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Old 05-26-2016, 02:08 AM   #1
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Default Build Complete: Tamiya DF-03Ra

This one surprised me. I found out about it a couple months ago, and I thought "hmm, it's old and it's not even close to TRF-grade like my XV-01s are, but it might be interesting to get a DF-03Ra kit for cheap just to compare to the XV-01." Famous last words.



I built the kit pretty quickly, as it's much simpler than the TRF-grade cars, with the only initial modifications being Tamiya hex-head screws (I have a pile of them left over from other builds), CVD axles, and TRF teflon shock pistons instead of the cheap nylon pistons that come with Tamiya's plastic shocks. At first, the lack of turnbuckles, flexible steering, awful Rally Block tires, wobbly plastic outdrives for the center driveshaft, and rear ball diff with plastic(!) thrust-plate adapters seemed to confirm my expectations that my XV-01s would blow this thing out of the water.



Then I actually drove it, and noticed an awful chattering coming from the drivetrain, and figured out it was actually rejecting the CVD axles I put in the rear! Since this is ultimately a converted buggy chassis, the rear axles are swept forward at a sharp angle to achieve a proper ~255mm wheelbase; because CVD axles have a dogbone joint at one end and a cardan joint at the other end, the difference in angular-velocity profiles between the two types of joints was making the rear wheels vibrate like crazy. This car couldn't even use fancy parts! Even more proof that I shouldn't expect much.

But the thing is, once I fixed the issue with the rear axles, it actually drove really nicely. It's not as oversteer-prone as my XV-01s, which makes it somewhat less exciting as a rally car, but it can powerslide if you give it a good shove, and when I took the thing on a 2.7-mile walk around a lake near a friend's house, I was impressed by how expertly it handled the bumpy walking trail and the acorn-strewn dirt off to the sides. (I was also impressed that the shaft-driven drivetrain is efficient enough that it actually ran over 3 miles, including loopbacks, on a single 5000mAh LiPo. At it's gearing-limited top speed of 25mph, it was actually pretty relaxing to shoot it up and down the paths to the entertainment of nearby children. The fact that it's a converted buggy chassis actually has a bunch of subtle benefits in handling uneven surfaces, which touring cars normally suck at, and despite having a comparable ride-height to my XV-01s it exhibits much less body-roll even with no swaybars installed.

So, I did my due-diligence and shopped around for parts that might improve the car's weaknesses, and now it looks like this:



The electronics are straightforward -- it's using the same Hitec HS-8775MG low-profile coreless servo that all my other touring cars use, the same Dynamite DYNS2210 60-amp brushed ESC that many of my vehicles use (it's cheap and effective, that's all I care about), and the same 12-turn Team Orion brushed motor with silver brushes and an endbell-mounted fan that two of my XV-01s and my MERV use. So there's nothing interesting in that regard, but...there's all that Tamiya-blue crack all over it, and that's worth talking about.



For starters, not all of the crack is blue, and not all of the blue is Tamiya. With my XV-01s I stuck to Tamiya parts exclusively, but Tamiya just doesn't make some of the necessary upgrades for the DF-03Ra. For instance, in the picture above, while the motor plate, heatsink bars (which are of questionable value, but...meh, why not), and center driveshaft are all Tamiya parts, the low-key black steel outdrives on the ends of the center driveshaft are actually made by a company called RC-Square. They eliminated the wobbly-driveshaft problem that the car had after I built it with the stock plastic outdrives. The blue servo-saver is made by Max Speed Technology and the blue endbell-cooling-fan posts are made by MuchMore Racing. Also, hidden under the spur-gear cover on the other side of the motor plate is a slipper clutch assembly for the DF-03 buggy, but it's running a 48-pitch 81-tooth spur gear from Team Associated. I had to replace the stock DF-03Ra spur-gear cover with the version for the DF-03 buggy to make room for the larger spur gear, but it was a direct fit.



The aluminum steering assembly is also made by RC-Square, and eliminates almost all of the flex from the steering system. It even has ball-bearing pivots for the center plate, like a Tamiya factory upgrade would; RC-Square definitely makes good upgrade parts. The blue pivot-balls are Tamiya, though the ones on the steering knuckles are actually leftovers from building a TB-04R kit; they have a 1mm spacer integrated into the base of the pivot-ball, which is just enough offset to minimize the bump-steer caused by the super-short steering links.



The shocks, of course, are Tamiya TRF shocks, which I now have on several vehicles in blue, black, gold, and purple (with assistance from some Max Speed Technology shock parts, which are interchangeable with TRF parts). On this car they're the normal blue color, but of course they work just as well no matter what they look like. Despite this being a rear-heavy vehicle, the leverage on the front A-arms is such that it needs stiffer suspension up front. The front shocks have the medium-stiffness tuning springs for the XV-01 and 60wt oil, whereas the rear shocks are still using the stock springs (which are the same as the softest tuning springs for the XV-01) and 45wt oil. Behind the shocks you can see the stock rear dogbones are still installed, sandwiched between O-rings in the stub axles and foam dots in the diff outdrives to keep the dogbones from rattling around or falling out. I'm not a big fan of dogbones, but this is one application where they are the only thing that works, and they do just fine.



