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Old 10-25-2015, 07:10 PM   #1
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Default Build Complete: Tamiya RR-01

Technically speaking, this is a Tamiya XV-01TC (i.e. the touring car configuration of the XV-01 chassis), but I decided to call it the RR-01 because I did something a little...different.



Yes, that motor is hanging off the back of the rear axle. I figured out a way to mount the top halves of the front and rear gearboxes in reverse configuration, so I could have a rear-wheel-drive touring car with a full-rear motor mount. This posed a number of secondary challenges regarding mounting the suspension, but replacing the stock plastic shock towers with flat carbon-fiber shock towers freed up some much-needed space, and some careful trimming of the rear shock tower allowed it to fit over the spur gear cover, as shown below:



I also had to brace the front bumper, since it no longer had a big solid motor and gearbox to attach to. A couple homemade turnbuckles solved that problem:



Once I got the gearboxes mounted in reverse configuration and the shock towers fitted, that was the end of the initial set of challenges. I wasn't done messing with the XV-01's chassis yet, though. I also wanted to reuse the carbon-reinforced touring car suspension from my FF-04 *and* widen the track width to 200mm, so it could fit a particular body shell I wanted to use. That involved a bit of trial-and-error regarding which toe-blocks to use (eventually I figured out I needed 1D/1D in the front and 1X/1D in the rear), and a bit more trial-and-error regarding which lengths of CVD axles to use (eventually I figured out 46mm was just right)...and then weeks of waiting for parts to show up in the mail. If only Tamiya parts were more readily available for reasonable prices domestically, I could've had this car finished a month ago.

So, with the track-width widened and the gearboxes reversed, that's it, right? Nope. I had a third trick I wanted to pull-off. I like the way RWD vehicles handle on-road -- they're a little more edgy and exciting to drive -- but I hate the way they brake. With some vehicles it's not a big deal because they have big-enough rear tires that they can still get significant grip, but they still have a tendency to skid and oversteer when braking hard, and that annoys me.



As a result of all the browsing of the TamiyaUSA website to find the axles and toe-blocks I needed for the widening conversion, I discovered that the XV-01 shares a few parts with the TA-06, and the TA-06 has a one-way pulley for the front axle. When I saw that, I realized I could get *really* tricky -- I could install that one-way pulley in reverse orientation, as shown above, and create a RWD car with 4-wheel braking. It's possible that other people have done this before, but thus far I haven't found any writeups about it. It works remarkably well, and it gives a significant amount of controllability to a car that would otherwise be very prone to oversteer and very hard to stop quickly. For the sake of making the front wheels behave as much as possible like freewheels when they're not helping to stop the car, the front diff is filled with 1000wt diff oil, just thick enough to provide decent lubrication for the internal gears, whereas the rear diff is filled with 30,000wt oil to resist diffing-out when accelerating.



The original (now discontinued) XV-01TC chassis has an exposed drive-belt, which is okay because it's strictly for on-road use only and the worst it should ever encounter is the occasional pebble or a few grains of sand, but with my reversed-gearbox configuration I had a different problem: The drive belt needed to pass directly over the electronics tray. At first I thought I could just leave the tray-cover off, but I realized there was no way I could guarantee the wiring would stay away from the drive-belt if I did that. So what I ended up doing was cutting a section out of the top of the tray-cover, and patching the hole with a section cut out of the no-longer-needed belt shroud. The result is an electronics tray that is still enclosed, still ventilated, and effectively keeps the wiring and the belt from becoming too familiar with each other.



It was one of several instances where the belt just barely sneaks past other components, the other ones being the motor wires and the servo-saver horn. On this car, the shimming of the servo-saver mount is actually dictated by keeping the servo-saver horn juuuust far enough away from the belt to be safe, which you can kinda-sorta see in the picture above.

Other than that, the chassis is suitably decorated with every shiny blue Tamiya upgrade part I could get my hands on, including the lightweight aluminum turnbuckles from my FF-04 kit (whereas my XV-01 rally car uses titanium turnbuckles and my XV-01T truck uses black steel turnbuckles), and a steering gyro was added to give the chassis a little more stability on takeoff, since even the wider rear tires aren't quite good enough to keep the car from spinning in circles if I don't ease onto the throttle carefully enough.

