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Old 2011.03.28, 11:14 PM   #1
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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!
Brian Ma

Greyscale RC

PN Racing | My TinyRC Blog

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Old 2011.03.28, 11:15 PM   #2
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The motor pod is attached to the chassis via a PN G10 #5 T-plate. I like these T-plates a LOT, they've proven to be stiff enough that the pod isn't floppy and sloppy but they're soft enough that the vast majority of the spring and damping work is handled by the tri-shock. For RCX, I left out my grub screw center pivot, as maximum traction was the priority. I was not incorrect in this judgment, I definitely needed all the traction I could get to battle the legion of SC430's!

Once again note the thorough use of titanium screws, I think on the simpler MR02 it makes less of a difference but on the MR03, replacing all the steel screws with titanium shaved me almost 2g off the total weight. That allows me to replace all that weight in the form of lead in the center tunnel of the chassis, lowering the CG and polar moment of inertia in all axes. I have neglected to take a picture of my lead weight, but it was about an inch long strip of lead, 1.5g total weight, mounted to the chassis center tunnel via electrical tape. I didn't press the tape all the way down into the center tunnel of course, just had the tape sealing off the bottom of the chassis. This kept the lead as low "in" the chassis as possible, and possibly had an aero benefit as well. I still think CG is king, and my setups and "hacks" are always going to reflect that.

The loads transmitted from the rear pod are handled mainly by the tri-shock, which is pictured here:

This is fairly obviously the PN tri-shock system, but the side springs are 3racing AWD Black springs. By feel they are roughly in the stiffness range of PN's Blue or Orange springs, but I don't have a proper measuring tool to prove that. I believe they are similar, if not the same as, the Black springs included in the Reflex tri-shock. The spring collars were adjusted till there was zero tweak and minimal preload, then I increased the preload by two full turns to make sure the springs wouldn't pop out under normal suspension loading. You'd be surprised how little the suspension actually needs to move -- even with a soft setup it's only about 1mm each way on a smooth track! Damping grease used is Kyosho 15k grease, this seems to be the best-damping, longest-lasting grease in these little tube dampers and I seem to be able to use it no matter what the traction conditions are. I had brought some Associated 7k grease in case the car wasn't hooking up, but I never even had to use it.

Please note the angle of the side shocks: to get the most linear feel you can, you want to mount these shocks perpendicularly to their direction of action. It's not always "perfectly flat" that produces linear motion. Mine are a little angled down, probably a little bit more than the setting that would create perfectly linear movement.

Meanwhile, the top shock is also PN:

The main spring is a PN Red, to provide a little more on-power traction at throttle tip-in, and increase overall steering a little, versus my typical setup which involves a PN Blue. Meanwhile, you may notice that my rebound spring has changed! Because I needed even more rotation off-throttle but didn't want to screw too much with the main spring, I switched from a PN MR02 Yellow spring (fairly hard) to an Atomic MR02 RCP Yellow spring (SUPER hard). This way, as soon as I lift completely off the gas at speed the tail end is lifted upwards more quickly than with the PN Yellow spring, hence more weight lies over the front wheels and I get more off-throttle steering. The Atomic spring is a little short though so I spaced it out with a Kyosho AWD spring spacer (about 0.5mm thick) to get some clearance with the PN shock pieces. Once again, damping grease is Kyosho 15k for its excellent damping and longevity.

For 94mm and full-height rear tires it seems that I had to raise the entire tri-shock system to avoid suspension binding and tire rubbing. I did not disassemble this for pictures but underneath the main mounting plate (on each side) are two Atomic AWD Spring Shims, one 0.4mm (blue) and one 0.3mm (red), for a total of 0.7mm spacing upwards. Above the plate there is an additional 0.3mm (red) shim to help the PN anodized washers clamp down on the main mounting plate.