So, what started out as a quick and dirty "hey, why not?" experiment turned into a car I plan to keep for a long time.
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Old 05-26-2016, 07:01 AM   #2
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TRF shocks are over damped for that car if you're running it offroad. The original box items are much better for that. The only upshot is that TRF shocks are shorter, thus limiting downtravel which as you found can be a problem (the chattering you heard is actually the inboard joint reaching maximum articulation). If you want to use CVD you'll need to find some shorter driveshafts, or use shorter outdrives.

XV01 is not a TRF grade car either, not that it matters.

TRF cars are not more difficult to build, people just do it more carefully, because they want performance and some things can be fiddly. Nobody is going to waste their time to properly shim a diff or driveshafts on a basher.

The DF03 is otherwise a rather competent little chassis, perhaps more than the complicated XV01.
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Old 05-26-2016, 10:01 AM   #3
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TRF shocks come with 2-hole and 3-hole pistons; I use the 3-hole pistons on all my Tamiya rally cars. Also, whether or not it's over-damped depends on the weight of the oil. The TRF shocks are the same length as the stock CVA shocks; I have 12 sets of TRF shocks now, so I'm pretty familiar with them.

The chattering was not the result of the inboard joints reaching maximum articulation; there were no bite-marks on the sides of the CVD shafts from the edges of the drive cups, and I could temporarily make the chattering go away by rotating the rear wheels so the axles were clocked 90-degrees to each other, causing their rotational harmonics to cancel-out. The stock dogbones articulate the same amount and do not exhibit any chattering at all.

The XV-01 is TRF-grade in the sense that it can use TRF suspension tuning components. It doesn't have a carbon-fiber chassis, but a carbon-fiber chassis wouldn't hold up to driving off-road and getting scratched by rocks very well.

I, for one, waste my time properly shimming the diffs and driveshafts on all my bashers. They work better that way.
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Old 05-26-2016, 11:12 AM   #4
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Yeah, but the piston holes are smaller hence you get more pack no matter what density oil you use and they don't have the side flat either. Try your car on a bouncy buggy track and you'll see.

So where was the chattering coming from then?

I think it's a long shot to say that using TRF suspension brings the car in the same class in any way.And there's absolutely no benefit to it in this case. The XV01 is just another Tamiya exercise in pointlessly overcomplicated basher design. No matter how many TRF parts you'd use on it, it still remains a basher car.
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Old 05-26-2016, 01:48 PM   #5
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I explained where the chattering was coming from.

The fact that the TRF pistons don't have a flat-spot on the outer circumference is a good thing, because it makes the damping more consistent. The reduced flow as a result of the "missing" flat-spot and slightly smaller holes can be compensated for by using thinner oil.

Why would I drive a 1:10-scale touring car on a buggy track with hills to jump over? That comparison makes no sense. Drive a buggy off some ramps at a skatepark and you'll discover a buggy makes a crappy monster truck, but that has no bearing on whether it's a good buggy.

Sorry you don't like the XV-01. I have 5 of them and I think they're great. I even have one that the guys at my LHS say I really ought to bring to a track day because it handles so well, if only I cared about racing. But this thread isn't about the XV-01.
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Old 05-26-2016, 02:24 PM   #6
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Great write up, and included photos!
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Old 05-26-2016, 09:32 PM   #7
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TRF-grade....
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Old 05-26-2016, 10:58 PM   #8
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Damn, a whole writeup and that's the only thing you have to say?

I get it, I get it -- track-car fanboys don't have much use for anything that goes less than 60mph and/or touches dirt on purpose. Point made. Carry on.
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Old 05-27-2016, 12:11 AM   #9
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Cool build fyrstormer!
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Old 05-27-2016, 12:48 PM   #10
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Nice write-up and presentation of what you did. You'll get more attention and appreciation on Tamiyaclub if you post it there.
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Old 05-27-2016, 10:09 PM   #11
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Thanks!

I've tried to register at TamiyaClub before, but I think that forum is dead. They still haven't approved my account.
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Old 09-16-2016, 08:22 PM   #12
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I replaced the steering knuckles on my DF-03Ra. After months of lamenting the discontinuation of RC-Square's upgrade parts for this vehicle, I found out that Yeah Racing's parts are actually pretty good too, so I ordered some steering knuckles and wheel hexes from them. The stock knuckles on this car were too flexible, and the plastic was soft enough that I couldn't get the kingpin screws to bite reliably. Aluminum fixes both of those problems.

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Old 07-12-2017, 06:18 PM   #13
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Several updates to this car.

First of all, the most obvious update:



Yep, I added headlights and taillights.



I keep saying I won't install lights on any more of my vehicles, but I keep coming up with reasons to do it anyway, and I'm starting to get good enough at it that I don't really notice how tedious it is. In this case, I've been driving after-dark a lot lately (which will only increase as the days start getting shorter again), I didn't have any touring cars or rally cars with lights, and this is the only one I have with proper light buckets included with the body shell. Since this car goes a reasonable speed for nighttime driving (28mph) and is fairly durable, I decided it would be a good candidate to be equipped with running lights.

