Associated B6.4 / Exotek CB6.4: Build / Run / Maintenance Thread

[lambdapriest]

I’m running an Associated B6.4 with the Exotek CB6.4 chassis conversion in the 21.5t stock class, on carpet. I just got a whole bunch of go-fast bits, and I’m (over)due for my first serious round of maintenance on the thing, so I thought this would be as good a time as any to make a thread. I’d like to document my experiences driving the car (as there’s precious little info on the Internet about the Exotek CB6.4), and I think it’ll be nice to look back on this over time and see how the car has progressed. Plus, y’all are a sharp bunch, and I’m looking forward to hearing what the community thinks.

Current setup:

• Exotek CB6.4 chassis with the LCG shorty cross brace
• Associated orange front springs, yellow rear springs; 35wt Associated oil front, 30wt Associated oil rear (so, kit oil, but with stiffer springs)
• 12mm ride height
• Exotek aluminum wing mount
• Associated aluminum 0deg bulkhead
• Associated aluminum bellcrank arms
• JConcepts Fuzzbite LP front tires and Nessi rear tires, on JConcepts Mono rims
• gensacearespammers 4000mah 130c 2s lipo
• Nitro Pro shorty servo with a Fantom servo horn
• Tekin Gen 4 Spec-R 21.5t motor, 52deg timing @ 4.4 amps
• 31/72 gearing with the Associated slipper eliminator
• Hobbywing XeRun XR10 Pro Stealth ESC
• Protek fan
• JConcepts 6 1/2” turf wing
• Kit everything else

Right now, the car sits around 1474g. My goal for the current round of changes is to keep the weight as close to 1474g as possible while making enough room to run a gensacearespammers 6000mah pack; since there are so many battery mounting options with the Exotek, this will allow me to tune my car’s handling by placing a large amount of mass as close to the front wheels as possible - and a bigger pack will have lower internal resistance and will punch harder for more of the race.

I went to the Exotek chassis because I bent the Associated chassis almost immediately (skill issue); the Exotek looked extremely cool and was only $30 more than the stock chassis, so I went for it!

At the moment, the car is in pieces; I’m going to clean the bearings and try to install parts tomorrow, and I’ll take photos. But earlier today, I fixed the most annoying anti-feature of the Exotek chassis, so I figured I’d talk about it for a bit.

Jeez, this post is already pretty long, so I’ll keep it short; the Exotek kit comes with these little threaded barrels that you’re supposed to mount between the chassis and the cowl. You’re supposed to use kit screws. The kit screws that hold in the mud guard are pretty short, and the Exotek chassis is thicker than the stock chassis through that section because of the carbon fiber side rails - so TLDR, the barrels strip right out. I fixed it by cutting and grinding that particular section off of the kit side rails. The replacement barrels from Exotek are $30, because they make you buy the machined aluminum kickup along with them!

Here are some photos of before / during / after:

 

[ahr43]

A factor of interest I have found in building modern kits is that manufacturers tend to use the shortest fastener possible for [ any and all ] applications. Checking thread depth against the fastener given for a particular install, frequently thread engagement is two threads or less. Two threads of engagement being the standard for minimum fastening. Is it any wonder all metal-to-metal interfaces need gluing together with loctite?

[ Edit: my solution is to sub in a fastener that engages more threads and provides a more secure fastening. To me it's worth the extra gram or two of weight gained. ]

Looking forward to the continuing adventure of the build/run/maintenance of your buggy, lambdapriest. Good luck. 'AC'

 

[lambdapriest]

Thanks, @ahr43 - now that you mention it, I've noticed this too! I have some bulk screws; I'll have to start paying more attention, and subbing in longer ones when I can.