And now, here's the body shell that inspired me to go through all this trouble to hack together a rear-motor RWD/4WB touring car chassis in the first place:





I don't want to kiss my own butt too much, but I have to say I'm absolutely thrilled with how well this body came out. I struggled for about a week to figure out how to match Porsche's fire-orange color on the real 911 GT3 RS, and eventually I figured out that a coating of Duratrax Candy Red translucent paint with Duratrax Competition Orange opaque paint underneath was close enough that I couldn't tell any difference. And the color-matched spoiler is pure eye-candy, completing the look perfectly.

For reference, here's what the real one looks like:



The real one is a slightly updated design for which there is no RC body shell yet, but I think I did a good job capturing the spirit (and color) of the car.



So I finally own a Porsche 911, with realistic finicky RWD handling and realistic 4-wheel braking. And the motor is right where it should be.
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Old 10-25-2015, 08:18 PM   #2
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Very nice work. It looks great!
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Old 10-25-2015, 10:59 PM   #3
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Thanks!
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Old 10-25-2015, 11:21 PM   #4
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Nice Rear Rear Motor =)

I need to find me a Lotus that i can put the body on my Team Magic E4RS as a Rear Mid
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Old 10-26-2015, 12:06 AM   #5
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Quote:
Originally Posted by iPearl View Post
Nice Rear Rear Motor =)

I need to find me a Lotus that i can put the body on my Team Magic E4RS as a Rear Mid
http://www.ebay.com/itm/1-10-Scale-C...MAAOSwBahVO00W

?
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Old 02-28-2016, 04:42 PM   #6
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Great build! I'd recommend looking into printable water slide graphics, you could print your own fender vents etc....
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Old 02-28-2016, 06:21 PM   #7
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Interesting idea. Where does one get water-slide decals printed?
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Old 02-28-2016, 06:32 PM   #8
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Very nice work! I like that !
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Old 02-29-2016, 01:55 AM   #9
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Nice job! Any video of running this? Does the thick rear diff fluid work ?
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Old 02-29-2016, 01:55 AM   #10
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Quote:
Originally Posted by kwkride View Post
Very nice work! I like that !
Thanks!

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Nice job! Any video of running this? Does the thick rear diff fluid work ?
No running videos, unfortunately I have no clean pavement to run it on, especially after all the salt and sand scattered on the pavement this winter.

The thick rear diff fluid works well, but I'm going to replace the gear diffs with ball diffs so I can tune them more easily. Also, I'm replacing the one-way pulley on the front gearbox with a normal pulley. The idea of a RWD touring car was interesting for a while, but it wears-out tires too fast, so I'm converting it to 4WD.

Also, I replaced the finned motor with a full 540-size motor, so I could use the same motor in several vehicles. That means 4WD will now be a requirement to make use of the power.
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Old 02-29-2016, 07:41 AM   #11
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Great build!! Does it love to oversteer?
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Old 02-29-2016, 05:23 PM   #12
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Oh yeah, it oversteers easily, and was almost uncontrollable without the rear spoiler, even with the gyro turned on. The rear spoiler makes it behave a lot better though -- odd considering there's already so much weight in the back, but whatever, if it works it works.

No idea how it will behave as a 4WD car yet; still waiting for the ball diffs to show up so I can finish overhauling the car.
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Old 06-12-2016, 01:06 AM   #13
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Man, I haven't updated this thread in forever.

The RR-01 (now called the XV-01 R) is now 4WD, with a ball diff in the rear and a spool in the front. The rear springs were stiffened from blue-stripe to white-stripe (the hardest TC springs Tamiya offers), and the carbon-fiber shock towers were "downgraded" to carbon-reinforced-plastic because they twist less. The Vaterra tires wore down too fast, and the Vaterra wheels cracked all around the rim, so I switched to HPI wheels and V-Groove Pro Compound tires.



After a couple gearing changes, it can now hit 45mph on a slight incline, and just today I finally motivated myself to finish a second body for it so I can save the first one for display purposes.









This is now my fastest car, slightly edging-out my RS4 rally car, and it handles marvelously. The gyro almost never has to do any work, as determined by shutting off the gyro and driving it around a bit. It handled almost exactly the same, but considering how fast this car can get into trouble, I'd rather have the gyro there to compensate for sticks and stones and damp spots on the pavement.
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Old 06-13-2016, 01:43 AM   #14
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Oh, I forgot another mod I made. Relocating the motor to the rear, and thus reversing the operation of the drive belt, caused the drive belt to sag and then slip off the front pulley when braking. I made a retaining bar to keep the belt from being able to move far enough to the side to slip off the front pulley, and I integrated it into the belt tensioner:

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Old 06-14-2016, 01:46 AM   #15
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Wow - nice work, great write up.
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