RCCrawler Forums - Re-Build Complete: Tamiya XV-01

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Re-Build Complete: Tamiya XV-01

This is a little different from my other Build Complete threads. You see, my new XV-01 didn't start life as an XV-01, it started life as an FF-04 Evo:

http://i.imgur.com/paHvvJP.jpg

After driving it a few times, I realized two things about it:

1) It needed more suspension clearance for the kind of terrain I have to drive it on;
2) FWD has amazing steering and terrible acceleration.

Thing Number 2 is no surprise, I suppose, but what I mean to say is that after trying the stickiest tires I could find *and* turning the punch-control all the way up on the *brushed* ESC I was using, I still couldn't get it to take-off without massive wheelspin. Upon further reflection it occurred to me that I might've had better luck with a high-turn motor and really high gearing, to minimize the amount of torque the motor could generate, but that didn't really satisfy my desire to have a reasonably high-speed car. And yet, I really liked the layout of the FF-04, with the motor hanging off the front, because it steered so well and had such a realistic weight-balance.

Then I found out about the XV-01, the 4WD rally-car platform that donated its gearbox to the FF-04. My interest was piqued, so I bought a kit and transferred as many of the fancy parts from the FF-04 as I could -- the aluminum shocks, the gearbox, some of the carbon-fiber parts, the aluminum steering assembly, and various shiny blue hardware bits. After a couple test-runs, I liked it so much I decided to buy all the other fancy parts Tamiya offers for the XV-01 and fully upgrade it. The result is this:

http://i.imgur.com/Qizt621.jpg

To be fair, it doesn't look as shiny as the FF-04 did, but that's because the XV-01 is a more enclosed chassis, so the shiny bits are harder to see -- and some of the upgrades are carbon-reinforced plastic, so unless you have a particularly bright light to shine on them, you won't necessarily be able to tell they're upgraded at all. That's fine, there's enough bling on this car, I don't need every single upgraded part to glitter in the sunshine. However, if you look closely there's still lots of shiny bits to look at.

http://i.imgur.com/HsA2exn.jpg

As with the FF-04, most of the serious business happens up-front. In the picture above you can see the FF-04's front gearbox that I lifted and installed wholesale into the XV-01, including the same 12T mod-motor with silver brushes that I put in the FF-04. I did eventually have to take the front gearbox back out of the XV-01 so I could install a slipper clutch in it, and of course I had to install a different idler-gear shaft that extends out the side of the gearbox to drive the belt that connects to the rear gearbox. The motor now has a fan installed to help keep the endbell cool, because more of the motor's power is actually getting used now that the car is 4WD.

I was able to keep the fancy double-cardan front axles that the FF-04 came with, but I had to replace the inboard ends of the axles with slightly shorter 42mm pieces that Tamiya thoughtfully provided so the axles could be fitted into tighter spaces. The shocks are mostly the same, though they're now sporting longer shafts from Yeah Racing's 60mm aluminum shock kit (I didn't like the rest of the shock kit, but the shafts were useful), so the car has a bit more suspension travel than it was intended to have. Eventually the Yeah Racing shafts will be replaced with Tamiya's Teflon-coated long shock shafts, when they come back in stock, but for now these work just fine.

The suspension arms, caster blocks, and steering knuckles have all been upgraded with carbon-reinforced plastic, and the turnbuckles have been upgraded with anodized titanium. (fun fact: titanium anodizing is actually transparent, and relies on light-diffraction to produce the color you see -- there's no dye soaked into the anodizing layer, like there is with anodized aluminum parts.) Those parts are all XV-01 specific, which meant I couldn't reuse the respective parts from the FF-04, though after more research it looks like I'll be able to use the FF-04's suspension parts on a different project. (the FF-04's suspension originally came from the TB-03 anyway.)

http://i.imgur.com/Wz6iYlU.jpg

In the back, there's a secondary gearbox, driven by a belt, that powers the rear axle. The stock dogbone axles were replaced with 39mm CVD axles, which got rid of a noticeable amount of slop, because the axles are no longer loose at both ends. Here too the suspension parts are XV-01 specific and upgraded with carbon-reinforced plastic, though as you can see the toe-blocks were upgraded with aluminum instead. (the front toe-blocks were also upgraded with aluminum, but they're hard to see.) The rear shocks also came from the FF-04 and were retrofitted with longer shafts from the Yeah Racing 60mm shock kit, giving both front and rear suspension about 1" of extension when the wheels are in the air. When it's on the ground, about 3/8" of that is used up as droop to keep the tires on the ground when cornering.

