this Anniversary “pre production” Optima Mid increased after trying the Tamiya Avante 2011/Black Special/Egress (and others) hybrid pin spikes on the Kyosho wheels. The fit is good. They are also too soft without foams so if I go this route they’ll need to be cushioned by likely just scavenging the kit inserts from the weird carpet block ‘Sand Supers’ that Kyosho keeps polluting their ReRes with. They’ll also need to be glued due to the lack of deep grooves in the wheels and stupid power available from brushless motors. 

Months after initiating this project, I’m still trying to get some vintage 8-spokes in billet to both look great on the shelf and to allow narrow fronts without jumping up to 2.2s. If anyone has ideas for different 50mm wheels please do throw them my way—I’d very badly wanted to utilize the Lazer’s Maddox wheels (yellow Kyosho dish wheels) and to add a bead of mint green to their rims but those things are hard as all #&$* to locate. 

This looks pretty convincing. Sorry for the reflections as the lighting in my shop is quite intense, though you can see the 1987 Kyosho OT66 tread pattern inside of Marwan’s packaging in the background.

On to the ball differentials. These were a first for me because I’d jumped from Kyosho to Yokomo for 4WD buggies in the early 90s and never got to learn how Kyosho built a ball differential. There is a fair amount of trust put in the builder to do these correctly when compared to modern diffs; the thrust bearings are not grooved and are very small diameter, there are two grease types utilized (that’s not surprising but easy to do wrong—true story!), everything is handed, and lastly there isn’t a single spare ball provided for either the differential gear or thrust bearing that you build. It was quite fun. Oh derp—perhaps there is a spare diff ball or two in the spare parts bag that Kyosho always included with their models. I’ll update later after taking a peek.

…getting closer here…

These should work. They’re rather finely tunable to my surprise. As such I can tell the difference between which I tightened for the front as it’s a bit more resistant than the rear as left nice and loose—but not slippery and they feel perfectly smooth like a Schumacher diff. Additionally, the pressure plates can be flipped over once these break in too far to lend some longevity but I don’t want to groove them right off of the bat with a berserker’s trigger finger. We’ll just have to see how it goes.

More soon, as Bag B gets straight to the joys of building the belt drive on both ends and I spotted and included factory hop-up already in the use of an ultralight lay shaft. The ‘22 and vintage Mids use heavy but nicely hardened steel axles for these. I’ll look it up though this one doesn’t even register in my palm, so may be a titanium alloy.  
 

—XOID

[Anthroxoid 190]

OK, I was able to sneak in another few minutes. Here was the first option part conundrum where the rear transmission casing assembly progresses there’s a brace which will connect the lefthand side of the case to the upper chassis deck. The kit provided a lovely, gunmetal part of anodized aluminum. I was very tempted to use it because of the coloration until comparing it to the same part that came with the chassis conversion. That is a carbon fiber plate and the latter is significantly lighter. I’d not have guessed that since it’s such a small part. This becomes a theme the farther that I look into the manual as the supplied Kyosho carbon parts are also thinner and much heavier than EXO’s. My guess is that the Kyosho plate is resin-laden FRP core with decorative face veneers of carbon fiber. I’ll try to evaluate this further as I destroy a part for Science.

Anyhow, some minor progress:

That’s the hardened steel counter gear. It replaces a rather heavy, pot metal part.

This little transmission case brace is nearly massless. The Titanium shaft with belt idler and second stage reduction gear, sadly a soft metal part requiring stocking of a few extras. It can be flipped over to get two lifetimes from one installation but it’d be nicer if one simply didn’t have to open the transmission up, well ever. To that end, the quality rubber seals on the bearings should keep crud out within reason.

As the components begin dropping in we can see the Optima Mid’s update: it’s an eccentric assembly with ~6mm ball bearings meant to allow the user belt tensioning instead of requiring a belt replacement as stretch sets in. I believe that we also used to slide the front gearbox in addition which was a bummer after driving into a tree and losing belt tension while out bashing.