Loaded in a whole mess of changes on the car today. I tend to try to only change one thing at a time... but I've been accumulating parts and I'm working towards getting the car lighter so I can run more battery, so I did a ton to the thing:

• Team Brood magnesium motor plate; titanium motor screws; magnesium slipper eliminator with a Kimbrough spur gear; magnesium idler pin; titanium cross pins
• RC Speed Secrets shaved idler gear
• Fixed my camber (it was at -3, I set it at -1) and installed fresh Fuzzbite LPs up front. The extreme camber was caused by adjusting my front shock tower mount right after I built the car, without re-adjusting the camber link to compensate (I didn’t know I needed to) - and it was wearing out only the insides of my front tires. Glued sidewalls, as always.
• Popped the seals on my bearings (all of them); ultrasonic cleaner + rubbing alcohol; Sticky Kicks bearing oil before the seals went on
• Moved diff height from 3mm to 0mm (no idea why the kit setup is 3mm on a carpet car - maybe something to do with getting more forward drive out of the CVAs? I have no idea, if anyone wants to tell me, I’m all ears)
• Installed a freshly-painted JConcepts S1 body
• Rebuilt my diff with fresh oil so I could install the titanium cross pins; running 20k for now. I might try 15k soon and see how it changes the car.
• AE Factory Team +2mm rear camber link mount to keep me from bending more ball studs
• Pulled the ESC fan; it wasn’t really doing much, anyway.

Overall, I saved enough weight that I could run a Fantom 4800mah 130c 2s pack and still be at minimum weight.

The car felt more stable and more predictable - I had a few great packs, until I broke my front camber link mount. By the time I finished repairing the car, the shop was about to close - but apparently today was “redo the track layout” day, so I stayed late to help the gang tear down and set up.

The old layout was pretty technical, with a lot of tight corners and short straights; the new layout is wide open with a few long sweeping corners. To my horror, the car felt pretty bad on it! It’s pushing hard in the fast corners - I’ve realized that the car felt like it has “a lot of steering” because I was negotiating corners by braking hard and getting the car to rotate via the combined effects of “weight transfer to the front wheels” and “on-power steering”. That won’t work with long sweepers, so it’s back to the drawing board.

One of the really fast local guys told me that I could get more steering by moving the front shock mounts up a hole (they’re slammed, at the moment), so I’m going to try that. Once I get that done, I really want to experiment with the longitudinal battery layout that the Exotek chassis supports, so that I can try to give the car more steering via placing more weight (the battery) at the front of the car.

I still have a few things I can do to save weight; I still really want to run that 6000mah gensacearespammers. I ran a few packs with it tonight and it felt okay, but the lighter Fantom 4800mah battery felt better and was consistently faster, lap to lap.

I also still have some work to do on the motor - I picked up some RC Speed Secrets hybrid ceramics, as well as fresh solder tabs and a new backplate / sensor board. My motor analyzer is telling me that my eyes are relative 0, -2, +1, and it’s my hope that a new sensor board will fix that. My timing is at 52deg, but I’m only pulling 4.4A and the car is coming off of the track between 101 and 105 degrees, even after a seven-minute run, so I think that I’ve got a few more RPMs in there. Battery fade is negligible on a 7-minute run, as well, so I don’t think I would cause myself any trouble by trying to get a little more out of the motor.

Here are a few photos from my rushed, hectic day of trying to get changes loaded into the car in odd moments between work-related tasks; I’m surprised that I didn’t strip, lose, or break anything, given how much of a rush I was in all day to get the car done. I’m definitely not going to make that mistake again - the next time I have maintenance to do on the car, I’m just going to get it out of the way, instead of letting “car chores” pile up. I’ll post a photo of the actual car itself later… it’s not much to look at, just another solid-color Tamiya Champagne Gold 2wd buggy.

 

[ahr43]

Hey lambdapriest. Looking good.

One thing I like about an ESC fan has nothing to do with cooling. The vibration coming through the chassis when setting the car reminds me that it is actually switched on and ready to run.

No worse feeling than ascending the driver stand or standing for an RC drag race, pulling trigger at the tone or when the tree comes down and nothing happens. Yikes. Won more than a few RC drag races that I probably would not have won when the car in the other lane didn't even budge when the green apple lit up. Wasn't switched on.

For what it's worth. Cheers. 'AC'

 

[lambdapriest]

Hey lambdapriest. Looking good.