Take note of the differential axle height adjusters and the damper arm height on the PN reconfig mount, this was the lowest I could set the arm and still have sufficient clearance between the tires and the Ti-screws on the bottom of the carbon tri-shock arm. For 94mm you can put the damper arm right in the middle of its "travel" (but to get to the lower parts of that travel you need to do some manual grinding of the damper arm mount -- FYI). For 98mm I try to get the arm as low as possible, and then of course lower the main mounting plate all the way.

Also note the top damper angle. The more horizontal the damper, the more linearly your bump stiffness will increase as you move across the suspension travel; angling down creates a positive progressive feel (stiffness increases exponentially) and angling up creates a negative progressive feel (stiffness increases less as you go through travel). Nobody I know angles the shock up on purpose, it doesn't make sense to have negatively progressive stiffness. I myself went in between linear (horizontal) and progressive (angled down); mine is a little bit angled down, and the spacer is a ground-down PN Delrin ball.

Now onto the front suspension! Below is the semi-exploded view of my front end, sans the lower arm. Mainly, I took it apart to show you guys all the shims and tricks that I used to get the right heights and handling feel I want out of the reverse-kingpin (aka dynamic strut) suspension.

Top and center is the PN MR03 wide tower bar, and attached to it the PN MR03 1deg camber suspension arms. These are mounted to the tower bar with two PN M2 0.2mm steel shims in the rear, creating about 2deg caster. This has been the optimal setting for me at most tracks, I keep finding that 4deg caster (Reflex tower bar) doesn't give me the turn-in I want and 6deg (turning the PN tower bar around) is entirely excessive. So basics: 1deg camber, 2deg caster. Considering my tire wear patterns I would have liked a 0.5deg suspension arm but unfortunately that is not available from PN. Ryan Sagisi used a 0deg arm instead and seems to have shimmed his front end to get some more camber out of it. I think this might be why a lot of us use the reverse-kingpin front end instead of the PN A-arm system, you can fine-tune it a lot more if you know what you're doing versus being stuck with only a few options for suspension geometry.

Below the tower bar as well as above the knuckles you'll find several pairs of PN M2 0.2mm steel shims -- these serve to raise the entire tower bar/suspension arm assembly 0.4mm, keeping my kingpins from dragging on the track (I didn't want to grind them due to heat/distortion concerns). It also raises the roll center a tiny bit and reduces slop a tiny bit (same joint movement, less leverage = less slop) so I am not complaining. The shims underneath the knuckle are a Kyosho MR03 stock shim (~0.6mm), a PN M2 0.2mm steel shim, and a PN M2 0.2mm anodized aluminum shim (orange). I used these because I was in a hurry, however it's worth noting that the PN steel and anodized aluminum shims have different properties. The steel shims can be stacked in different ways to get different heights, you can change about 0.1mm worth by stacking differently. It's worth playing with. If you look very closely back at the picture, the shims under the tower bar are both cone-in and the shims above the knuckles are one cone-in, one cone-out. This is how I stack them in my actual build, under the tower the cones both face down, and above the knuckles the cones face opposite directions (outwards, both). The anodized aluminum shims, on the other hand, are 100% flat when new, so you know they're always precise and I make ride height/preload/droop adjustments with these whenever possible. Obviously, I ran out underneath my knuckles but I'll be getting a new set.

Now the front clip: because my front end is shimmed up so high I didn't want to buy a crapload of spring shims to use. Instead I put two Ti-screws through the front clip, secured them with 1.6mm thick steel nuts, and put two PN M2 0.5mm anodized aluminum spacers (blue) on them as my preload "stack". This preloads the springs just enough such that with batteries and body on, the car sits with zero preload and zero droop. Just touching my front end lightly will depress the front suspension (that's how you know there's no preload), but letting go reveals there's no downtravel left when the suspension rebounds (that's how you know there's no droop). Note that this is my low-roll-center setting, for low-grip tracks such as RCX's. For high grip tracks, the orange PN shim moves from below the knuckles to below the springs: as you might imagine, this has the effect of angling the suspension arms upwards, raising the roll center, and raises the ride height as well, letting me use smaller tires to avoid traction roll. Because one shim was moved from inside to outside, the preload and droop settings don't change.
Brian Ma

Greyscale RC

PN Racing | My TinyRC Blog

Last edited by color01; 2017.04.06 at 03:04 PM.
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Old 2011.03.28, 11:16 PM   #3
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All assembled, my front end looks like this!

