Re-Build Complete: Tamiya XV-01 FF

[fyrstormer]

My XV-01T Asterion is no more. It was an interesting concept, a pickup truck built on a touring car chassis with rally car suspension, and it worked pretty well, but as time went on I decided its drawbacks (specifically, flagrant traction-rolling in corners) outweighed its novelty. So I converted it into this:



If this body looks familiar, that's because it was originally the body I put on my Tamiya FF-04 Evo last year, minus a few of the more problematic decals:



The irony is not lost on me that my first Tamiya kit was a front-wheel-drive car, my dissatisfaction with which eventually sent me on a months-long quest down the rabbit hole of multiple XV-01 builds, only to end up with my last XV-01 build also being front-wheel-drive.



Yes, my XV-01T has had its drive belt and rear transmission removed, so the rear wheels are just along for the ride, but despite the similarity in drivetrain layout, the XV-01 FF handles very differently from my long-gone FF-04.



The first and most obvious difference from the FF-04 is the suspension; whereas the FF-04 had 55mm TRF shocks, the XV-01 FF has shocks cobbled together from a variety of parts -- TRF pistons, upper and lower caps (limited-edition black parts, no less!), and shaft seals; springs and shafts from the long-damper spec CVA plastic shocks; and longer shock bodies from the Yeah Racing 60mm shock kit. All put together, the difference in shock length is significant:



That extra suspension travel, combined with the XV-01's suspension design, gives the XV-01 FF a LOT more ground clearance, and more ability to keep the front wheels planted when leaning in corners.



Another significant difference between the FF-04 and the XV-01 FF, which can't be seen from the outside, is that the differential has been replaced by a spool. My experience with the FF-04 taught me that traction is desperately limited on a front-wheel-drive RC car, and I decided that faster tire wear was an acceptable tradeoff to ensure that the front wheels would always be able to put power to the ground. If I had the FF-04 to build over again, I'd have replaced the diff with a spool straightaway and not give it a second thought. I think all FWD RCs should have spools; it really does help that much. (there might be an exception for FWD RCs driven on perfectly clean tracks, but not for any others.)



The third important difference between the FF-04 and the XV-01 FF, another thing I learned from experience, is the gearing. The FF-04 comes with 26/68 Mod 0.6 gearing, which translates to 29/77 gearing in 48 pitch. I have no idea what Tamiya was thinking when they equipped a FWD car with gearing that low -- the amount of wheelspin on that car, even with the best tires I could find on warm dry blacktop, was frankly atrocious. The XV-01 FF, on the other hand, is running 38/69 48p gearing with the aid of a Team Associated spur gear -- 46% higher than the FF-04's gearing -- so it can run a higher-turn, lower-power motor without being dog-slow. Whereas my other XV-01s run 12-turn modified brushed motors or 3930KV brushless motors, the XV-01 FF is running a Holmes Hobbies 27-turn disposable motor. (Holmes Hobbies' disposable motors have ball-bearings installed on the pinion side so they doesn't waste power scrubbing the spindle against a bushing, and it will last longer before wearing out.) The slower motor combined with the higher gearing work together to significantly limit torque to the front wheels. 38t is the largest 48p pinion gear that will fit under the gear cover without shaving the tips of the gear teeth (not worth the effort for a non-racing application), though I could go with a smaller spur gear (possibly as low as 65t) if I were willing to ditch the slipper clutch and bolt the sput gear directly to the input shaft. If I had the FF-04 to build over again, I'd definitely do that, but for the purposes of running off-road I definitely want to keep the slipper clutch -- plus the slipper clutch gives me another way to limit torque to the front wheels.



As previously mentioned, the rear gearbox is hollowed-out and empty, the wind whistling forlornly through its vacant interior as the car whizzes down the road -- but the side effect of this is a significant weight reduction as there are no ball-bearings, axles, gears, or outdrives in the back anymore, and most of those parts were steel. So the rear suspension is using the softest long-damper springs Tamiya offers, and 20wt oil in the rear shocks, whereas my other XV-01s require stiffer springs and 30wt oil in the rear. (except for the XV-01 R, which has the motor in the back and thus has even stiffer rear suspension than the rest.)

