2018 - Tamiya DF-03 "Dark Impact"
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Finally I found a RC that's as dark as my soul.
goth buggy is so dark
Okay, not really, I just couldn't resist the urge to make fun of the "Dark Impact" branding on this kit.
So anyway, this is my new track buggy, for driving at the local indoor track when the weather is icky or I just don't want to risk being bothered by neighborhood kids.
I can hear you thinking: "Why on earth did you buy that thing to drive on a track? It's so fragile! What a waste of money." Well, I had two reasons for choosing a DF-03 instead of a different kit: 1) I have two other DF-03-based vehicles, so I have a large stash of spare parts for this platform and the only additional parts I need to keep on-hand for this buggy are the A-arms and the CVDs, and 2) I felt like it. ;)
Of course, I am aware that the DF-03 is fragile as track vehicles go, which is why most of the work I spent on this build was to figure out how to make it durable enough to survive motocross-style jumps. Hence the carbon-fiber shock towers and thick nylon wing, with rounded corners to avoid digging into the dirt if the buggy lands wheels-up -- which happens several times per track-day because any kindergarten teacher would grade my track driving skills as "N" for "needs improvement". And in case you're wondering, yes, the very first time I drove this buggy on the track, I broke the front and rear bulkheads. My driving has improved significantly since then, but for obvious reasons I still had to figure out ways to strengthen the buggy some more to minimize breakages. For me, that's part of the challenge.
So here's what I came up with:
The DF-03 has a rather large Achilles'-heel in the design of the rear shock tower, which mounts to the top of the rear gearbox, with no support on the back side of the mounting point. These two turnbuckles I've added anchor the top of the shock-tower mount to the bottom of the gearbox using screws that needed to be removed to access the inside of the diff case anyway, vastly improving the strength of the rear shock-tower mount without adding any complexity when opening the diff case for service. The turnbuckles are adjusted to be slightly pre-tensioned, so the shock-tower mount doesn't have to flex before the turnbuckles will carry their share of the load.
The front shock tower doesn't have the same problem, but the A-arm mounting block desperately needed reinforcement to survive cartwheels; the A-arms themselves are made of fiberglass-reinforced nylon, but the mounting block is made of plain old ABS plastic. (or maybe it's POM plastic, but either way it's not the strongest stuff.) I looked into having a custom brace made, but while I was waiting for turnaround on that, I realized the brace used on the HPI Nitro RS4 3 / Nitro MT2 has the same eyelet diameter and spacing, so I fitted one of those instead. The pivot pins were long enough to accommodate the brace without modification, which begs the question why Tamiya didn't just include a brace to begin with, but that's water under the bridge now.
One advantage of using the RS4 brace is, the RS4 brace has an alignment tab on the underside, so when one A-arm takes a hit, the brace can transmit force to the chassis as well as the opposite-side pivot pin, reducing the risk of a hard hit breaking both pivots. The most tedious part of this mod was carefully filing the rectangular hole shown above, but it's worked out very well so far.
My other DF-03-based vehicles are a rally car and a touring car, which have a lot more space under the body shell for the electronics to fit. This buggy has much more stringent space constraints, so I had to get creative to make everything fit. To start with, since I'm using LiPo packs with built-in power leads, I had to find room to route the power leads out of the battery compartment:
That meant the receiver and ESC needed to be pushed out of the way, so I had to clearance the side of the chassis tub so the ESC could fit as far forward as possible:
And that, combined with the minimal space available to begin with, meant I had to cram the power and motor wires into whatever space was available:
And then, because there's no way to heatshrink the battery-plug terminals with the wires soldered onto them at such a weird angle, I needed to add some insulation to the inside of the body shell, to make sure the battery-plug terminals wouldn't short-out against the aluminum-foil tape I applied to the inside of the body to keep the wires from rubbing the paint off:
It's too bad there isn't a Nobel Prize for fitting things into tight spaces, because I'd like to think this would at least qualify for an honorable-mention.
And yes, I know this would've been a lot easier if I'd used a battery that has bullet sockets built into it. When I start replacing the batteries I have now, I'll switch to that design, but the hobby shop where I bought my current batteries didn't have any of those, and I didn't know it would matter someday, so I just bought what they had available.
Beyond making the chassis stronger and making the electronics fit, I've never intentionally done a lightweight build before, so I decided to see how light I could make this buggy. There are only two steel screws on the entire chassis -- the screws attaching the wing-mounts to the rear shock tower -- and the rest are titanium. The rear CVDs are aluminum instead of steel, and a bit of experimentation plus a lucky guess resulted in me figuring out the Yeah Racing aluminum diff for the F201 would fit the DF-03 as well.
I had to shave 2mm off one side of the ring gear because the position of the ring gear in the F201 diff was slightly different than the DF-03 diff, and the ring gear would've rubbed against the inside of the diff case without being shaved. However, the amount of gear material removed isn't enough to have a meaningful effect on its strength.
The result of the various weight-saving measures are a buggy that weighs 1386g without the battery installed. That's lighter than a couple of my touring cars. I could've saved a little more weight by using the stock plastic shocks instead of optional aluminum shocks, stock plastic shock-towers instead of optional carbon-fiber towers, stock plastic hubs instead of optional aluminum hubs, aluminum CVDs in the front as well as the rear, and a flimsy Lexan wing instead of the thick nylon wing, but there were certain things I was unwilling to compromise on. I could've made an even lighter buggy if I'd made it out of origami, after all, but one of my stipulations was that it needed to be able to survive driving on a motocross-style track. And this buggy does that.
So, that's my take on a cheap track buggy. Will it win any races? No, not a chance. Between the full-size LiPo pack, the sensorless motor, and the treaded tires, it lags behind other buggies at the track that have shorty packs, sensored motors, and slicks. (also I don't practice for hours every week like those guys do.) But the goal with this build was never to win races, it was to give me the chance to drive on a track without having to borrow someone else's buggy. And it does that quite well. Thus far I haven't gotten hooked on track driving, but if I ever do, rest assured I'll build a "real" kit for that purpose.
I said I'd rewire this buggy to use bullet connectors, and that's exactly what I did. The motivation came from a freak accident that tore the front bulkhead clean off the vehicle and damaged one of the screw holes on the chassis, so as long as I had to replace the chassis anyway I went ahead and modified it to fit a battery with bullet connectors instead of an XT90 plug. I had to cut off the mounting points for the front body posts, but that's not as big a problem as it might seem. The shock towers completely protect the body from contacting the ground, so I was able to attach the body with strips of Velcro around the sides without worrying about whether the Velcro would rip loose in a rollover.
That is so much cleaner than the original wiring.
My DF-03 got new wings a couple weeks ago.
The rear wing is TLR brand, and required drilling new holes in the rear shock tower for the wing brackets to fit, because the stock spacing wouldn't fit any of the name-brand wings sold at my local track. The front wing is JConcepts, made for some Tekno buggy. I'll be honest, it's probably totally useless, but it looks pretty trick, and it was easy enough to install with some cylindrical spacers and a pair of longer screws in the front shock tower mounts.
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