One thing I like about an ESC fan has nothing to do with cooling. The vibration coming through the chassis when setting the car reminds me that it is actually switched on and ready to run.

No worse feeling than ascending the driver stand or standing for an RC drag race, pulling trigger at the tone or when the tree comes down and nothing happens. Yikes. Won more than a few RC drag races that I probably would not have won when the car in the other lane didn't even budge when the green apple lit up. Wasn't switched on.

For what it's worth. Cheers. 'AC'

Oh I totally know what you mean - but I only pulled the ESC fan - I left the motor fan in.

Interesting - do drag cars not use motor fans? I mean, I suppose that makes sense - you don't want to waste a single drop of battery (or gram of weight) on spinning a fan against a motor that's only going to run for about three seconds.

Reading your posts about drag racing really make me want to do a build and give it a shot sometime - I might be convinced, if my club ever starts hosting drag events. I've done a few parking lot grudge matches with my friends, and it was a ton of fun.

Always appreciate the perspective!

 

[ahr43]

Regarding motor fans on drag cars. Not in my day of running full-prep. Current no-prep cars may have different requirements. The heavier class-standard chassis loads the motor more and demands more of the ESC. Perhaps it or they are needed for no-prep racing.

Back in the day, I raced against guys that had even removed the ESC from its case to shave a gram or two. And you're correct in your assessment of conserving the battery. Every mini-volt counts for runs that are often won by 1/100th second. Me personally, I'd always do a motor spin up before setting the car in staging just to double check everything. Most didn't. Again, they were all about conserving battery voltage for the run. What it came down to is if one wants to win races or championships. Set-up and strategy are altogether different between the two.

Hope you give RC drag racing a try if it develops in your area. It's a lot harder than it looks. Cheers and good luck. 'AC'

 

[lambdapriest]

Copied paste from the "Who was wrenching today" thread:

No photos from me for now but Christ alive, wrenching on my B6.4 is going to put me into an early grave. Running one car but also trying to do a Really Good Job of it is flat-out exhausting.

Since I last posted (and I should really talk about this in my build thread for the car), the following things have happened:

• I redid the layout on the Exotek chassis to run the longitudinal battery layout. Switched to an 80a Hobbywing ESC that I had laying around to cut weight, and the car down to minimum weight, even with a 600mah G*ns Ace battery in, but I was struggling big time to get cooling right, because I...
• Tried to rebuild my 21.5t Tekin Redline Gen 4 Spec-R - I didn't like that one of the eyes was 2 degrees off from the others, so I tried to put in a new sensor board (and threw in some hybrid ceramics while I was at it) - and somehow the timing is now worse on both the new board and the old board, it's like 5 degrees out???? (Now that I'm thinking about it - maybe the new bearings messed with the rotor position a little, and now my shims are wrong? I don't know, I have no idea.)
• So I switched back to my Reds 21.5t motor, which read out better timing data but runs about 40 degrees hotter (what the hell). The longitudinal battery layout was forcing me to run 2 fans in order to get acceptable cooling, so I decided to think really hard about how to improve my cooling.
• Wrenched on the car for hours at the club until the boys convinced me that I was going to be quicker on the stock AE B6.4 chassis, so I picked one up and we slapped it together - and right away, my consistency shot up like a rocket. Guess the Exotek is not the move.
• My club started racing on Monday nights, and my schedule allows me to be there every single Monday - but 99% of the crowd that shows up is running 17.5t, so I said "f it" and grabbed a gently-used R1 Wurks 17.5t with titanium screws, a hand-picked rotor, and aligned sensors.
• The car is now a howling menace. About 20 grams over minimum weight following a few other changes.
• That stupid Broods magnesium motor plate is about as stiff as pool noodle, so I'm back to the stock motor plate.
• I ate my fancy RCSS shaved idler gear after catching the front of the car wrong on the back edge of a tabletop that was about 1/2" taller than the "table" portion, so I get to rip the transmission case out today and put a stock idler gear back in. I picked up a carbon fiber transmission case, so that's going on, too.
• Realized that my ride height was way too low, so bumped it back up to a sane number (13mm front/rear).