However, despite the lightened load in the back, there's still a swaybar in the rear, in fact the stiffest of the three swaybars in the XV-01 swaybar kit, whereas the front swaybar is the softest of the three. This chassis absolutely needs swaybars to prevent ridiculous body-roll with all of that suspension travel, but why the imbalance between front and rear? One word: Powerslides. This front-wheel drive car oversteers beautifully; while it can't carry a powerslide as long as a RWD or 4WD car can, it can still get sideways with ease, which makes sharp corners fun. The tires hate me for it, but I don't care.



So there you have it, my Tamiya touring car collection has come full-circle, from building a FWD touring car and not liking it, cannibalizing it to build a 4WD rally car, building several more cars of various configurations on the same platform, and ultimately ending up converting one of them back to FWD and applying the lessons I learned along the way. This one I think I'll keep.

[fyrstormer]

A video demonstrating its off-road capabilities:

https://www.youtube.com/watch?v=Mvu-9V_SK-w

[fyrstormer]

My blacked-out XV-01 chassis got a little blacker today.



You'd be forgiven for not being able to tell what I changed. Most of it was replacing steel pivot-balls with "limited edition" black aluminum pivot balls, and black plastic spacers with "limited edition" black aluminum spacers, but there are a couple bits that are readily visible. The first is the motor-mount, which used to be silver and is now black, the second is the motor/bumper brace, which used to be black plastic and is now carbon-fiber; and the third is the steering system, which used to be black plastic and is now black aluminum.



These pieces all came from an FF-04 Black Edition kit that I bought specifically so I could get these "limited edition" black pieces. At this point, the only bits that are aluminum on my other XV-01s that are still plastic on this one are the toe-blocks, and sadly they will probably always be plastic, because I doubt Tamiya will ever make a "limited edition" black version of the special 1XJ and 1XM toe-blocks used by the XV-01.



Under the gear cover I also replaced a couple parts. The slipper clutch is gone (at least until I can trim-down the pressure plates to accommodate smaller spur gears), and in its place is the direct-drive spur mount from the FF-04 Black Edition. This, combined with a Kawada 65t spur gear and a Robinson 40t pinion gear (which required a little trimming inside the gear cover to accommodate it), allows the XV-01 FF to hit a blistering 25mph with a Holmes Hobbies TrailMaster Sport 27-turn sealed motor. Admittedly that doesn't sound very fast, but it's more than fast enough to have fun driving on the terrain that a FWD rally car can handle. Remember, this isn't an E-Revo, even if it could go 60mph on grass/dirt/gravel, you wouldn't want to, it would be impossible to control. But that's cool, I have other vehicles for that. This one is for scale-accurate rally driving.

Oh, and the wheels are now black too, though that's more because I already had the tires I wanted to use mounted on the wheels I wanted to use, except the wheels are black instead of white.

[fyrstormer]

Another update: I didn't like the direct-mount for the spur gear, because even with moderate throttle I could see the front of the car chittering as the tires stick-slipped while the car accelerated. I knew I needed to find a way to get a slipper clutch back in this car. Unfortunately, nobody makes slipper-clutch-compatible spur gears this small, except for mini vehicles, but they use 0.5mod instead of 48p and there was no way I could get a 40t 0.5mod pinion gear with a 1/8" bore.

The input shaft has a 5mm diameter, so that's not a problem, but as I discovered, the hole in the middle of the spur gear isn't 9mm, or 10mm, or 11mm, it's some weird size (probably English Imperial), which meant that finding a bushing to adapt the spur gear to fit on the slipper-clutch input shaft was going to be an enormous pain.

Or was it? While I was fiddling with some spare Tamiya parts, I noticed an inconspicuous donut-shaped piece of plastic on one of the parts trees -- lo and behold, it was a perfect fit for the spur gear! Problem 1 solved. Now I just needed slipper pads.



