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Old 2011.03.28, 11:14 PM   #1
color01
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Join Date: Dec 2004
Location: Los Angeles (Pasadena), CA, USA
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Brian's RCX 2011 Final Setup

I've wanted to do this for quite some time, but had to wait till I had some race results to back it up haha. Documenting my setup, and setup theories as applied to a Stock-class Mini-Z Racer. It's gonna be comprehensive, so stick around for a nice long read.



Let's start by saying that this setup is geared towards the PN 80t Stock motor, and for a VERY slippery, brand new RCP track. I'm not going to cover the setup I had at the end of Saturday, only the one that I finalized on Sunday. Most of this setup was in the wheels and tires -- not only are picking the right tires and offsets 90% or more of a good chassis setup, tire management throughout the race day has proven to become increasingly important with one- or two-run tires like the PN 6 radial rear tires. So for the all-important rears, the tire of the weekend was the super-gooey PN 6 radial:



Interestingly, some of these tires were molded super-wide and super-fat (13mm wide mounted, WTF??), and if you happened to get one of these, you had to either A) make it fit, B) trim it so it fit the rim, or C) screw it and deal with the funky looks. The compound on the super-wide 6's was particularly soft and particularly fast-wearing, so I picked through several packs of PN 6's and got the ones I thought were the least "fat". For maximum grip we found that these tires should NEVER be trued: when I tried, the rubber compound turned to silly putty, warm silly putty in fact, and picked up so much track dust they became unusable. So the tires you see here are untrued, and the radial pattern has been worn down by racing action. For their part, these 6's were mounted on Atomic S6 20mm rear Delrin rims, +1.5W offset. I then spaced the rims out on each side with three PN M3 0.2mm shims for a total offset of +2.1W in the rear. These wheels are plenty strong (only have one small dent, thankfully they did NOT crack like their black plastic counterparts) and are some of the lightest rims available. A bearing was used in the rear left as well as rear right wheel: the rear right wheel bearing is a Reflex high-grade 3x6x2.5mm until I can get another ceramic, and the rear left wheel bearing is a dead Reflex high-grade 2x6x2.5mm. I tend to use bearings here instead of a plastic bushing for precision, and I pick bearings over the Qteq nut because the Qteq nut's centering mechanism could easily crack a rim hub if you crank the nut down too hard and subsequently get hit. Hence, metal bearing. Purely a precision and durability decision.

Meanwhile, The front tires were not so finicky, I used up completely only one set of PN X-Pattern 15 tires and the second pair, as you see here, still has plenty of tread left.



I really have no complaints about this tire, it's very versatile and can be adapted (read: trued or prepped) for many different track conditions. I true this tire down to 23mm (mounted on 20mm rims) when I run at Kenon, then it warms up nicely and provides lots of grip without traction-rolling or overwhelming the rear. At RCX though, not even the trued tires would hook up, so Grant's idea was to run untrued, full-height X15's on 19mm rims. The X-pattern tread reduces the amount of rubber in actual contact with the track, so what did contact the RCP heated up better, providing more grip. This was one of the primary factor in transforming my car from a mid A-Main car to a definitely-the-fastest car. The full-height X15's had a bit of scrub, but also tons of steering. The scrub wasn't excessive; it allowed me to brake using the front tires, meaning that I never actually had to get off the throttle completely, and the steering advantage took care of the mid-corner and exit.

A short discussion on front wheels and front wheel bearings. To get the maximum amount of steering with very little setup time, I decided to mount the X15's on Atomic S6 19mm front Delrin wheels, +0N offset. The zero offset reduces scrub, but increases steering responsiveness so I can chuck the car into turns faster and turn in inside other cars. Yes, it did make the car difficult to drive when the rear tires started to fade, but given fresh rear tires I had wonderful amounts and balance of steering and traction, and that's what gave me the ability to keep that TQ even after Ryan Sagisi got his binding problems fixed. As for the front bearings, you may have observed that one of them is a Reflex, the other not a Reflex. For whatever reason, two AVID bearings did not have enough material on their inner races to avoid binding up when I cranked down the wheel nut on the entire bearing stack! So, feeling adventurous I dug out some old Reflex bearings, cleaned them, put them in the outside hub face, cranked everything down and -- it works! Everything spun more freely than I had seen in a very long time. So that's the setup I'm putting in these particular wheels for the time being.