For smoothness, the upper and lower balls are all PN Teflon balls, lubricated with Kyosho Fluorine oil: this provides that silky-smooth frictionless feeling that you get with the PN A-arm suspension, and it lasts a pretty good while too before you have to reapply it. I also Fluorine'd the metal-metal hinge for the suspension arms... as metal on metal joints wear rather quickly I wanted to do everything possible (short of Teflon sleeving the hinge pin... that'd be ideal, but too much work!) to make everything smooth and reduce wear as much as possible.

Take note of the suspension arm angles: if you want perfectly even handling left-right you'd better make sure these angles are equal, and that nothing else is messing up the front suspension geometry that you need to compensate for. Check the arms occasionally too, if you bend one and don't notice, your setup is going to be negatively affected. I myself bought the PN MR03 tower bar and lower arm because I didn't like how the Kyosho ones could tweak randomly and reversibly, so I switched them out for rigid versions and now my suspension geometry woes are all gone.

Now I've covered everything except batteries, body and electronics I believe, so give me a short moment to discuss batteries. I alternate between TRP 900's and R1 990's, and I honestly cannot tell which one is better. I have charged both at various rates between 1-2A, and documented the results, and I know only that my TRP's do not like being charged over 1.2A, and the R1's don't like being charged over 1.5A (charger: PN S6, using the PN aluminum charging tray/heatsink). At these settings, both cells have excellent punch, the R1's have better initial punch and the TRP's lower punch lasts a couple minutes longer. Interestingly charging the R1's at 1.2A does not change its characteristics at all in my experience, so I've just been charging them at 1.5A (it's faster, lol...). I only discharged the TRP's and R1's for the first three cycles, after that I just ran them, let them cool, then pop back on the charger. I run the cells for several cycles a day if need be, I don't seem to have any punch problems after the 2nd cycle, as other racers have warned me about for years. In fact I ran the same TRP cells four times on RCX Sunday, for Q1, practice, Q3 and the main! I don't think I ever lost my punch or top speed advantage (granted that advantage was probably all the motor's credit). So I personally don't buy into all the battery charging and discharging relgions there are out there -- I just take good care of them, cycle them consistently and expect that they get used to and perform well for the duty cycle they're responsible for.

OK, onto the electronics then. First of all I should of course mention that I'm still using the original MR03 PCB -- although I think other electronics might be allowed I find that the MR03 PCB is hands-down the smoothest, most positive-feeling electronics system for Mini-Z. The servo is so fast that the fastest digital servos, costing hundreds of dollars each, are barely equal to it! Anyways, for Stock racing the question is always power, so Philip convinced me to get a 3x2 FET stack using his AN0113 FETs. The car definitely feels a little punchier, top end has increased, and overall I don't know a whole lot about FETs but I like the ones I have. Now for ICS settings, Philip and I worked out the following settings back when I first got the car that should be fairly optimal for Stock-class racing.

GAIN: Medium
D.BAND: Narrow
DUMP: Over
D.FREQ.: 1.2kHz
ST.GAIN: 250
TH.GAIN: 250

GAIN describes the amount of force the servo motor will apply to hold the servo at a certain position: obviously, to have positive servo feel and inspire confidence in the driver, we should have the strongest servo action possible unless it reduces the amount of power going to the drive motor. I thought I had the GAIN set to Strong, but it seems that somewhere along the line it got changed back to Medium. No broken servo gears yet, though I do have a prototype aluminum 4th gear just in case.