Oh, I also finally installed the ABS plastic spoiler that came with the car; of course I color-matched it so there wouldn't be a plain white spoiler on a silver car. It seemed more reasonable to do now that the car has a good track-record for not flipping-over or tumbling end-over-end, which would nastify the spoiler really fast.



Underneath is sort of a typical Fyrstormer wiring job, with a separate current-limiting resistor for each LED, except for the taillights which could be linked two-in-series without requiring more voltage than the ESC could supply. The wires are taped securely to the body, except for the bundle in the middle, which is loose because I plan to do something more elegant with it in the future. Unfortunately the spring-loaded-contact setup that I used on my scale crawlers isn't compatible with the body supports on this chassis, but I'll figure something out eventually. In the meantime the wiring harness connects using a JST plug, which isn't too much of a hassle because the DF-03Ra has a bottom-loading battery tray, so I don't have to remove the body except to perform maintenance.



Third, I replaced the original plastic shock towers with carbon-fiber shock towers and aluminum mounts. That might seem like a superfluous thing to do on a chassis made of flexible ABS plastic, but it's actually quite beneficial, because the original shock towers were *also* made of flexible ABS plastic, and the camber link mounts were able to flex enough to override the camber settings I dialed-in. It also eliminates a little undamped-spring action from the upper shock mounts flexing, so the dampers are better able to keep the car from bouncing over sharp impacts.

Speaking of which, I reduced the oil weight in the rear shocks from 45wt to 30wt, and that helped the rear of the car settle better; I overestimated how much damping would be necessary to keep the rear of the car from bottoming-out on the terrain it's actually able to drive on.



Fourth, I installed slightly longer damper shafts in the shocks, to give the suspension more travel and increase the car's ride height a little. (this is another reason I was able to thin-out the oil in the rear shocks.) It is now able to drive fairly well on grass, as long as it's matted-down a little. I had to modify the front caster blocks to allow them the range of movement necessary to utilize the longer shock travel, as seen below:



You can also see the double-cardan front axles I installed, after proving the concept on my other, 2-speed DF-03Ra chassis. This required sending the front hubs to a machinist to have the inboard bearing sockets milled a little deeper, and tracking down some 5x11x3mm inboard wheel bearings, which was a pain because that's not a common size. (Boca Bearings saved the day on that one.) Now there's no chattering from the front axle when cornering, which I much prefer; if only I could fit DCDs to the front axles of my HPI RS4s.



Lastly, I rebuilt the motor. In the past couple months I've been overhauling all of my brushed motors, switching them to use the highest-quality parts I can get, largely because I finally got sick of the Team Orion Method Pro motors trashing my expensive ceramic bearings on a regular basis. I hadn't noticed before, but the bearing sockets were almost always slightly crooked, so it was time to upgrade to better-quality motor cans. This motor still uses the Team Orion Method Pro 12x2 armature, but it has been transplanted into a Sagami can and endbell from Team Tekin. (why not Holmes Hobbies? Because I wanted the chrome-plated motor cans, no other reason.) It was originally one of their Pro Hand-Wound motors, so it has stronger "FB12"-grade magnets, which slowed the motor down a little but significantly increased its torque and power-efficiency. The Reedy Plutonium silver brushes I originally used have been replaced with Reedy 729 copper brushes, for the sake of reducing wear on the commutator, though it's possible the copper brushes might need replacing more often; I'll have to wait and see how that works out. The medium brush springs were replaced with stiff springs to prevent arcing at high RPM; I hadn't noticed an arcing problem with the Reedy Plutonium brushes, but switching to copper brushes caused tons of arcing, and ruined a different motor before I figured out what I needed to do to fix it. Fortunately the stiffer springs don't seem to be wearing the copper brushes faster (increased friction causes minimal damage compared to arcing), and the commutator is staying round longer thanks to the gentler copper brushes, so this should be a better setup overall.

I still like this car a lot. It's a shame there is no DF-04Ra, because it's a lot of fun to drive a rally car with a big heavy butt to swing wide in corners. Whereas my front-motor XV-01s bring the rear axle back in-line as soon as I straighten the steering, the DF-03Ra requires precisely-timed countersteer to prevent spinouts, and it rewards skillful driving with really cool-looking slides.
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Old 07-18-2017, 12:46 AM   #14
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Great build

Thanks to this build I finally found whats wrong with Tamiya CVDs and why they chatter like crazy... They have wrong angle between dogbone and CVD ends, so instead of cancelling difference of velocity, they multiply it... Pin on dogbone has same fuction as barrel in CVD, so they should be parallel.
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Old 07-19-2017, 01:45 AM   #15
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It's always nice to know my build threads actually help someone from time to time.

Tamiya CVDs work fine for most of my touring cars. The DF-03Ra is a special case, because of the strange angle of the rear driveshafts. For this car, GPM CVDs work better in the rear. But all CVD designs will chatter if used in the front, when cornering sharply. Double-cardan driveshafts fix this problem, and that's why I hired a machinist to customize a set of front hubs to use double-cardan driveshafts.
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Last edited by fyrstormer; 07-19-2017 at 02:25 AM.
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