R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Electric On-Road

Like Tree1Likes
  • 1 Post By fyrstormer
Reply
 
Thread Tools Search this Thread
Old 11-18-2015, 08:21 PM   #1
Tech Master
 
fyrstormer's Avatar
 
Join Date: Mar 2014
Location: Maryland, Near DC, USA
Posts: 1,817
Default Build Complete: Tamiya XV-01 SH-AWD

There comes a time in every RC enthusiast's life when he needs to put the race cars away, settle down, and build a sensible vehicle.



Looking at the picture above, you might think either I've lost my mind or I simply had no *good* ideas for my next project. Neither of these are true. (well, I *might* have lost my mind, but at least I don't miss it.) In fact what this practical-looking minivan represents is my original interest in the FF-04 come full-circle. You see, after building the FF-04, I was immensely impressed with its handling, but severely disappointed with its acceleration. Even with the motor hanging off the front axle, it just couldn't get enough traction to make use of the power provided by a brushed motor, and it didn't help that HPI has discontinued almost all of their high-traction tires. (in retrospect I could've solved this by using a crawler motor and gearing way up, but that's water under the bridge now.) So I ended up cannibalizing my FF-04 and using the parts to upgrade a couple XV-01 kits, which use the same gearbox and motor-mount assembly but have the benefit of a 4WD drivetrain.



The XV-01s I built accelerate worlds better than the FF-04 did, and their suspension offers better ground-clearance for the poorly-maintained pavement available to me, but I missed the laser-like precision of the FF-04's steering; not having the rear axle shoving the vehicle straight forward makes a huge difference in steering precision. I kept thinking "If only there were some way I could get the acceleration of 4WD only when needed, and keep the precision of FWD the rest of the time." Well, ladies and gentlemen, I figured out how to do it:



When I was building my "RR-01" rear-motor track car, I fitted a TA-06 one-way pulley onto the front gearbox of that car (which would normally be the rear gearbox on any other XV-01), so the front wheels could freewheel when the car was accelerating, but they could still engage with the rest of the drivetrain while braking, to produce a RWD car with 4-wheel braking. That one-way pulley is one of the key parts in this build. While I was browsing the TamiyaUSA website looking for upgrade parts for my XV-01s, I came across the other key part: a 16-tooth pulley from the now-discontinued TRF415.

By putting the 16t pulley on the front gearbox output, and putting the 18t one-way pulley on the rear gearbox input, I was able to create a drivetrain setup that would allow the rear wheels to freewheel *unless* the front wheels started spinning. The difference in tooth-count between the 16t and 18t pulleys allows for the front wheels to spin up to 12.5% faster than the rear wheels, and after doing some math I concluded this would be enough to ensure the front wheels do all the work even while turning as sharply as the steering system allowed -- unless they lose grip, at which point the one-way pulley locks in-place and the rear axle starts helping. Of course, this setup with one undersized pulley results in needing a slightly shorter belt, but there isn't a slightly shorter belt to be had, so instead I built an oversized tensioner using 5x10x3mm bearings to take up the extra slack. (the stock tensioner uses 3x6x2.5mm bearings.) You can see it just in front of the rear pulley in the picture above.

Having figured out how to make this work, I needed a body shell that would make sense for a front-motor, front-wheel-drive-with-4WD-assist drivetrain, and conveniently enough that's basically how Honda's SH-AWD system works. (it also gave me an excuse to buy the ABC Hobby 190mm Honda Odyssey body that I first discovered about a year ago.) The real SH-AWD is somewhat more complex than this, of course, but the basic principle is the same -- the front wheels do all the work until they start to slip, then the rear wheels start helping. I'm tickled pink that I was able to figure out how to do the same thing in an RC car.



Besides the nifty hybrid-drivetrain setup, this build is pretty much a cut-and-dried XV-01 build, with the only other upgrades being a few blue pivot-balls and carbon-reinforced-plastic parts everywhere I could get them. I might replace the turnbuckles and toe-blocks with shiny blue parts eventually, as the original parts start to develop slop, but for the time being it works just fine as-is. The stock plastic shocks are using TRF pistons because they're actually completely round like shock pistons should be (the stock pistons have a flat-spot on one side), and a spare set of TiN-coated TRF shafts that I had leftover from another build. It has the optional spring kit installed, with the stiffest springs in the front and the middle-stiffness springs in the rear, unlike my XV-01 rally car which has the softest springs in the rear because it has more ground-clearance to work with. Front and rear swaybars are a must with this chassis, because even with stock-length shocks it still rides higher than a normal touring car, so this one has the stiffest swaybar in the front (yes, even with the stiffest springs in the front too -- remember, most of the weight is up front) and the softest swaybar in the rear, to help reduce leaning while also minimizing oversteer in hard corners.