SPEED describes the max speed the servo will move: given how small and quick these cars are I saw no reason to limit the car's own reaction times, hence Fast was the setting chosen.

PNCH describes the initial movement strength of the servo: I wanted my car to feel linear, not twitchy, and thus I left this setting at its stock, very mild-feeling setting. PNCH actually affects the feel of the car quite a bit! With high steering punch the car will actually feel much more aggressive, whereas mine, with a low punch setting, is very mellow despite having fast turn-in and high corner speed.

D.BAND describes the deadband of the servo movement: to get minimal response time you always want the narrowest deadband possible, hence I had mine set to Narrow. It doesn't affect the car's stability down the straight at all, also thanks to the low steering punch setting.

DUMP is a strange setting to me, basically it dictates whether the servo stops its centering action just before hitting center (Smooth), or just after (Over). I left it at Over, since I normally don't let the steering wheel center fast enough to hit that braking limit anyways. If you have fast hands, I suggest you try both settings and see which one you like better. I have heard in the past that Smooth makes the servo a little sluggish compared to Over.

D.FREQ is the drive frequency: the lower your drive frequency the more power you can apply to the motor, that is the theory taught to me by 1/10 scale racers. So for Stock Philip and I set the drive frequency to the lowest one Kyosho allows, 1.2kHz.

NUTRAL describes the throttle deadband: I didn't want to reduce my capability to reverse so I've left it at Mid for now. Making it Wide could potentially reduce the initial throttle response at tip-in so I didn't want that either, hence it is still set at Mid.

VINERTIA is a "virtual inertia" setting which keeps providing a little power to the motor even after you lift off entirely. I think this feature is useless, as I rely on weight shifting to rotate the car and really, unless you're a habitual user of the brakes typically lifting off is the only way you slow down a Mini-Z in a race. Hence, OFF is the setting of choice here.

BAKTIM is a limiting setting, to keep you from accidentally engaging reverse if you pump the brakes. I don't even brake, so I put this setting all the way down to 1 (basically zero reverse lockout -- a quick double-tap instantly engages reverse) and I can reverse as quickly as I need to in order to get back in the fray after I screw up.

ST.GAIN and TH.GAIN are technically supposed to be gyro settings, and are not supposed to take effect when there's no gyro in the car. HOWEVER, what Philip and I found was that ST.GAIN and TH.GAIN could be tuned for each individual servo to reduce the servo jittering that plagued many early MR03's such as my own. 250 and 250 are just five points short of the max on both settings and I found that this is what worked to stabilize my servo after setting the GAIN to Strong. Your mileage and results may both vary on these last two settings, have fun!

Now for the body, which I'm sure many people are curious about. I got my 911 GT1 back from Landon (hrddrvr) just days before RCX, so the only modifications I've done to it are some cutouts for tri-shock clearance and shaving of the fenders for tire clearance.

This scoop wing was taken off the back of one of Philip's Lexan Pan Car bodies; I just sharpied it black, slapped a sticker to it and mounted it to the stock wing location via two PN disk damper posts (the low-profile version intended for the V3 94mm LCG motor mount, and now the reconfigurable LCG motor mount as well). Altogether the rear wing sits at a height of 44.5mm, easily passing tech at RCX. The low decklid and overall smooth profile of the shell feed the rear wing lots of clean air, and as a result this wing gets to produce a lot of rear downforce. Good thing too, because there's not much left of the rear bumper (old pic):

To reduce the parachute effect and reduce rear lift I cut out the rear bumper almost to its maximum extent allowed by PN rules; the top of the cutout is about 19.5mm off the ground with full-height tires. This plus the rear wing provides a significant force sticking the 911 GT1 to the ground. In my experience my 911 has absolutely the most planted down rear end out of all the bodies I've tried at Kenon, where bumps are both tall and frequent. Where F430's, SC430's and even my GT-R and Mosler can be seen jumping around a little, the 911 is just always planted, pushed into the track, and the suspension is really forced to work to keep the tires following the tile gaps. To me that is proof that it's the highest downforce body I have.