Possibly my favorite sound in all of RC is this transmission silently pulling along an electric buggy at speed. Much more remains although I’m already suffering from the early phases of postpartum  so this build will be intentionally drawn out, otherwise I’d have to move on to something resembling chores. 
 

—XOID

[BuggyDad 5904]

10 hours ago, Anthroxoid said:

The belt race for a Mid goes over the top of the chassis, not under it as with a 1987 Schumacher innovation (the CAT XLS shows this clearly—the belt runs under the chassis and is protected by the undertray) so this requires mounting the battery up on blocks with the Optima Mids and it’s above the chassis in order to clear over the entire lower belt race and its protective dust cover. Landing your power source on the lower deck drops the battery a fat quarter of an inch.

Ah yes. Of course. I forgot about that. 

[BuggyDad 5904]

Incredibly in-depth descriptions and knowledge here. I'm looking forward to the rest of the build!

[Anthroxoid 190]

11 hours ago, BuggyDad said:

Incredibly in-depth descriptions and knowledge here. I'm looking forward to the rest of the build!

I have no idea what I’m doing but thank you for reading my build log. 

[Big Jon 686]

Ugh those fiddly thrust bearings. Even with sticky grease, good tweezers, a 10x visor, and good lighting, they’re the hardest thing for me, especially without grooved races.

Belt cars, for whatever reason, scream “race car” to me. This current generation of shaft wheelers just doesn’t seem as cool as the previous belt cars, and they sure don’t whisper around the track.

[Anthroxoid 190]

27 minutes ago, Big Jon said:

Ugh those fiddly thrust bearings. Even with sticky grease, good tweezers, a 10x visor, and good lighting, they’re the hardest thing for me, especially without grooved races.

Belt cars, for whatever reason, scream “race car” to me. This current generation of shaft wheelers just doesn’t seem as cool as the previous belt cars, and they sure don’t whisper around the track.

Oi, you’re not kidding. I used my magnifaction lamp and picked each thrust bearing ball out of a grease cup top using a #11 X-Acto tip, then carefully transferred them one by one into the awaiting blob of black grease on the studs. They were pretty manageable and as you can see the head of the stud is broad enough to balance the sub assemblies upright on the bench while preparing for the diff assembly. My only guess as to why they don’t have grooved races is cost of machining hardened steel parts this small as the thrust bushings are a mere 5mm diameter!

Well you know that I’m a diehard fan of belt-driven cars too, though the Associated B74 shaft drive is so perfectly manufactured that a completed chassis sans wheels and tires will actually keep freewheeling after you flick the spur gear. They’re by far the most well-fitted shaft-driven systems I’ve toyed with straight OOTB, even outdoing Losi’s 22X4 for fitment. The latter is a superior car for different reasons and their drive trains are near-identically implemented 3-diff systems so it could be higher ABEC ratings in the AE bearings or bearing grease, gear cut, or gap. I’m not sure but before building a B74 I’d never once seen an RC car’s transmission run so freely prior to extensive tuneup such as bearing grease removal and parts break in. 
 

Here’s a nice clip of a CAT L1 EVO screaming “race car” to me!

Casual Sunday driver here.

[Anthroxoid 190]

This afternoon was a good moment to focus on the Mid for a couple of hours. Following closing of the rear casing, the manual has you add shock stays, suspension pins and some other bobs and bits. The front goes together while cleanly capturing the belt. If it looks like this may be an easy-access front diff, no, not at all. It’s going to get locked under a dozen other features requiring a near total teardown of either end of the buggy for maintenance. That considered you really want to assemble this kit cleanly on first pass.