The wheels and tires are from the HPI "Vintage" series; they are mostly-normal 1.9" touring car wheels and tires, but the tires have an extra-tall outer lip that hangs over the outer face of the wheel, to make it look like the tire has a taller aspect-ratio than a normal 1.9" touring car tire. I decided to give these a try on a lark, and it turned out they looked spot-on with the minivan body, looking much more "scale" than normal 1.9" tires would. While I'm not thrilled with the D-compound rubber that the tires are made from, they have enough grip for parking-lot driving, and I have to give them credit for lasting longer than I thought they would; as shallow as the tread is, I thought for sure the front tires would be worn bald by the time I was done testing, but they show almost no wear except on the shoulders.



The electronics are the same setup I used in my XV-01 rally car: a Spektrum 2-channel receiver, a Dynamite DYNS2210 45-amp brushed ESC, and a Hitec HS-8775MG 25-spline coreless digital servo. Because this car is intended for on-road use only, electronics cooling is passive, with the dust shrouds removed to allow heat to convect away from the ESC without a cooling fan to make the wiring more complicated.

The motor is also mostly the same, a Team Orion 12-turn brushed motor with a comm lathed by yours-truly prior to use, and a cooling fan to keep the endbell from overheating, but I managed to do something a little different with the endbell itself, just for the sake of trying something new:



If you look closely at the brush shrouds, you'll notice they're mounted at a 45 angle. That's because the endbell was cannibalized from a Team Orion Method SV2 motor, which used "Revolution"-style round brushes. This design came along right around the time brushless motors became practical for the average RC hobbyist to use, so "Revolution"-style motors never expanded beyond Team Orion, and were discontinued in just a few years. Nowadays parts are hard to find; I scored a few extra sets of brushes from my LHS, where they were hanging on a rear-facing wall at the back of the car-parts counter, and the guy who found them for me said they'd been there longer than he had. (he's worked there for 8 years.) A few extra shims on the motor spindle was all that was necessary to make this endbell work with a normal standup-brush motor. Time will tell how it holds up, but I like vintage brushed-motor technology (except for Oilite bushings, hiss) so it's nice to have a chance to run it and see how it works.



One last thing I did differently on this car is I soldered the battery plug to the power wires at an angle. The XT90 plugs I use are big, and the XV-01's electronics compartment is small, so it had been challenging every time I wanted to run one of them to have to stuff the large plug into the electronics box. One day I realized I could turn the bullet connectors inside the plugs *on purpose* (unlike how they sometimes loosen slightly and rotate on their own, which I always saw as a "bug" instead of a "feature"), and I could solder the wires at an angle to improve their clearance inside the electronics box. Lo and behold, it worked so well that I spent a couple hours carefully re-soldering the battery plugs on all my other XV-01s to get the same benefit.

So there you have it; now I own four XV-01s, each similar but tweaked to work well in different conditions, and this last one in the collection brings me back to the front-wheel-drive setup that I appreciated so much about the FF-04 I built this past spring -- minus the only downside it had. It's been a fun (though expensive) adventure.

haplm likes this.
fyrstormer is offline   Reply With Quote
Old 11-23-2015, 11:25 PM   #2
Tech Adept
 
Join Date: Dec 2008
Location: San Fernando Valley (818)
Posts: 116
Default

Looks great and I've seen you post on URC as well. For others looking at picking up a XV-01, Tamiya USA is having serious discounts on the Asterion and the Gazoo GT86 Rally car.

The truck can be had for just over $112 and the GT 86 for $117 and change.
djfourmoney is offline   Reply With Quote
Old 11-24-2015, 02:18 AM   #3
Tech Master
 
fyrstormer's Avatar
 
Join Date: Mar 2014
Location: Maryland, Near DC, USA
Posts: 1,817
Default

If people keep reminding me that the Gazoo is on sale for less than $120 I'm going to end up buying a fifth XV-01 even though I already have four of the damn things.