Given that RCX was mostly low-speed infields linked by only one long high-speed straight and sweeper section (both days), IMO the 911 is not the ideal body choice (no speed = no aero...) but I got away with it due to having adequate low-speed handling and making up time in the high-speed section. Drag doesn't seem to be too bad either, in fact other racers like Ryan Sagisi eventually took out their Reflex spoilers and went back to the stock ones so they could reduce drag and keep up at speed! With my lucky motor and the aero-efficient 911 GT1 I was able to make up for the body's shortcomings and even press some of its advantages -- passing people on the outside of the sweeper multiple times, it doesn't get much cooler than that.
Brian Ma

Greyscale RC

PN Racing | My TinyRC Blog

Last edited by color01; 2017.04.06 at 03:05 PM.
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Old 2011.03.28, 11:17 PM   #4
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The real hidden gem though IMO is the diffuser: here is an older picture, but it clearly illustrates the shape as well as shows how similar it is to existing designs in real life (think Le Mans). The overall shape hasn't changed since then, just repairs.

I no longer make my diffusers out of this thin Lexan as it is VERY prone to cracking (one hard collision during RCX nearly broke the entire diffuser in two) but this original prototype proved it's still got the goods at RCX. It weighs under 1 gram and features five distinct sections. Section 3, the center section, is a flat panel because there isn't anywhere to route the air directly under the front clip. So I let it continue underneath the chassis for a moderate reduction in lift (confirmed by Eugene (EMU)). Sections 2 and 4, immediately besides the center section, are aggressively curved upwards to quickly route the air upwards and expand the volume of the air column. This is now diffusers produce downforce in real 1/1 scale cars and it seems to carry over to 1/28. Sections 1 and 5 are designed to get around the headlight buckets, and curve upward aggressively once they clear those buckets. Downforce is probably reduced versus cutting out the headlight buckets entirely, true, but this wasn't a bad compromise I think. At least it doesn't hurt performance.

The actual effect of the diffuser as I see it is that initial steering response is stabilized a little bit due to the additional gram up front, but the rest of the turn-in is improved because the diffuser actually increases overall steering. If the mid-corner is relatively fast, the effect continues all the way till the car is completely out of the corner -- noticeably increased front grip without adding any scrub, which translates into more corner speed, all without upsetting the rear end. If the mid-corner is slow, then as the car slows the amount of steering ALSO drops! This was my primary proof that the diffuser works as I have never experienced that kind of feeling out of a Mini-Z before starting to play with aero. Then once speed picks up at the corner exit the diffuser "kicks in" once again and you could see the car catapult itself out of the corner very quickly.

For the purposes of this article I'm going to ignore my hood vents and front intakes, as those were very experimental and I have had little to no evidence that it actually works. However, the front diffuser works, and balanced with the PN Lexan Pan Car scoop wing I achieved a good handling balance at higher speeds to match the balance provided by the tires (PN X15 and 6 radial if you recall) at low speeds. So to wrap this up, here is the final image of how my setup for RCX 2011 looked, the exact updated configuration. If you look closely, you can see all of the other less-significant fine details, like the glued-in mirror holes, roof scoop block-off plate, and the holes required to run the PN tri-shock setup, with full-height tires, at 94mm. All put together this was a package that was extremely quick, extremely dependent on the rear tires' condition, and was good enough for a TQ, Lap Record and 2nd place overall on RCX Sunday!