Next up, the diff! This is my personal interpretation of the Qteq/Kyosho/PN hybrid, it's been a very dependable diff and has only failed me once when the thrust bearing died on me mid-qualifier. Actually, I didn't even notice the thrust bearing failure when driving, I was bench-testing it after rebuilding my diff when I finally noticed.



To the right of the diff are those PN M3 0.2mm shims I mentioned before, for increasing my offset 0.6mm. Here's the diff internals:



Up top is the PN lightweight diff shaft, which to me is the ultimate diff shaft until somebody figures out a good implementation of the 1/12 carbon axle and hub clamp. You can see that the Qteq diff hubs are super-miniscule and definitely very lightweight looking. The hubs don't have a whole lot of traction with the Kyosho diff plates so you're supposed to glue the plates to the hubs; as you might have guessed, the left side glue has come apart while the right side is still glued tight. I will fix that, haha... For their part, the Kyosho pressure plates have held up very well, this is the only pair I've ever bought, never replaced it once this diff was finished. Notice that there is an inside and an outside groove on the left Kyosho plate -- standard spur gears like Kyosho, Reflex, Atomic spur gears cause that groove, whereas the newest PN spurs space the balls out WAY far, to the extents of the plate, and hence you get the outside groove. All the way to the right is my replacement thrust bearing, now a Reflex high-grade bearing originally in my rear axle.

A quick note about the E-clip at the end: I'm using Qteq E-clips so this may not apply to everyone, but always note which side of the E-clip is facing outwards when you remove or reinstall it. For some E-clips it seems the sharp outer edge (a byproduct of the E-clip stamping process) can interfere with the thrust bearing, making the diff feel notchy. I myself was having this problem for a few minutes till I flipped my E-clip around and that fixed everything.

As for spur gear choices, I like the latest PN 126p spur the best: although it's a bit fragile it's super-light (0.1g off from the Reflex V2 spur), provides the on-acceleration limited-slip effect I've come to rely on, and holds the bearing just tight enough that I don't need glue but the spur also doesn't wobble at all. Here's the spur in detail:



I left the balls (TOP Racing ceramics 3/32") in the LSD-action holes. This spur has the option of non-LSD holes but I've really come to rely on the limited-slip effect, especially for getting away with tuning more turn-in steering into the car (the locking effect balances out the additional steering on corner exit, it's perfect!) The balls themselves were the best deal I found at the time, they've lasted some three years now and I see no reason to switch out yet! They're each held in place by a small film of Kyosho Ball Differential Grease, this is hands-down the best grease for Mini-Z ball diffs as it's light, SHEDS dust and grime rather than attracting it, and the diff gets freer as you run it! Just don't ever blow dust into my diff, that definitely introduces more crap than the grease can handle and the only option then is to rebuild the diff entirely.

Continuing around the rear end, the diff interfaces with a very tired-looking 126p pinion (27t, for a total gear ratio of 27/106, about 3.94 which is fairly tall):



Here you can also take a look at how my PN reconfig motor mount is set up, it's actually not very special lol. I did replace the full gamut of steel screws with titanium socket-head screws, reduces weight and makes maintenance easier. The RCX handout 80t motor is completely unmodified, in fact I didn't even break it in other than running it HARD for as many laps as I could before qualifying started. I got very lucky with this handout motor -- gearing up to 3.94 made me equal to everyone in the infield but a relative rocket down the long center straight!
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Last edited by color01; 2017.04.06 at 02:58 PM.
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