For all of this toil and expense? I ran a qualifier last Monday at 95% consistency and qualified into the A-main for the first time - I've either never made it, or been in a small class with no B-main. It's coming together, and it's coming together fast.

It's not an Exotek anymore. Good riddance, too... the AE chassis is much, much more consistent.

 

[lambdapriest]

Good god... running one car and doing it right is kicking 100% of my a-double-s.

Yesterday was a disaster. I thought I had blown my idler gear, because the car was running crunchy and the spur and pinion seemed OK. I'm running a slipper eliminator with a RC Speed Secrets shaved idler gear (gotta save grams baby) and a monstrous R1 Wurks 17.5t motor, so I assumed that I had killed it; right before my main on Monday evening, I nosed in a little too hard to a tabletop that had been landed on wrong too many times, and the backside of the jump was sticking up about 1/2" above the top of the table; I caught it with my nose, and the car started yelling at me afterwards.

I had picked up the AE Factory Team carbon fiber laydown gearbox and chassis brace, so I needed to get in there anyway; so I spent the requisite several hours (probably a skill issue) swapping it over.

Naturally, when I pulled the stock gearbox apart, my idler was fine. No trace of plastic shavings. All teeth were fine. Diff case was in good shape, too.

Upon closer examination, the spur was the culprit; my pinion had been cutting into it at an angle, thanks to that stupid Team Brood magnesium motor plate. I stitched everything back up, replace the spur, and headed to the track.

I got four laps in before my car just kind of... slowed to a stop. I assumed that the pinion had taken flight (happens to me more often than I'd care to admit) - but it was still attached. Gear mesh was fine. Car was on - but when I pulled the trigger, the ESC light would fire indicating activity and the fan would dip down and the motor would make noise, but it wouldn't go.

Pulled the pinion and noticed a tight/rough spot in the rotation of the gear train. I was prepared to pull the gearbox again; step one was to remove the spur, so I did. Spun the wheels - buttery smooth.

I realized that I'd mounted the spur on backwards, and that the screws were digging in to the motor plate. Turned it around and put it back on.

Put the car back on the track, and after four laps, it started not-going again.

This might be a good time to mention that I've been running an 80a Hobbywing XR10 in the car, to save weight. This was fine when I was running 21.5t, but I started thinking that maybe the 17.5t monster with a 6000mah battery might be a little much for it. I asked around, and the advice was to try to get some cooling to the ESC.

We had fans in stock - but no screws - so I drove home to get a fan that I knew I had somewhere, and the screws to go with it. Got back. Screws didn't fit, because: of course they didn't.

Decided that maybe it was time to just bite the bullet and replace the ESC, so I grabbed a 160a Hobbywing XR10 and soldered it in (which was a process, because my stupid iron was acting up). Powered her up, pulled the trigger - for half a second, the car sounded good, and then the rear wheels just sort of lost power, and a new grinding noise entered the scenario. At that point, I had to get home, so I packed my stuff and left.

Got up this morning and started poking at the car. I decided to try a different motor, to see if that would make a difference - I desoldered the R1 Wurks and soldered up an old Fantom 17.5t that I had laying around - the motor was fine, but the mysterious grinding noise and lack of power remained.

I pulled the spur off again, to find that the "new grinding noise" was because that stupid Team Brood magnesium slipper eliminator was stripped out on the inside, and more or less spinning freely on the shaft. I replaced it with the AE slipper eliminator and spur gear, and everything sounded OK.

Then, I had to desolder the Fantom, resolder the R1 Wurks, resolder my fan to the ESC (can't get enough cooling otherwise), and redo my layout. Since the new ESC is a bit heavier than the old one, I got rid of the 24g AE weight that sits under the ESC and receiver, so the car is sitting pretty around 1500g now.

Reprogrammed the new ESC to make sure it was set up correctly. Reapplied chassis protector.

I think I have a car again; I might try to run a few packs through her this afternoon. I won't be able to focus on much until I know that the car's good for Monday's race, so I'd like to get that sorted out sooner than later.