Kyosho’s FRP molds have tradionally always been excellent with near perfect closures on all registered parts and on spru trees with minimal injection blemishes to remove. The resin used is really tough and as you shave down any spru flush with any component it becomes immediately clear how much fiber is present within the plastics—they’re vastly harder and stronger than say a greasy Tamiya chassis from this era. It’s one thing that Kyosho had a really early eye on in making their parts strong. Conversely, they were not designed to flex like a Traxxas basher, so when you crash hard you will likely break something or with the original Optima Mid, the aluminum lower deck can be warped by a bad impact. As with most buggies of the 80s however, the main concern typically fell to protecting your uprights and A arms from brutal collisions. 

A nice and precise fitment makes for an enjoyable build.

The rear casing gets expanded to include the motor mount, the brace mentioned earlier, and some shock towers. Edit: I forgot to mention the slipper clutch. It’s shown here at the factory recommended pressure with the hex nut tightened flush to the end of the shaft:

The carbon as viewed in close is notably a superior laminate with the Exo layup as compared to the Kyosho resin core (seen as the darker interior). These parts weigh the same while the Exo shock stays are a full mm thicker—top part seen here for clarity. Something is odd here in what Kyosho sourced for their plate:

The only modifications that I felt were necessary while building up the shock towers were to replace the 3mm hardened steel nuts with Tamiya’s aluminum spacers and to also spread compression load on the carbon faces via the inclusion of stainless washers. The panheads that Kyosho includes with the kit would be fine to crank up tightly to their original aluminum shock towers but I feel that a 4mm head is too much PSI loading to apply at the edge of a carbon sandwich.
 

If you’re wondering why I haven’t edged the carbon parts in CA yet that’s because they feel incredibly tough, so I’ll first see how the kit handles some rolls and scuffs before dousing the parts in a bottle of thin CA.

Hey, this may add up to a vehicle some day!

I’m truly curious as to what makes this white, “Low Friction Belt” option part from Exo an actual low-friction part. It’s impossible to tell with fingers, that’s for sure. 
 

—XOID

[Anthroxoid 190]

A chassis and battery conundrum presented themselves as the next phase of the build. I’d had every intent to keep a shorty 2S or low CG stick smashed down to the deck with this modified chassis until looking at what could and couldn’t fit, or be balanced via opposing servo/ESC/receiver. None of my long hardcases will nestle up to the belt casing unless I relocate the first upper deck post.

OK, a quick recap on the build gets us to the presently installed gearboxes and shock towers, with some thought into component layout causing an ongoing pfaff:

Will this be a sufficient belt clearance? I think no, that it’ll lash a touch and will need some graphite dressing while running in.

It’s a bit of a slack belt prior to rotating the eccentric belt tensioner.

A Quick Look at the 1mm lexan parts which I’m using due to their strength. The lower belt case gets 2mm neoprene closure strips before being clamped down to the chassis:

Another brief moment of befuddling was presented by the resin-vs-anodized aluminum rear deck tower. The plastic part weighs in at 8g and the aluminum is a hefty 11g even with all of that lovely webbing. Let’s use the heavy part because it’s so pretty!

All four types of shortie LiPos in my stash are all rather heavy, 6+Ah affairs so this got me scratching the noggin and looking at the tried and true transverse pack installation. Despite Exo showing their chassis sitting on a SkyRC weight distribution scale at exactly 50/50 with near perfect lateral distribution as well, I’m not sure how they got there. Perhaps it’s a really low capacity battery in their ad or just plain ol’ false adverting, though the chassis conversion can take any hardcase from the inventory across the belt race.

The aforementioned weight distribution dilemma. What is a mother to do? At least there are options here, though I may be on the hunt for a little bit of brass to keep things on the level, or perhaps relocate the front deck post to allow longer packs to seat between the gearbox and front edge of the chassis. That seems a bit silly when this can work:

Here’s a sneak peek at the chassis. It’s nice and light and very rigid even prior to anchoring the top deck to the front diff case. A cursory tensioning of the belt reveals that there’s going to need to be a bit of a break-in period on this model before it really takes off. Perhaps I’ll slack the included belt tensioner and look at drawing the slack out in the center of the buggy with an overhead bearing. I’ll begin with the included tensioner a bit slacked from the current images and reassess from there:

Onto the suspension! Edited for massive English failures.

