Build Complete: Tamiya DF-03Ra

[fyrstormer]

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.

 

[pixelnate]

So how does it run with all that new stuff? Any better? How does it compare to your XV-01?


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[fyrstormer]

The aluminum steering makes the steering more precise. The steel center-driveshaft cups make the center driveshaft spin more smoothly. The aluminum shocks don't work significantly better than the CVA shocks (and Tamiya plastic shocks might be the only plastic shocks I'll ever say that about), but having threaded preload collars makes suspension tuning a lot more precise. The endbell cooling fan on the motor helps keep the commutator at a reasonable temperature despite the motor being stuffed into a little cubbyhole between the battery and the rear gearbox. The blue stuff doesn't really matter, but it looks pretty.

I like it. The mid-rear motor position gives it a more touring-car-ish weight balance, so it's not as good specifically for rally-style driving where you powerslide around every corner, but it handles rough pavement really well and doesn't exhibit much body roll, unlike the XV-01s -- it's kind of like a touring car that was built for walking trails. The Pirelli S-compound tires with 3mm-offset wheels are perfect on this car.

 

[Ausomecrawl]

Great write up. I have an xv-01 pro and always wanted a df03ra. Very interesting to see your opinion on how they compare. I had always thought the df03ra would have less precise steering due it's location near the midline of the car opposed to the xv-01's more forward position.

 

[fyrstormer]

The XV-01 is a lot more tail-happy than the DF-03Ra; that's where the DF-03Ra's superior handling comes from. Not as good as a rally car in that respect, but better as a touring car to take for a walk.

 

[bvrc]

How about an under body cover? Is there a buggy body that fits on the DF chassis?

 

[OSRC]

Several - Keen Hawk, Avante, and Dark Impact. The latter being still somewhat easy to find.

 

[fyrstormer]

I have a Dark Impact body stashed away that I'll use as a tray cover if I ever decide I really need it, but thus far it hasn't been a problem. Turn the car upside down and shake out the debris. It's not like the Traxxas 4Slash/4Pede where the driveshaft is down at the bottom of the chassis tub where it can get buried in abrasive grit during a hard run, and all of the gears are completely sealed, also unlike the 4Slash/4Pede.

 

[fyrstormer]

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.

 

[fyrstormer]

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.

 

[haplm]

This is interesting. Believe our not, but I've heard that this car was build after Tamiya interviewed some of the rally races around the world, including those in Central Europe. And as was said in other threads, this is exactly what we are trying to achieve - take a touring car, and put it on to a trail. But for some reason, people hated it here. After seeing the amount of upgrades you had to install, I kind of understand it now. But anyway - great job!

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[fyrstormer]

People can hate things for any reason you can imagine, whether or not that reason is actually related to the thing they hate. People can even hate things for no reason at all.

The biggest drawback to a RC rally car that's built to the same scale as a RC touring car is the scale of the terrain doesn't change. A typical full-size car can drive on gravel and dirt roads without modification, but that's because a typical full-size car has about 9 inches of suspension travel. You can build an accurate 1/10-scale car, but the gravel and dirt don't get shrunk down to 1/10-scale, so the vehicle needs to be able to handle the terrain that actually exists. It is very difficult to give a 1/10-scale touring car enough suspension travel to drive on gravel and lumpy dirt. That's why Traxxas' rally car is based on a short-course truck with smaller tires, and HPI's rally car is based on a buggy -- RC short-course trucks and buggies are built large enough to have the necessary suspension travel to handle gravel and dirt.

This car handles scale-accurate obstacles very well. I can drive it at top speed on a sidewalk and it will bounce lightly over cracks and uneven seams between the concrete slabs, and if I want to cut a corner, it will drive on the grass just fine. If I lived in an old European city with cobbstone streets, it would drive well on those too. I can drive it on smooth dirt, but it's not suitable for driving through the forest; even a short-course truck would struggle with that. But that's okay, because this car is still a lot of fun to drive without worrying about damaging it when it runs over rough pavement.

 

[haplm]

I shouldn't have used the word "hate". Way too easy to use it for somebody who is not native speaker, and way too strong.