 

[lambdapriest]

Well, car’s good; for now, at least.

Got a few packs through her on Thursday before an unfortunate mistake folded one of my arms. I switched to carbon arms a few weeks ago, and this is the first break I’ve had with them, despite multiple glancing impacts to the pipes at full speed off the back straight - and for a few bucks more per pair, the lack of slop at the front of the car is more than worth it.

Also started doing some tire testing on Thursday; at the behest of the manager at my club, I’m trying out Proline Harpoon soft fronts and medium rears. Coming from JCon Fuzzbite LP fronts and Jcon Nessi rears, the increased amount of steering is just nuts - funny how loosening up the grip at the rear will make the car rotate more eagerly - who would’ve thought! Not quite as consistent yet, but I dropped some hot laps within a few tenths of hotlaps on the old setup, and I cannot over-emphasize how much more steering I have now - so I expect those times to continue to drop.

I got the replacement arm on, and threw carbon arms on the back, as well - so now both ends of the car are less loose. My 3-year-old was helping me put the new arms on, and he noticed that my rear sway bar wasn’t actually secured inside of the gearbox - I overlooked that detail when re-assembling the car the other day. I noticed that on the new tires, my inside front tire was lifting through the corners, and I’m curious to see if that behavior is related to having my rear sway bar not connected to the car in a meaningful way.

Picked up the Factory Team X-rings and machined Delrin spacers, and I used all of my rewards points at my club to pick up the Kashimax shocks for almost no money at all - so I’m going to try to build up a second set of shocks tomorrow with the X-rings and Delrin spacers, running the same weights of oil and same springs (35wt and orange up front, 30wt and yellow in the rear). It’ll be interesting to see if there’s any noticeable difference on the track.

Looking forward to Monday’s race.

EDIT: One last sidenote - the other day, I soldered my fan directly to the battery leads, at the ESC. One of the faster locals recommended it, and my motor’s running 10 degrees cooler now, on average (down to 130, from 140). It’s actually really nice, because I can plug in a spare battery after a run to cool the car down, without having to run the ESC and receiver, or fiddle with the ESC power switch. Little things that make maintenance and running easier and faster stack up and turn into compounding advantages; the cooler I can get the car, the more quickly I can get back on the track, the more packs I can run in a day of practice, the sooner I can stop stinking up the A-main as lapper traffic.

This build / run thread is already worth its weight in gold; I am finding it helpful to document the process.

 

[ahr43]

Quoting lamdapriest out of context here: "My 3-year-old was helping me put the new arms on, and he noticed that my rear sway bar wasn’t actually secured inside of the gearbox. . . "

Natural born crew chief and mechanic there. Before long he'll be wrenching for you in the pits.

'AC'

 

[lambdapriest]

Oh yeah @ahr43 - dude's all about it. He loves helping me work on the cars. Quality father-and-son time.

 

[Lumikko]

I noticed that on the new tires, my inside front tire was lifting through the corners, and I’m curious to see if that behavior is related to having my rear sway bar not connected to the car in a meaningful way.

Sounds exactly like something a disconnected rear sway bar would do.

Connecting it will probably increase steering and loosen the rear end quite a bit.

 

[lambdapriest]

Oh boy, did it ever @Lumikko.

Fought and fought (mostly with my own incompetence) to get the Kashima shocks built, last night and this morning.

Between that, and re-attaching my rear swaybar - I was rewarded for my trouble with my most consistent day of practice yet.

The Harpoons are wearing in nicely; I have to be more delicate with my inputs, but the car is absolutely faster. I don't have to turn the wheel nearly as much, and I've realized that feeding the car smaller inputs means that I can react to unexpected situations more easily.

The best part is that I no longer have to rely on full brake to get the car to rotate, which means that I can drive more smoothly. It's far less exhausting and doesn't feel like nearly as much work.

Next up: I'm going to experiment with the Avid -2 C block to see how the car feels on 0deg toe-in, and I'm going to try drilling my own 3-hole pistons on Avid blanks; but probably not until next weekend. Racing tomorrow.