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speedy_w_beans

Speedy's 3Racing M4 Chassis Build Thread

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Six or seven years ago I took one of my TT01s and converted it to a shaft-drive 4WD M-chassis using 3Racing's TT01 Mini conversion kit.  At the time I think Tamiya had their TA05 M-Four belt-drive chassis kit available, but it was limited to 380 motors and the unique LiFe battery they had adopted in Japan.  So, I went the conversion route, blinged it out, and topped it with a HPI Datsun 510 shell from their Cup Racer series (225 mm wheelbase).  Overall I was happy with the result:

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I've been dabbling with 3Racing builds over the past couple years in addition to Tamiya builds, having completed D3, D4, and more recently FGX EVO 2018 chassis.  Some chassis builds have been better than others; I found the D3 had some fundamental problems in materials and design, but the D4 was substantially better.  The FGX EVO 2018 was pretty satisfying overall, but it too had some quirks possibly from the original FGX.  When I saw the M4 belt-drive 4WD M-chassis offered for $80 USD recently, I jumped on it as an impulse buy to try with a HPI BMW 2002 Cup Racer shell that's been in my stash of bodies for some time.

I reported yesterday (Thursday) that the M4 kit arrived in the "postman brought me" thread, and @Badcrumble responded to my offer to do a quick and dirty build thread on the chassis, so here it is.  It was raining throughout the day today, so I used it as an opportunity to finish the chassis and collect some thoughts even before this thread is approved.  The posts below will have some insights gleaned from building the chassis all at once.

First, a quick word about packaging and documentation.  There is a sticker on the top left corner of the box announcing 3Racing plans to not include hardcopy manuals in future kits; they include a few QR codes which represent web addresses for the product page and the manual page.  The M4 kit I received did have a manual included with it, but it was bound in the same way as the FGX EVO 2018 manual -- essentially photocopied, punched with a few holes, and secured with a binder strap.  I moaned about this some in my FGX EVO 2018 build thread, but the reality is it won't make any difference as 3Racing moves to electronic distribution of documentation in future kits.

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Like the other 3Racing kits I've built before, the parts are organized into roughly 10 bags representing the major steps of assembly.  Some kits have a few more bags; the M4 kit includes 9 bags.  Wheels with pre-glued tires are included, but there is no body.  This is purely a chassis kit.

The first bag covers the front spool, rear gear diff, and center spur and pulleys.  The gear diff is clearly not the same as the FGX EVO 2018's gear diff, as there is sufficient clearance to install the cross pin in the deeper case half without grinding any material.  The front spool is typical and familiar from their D3/D4 kits.  The center pulleys are a little unique in that they clamp the spur in the center.

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The gear diff went together smoothly, as did the front spool.  However, I found assembling the center spur and pulleys to be a little delicate as the small screws and thin flanges on the pulleys made it easy to strip holes.  Coming from the previous step of building the spool, my sense of feeling was calibrated for beefy M3 screws threading into plenty of material.  Going to M2 screws with minimal mating flange material, I managed to strip the first screw hole but then install the remaining three screws correctly.  In the end I backed out the first screw and added some CA to the hole and figured it was good enough.

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The next bag was for the main chassis plate and suspension arms.  You might notice the plate has some scuffing on it, likely from handling in the factory.  It's not a huge issue; it's just a detail I noticed after removing the contents of the bag.

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The arms went together quite easily.  In addition to the ball connectors for the shocks, there are ball connectors for roll bars too.

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The inner split suspension blocks are normal for belt-drive cars these days; one thing I found interesting was the outer blocks only use one screw each to hold them in place.  Each outer block has a pair of metal pins pressed into it and these pins in turn mate with holes in the chassis plate.  This means it's a little faster/easier to remove the outer suspension blocks than regular 2-screw designs, but they should still be able to take some impact thanks to the pins.  All of the suspension arms moved freely and didn't require any filing or fitting.

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Bag 3 is all about the motor mount, belts, and bulkheads.

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Everything went together smoothly.  Each lower bulkhead is located with a molded-in pin and secured with a pair of countersunk screws.  Threaded aluminum spacers add some rigidity between pairs of bulkhead parts at each end of the chassis.  The motor mount is actually aluminum.  The front spool, rear diff, and center spur/pulley assembly all drop into their respective bulkheads and have some default settings for belt tension.  Note the front steering rack is now part of the front bulkhead; this is a modern trend with several manufacturers doing this now.  The TB05 and EVO7 do this too.

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Bag 4 introduces the upper deck and damper stays; the main parts are cut from FRP.  In particular, the damper stays are extra thick.

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Here are the upper bulkheads and stays for the front and rear.  The ball connectors get their own plastic mounts that are then attached to the upper bulkheads.  The combination fo the FRP stays and aluminum spacers make the overall assemblies very rigid.

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There's a fair number of button head screws holding the upper bulkheads and top deck in place.  I noted in the FGX EVO 2018 build thread that all of the button head screws for that kit were tight on the end of my 2 mm driver; this had been the case in my D3 build as well.  In the case of the M4, all the button head screws fit my driver just as well as the countersunk screws.  No problems at all.

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Bag 5 is all about building and installing the roll bars for the front and rear of the chassis.  I was impressed to see the bars are supported by collars inserted into ball bearings; this is normally a feature found on more expensive touring car kits.  I think the first time I came across this feature was with an Associated TC6 Factory Team kit a few years ago.

