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Color0's Micro RC Blog -- A technical brain dump from the mind of yours truly...
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MR-03 Chassis Configs: Stock Black vs. SP Grey

Posted 07-29-2012 at 07:21 PM by color0
Hi again after another break, everyone. For the past 2 months I've been switching back and forth between the grey SP chassis and the stock black chassis on my MR03 -- which covers both Stock and Mod class racing -- and I think I have enough data to report now. But especially since this seems to be a somewhat controversial topic with mixed results, I can only present my own impressions and it would be great if you guys and gals reading my blog could respond with your own.

So first testing started with the stock black chassis, which I've posted about before:



This setup, reverse-kingpin and all, is decently quick and forgiving to drive, but I did notice that it lacked steering. So, I cut the chassis tabs and popped on the PN Double A-Arm again, and that is our new baseline for this experiment.



(Don't forget the 1 degree lower arms! Necessary on the MR03.)

My baseline setup follows.

----------------

Front Suspension:
PN Double A-Arm
Camber setting 0deg
1deg camber lower arms
Purple springs
Preload/height: make lower arms flat on bottom, then lower 1/2-turn more
Total camber: Almost 2deg
AA +0.5deg tierod (double A-arm specific tierod)
Total toe: About -0.5deg (toe out)

Rear Suspension:
PN 98mm LCG V4 motor mount
Motor in lowest position
Axle height: #1 eccentric with # facing down (axle in raised pos.)
PN G10 #3 T-plate
PN Alu T-plate mount
PN Tri-shock: Blue side springs
PN Top shock: Green main spring, MR02 Purple rebound spring
Ver. 2 tri-shock mount (lowers inboard mounting of side shocks)
Raised outboard mounting of side shocks 0.5mm
Kyosho 15k grease on all shocks

Drivetrain:
PN 70, 80, or 33t
Geared at 14/53, 13/53 or 9/53
PN Gear Differential
3x2 AN0113 FET

------------------

So, what gives? Honestly, the black chassis is impractically fragile -- you do one too many rounds of maintenance and a screw hole WILL start to strip. Then you need to save it with whatever methods you have (vaseline/epoxy, etc.) and eventually all your screw holes will be partially made of adhesive lol. The stock black chassis also has a weakness on the top cover, you install anything to that top cover and it will bow outwards, letting dirt into the electronics compartment of the car. Tri-shock mounting to the black cover is a nightmare since screw tension will raise or lower the mounting point! And of course, installing batteries in an older stock black chassis will noticeably bow the chassis as well. It's just a very flexible part.

That said, the flex that the black chassis provides makes it fast. On low-grip tracks, the MR03 has no weight to warm up the tires so the flex helps generate grip. In Mod, the flex also slows down the car's reaction time, so if you're a twitchy driver it staves off a lot of traction rolling.

So, fast and forgiving -- the only problem being the complete lack of durability. A possible remedy for at least the top cover is the Reflex replacement top cover, which I have in black (sorry no installed picture). I threw it on for the next test, and noticed 2 things:

1. Precision is great. I suppose what they say about rigid suspension attachment points is true, the car does feel more consistent.

2. Chassis got stiffer, and front end traction dropped. The Reflex top cover raises CG and stiffens up the black chassis, so it's either the extra roll or the extra stiffness that's reducing the car's total grip. More on this later.

My rate of traction rolling, however, increases with the Reflex top cover, and that's more than likely due to the extra CG height (the Reflex cover adds 2g up top) which I normally don't lug around. I haven't changed the setup yet to match the Reflex top cover though, because at this point the experiment still needs to be controlled.

To diagnose point #2 above, I then overhauled the car and replaced the black chassis with the grey SP chassis and now the car looks like this:



As you can see, the top cover is back to bowing out with the tri-shock installed -- this is with barely enough torque on the screws to keep the tri-shock mounting plate secure! But at least it's stiffer than the black chassis and bows out only about half as much.

And what of traction? It's about the same really -- and without an extra 2g of weight up top to move around the only way to induce this car's traction rolling last Saturday was to yank the steering and brakes at the same time, which thankfully is not necessary in my car. Again, the suspension and drivetrain setups did not change, so I could see what the chassis swap/mods themselves do. It is another experiment entirely to change the chassis and then optimize around it. A good one, yes, but I haven't gotten there yet.

At this point, it's worth testing the final combination of grey SP chassis + Reflex top cover, and then see if it miraculously makes the car better, or worse (which is what I think will happen). Yet I've seen the grey chassis + Reflex cover combo work for several very fast drivers, so it will be fun trying to figure out how to make these different combinations of chassis and top cover work for me.
Total Comments 1

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arch2b's Avatar
look forward to the final testing combo.
Posted 08-15-2012 at 08:04 PM by arch2b arch2b is offline
 

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