I think that more accurate would be say that people were sad seeing, that this car went the right direction, but only half way. And you have discovered most of the deficiencies, comparing to what I have heard about it.

I was actually tempted to get one myself to accompany my XV-01, but then I have decided differently.

And you are quite right saying that the surface doesn't scale down to 1/10. Well, to a point it does, if you have a well prepared track. There you can make sure that there are no obstacles that 1/10 car wouldn't be able to handle...

But once again - I like what you have done with this car a lot!

People can hate things for any reason you can imagine, whether or not that reason is actually related to the thing they hate. People can even hate things for no reason at all.

The biggest drawback to a RC rally car that's built to the same scale as a RC touring car is the scale of the terrain doesn't change. A typical full-size car can drive on gravel and dirt roads without modification, but that's because a typical full-size car has about 9 inches of suspension travel. You can build an accurate 1/10-scale car, but the gravel and dirt don't get shrunk down to 1/10-scale, so the vehicle needs to be able to handle the terrain that actually exists. It is very difficult to give a 1/10-scale touring car enough suspension travel to drive on gravel and lumpy dirt. That's why Traxxas' rally car is based on a short-course truck with smaller tires, and HPI's rally car is based on a buggy -- RC short-course trucks and buggies are built large enough to have the necessary suspension travel to handle gravel and dirt.

This car handles scale-accurate obstacles very well. I can drive it at top speed on a sidewalk and it will bounce lightly over cracks and uneven seams between the concrete slabs, and if I want to cut a corner, it will drive on the grass just fine. If I lived in an old European city with cobbstone streets, it would drive well on those too. I can drive it on smooth dirt, but it's not suitable for driving through the forest; even a short-course truck would struggle with that. But that's okay, because this car is still a lot of fun to drive without worrying about damaging it when it runs over rough pavement.

 

[Big Bill]

Nice to see someone else that still uses Brushed motors. I still use them myself and like them, because I understand them Brushless not so much. I looked on-line the other day and could not find very many Brushed items, other than High Turn (35 and up) Crawler motors.

 

[JatoTheRipper]

I absolutely hated my XV-01 and everything about it. It's a flawed design. There are too many interferences in the front suspension and steering with the stock setup. This is what sometimes happens with parts bin engineering. I drove it a few times and sold it. This car, on the other hand, looks like a lot of fun.

I'm not a silver fan, but the body looks good. One suggestion is to get a black ultra fine Sharpie and use it in the door seams and some body panel lines. It really adds a minor, but realistic touch.

 

[fyrstormer]

I haven't had any problems with steering interference on my XV-01s. Everything works as it should. I don't recall making any modifications to the steering system to make it work right, so if I did make any modifications they must've been really minor.

The DF-03Ra is a fun car, but it requires a lot more cutting, grinding, and sanding to make it work well. Also, the chassis is ABS plastic instead of fiber-reinforced nylon, so it's bound to crack eventually. Hopefully that won't happen any time soon, but I have a bag full of spare parts on-hand just in case.

 

[fyrstormer]

Fixed all image links in this thread.

 

[fyrstormer]

Today, on an all-new episode of Fyrstormer Mods A Car That Nobody Cares About Anymore, I fitted a front swaybar to my DF-03Ra.

I geared it up just for fun, and quickly discovered that the taller-than-stock suspension was not up to the task of keeping the car going in a straight line. It's always had a tendency to wander a bit, but after gearing it up, it wandered so much during a quick test drive that I was seriously concerned it would crash into a curb before I could bring it to a stop. In addition, this car has always been a little too easy to powerslide, requiring immediate countersteering as soon as the rear breaks free or else the car would just spin-out on the spot. So, a front swaybar seemed like a good way to kill two problems with one stone.

The swaybar I fitted is a XV-01 medium swaybar, with the arms bent to a slightly sharper angle and trimmed about 4mm shorter. I also drilled a couple holes into the front swaybar mount so I could install set-screws, because for some reason Tamiya didn't include that themselves. Everything else was just stock XV-01 parts.

It drives much better now. It still powerslides easily, but all I have to do to rein-in the slide is let the steering return to neutral. And it goes in a straight line much more reliably now, too.