Swaybars were necessary front and rear because the car leaned like crazy in corners with the taller, softer suspension; I went with the soft swaybar in the rear and the medium swaybar in the front. The shock springs are soft in the rear and hard in the front, with 30wt oil in the rear and 80wt oil in the front. That might seem like a huge jump in shock stiffness, but it makes sense on this chassis because the front axle is heavy and has a tendency to plow into obstacles, whereas the rear axle is much lighter, and also has the benefit of having the front axle already lifting the chassis over the obstacle by the time the rear axle gets there. The weight balance on this car is seriously realistic, somewhere in the vicinity of 65F/35R with a 2S LiPo installed, which makes for a very entertaining drive.

http://i.imgur.com/awZvnpf.jpg

As you can see in previous pictures, the drive belt is fully shrouded except for a little bit at the front; the belt rotates in reverse compared to the rest of the drivetrain, since it's connected to idler gears, and the open bit at the front means the belt can sweep out any debris that manages to find its way under the shroud. Here's a picture of the rear portion of the belt-drive, where it connects to the rear gearbox and where the tensioner is mounted. As you can see I upgraded to aluminum pulleys, which did a nice job of giving the belt-drive a more solid feel. The rear axle no longer feels like it's connected to the motor by a piece of rubber, though I assume that sensation was actually caused by flex in the stock plastic pulleys, not the belt itself.

http://i.imgur.com/sVqy4fs.png

The underside of the XV-01 is flat and mostly sealed, with a few holes for debris to fall out through. The battery door was upgraded with carbon-reinforced plastic for extra strength; it bolts shut from the underside with a pair of 2mm hex screws, which some people have complained about, but I really like it. The battery is held securely in-place and can't come loose short of a truly catastrophic crash, and I always have a 2mm hex wrench near my RC cars anyway, so it's not like I have to go down a flight of stairs into the basement to open the battery box.

I had to cut away some plastic from the battery-cable pass-thru port inside the battery box, to make room for the huge XT90 battery plugs I use, but it does fit, so there should be no problem using any type of battery connector you prefer. (the new Traxxas connectors might be a problem, but that's the only one I can think of.)

http://i.imgur.com/W08vVO9.png

From the top you can see a glimpse of the blue aluminum steering assembly, now obscured underneath a carbon-reinforced-plastic bulkhead that keeps the front gearbox firmly anchored to the top of the chassis, in lieu of having a full-length upper deck like the FF-04 has. You can also see the motor wiring, and the extra wiring I added for the endbell cooling fan. (it works wonders, by the way; I'm now convinced that endbell cooling fans are a necessity to safely run brushed motors with LiPo batteries, because of how much power a LiPo can shove through the motor.)

From the top you can also see the cover on top of the electronics tray, which keeps water and debris away from the receiver and ESC. It's a cramped space in there, but I was able to fit my favorite brushed ESC in there, the Dynamite DYNS2210 -- it's not fancy, but it doesn't need to be, and the braking actually works properly, unlike all the other brushed ESCs I've tried. Even the ridiculously expensive Tekin FX-R operates the brakes on a timer, so if the car is still coasting when that timer expires, tapping the brakes will send the car into reverse instead of just slowing it to a stop. The Dynamite brushed ESC gets that right, and it costs a LOT less.

It gets pretty hot inside that little box, but Tamiya thoughtfully designed the front shroud on the electronics-box cover to fit a 30x30mm cooling fan, so I bought a little Sunon fan from Jameco Electronics and installed it. I had to make a Y-connector so I could connect both the motor fan and the ESC fan to the same port on the receiver, but everything just fits, and I tested the airflow with a smoldering match to make sure I hadn't somehow managed to block off the airflow with all that wiring inside the box. The ESC runs noticeably cooler now.

That's it for the nuts and bolts, now it's time to show off the body:

http://i.imgur.com/IPv8zb4.jpg

I love the way this body looks, even though I had to cut each decal by hand because the decal sheet wasn't pre-cut. (let me tell you how much fun it was to cut and attach all of those little black stickers in the lower grill.) I relocated a few of the sponsor decals away from places that I knew they'd get scratched up, and I decided to skip the swoopy red-and-blue livery decals that were impossible to conform to the fenders and I knew would get torn up on the first rollover, but other than that it looks exactly as the manual specifies. The selective-yellow headlights were a spur-of-the-moment idea I had, and the Tamiya transparent yellow paint worked perfectly on top of the chrome headlights.

However, I think I outdid myself, because I just can't bring myself to actually *run* this body, at least not yet. For now, my XV-01 will continue to use the body I originally prepared for the FF-04, with enlarged wheelwells to accommodate the taller rally tires:

http://i.imgur.com/lP4gFJh.jpg

Either way it's a great car to drive. I would definitely buy it again -- in fact, I did, but that's a different thread...