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There was something weird about the included roll bars, though.  I was careful to position the collars the same distance from each end of the wire, and generally tried to center the bar and orient the collars in the same direction (set screw facing up), but when I went to test the coupling between suspension arms (which were 100% free/unbound), I found one arm would sag lower than the other arm.  I played around with offsetting the bar to one side or the other, but what ultimately helped me balance the roll bar effect was to take one collar, loosen it, rotate it, and retighten it in a different orientation.  This introduced an elevation change on that side of the bar and helped balance the spring effect.  I found I had to do the same adjustment to both the front and the rear bars, although the front bar was less of a problem than the rear one.  You may also notice one of the bars has stripes painted on it; the other one does not.  There were no instructions or noted differences; I checked them with calipers and found them to be the same diameter wire, but it was still a little concerning there was a visible difference between the two.  Ultimately I put the painted bar in the rear and the unpainted bar in the front.

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Bag 6 included parts for the front and rear uprights, as well as CVDs and turnbuckles.

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The CVDs came preassembled; I took them apart to check the cross pins for flats.  Like the FGX EVO 2018, I had to use a Dremel to grind some flats in the pins to make sure they don't slide out during use.  The uprights themselves were a snap to build up.  The turnbuckles took a few extra glances at the parts list to confirm which adjuster to use at each end of the turnbuckle shaft; there are different lengths, closed and open cups, some that allow more angle than others, etc.  It pays to check this carefully.  Also, installing the steering turnbuckles on the center bridge is a little challenging given how close they are to the chassis plate; it may make sense to change the sequence of the instructions and install the turnbuckles on the center bridge before installing the steering assembly to the front bulkheads.

Front and rear uprights, CVDs, and turnbuckles installed.

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Bag 7 included the damper parts.  Probably the most exciting aspect of this bag is how 3Racing provided distinct springs for the front and rear of the chassis; it implies they did some testing and intentionally selected the springs instead of throwing four of the same springs into the kit.

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Assembly was straightforward.

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Dampers installed.

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I wasn't ready to install electronics or a body onto the chassis just yet, so I omitted certain parts from bag 8 and bag 9 (servo arm and turnbuckle, antenna tube, servo tape, motor screws and pinion, and body posts).  It did seem useful to wrap up the chassis portion of the build installing the battery tray, servo mount, front bumper, and wheels/tires.

Here are the battery tray and servo mount parts from bag 8.  The battery tray accommodates either standard or shorty LiPos, and has adjustments for length/width/height via fasteners and sliding parts.  The servo mount is a modern floating design secured to the center of the chassis.

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Straightforward installation.

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Front bumper and tire/wheel parts from bag 9.  One thing to note is the front body posts don't line up with Tamiya's M-chassis offerings.  Swapping body shells between Tamiya and 3Racing chassis might mean an extra set of holes up front.  The axle nuts are nice -- they're serrated and flanged.  The tires come glued on the wheels already, and the rubber compound feels slick.  They might be good for a test drive, but they don't seem to be a great compound for grip.

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Parts installed.  There's no extra axle stub length beyond the serrated nuts; this means you may not be able to use regular nylon lock nuts.  Just something to keep in mind if you're picky about axle nuts.

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Based on building this chassis to this level, here are my thoughts:

Good

  • Interesting, thoughtful, modern design features – single-screw outer suspension mounts, bulkhead-mounted steering, floating servo mount, convenient LiPo tray
  • Intentional damper spring selection?
  • Good materials and fasteners overall
  • Minimal slop in finished assembly, smooth operation, things work as expected

Neutral

  • Documentation – print presentation, transition to online
  • Some assembly sequencing – steering bridge and turnbuckles
  • Axle stub threaded length
  • Not much Ackermann

Bad

  • Center pulley mounting holes easy to strip if you’re not careful
  • Some aspects of quality control – scuffed chassis plate, roll bar tweak, CVD pins
  • Could use droop screw plates to protect the chassis plate

If I had to rank the four 3Racing kits I've built so far, then from best to worst they would be:

  • M4 M-chassis:  In general this kit went together very well.
  • D4 drift chassis:  Close second to the M4; the black edition is really pretty good.
  • FGX EVO 2018:  Cool design and glad I own one, but there are some weaknesses in the execution of the kit.
  • D3 drift chassis:  Too many design and quality issues; it took a bit to fix things and make it work.

I haven't taken the plunge and bought one of their high-end kits yet (like the Advance 2K18 EVO or the M4 PRO), but I'm getting closer to considering it as the experiences with these entry-level kits continue to improve.

When I get around to painting the BMW 2002 shell I'll update the thread appropriately.  In the meantime, I'm happy to field questions or take measurements for anyone who wants to know more.

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Many thanks @speedy_w_beans! After your recent build, I was interested in this chassis as it is non-Tamiya, M-sized but 4WD.

Whilst that was a condensed build you gave lots of detail!

Thanks for ranking it against the others too, it certainly seems a bargain.

Will it take a normal nimh stick pack or is it LiPo only?

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@Badcrumble, I took some measurements of the battery tray and it can take a pack up to 133 mm x 47 mm x 26 mm.  The "fingers" at each end of the tray are below half height, and the mounting posts are inboard.  I think the wiring coming out of a regular NiMH pack would fit without a problem.

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