—XOID

[Anthroxoid 190]

There’s isn’t much to say about the front suspension other than if you’ve built any Kyosho Optima this will all seem familiar to you. I do appreciate that the aftermarket sway bar is so closely distanced from the front dogbones though all points of suspension articulation as the clearance is minimal:

 

No fewer than three E-clips transmogrified before my very eyes during this portion of the build. 

[Dtn8. 9]

Thanks for sharing your build with such a high level of detail, I too am looking to build a LWB from either a rere optima mid or the 60th edition, regarding the EXO conversion kit what are your thoughts? 

Regarding the battery placement I am also looking to have to deal with normal sized batteries as I currently don't own any shorty packs, so I am interested to see how you tackle it.

With the bottom deck belt cover, is there any concerns that the belt is exposed at the rear gearbox? 

looking forward to future updates. 

[Anthroxoid 190]

12 hours ago, Dtn8. said:

Thanks for sharing your build with such a high level of detail, I too am looking to build a LWB from either a rere optima mid or the 60th edition, regarding the EXO conversion kit what are your thoughts? 

Regarding the battery placement I am also looking to have to deal with normal sized batteries as I currently don't own any shorty packs, so I am interested to see how you tackle it.

With the bottom deck belt cover, is there any concerns that the belt is exposed at the rear gearbox? 

looking forward to future updates. 

The classic version of the LWB kit is really nicely milled and is certainly a good deal considering just how much carbon conversion it lends in addition to hardware, and the quality is superb. If you scroll upthread a bit you’ll note that I’m comparing Kyosho’s carbon quality to that of the EXO kit and the latter is lighter, thicker, and stronger. I’m fairly certain after doing some composites work over the years that Kyosho is using more laminations of an FRP, or carbon hybrid with too much resin, then plating that within two face veneers of standard 3K weave for appearances. The EXO carbon is all 3K laminations and the carbon/resin ratio is notably stiffer in addition to being lighter. Either would work, just something to take note of. The upside is that if you have two or four Mids in your garage then you can move a lot of the carbon over to one of the standard kits for “free” hop ups. 
 

Re: battery placement, all eight of my shorties are over 6 Ah and they are simply too heavy to be counter balanced by racing ESC, servo, and small receiver due to the Mid’s very good central motor positioning. If the miter was off center then maybe it’d be possible. I don’t want to buy low capacity, low-C rating shorties so a traditional mount seems likely. I do have time to poke around at it before deciding. Perhaps I’ll run a saddle and get the best of both worlds. 
 

If you want to make be,t closure easy on yourself then purchase one of the purpose-made LWB belt cover kits. I see that Blue Groove is making a lexan pull of the original race covers, and the upper would me smart to employ for lower CG, but I’d keep the provided hard cover for the bottom chassis plate due to the simplicity and rigid protection that it oxfords. Yes, it does leave 20mm open underneath the motor. This is a problem for me as I’ll introduce graphite powder on the belt’s backside and don’t want any dust getting drawn into the tranny at any location. I’ll simply take some scrap lexan and form a small bridge to cover these gaps and use Kapton tape elsewhere as needed in order to complete a seal while leaving it easily serviceable with nothing glued in.  
 

With that in mind I’m sure that there are many ways to solve all of these problems and will look forward to seeing how you tackle them on your own custom LWB. Thanks for reading my build log. I’m concussed and building my kit slowly with two broken shoulders in addition to the TBI, so my updates will be slow due to those injuries and seeing as I’m also awaiting a whole bunch more aftermarket components from various countries I’ll post as I go. I do very badly also want to build my Tamiya Egress and may dither if shipping delays get extreme, though I’ll take this to at least a base runner before dropping on more bling. 
 

