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Color0's Micro RC Blog -- A technical brain dump from the mind of yours truly...
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Mini-Z MR-03: First Drive

Posted 11-27-2009 at 09:15 PM by color0
Updated 03-08-2011 at 10:32 AM by color0
So, I finally took delivery of my MR-03, and I have to say, this is the most exciting purchase I've made in a long time. Like Cristian from Reflex Racing has done, I wasted no time in hooking this car up with the latest PN Racing hop-ups in preparation for a track test of this baby, to see whether or not Kyosho's 02 successor can live up to its older brother's racing pedigree.

As noted before, the new 03 chassis is very narrow. So narrow that if you install a disk damper, the battery clips no longer clip on properly! So I had to trim off half the clip (saves weight!) just to have them clip to the chassis properly.

My car is from the second batch of 03 shipments; the motor wire problem that plagued the first batch seems to be gone, although for safety's sake I have clipped the motor wire terminals into the shape of a small square. Then screw them into the board (I didn't direct solder yet, in case the board fried I'll need to show that I'm innocent!), bend the tabs 90 degrees upwards, and route the wires out the disk damper. Safe and easy. Make sure those square terminals are aligned properly with the pads on the PCB when you screw them in, or you WILL be risking a short circuit.

All the Kyosho Mini-Z cars have these two odd little tabs on the rear of the main chassis, presumably for keeping the body from mounting too low. Unfortunately they're closer together on the 03 chassis, and they get in the way of adjusting the disk damper post on a compact motor mount such as PN Racing's 94mm LCG pod. So clip those too or you'll have to flex your rear suspension to access that screw (not ideal).

In other news: the 03's T-plates are vastly improved from the last generations'. Why? Because there are now 6 tabs locking this part to the chassis instead of just 2. While this may sound funny, I'm happy to report that the new PN T-plates lock perfectly straight into the chassis, and stay there very, very tight and straight. The increased mounting area will help keep the T-plate straight in a collision as well as during installation. Can't praise this design change enough, they should've thought of this years ago!

The 03's body mounting system is the same as other Mini-Z's, except that the front body mount now becomes a stressed member, supporting the front spring perches. This wouldn't be a problem except that the MR03's front ride height is just too darn high! The front suspension/clip becomes highly annoying when a) you're trying to lower the car, thus preloading the front springs (nobody's made shorter front springs yet) and b) you're trying to lower the body, requiring washers. It's virtually impossible to get all this stuff secured in the right place long enough for you to put a screw through it. I highly recommend picking up a PN aluminum/carbon front clip for the 03 chassis, to rid yourself of this hassle and lower the body at the same time.

Anyways, I took my car to a dusty local RCP track for my first drive, and boy am I impressed.

First things first: Old Kyosho 20's are old. The track hadn't been cleaned in eons, so it's extremely dusty and low-traction. Kyosho 20's weren't chattering like they normally do, rather they were slipping and sliding all over the place. I switched up the tire combo from PN20 front, K20 rear to a low-traction combo of K30 front and PN6 rear. However, these are my old worn down K30 slicks, which meant that I was down on front traction, and the car would only turn if I braked first. Turning at high speeds also suffered because the servo surprisingly didn't seem strong enough to handle it.

Secondly: ASF ICS tuning is necessary to get that 03 servo working right! In stock trim, the servo is quick, but very weak. Even on the low-traction, dusty surface, the servo didn't have enough holding torque to get the car through the decreasing-radius hairpin on the current layout. Kind of sad. The track owner and I put it on the computer and programmed in the following settings:

GAIN: Strong
PNCH: 2 (Don't mess with this, it'll screw up the servo real bad!)
D.BAND: Narrow
DUMP: Over
D.FREQ.: 1.2kHz
ST.GAIN: 250 (Don't set to Max, you'll screw it up)
TH.GAIN: 250 (Ditto)

Update 12/4/09: If your servo shakes with these settings, set GAIN back down to MID, that should take care of the shaking without sacrificing the rest of the benefits of faster and more precise response.

With these settings the servo is completely transformed, not only does it respond sooner and faster, but also holds its position much better. Feel free to copy those settings as a baseline, as it's much, much better than the stock config (I've no idea what the Kyosho boys were thinking). The K30/PN6 tire combo could actually be put to better use now as I had a much better idea of where the car was going when I slammed on the brakes (which I've detuned to 75% after the ICS tuning). It results in the perfect amount of speed drop for going into the low-speed technical section, and because the front tires are old and slippery, the 03 carried more speed than expected going into the high-speed sweepers and transition sections. With this fantastic servo, the 03 could cut the corners closer than anything else I've ever driven. The steering feels even more telepathic than when we first got our ASF MR02's, and that is very high praise for a car we haven't even figured out yet.

At this point in time I popped some legitimate batteries (TRP 900's) into the car and went for some hot laps, albeit not timed. The new PN spur does its job admirably, it definitely locks in the rear end better under acceleration, but it's a relatively mild effect that won't throw off your cornering line. As I figure out how to use this part more effectively, I'll write some more about it.

My ride height complaints were fixed with a set of prototype knuckles that lower the car by 0.7mm, which allowed me to take out one of my 0.25mm washers for the perfect ride height. I now have 1) perfect ride height and 2) sufficient travel, which made the car so much more stable over the bumps. I still don't like the amount of preload that this suspension design puts on the front springs though, so I'm waiting on someone to make some modified front arms, as well as figuring a way to get rid of the front spring perch piece (that itself will free up nearly 1mm of spring preload if I can do it). I'm running PN green springs in front at the moment, but I suspect they may be too soft so I'll switch back to at least purples before my next test.

So, the verdict? This car is worth it, even if just for the servo. The suspension dynamics will have to be ironed out, as with every new platform, but the controls on the 03 are just leaps and bounds ahead of everything else I've ever driven, as soon as the ICS tuning is done right. Right now the front end is still largely stock -- I don't have enough camber, the front springs are too preloaded from my low ride height, and I bet there's still not enough travel afforded by the short kingpins -- but still this car is completely able to perform, and feels great while doing it. As more parts arrive for the new platform and more discoveries are made regarding its performance, I'm fully confident that the new MR-03 will be a force to be reckoned with on the track. I'll be keeping mine.
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