Tamiya DF-03 Dark Impact Review
1 February 2007.
When pictures of this chassis first got leaked on the Internet, everyone was talking. Tamiya fans were hoping it
would be the company's first successful racing buggy. Skeptics were calling it another plastic basher. When it
was released, I resisted getting one because owners had mixed opinions about it. After waiting a few months, I
caved in and got one to tinker with. Here's my very late and on-going review of the DF-03 Dark Impact.
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The kit includes an extra set of wing mounts at a different angle. (The one on the left is steeper). I picked the steeper mounts.
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The rear gearbox is a mix of gears and strange bearing sizes including two 1050 bearings, three 950 bearings,
one 830 bearing on the "upper floor" plus the usual two 850 and two 1510 bearings for the ball differential underneath.
In this picture, I actually have an 850 mistaken for a 950 and didn't find out until much later when I was looking
high and low for that last bearing for the front diff.
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The kit comes with a 78-tooth spur and a 85-tooth spur. Since I also bought the Tamiya slipper set (53925), I installed it.
This slipper set comes with a 82-tooth spur but I installed the kit 85-tooth onto the slipper unit.
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The rear hubs and front C-hubs hang onto their hingepins with the help of M3 grub screws. You will need to drill 2.5mm holes
for these. The hingepins have a flat slot for the grub screws to sit in, so it's not necessary to tighten them to the point
where the pins are totally immobilised (it's not possible anyway, you'll just end up stripping the screw threads). The pins
can still move a little but shouldn't come loose as long as the grub screws are touching the flat slots.
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The dogbone pins on most DF03's I've seen eat into the diff cups for some reason. The two shafts on the left are
the stock dogbones. The ones on the right are the Tamiya DF-02 Assembly Universal Shaft set (53791) with the bottom
one inside a TRF415 Swing Shaft Protector (53890). The protectors won't fit the stock dogbones because they have
longer pins but they fit the DF02 universals perfectly. The other interesting thing I noticed was that the stock
dogbones had slightly smaller balls, which meants they probably rattle around inside the diff cups quite a bit.
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Using the protectors presented a few challenges because the slots in the diff cups had to be widened quite
significantly and that meant the diff nut holders needed to be changed to the TRF415 ones as well. The swing
shaft protector set gives 4 protector sleeves but only one diff nut holder, so you will need to buy two sets
(for the front and rear diffs). I'm a little concerned that the diff cups are now much weaker. We'll see.
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There's a little extra play between all the inner suspension arm hingepins, so the rumour is that Tamiya
is planning to come up with some suspension brace plates to fill these gaps and strengthen the buggy later.
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I wasn't going to wait, so I made my own brace plate out of some scrap aluminium. This is on the front.
Haven't made one for the rear yet but it looks like there might just be enough space for one under the motor.
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The steering rack is quite limited by this tall stub that helps hold the front kickup plate to the chassis. I shortened this and the screw
inside by about 1.5mm for the steering rack to clear it and this gave a little more steering. I first read about this mod from
this page.
Update: BloodClod
just pointed out to me that this mod doesn't do anything when the stock servo saver is used because at full lock,
the steering rack doesn't get obstructed by the stub.
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I'm running a set of aftermarket shocks from 3Racing. They look great but come with some cheesey-looking mounting hardware. I used some M3
stainless steel screws instead of their long black grub screws. The DF-03 manual says to use the innermost mounting hole on the arms for the
front shocks and I've found that the steering rods bind against the shock towers if you use any other hole. I'm disappointed by this design
so I'll try and flip the front arms around later to get the shocks out of the way. The 3Racing springs turned out to be very stiff and allowed
no droop in the front and very little in the rear. Couldn't seem to find a good set of springs for them (Tamiya's were too narrow. Losi's
were wide but usable; fronts were too long hence no droop again). Might go back to kit shocks with two-hole TRF pistons and some thick oil).
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Note: I've switched back to the kit shocks with one-hole pistons and Tamiya 400 oil all around, and the gold (medium) DF-03 upgrade springs
(53927)and I'm getting a good amount of damping now.
Lunsford turnbuckles complete my buggy. Two pairs of 2" and one pair of 1 7/8".
The final product, more or less.
