New 1/28 pan chassis, Greyscale Racing MRCG
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Introduction
The MRCG project was intended from the very beginning to create the most effective chassis to ever compete in 1/28 RC car racing; to be a user-friendly, versatile machine that maximizes the driver’s potential on any given track. Based on Kyosho’s proven Mini-Z MR02 platform, we have created a new chassis from the ground up that combines smart engineering with specially-chosen materials to gain an edge in the budding market of 1/28 open-class competition.At a glance
– Built on the race-proven Mini-Z MR02 platform; uses many MR02 parts
– Super-soft, highly adjustable flex plate suspension
– Tools-free quick-release battery system designed for endurance racing
– Ultra-low center of gravity and polar moment of inertia
– Durable 1.5mm/0.8mm FRP chassis
– Lightweight FRP/Delrin rear pod
– Unique 2-piece motor mount works with any 130-can motor
– Unique tierod steering system with optimized Ackerman
– Fully adjustable suspension: spring rate, preload, droop, ride height, camber, toe, roll center, damping
– 94 or 98mm wheelbase
– Compatible with Mini-Z MR02 bodies and polycarbonate bodies
– Hand-finished and pre-assembled chassisFeatures
Ultra low center of gravity and polar moment of inertia
Like any good racing chassis, the batteries, motor, servo and electronics are positioned as low as possible to achieve an optimal center of gravity. But more gains are achieved in the actual chassis itself: the upper deck of the chassis and the top plate of the rear pod are reduced in size, thinner material is used for the servo strap, tierod, and battery strap, the upper tower for the front suspension is entirely removed, the motor mounts secure to the bottom of the rear pod, etc., all of which lower the CG even more. With the motor placed amidships and the narrowest battery configuration possible, the MRCG also achieves an extremely low polar moment of inertia. This combined with the ultra-low CG provides unparalleled steering response and corner speed.Unique rear suspension
The MRCG’s unique interpretation of the side flex plate suspension uses FRP flex plates instead of carbon fiber items. Being softer and more durable than carbon fiber, these flex plates give you more traction and less breakage in collisions. The chassis has been entirely cut out below the flex plates, allowing full freedom of suspension travel to maximize traction and improve consistency. A side-effect of this change, however, is a lowered roll center, which increases traction still. Optional side springs (not included) can be used in conjunction with the flex plates; preload is adjustable via threaded screws. Ride height is adjustable in 0.25mm increments using a combination of shims and the differential height adjusters; the shims can also be used to adjust roll center and droop.Completing the rear suspension is a small disk damper. A Delrin post reduces unwanted friction for smoother action. The disk damper uses the same springs (not included) as other systems, and can be fine-tuned with combinations of springs, damper oils, shims and the top adjustment nut. Additional damping can be provided by an optional tube or oil damper (not included).
Lightweight, versatile rear pod
The rear pod is constructed completely of FRP and Delrin. The bottom plate is designed with more material for stiffness; the top plate is conversely thinner to save weight, and is open on the left side to improve motor access. And rather than using a large single bulkhead on each side of the pod, we split each one up into a bulkhead and motor mount to reduce weight.The 2-piece motor mount clips onto the motor can and endbell, and then bolts to the bottom of the rear pod. Not only can it be used with any 130-can motor (since it doesn’t require drilled holes in the can), but it saves even more weight and sligihtly lowers the CG of the rear pod as well. This system makes removing/installing motors easier by giving you much more space to work with than other cars.
Some more rear suspension features are built into the rear pod: the differential height adjusters allow ride height adjustments in increments of 0.5mm, an optional tube or oil damper can be mounted to the hole in the rear pod’s upper plate, and the lower plate has a center mark to take the guesswork out of setting up the rear end.
Robust, lightweight front end
To create clearance for low-slung bodies without sacrificing durability, the MRCG uses two machined arms instead of a top brace to hold the kingpins. The minimalist design and Delrin construction of the arms keeps the total weight down. The FRP lower arms can be switched out to adjust caster; the kit comes with 0°, 2°, and 4° lower arms.In addition, we utilized the servo strap as a tierod stay and created a linear steering rack like that of the Mini-Z MR02. Ackerman is optimized to provide smoother, more consistent steering. The kit comes with three tierods: 0°, 1° toe-in and 1° toe-out (abbreviated as -1°).