Traxxas saved the day with some old-school tech, in the form of Teflon friction pegs that fit into the screw-holes on the spur gear. I knew about these from the T-Maxx Classic I have, but I'd tossed the friction pegs along with the stock spur gear for that truck as soon as I got the slipper clutch upgrade kit. So I had to buy some new friction pegs. It turns out the replacement ones are made of Teflon instead of compressed fiber, which is a nice improvement. Problem 2 solved.

The last step was spending a couple hours carefully reducing the size of the pressure plates until they wouldn't rub against the spur gear's outer shoulders. That was a very tedious process, and once I got the plates close to the right diameter, I had to invent an adapter to chuck them into the Dremel so I could lathe them into a proper circular shape again. Problem 3 solved.



Now it has a slipper clutch again, and I can once again maintain traction while driving on dirt.

[fyrstormer]

My XV-01 FF got a new body, and a hard-mounted external bumper to keep it safe when rallying:





This Lancia Delta body came with the newer pre-cut decal sheets, which have a bunch of the formerly-separate decals integrated together. So to get rid of the sponsor livery, I had to trim a bunch of the decals to extract just the door handles, window trim, etc.

[pixelnate]

So, an AWD chassis running as FF, and wearing a body from one of the baddest AWD cars to run a rally. Mind blown.

I like your general approach to rally cars -- XV-01 all the things, even FF and RR things. Tell me you at least used a 911 body on that one. I'm trying to do something similar with TT-02s. I've got two Mid engine AWDs and will be trying a MR soon.


Sent from my iPhone using Tapatalk

[fyrstormer]

Actually the Lancia Delta was also available as a FWD version, which is why this one looks like a consumer model with no sponsor livery. So I've got the AWD one running sponsored livery, and the FWD one looks like a private owner's weekend toy.

The XV-01 is a great chassis in terms of flexibility; that's why I was able to make so many different versions of it, including one that has part-time 4WD just like a real Honda minivan.

Yep, the rear-motor conversion has a fire-orange Porsche 911 GT3 RS body on it. Being able to use that body was actually my inspiration for building the rear-motor conversion in the first place.

[nor500]

Dear fyrstormer. I would like to install the same hard-mounted external bumper on my xv01 as you have. Can you tell me the brand and type of that bumper and where did you get it?

[fyrstormer]

The bumper is from the XV-01T "Asterion" truck: Tamiya B-Teile (Stoßfänger) XV-01T #19000458, Tamiya Axial

[nor500]

Thank your for the answer. I am just thinking of raising the ground clearance of my xv01. My other question is, do the Asterion wheels fit when using with the lancia body. I have got the standard x01 kit.

[fyrstormer]

The Asterion wheels might have slightly too much offset, but I'm not sure. The Asterion tires are definitely too tall.

[nor500]

The ground clearance of your car look bigger than the standard. How high is that? I would like to increase the ground clearance of my standard xv01 chassis. How can I do that?

[fyrstormer]

You need these parts:

Tamiya America Item #54581 | RC Carbon Long Damper Stay - XV01 Front
Tamiya America Item #54582 | RC Carbon Long Damper Stay - XV01 Rear
Tamiya America Item #50519 | RC CVA Mini Shock Unit Set II x2

[Ausomecrawl]

Just curious. To run the xv-01 front wheel drive wouldn't only removing the rear belt to disengage the rear wheels?

[fyrstormer]

Yes, you can remove just the front-to-rear drive belt, but you might as well remove the internal parts from the rear gearbox too, to reduce weight. Also, the rear wheels will never roll completely freely as long as they're joined together by a differential in the middle.

[Natedog]

Very nice build, lots of Tamiya parts swap research involved and end result looks great!

[fyrstormer]

Thanks! It was a lot of fun (and also very, very expensive ) to build all these different variations on the XV-01 chassis. I have 3 gallon-sized Ziploc bags full of spare parts now.

[fyrstormer]

Fixed all image links in this thread.