Front end:
  • PN Reverse Kingpin Front Suspension
  • Tower bar raised 0.4mm
  • PN steering knuckles, 0.4mm shims above knuckle, 1.0mm below
  • PN MR03 Orange springs
  • Custom spring holder: 1.6mm thick nut + 0.5mm shims under spring
  • 0 preload
  • 0 droop
  • 0 toe
  • 2deg caster
  • 1deg camber arms: 1deg static camber
  • 1.5mm ride height
  • Atomic 19mm S6 Delrin front rim +0N
  • PN X-Pattern 15 front tire, not trued
Rear end:
  • PN FRP T-plate #5
  • PN Reconfigurable Motor Pod (94mm)
  • PN Tri-shock
  • Side springs: 3racing AWD Black (soft)
  • Side damper grease: Kyosho 15000
  • Main spring: PN Red (3rd softest)
  • Main rebound spring: Atomic RCP MR02 Yellow (Super hard)
  • Main damper grease: Kyosho 15000
  • Lightweight differential: 106t 126p PN locking spur, 6 ceramic balls
  • PN 80t Stock motor: 27t 126p pinion
  • 2mm ride height
  • Atomic 20mm S6 Delrin rear rim +2.1W (+1.5W rim + 0.6mm shims)
  • PN 6deg radial tire, not trued
  • 3x2 AN0113 FET stack
  • GAIN: Strong
  • SPEED: Fast
  • PNCH: 2
  • D.BAND: Narrow
  • DUMP: Over
  • D.FREQ.: 1.2kHz
  • NUTRAL: Mid
  • BAKTIM: 1
  • ST.GAIN: 250
  • TH.GAIN: 250

Tx settings: KO Propo EX-1 UR:
  • Steering Travel: 70
  • Steering Travel: L70/R70
  • Steering Dual Rate: 82%
  • Steering Trim: R5
  • Steering Subtrim: R1
  • Steering Trim Rate (step size): 2
  • Steering Config: Normal (not reversed)
  • Steering Punch: 0%
  • Steering Curve: 0%
  • Steering Quick-Response: OFF
  • Steering Speed: L100%/R100%
  • Throttle Trim: 0
  • Throttle High Point: 60
  • Throttle Brake: 45
  • Throttle Subtrim: 0
  • Throttle Trim Rate (step size): 10
  • Throttle Config: Normal (not reversed)
  • Throttle Punch: F0%/R0%
  • Throttle Curve: F0%/R0%
  • Throttle Quick-Response: OFF
  • Throttle Speed: F100%/R100%

Hope this article provided some insights into how I build and tune my cars! Thanks for looking!
Brian Ma

Greyscale RC

PN Racing | My TinyRC Blog

Last edited by color01; 2011.06.02 at 07:50 PM.
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Old 2011.03.29, 04:29 AM   #5
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RCX Setup

Wow! Awesome post. LOTS of info!
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Old 2011.03.29, 04:34 AM   #6
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Now thats a write up! Excellent.

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Old 2011.03.29, 05:01 AM   #7
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Very nice write-up Brian. I can't tell you how helpful your explanations and analyses are to a non-engineer like me. Thanks!
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Old 2011.03.29, 05:04 PM   #8
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Excellent write up! Thank you for sharing.
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Old 2011.03.30, 01:03 AM   #9
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pretty nice read... thanks for the info & thanks for sharing too...

for body choice... wondering what made you choose the 911 over any other body kyosho made? was it purely aerodynamics? could any other body perform as well, if you added diffusers or modded the body within the pn rules?
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Old 2011.03.30, 05:51 AM   #10
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It was on hand. I didn't have a single 94mm body in my stable the week before RCX and Landon (thank you SO MUCH btw) emergency-sent me a package of three: my 911, his F430, and his VERY clean 360GTC.

I looked once at his 360GTC and decided I didn't want to be responsible for scuffing it up; I ran the F430 Saturday and decided I still don't like it; and then I ran the 911 Sunday and it was as good as it was gonna get, so I stuck with it.

I don't doubt one bit that the SC430 could be made better than the 911 GT1 with lots of aero and misc body work -- it has been a good body for so long, and so very versatile across so many different tracks that I'd be surprised if I built up an SC430 and it didn't kick my 911's arse. In fact, that's just what I'm doing now, I picked up an SC430 while at home and will be putting it together whenever I find spare time.