Quick-release battery system
The tools-free quick-release battery strap keeps chassis tweak consistent from pack to pack and allows for ridiculously fast battery changes. Twist both latches outwards and the entire battery strap comes off — no need to fumble with clips, screws, or nuts. For those who would rather use tape to secure the batteries, we have cut two additional slots in the chassis to thread the tape through (not shown in prototype). Additionally, there is enough space in the car to fit a variety of lithium-polymer battery packs so you can choose how much power your want your car to put out.Optimized for both 94mm and 98mm wheelbases
The MRCG’s unique wheelbase system shifts the batteries backwards in the 98mm configuration and forwards in the 94mm configuration. This gives the car greater stability and traction on fast, flowing tracks and unparalleled agility on small, tight ones. All that is required to change between the wheelbases is to shift the front end forwards or backwards, and move the side body clips to the other slot.Accepts both hard plastic and polycarbonate bodies
The chassis accepts both hard plastic bodies (Kyosho Auto Scale Collection, Atomic VDS and VDSII, PN Pan Car, etc.) and polycarbonate bodies (using body posts and an optional upper brace, not included). Because of its 94mm and 98mm wheelbase compatibility, the MRCG will fit any Mini-Z MR02 body and several other Mini-Z bodies as well. For polycarbonate bodies, an optional upper brace is available; the mounting points for the body posts are spaced far apart to provide extra stability to the shell.Compatible with many Mini-Z MR02 parts
Being based off the Mini-Z MR02, the MRCG is compatible with all sorts of MR02 option parts: kingpins, front knuckles, springs, bearing sets, motors, differentials, oil dampers, wheels and tires, etc. (In the name of cost-effectiveness the base chassis kit does not include any of these.) You can convert your MR02 to an MRCG or build your MRCG kit from the ground up, the choice is all yours.Option parts
As part of our policy of continuous development, we are developing a wide range of option parts to exploit the MRCG’s immense flexibility. In the works are a super-lightweight ball differential, two RM rear pod conversions (one for “sane” and one for “insane” motors) and more machined Delrin parts; these will make the car even lighter, stronger, and faster, and we look forward to offering them in the future.Partially-preassembled chassis
Every part in the kit is hand-finished before being put together and the entire kit checked for tolerances. Everything comes under scrutiny: the alignment of the front and rear ends, chassis tweak, proper action of the rear suspension, the ease of fitting screws and bearings into their holes, etc. With this process, we can guarantee the quality of the kit and you can have a perfectly-running car the first time around.What You’ll Need
– Superglue/CA glue
– Light threadlock
– Mini-Z MR015/02 knuckles, kingpins, springs, spring perches, c-clips, ball differential
– Aftermarket Mini-Z disk damper spring set (Atomic, PN, etc.)
– Mini-Z MR01/015/02 wheels, tires, bearings
– M2 locknuts (4)
– Micro servo (no wider than 23mm), servo saver
– Thin double-sided tape for servo
– Receiver and ESC (or combo)
– Receiver-compatible transmitter (and transmitter battery pack)
– Mounting tape for receiver and ESC
– 130-size motor, Mini-Z pinion
– Battery pack
– Charger appropriate for battery pack
– Hard plastic or Lexan/polycarbonate body, 94mm or 98mm wheelbasePrototype Pictures
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I was using the wrong units! D’oh. I have the feed rates right this time, and edge quality is much better, though the cutting bit didn’t go deep enough to separate the pieces entirely from the stock. (It turns out that this plate of fiberglass is slightly thicker than 1/32″.)
If you look closely at the picture, you’ll notice there are two “kinds” of edges. I was playing around with the settings and found that really slow speeds (6mm/min) are really good but take forever, slightly higher speeds (15-30mm/min) are terrible, and the proper speed (150mm/min) nets nearly perfect cuts (check the outside edges of the flex plates).
So that’s my update. Since I have a 3-day weekend I should be able to do some more work on the fiberglass and get that all sorted out and perfect. The Delrin and aluminum parts may have to wait since I still need some screws to mount my micro vise to the rotary table. Rest assured I will get this done as fast as I possibly can!
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Ok, I’ve got good and bad news.
Good news first: edge quality is perfect on the longer cuts.
Bad news: edge quality on the countersinks has gone down.