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After some consideration, I decided to swap the regular steering servo with a low profile one. I had an extra Bluebird BMS-706MG
(check out the review here), which didn't seem to fit in my
other cars but turned out to be a very good fit here. I had to cut the rear servo posts on the chassis a little shorter. I
could have done the same with the front servo posts but got lazy and just installed the small plastic servo extension above the
servo ears rather than below them. The ball stud had to go above the servo saver horn. Just when I thought everything was done, the
servo saver binded against part of the chassis, so I grinded down a little of both to get back full steering throw. Quite a bit of work,
but everything sits lower now. I later added an O-ring (sink tap washer) around the servo saver which took out a lot of the slop.
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After the maiden run (street bashing in front of the house), I managed to flip the buggy several times but avoided hitting anything
head-on. Nothing broke or popped out but I did notice one screw was missing from the bottom of the chassis. It was one of the four
screws that hold on to the rear gearbox. I later realised I'd been using M3 X 10mm self-tapping screws instead of M3 X 12mm that were
meant to go here.
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Another thing I noticed is that small pebbles like to bounce around inside the motor area and scratch up the chassis and the
motor. Not a major problem for me but worth mentioning in case anyone is thinking of testing out a brand new motor in a DF-03.
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The first track I tested the buggy on was a small track meant for 1/18 trucks.
It's a bit tight for 1/10 scale racing but since I was the only one there, it was about the right size for a test drive.
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I ran the buggy with a Novak XBR brushless ESC coupled to my old SS5800 motor. It was a bit of a handful with the first set of
tires I tried (some cheapo China ones which had a squarish profile and lots of X pattern lugs). I swapped them for a set of simple
spike tires (similar to Tamiya DF-02 stock tires) and the car had a lot more grip on the loose dirt. The buggy still had a little
more steering than I could handle, but it was fun doing just a slight bit of fish-tailing and counter steering on some of the hairpin turns.
Every now and then, the buggy did slide around the corner perfectly, so I think the buggy definitely would have been much faster if I
could only drive it consistently. I think the short wheelbase and mid-mounted motor gives the buggy quite a lot of steering
so I don't feel the urge to try out the centre or front one-way units - at least until I get much better driving it with the diffs.
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Dirt everywhere. The inside of the bathtub chassis wasn't too bad even though I had a ventilation hole where the ESC and fan was, but
the rear gearbox was coated with dirt. A bit of grease around the gearbox seams would definitely help to keep diff rebuilds further apart.
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Bad news to report on my custom mods on the diff cups. After the dirt track test, I noticed one of the front cups are a little bent out of shape.
It's probably caused by some rocks. The buggy still runs okay for now but I foresee it failing at some point. After that, the 3Racing diff halves
are going in. The modded rear cups are holding up very well though.
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More bad news on the front diff halves. I was practising on a small indoor carpet track and one of the 3Racing output cups
were slightly bent out of shape when a universal shaft popped out. The culprit was a loose camber link ball nut that let
the rest of the assembly down. I didn't want to end my race day, so I put the front one-way set in and the buggy drove
very well. The lack of front brakes hardly affect my jumping because I almost never hit the brakes when jumping at that track.
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When I first built the buggy, I got overzealous with my hex screw installation and used some button head M3X10 screws as the lower
steering kingpins. They looked great but after a few runs, one of them fell out. In this pic, I've gone back to using the kit M3X12mm Phillips
head countersunk screws. The countersunk screws have less contact with the flange tubes that they fit through, and have a smaller chance
of getting undone in a race. If you do use hex head screws here, make sure they are M3X12mm countersunk ones.
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Update:
I turned the buggy back to full Tamiya-legal specs and raced it in the first round of the Tamiya Asia Cup qualifiers in Malaysia for 2008.
To read the race report, go here.
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Update 6 May, 2008:
The DF-03 showed a tendency to nose-dive and didn't jump well at the TAC qualifying first round.
Here's a picture of the DF-03 (right) and a DB-01 with the rear axles lined up.
It's hard to judge where the centre of gravities are but it is clear here that changes in battery weight grossly affects the
DF-03's weight distribution front to back. With the 445 gram 4600mah stick packs I was running, the poor buggy was just way too
front heavy for big jumps.
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