That said, on way-open tracks the LeMans-type bodies such as the 911 GT1, longtail McLaren GTR, and the actual Kyosho LM bodies (962, 787, C9, R390) will have an aero advantage over their stubbier brethren, given their length (pretty much the longest of all Autoscales), height (lowest of all Autoscales), and shape (all wedges except for the 911). For its wedge-shape deficit the 911 has an especially low tail IMO, which lets you high-mount a wing and produce lots of efficient downforce without 1) exceeding PN regulations and 2) actually mounting the wing too high, which produces a drag-induced lifting of the front wheels.

So my decision of running the 911 isn't entirely random, it does have one aero advantage that can be pushed or used to compensate for other shortcomings, like the fact that it SUCKS at bouncing off the walls. The front fenders like to scrub the car to a near stop if you rub the RCP foam rail, so to "wield" the 911 GT1 successfully you pretty much need to be a flawless driver. Not so with a race-prepped SC430 and especially not with the F430, that thing is content to ride the rails all day long.

In in another thread I mentioned that I also made a diffuser for my F430 before selling it, but I felt that it provided less improvement than the one I made for the 911. I am not sure why, it may be because the F430 has a lot of inherent steering built-in already. A diffuser for the SC430 is pretty much impossible, but a flat plate under the front bumper is easy and it does the same thing (weaker effect though, in my experience). Let me outline my "work plan" for the SC430, to give an idea of where I think the body could be improved:

Shave front splitter completely -- improve wall handling
Front under-plate -- can't diffuser, so install a plate
Interface front under-plate with the front clip -- max aero with inferior plate design
Fill all front bumper holes with plastic cement -- no air leaks in front end
Shave headlight bucket mounting points -- tire clearance
Shave inside of roof -- overbuilt in stock form, lower weight and CG
Cut out all windows, install individually -- lower weight and CG
Install side panels, smooth out sides -- improve wall handling
Trishock clearancing -- oh dear... looks like PN TDS doesn't fit...
Shave rear fender inside -- tire clearance
Cut out rear taillights -- very thin from factory, might as well reduce drag
Cut out rear bumper -- already high, but go to 19.5mm anyways
Create angled surface on decklid -- for mounting Reflex wing

I decided not to shave and slam the front end of the SC, as it would necessitate I shave the side skirts as well, and that would make them sharper (dig more into the rails) and prevent my installation of the side panels, which are specifically to avoid rail digging. Now for the last item, I noticed that a lot of SC's with Reflex wing have to run it in the forward mounting holes, which puts the wing back (good) but angles it up too much. So, I will deliberately shave an angled-back surface into my decklid before mounting the Reflex wing, allowing me to run the wing at the proper, level angle, and keep a good height and position behind the decklid. I'll have to buy and cut a new Reflex wing specifically for this body, which is a bummer, but with everything done it should thoroughly kick the arse of my 911.

Trishock clearance appears to be an issue with the SC -- I either need a significantly lower setup or a significantly narrower one, or scrap the tri-shock and fabricate a single side damper system.

I've started to ramble so I'll stop here. To actually answer your question, herman, I think any body can be made to handle much better than in its original form -- however, I don't think all bodies have the same "maximum" performance attainable. Even if I aero-modded and did everything I could to a Lancia Stratos it's not going to be as good as the SC430, due to its offsets, overall shape, and body details. I think certain bodies respond better to mods as well -- the 911 transformed completely after I gave it the downforce it needed, the F430 not so much. I've never aero-modded the SC430 so we'll soon find about about this shell too.