Worse news: the mill seems to jam up right around this one spot of travel. I have no idea where to look for the cure; the mill is freshly lubed up with WD-40 and the rails are clean. Yet there’s a slight grinding noise and sometimes the whole thing just jams while the CNC control software believes it’s still going.Check Exhibit A:
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First functional prototype!
Pics first.
Comments:
1) The mill countersunk two of the holes a little deeper than the rest. This might have something to do with my fixturing platform (it’s not perfectly trued yet), so I’ll look into it.
2) I accidentally used climb milling for everything, and had to file the parts a bit to get the finish you see here. Still, not bad.
3) The chassis went together very smoothly. After the finishing filing, I had only minimal filing to do to make the kingpins fit into the holders. And once in, they are very snug.
4) The rear suspension is a good stiffness up and down, but the roll stiffness is rather high, even for my tastes. I do not know how this will factor into real-world driving yet.
5) The front end will not flex unless you hit something really hard. I’ve been testing it with Kyosho hard springs and so far there is no visible flex.
6) The tierod movement is a little bit stiffer than the MR02, although this is partially because I preloaded the hard springs.All in all a decent job, I hope to have the elecs soldered together quite soon and some bearings, wheels and tires (doh, I sold ’em…) and this car will be ready to go!
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Got some more work done. The car is currently riding on plastic and metal bushings (!) so don’t expect it to run quite yet.
Note the new uber-low oil damper config. Now the only things that even reach wheel level are an antenna, two motor wires and a crystal holder. That’s pretty darn low if you ask me. 😉
Front end detail: Kingpins are held up by exactly 1/8″ of fiberglass milled to spec, it’s stiff. I also got a clean conversion on the HS-50; you’d have to know beforehand that it was a 3-wire servo… 🙂
Rear end detail: Got those side springs in, they work well and don’t click on the spring perches as I had worried about earlier. Also illustrates the height of the oil damper and the amount of leeway you have to shift the batteries back and forth.
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The horn pokes up from behind the tierod, and two flat G10 pieces are to be screwed on perpendicularly to the tierod to form a slot around whatever’s poking out of the servo horn.
It’ll make sense when I finish the build. 🙂
Edit: and it is, with the exception of a battery pack and a bearing set, complete! The tierod “horn” consists of two glued-on G10 pieces right now but as mentioned above will be screwed on in the final car.
Edit: Considering the ball diff, motor mount and oil damper, it appears I’ve managed to shave a few grams off the MR02’s chassis weight:
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Funding isn’t a huge issue, but I’ll let you know ASAP when I can put a delivery date on these chassis.
I took the RM car to the tennis court recently, drove over 2″x1″ ruts (2″ wide, 1″ deep!) in the concrete, heard the chassis smack the ground each time, but nothing broke or loosened up. That’s good from a durability standpoint. 🙂
Even with the batteries pushed full forward, the car has massive rear grip. I was still using medium-compound GRP foams front and rear so it should’ve spun like a top, but all I got was a moderate degree of understeer and a little slide if you brake too hard and wrench the wheel. I’m more than happy with the results.
Cleaning is about the same time-wise as your average MR02. For those concerned about electronics: I didn’t have any glitching issues despite all the dust on that board, but you may want to seal/heatshrink/case electronics if you drive in more rigorous environments. Indoor cars will have no issues.
I’ve also been working on the MM production car, of course, and the G10 chassis parts are already done:
And I’m just working on the production motor mounts (Delrin rear axle bearing carriers are done, just need to change some settings to make it easier to slip the bearings in). My apologies for the picture quality, but it’s tough to lean into the enclosure while trying to hold a steady hand, lol…
Anyways, we’re pretty close to release and you can rest assured that the pictures and news will be everywhere when that happens. 🙂
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To tide this thing over until my final exams are done, here’s the latest render straight out of the manual:
Special features include infinitely-adjustable suspension stiffness (yes, infinite :)), quick-release battery strap, Delrin everything in the rear pod, and a new motor mount that doesn’t need drilled cans.
I haven’t come up with a good enough servo saver so you’ll need a servo saver intended for 1/18.
With a Ti-shaft ball diff and the small electronics (the new ASF board is just one possibility) the MRCG should weigh around 135g without body; that’s 5-10g less than a similarly equipped MR02, not too bad.
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