—XOID

[Anthroxoid 190]

13 hours ago, Dtn8. said:

Thanks for sharing your build with such a high level of detail, I too am looking to build a LWB from either a rere optima mid or the 60th edition, regarding the EXO conversion kit what are your thoughts? 

Regarding the battery placement I am also looking to have to deal with normal sized batteries as I currently don't own any shorty packs, so I am interested to see how you tackle it.

With the bottom deck belt cover, is there any concerns that the belt is exposed at the rear gearbox? 

looking forward to future updates. 

Here’s a high-resolution look at the present gap below the motor. Click to embiggen:

[Anthroxoid 190]

Here’s a small update for morning:

 

Most importantly, I must’ve not fully seated a bearing in the rear transmission casing because after assembling a few parts of the front end I wanted to check to see how true the single-cardan & dogbone shafts ran both straight and canted. I always check this by pulling the belt back and forth. The friction on the belt race went from feeling slightly draggy when suddenly I felt a small click in the rear case as a bearing fully seated and then the full 4WD drivetrain including both front knuckles castered a full 45° in either direction began to run with dramatically less friction as an Optima Mid should feel smooth right out of the box. 
 

Takaway: don’t be quite as gentle as I was in seating the gearbox bearings. They can appear seated when not fully bottomed in their respective apertures and this causes a lot of drag. A first for and surprising mistake for me, so lesson learned.
 

Some time go I’d made an order for many of the aftermarket parts that I wanted to add to this kit and I chose to the Yeah Racing turnbuckle set. They’re a really standard style of titanium turnbuckle and take a little wrench gripping to get your ball joint sockets threaded.
 

I’d like for this kit to sit on its own tires before my wheels and other trinkets arrive so I’ve just built up the front and rear with the included nylon FRP suspension components and cast aluminum hubs. Regarding the latter, if you want to save money but still show some polish these are perfectly serviceable parts, and some time with a Dremel and buffing wheel would have them gleaming:

The buttocks coming together sans linkages and the rear sway bar. Note that the included rear hubs are a bit of a snug fit when articulating the freshly assembled suspension. You may be tempted to sand down the face or faces of each hub but do not, there’s already a considerable amount of slop in all Optima suspensions so let the plastics break in over a run or two. You could similarly dash some graphite powder in, but don’t grease the pins or the plastic faces or they’ll collect a nightmarish dirt rouge and really abrade your parts slack. Dry lube only: 

The ‘87 Mid kit comes with only front universals and in my experience the rear dogbones will get thrown eventually into the aether. This is worth the twenty bucks to import some aftermarket CVs for both efficiency and part retention. Again, I’ll complete this build as a roller and then change out parts as they arrive so it will make a decent before/after comparison for those new to Optima Mids.

Cheers,

—XOID

[Anthroxoid 190]

This morning I went back to attempting to engineer out the weight distribution problem. The best solution that I came upon was finding an ultralight low-CG 2S shorty made by Protek. It’s only 4.4Ah and 85C (yeah, right!) but is a mere 141g. My 6+Ah packs weigh north of 200 grams, so I may import one and see if I could make it work, or go with the sacrifice in runtime and punch that a larger pack would offer and mount the low profile shorty across the belt. Head scratching will continue on that front. Perhaps I’ll try three configurations, though the battery quality is important as I do intend to run this with a fairly high Kv brushless setup. More on this later.

—XOID 

[Dtn8. 9]

Thanks for the detailed reply, I will be adding the EXO conversion to the shopping list.

Yes,..... it was that photo that prompted my question, for me the conditions that I run in, it is a must to have the belt completely covered. The way that the rere belt covers are shown installed on the EXO Designs LWB photos (on their site) doesn't have me feeling confident that it would be sufficient so as you suggest I will be looking at aftermarket LWB belt covers.

Sorry to hear about your injuries, I wish you a fast recovery.