So no, certain bodies will always be better than others, but if you like a certain bodystyle enough you can mod it to be within workable range of your competitors. If you're dead serious about winning though, obviously you need to start with the best, mod it to its full potential, etc.
Brian Ma

Greyscale RC

PN Racing | My TinyRC Blog

Last edited by color01; 2011.03.30 at 06:05 AM.
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Old 2011.03.30, 06:44 AM   #11
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Great writeup! Thank you for sharing. Thoroughly enjoyed reading even though i drive 02s
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Old 2011.03.30, 06:45 AM   #12
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Sweet car Brian Thank you for all the good info!
....And congrats on your podium
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Old 2011.03.30, 11:30 AM   #13
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Thanks for sharing all of the detailed information

Glad to see the 911 work that you have done come to form. I drove the GT1 for a little while, but retired it due to the wide rear fenders that when contact is made with anything, angles the car in the direction that contact is made. This means if you graze a wall, it will suck you right in, and make it difficult to steer off of without slowing down...

The downforce produced by the front diffusor is definitely there, but as you stated, your old f430 (that I purchased), has more downforce on the body than the GT1 due to its cab forward position, while the GT1 is more cab rear. So the steering increase would be more noticeable with the GT1 from the effect of the diffusor.

While the PN and Reflex TDS are similar in design, the fact that the Reflex TDS is a smaller package comes in handy with such bodies as the Lexus SC430 which just needed a little modification to clear the Reflex TDS. You may want to consider trying the Reflex TDS, or develop your own with modifications to the PN shocks with a fabricated mounting plate that has a similar size to fit under the SC430. You may need to use different springs than the original PN TDS as well, but there are plenty of options if you decide to go this route.

Congratulations on your podium. Look forward to hearing more about your setup adventures.
Micro RC Syndicate /DG Designs /GSR /Reflex Racing /Fast By Faqish /MurderTown Racing
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Old 2011.04.01, 03:10 AM   #14
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thanks for the reply and congrats on your podium win too...
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Old 2011.04.06, 01:35 PM   #15
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...perhaps one of the best write-ups I've seen here in the past ten years from both a theoretical and practical perspective. (I don't race, but our tracks do require cars to run straight and handle well on the high speed ovals).
From an engineering standpoint, I do question the relevance of aerodynamics on a car that travels about 20 MPH full scale speed. But I've seen theory washed down the drain more than a few times, and even if your wings and diffusers are all a placebo effect, if it makes you a better driver than that is all good. (What I do suspect is you may be ever-so-slightly altering the CG/balance and handling to a positive outcome). That said, I can vouch for the front under-chassis air "smoother" as to keeping anything from touching the track during heavy suspension loading or bumps, and of course any mod that cools the motor is also practical. (If you've ever seen an under-car view of a modern full-scale Ferrari, you'll notice the exact science that colour1 has applied here, in that the air flowing/aerodynamics underneath the car is as important as airflow over the top of the car.)

I will definitely try some of the body tricks, and I do agree with the importance of CG... cantankerous cars behave so much better with a little lead in the right spot. (We use this trick on d'NaNos to get them "glued" to the track.)

I especially liked your ICS setting explanations ...everything you mentioned I can certainly verify ...the best example being that a strong gain setting helps reduce understeer in fast sweepers or banked corners that really load the front tires. I have not tried the ICS gyro settings you suggest to reduce servo jitter, this is one problem we've just learned to live with. Your testing and explanation of these settings from a practical standpoint, finally make sense of what Kysoho was trying to do but never properly explained.
What became very evident from your writeup, is the quality and construction differences in many of the bearings (even supposedly good ones), nuts and screws. Durability does matter big-time to our rentals and I may well switch to those rather expensive ceramic balls if they last that long. I've also suspected that improperly made front bearings and wheel are the culprits for not being able to tighten down the front wheels without binding. (And I've noticed this even with stock Kyosho parts). I'll now experiment with some of the Reflex parts you've mentioned.
Again, thanks for the extensive detail and your theory behind it all've raised the bar of both technical write-ups and what the MR-03 is capable of.
Lorne Cherry
R/C Track Designer

Last edited by lornecherry; 2011.04.06 at 01:37 PM.
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