I would go as far as to say no touring-car collection is complete without an XV-01. It's a unique platform and its suspension and weight-balance give it the ability to work well even on crappy "real world" pavement. And given the current sale, it might well be the best value on the market right now. How many other RCs can you get for $120 that won't either be off-brand junk or used cars that have been beat to hell and will require another $120 in repair costs before they're driveable again?
fyrstormer is offline   Reply With Quote
Old 11-26-2015, 07:24 PM   #4
Tech Regular
 
Join Date: Apr 2007
Posts: 272
Default

Quote:
I was able to create a drivetrain setup that would allow the rear wheels to freewheel *unless* the front wheels started spinning
Well thought out. Thanks for sharing.
ic-racer is offline   Reply With Quote
Old 11-27-2015, 12:26 AM   #5
Tech Adept
 
chad_h's Avatar
 
Join Date: Jan 2013
Location: SE WI
Posts: 187
Trader Rating: 22 (100%+)
Default

very nice system! I like it.
chad_h is offline   Reply With Quote
Old 11-27-2015, 09:36 AM   #6
Tech Master
 
fyrstormer's Avatar
 
Join Date: Mar 2014
Location: Maryland, Near DC, USA
Posts: 1,817
Default

Thanks! It works quite well. The only downside is it has front-wheel-only braking, but that's a small price to pay. All it really means is hard braking tends to cause understeer, whereas rear-wheel-only braking tends to cause oversteer. Understeer is much easier to correct -- just ease off the brakes a little and it will start cornering properly again.
fyrstormer is offline   Reply With Quote
Old 03-12-2016, 01:15 PM   #7
Tech Master
 
fyrstormer's Avatar
 
Join Date: Mar 2014
Location: Maryland, Near DC, USA
Posts: 1,817
Default

I haven't driven this car much, partly because I finished it up as the weather was getting cold, and partly because I sidetracked myself with a ton of other RC-related projects in the meantime. However, I recently made a change to the chassis that I thought was worth mentioning.

I finally managed to diagnose an infuriating suspension-bounce problem on my other on-road XV-01, the rear-motor conversion I dubbed the "RR-01", and the problem was the fancy carbon-fiber shock towers I'd installed. Carbon-fiber is stiff, but because it's a *woven* composite, it's only stiff against certain forces. The rear shocks on the RR-01, like the front shocks on this vehicle, have large spacers inserted between the upper pivots and the main body of the shock tower, which gave the shocks significant leverage to twist the shock tower -- the shock tower was effectively being converted into an undamped torsion-spring, and that's why no amount of stiffening the rear shocks made any improvement to the bounciness problem. The spacers I'm referring to are visible in this picture of the RR-01 below; the spacers on this vehicle's front shocks were exactly the same:





I switched back to the less-fancy carbon-reinforced-nylon shock towers on that car, which are thicker and have carbon fibers mixed into the plastic at all different angles, so they resist twisting much better. It improved the suspension response on the RR-01 so much I decided to "downgrade" this vehicle too:





So, the lesson I learned from this is: If the shocks are mounted on spacers, don't upgrade to carbon-fiber shock towers, stick with bulkier reinforced-plastic shock towers -- the suspension will work better. Unfortunately there are no reinforced-plastic shock towers available for my off-road XV-01s which have taller shock towers, but they also run softer springs so the torsion issue is MUCH less severe than it is for my on-road cars with stiff springs.
fyrstormer is offline   Reply With Quote
Old 03-12-2016, 09:51 PM   #8
Tech Regular
 
firefoxussr's Avatar
 
Join Date: Oct 2013
Location: Naples FL
Posts: 342
Trader Rating: 4 (100%+)
Default

The rr01 is sweet. I was thinking of doing a similar thing for my 911gt2 shell. Use the mf01x in lwb config with extra wide wheels.
firefoxussr is offline   Reply With Quote
Old 03-13-2016, 09:27 AM   #9
Tech Master
 
fyrstormer's Avatar
 
Join Date: Mar 2014
Location: Maryland, Near DC, USA
Posts: 1,817
Default

Thanks! I have a thread detailing that build as well.

I'd be interested to know if the MF01X conversion you're planning actually works. Can you get the MF01X all the way out to a 255mm wheelbase?

Last edited by fyrstormer; 03-13-2016 at 08:33 PM.
fyrstormer is offline   Reply With Quote
Old 03-26-2016, 10:03 PM   #10
Tech Regular
 
firefoxussr's Avatar
 
Join Date: Oct 2013
Location: Naples FL
Posts: 342
Trader Rating: 4 (100%+)
Default

Quote:
Originally Posted by fyrstormer View Post
Thanks! I have a thread detailing that build as well.

I'd be interested to know if the MF01X conversion you're planning actually works. Can you get the MF01X all the way out to a 255mm wheelbase?
Haha, I'd be delusional to think so. The 911 GT2 shell I have is for the TA02SW (which has a 236mm wheelbase, in spite of being a regular 190 wide touring car).
__________________
Parking lot heroes: M06, TA05sw, XV01, XRay T1, SC10B
Partially disassembled: HPI Cup Racer, FGX, M04, TA02, TA05 IFS
Newest acquisitions: A210SS Exige, HPI MX-5, Tamiya F40
firefoxussr is offline   Reply With Quote
Old 03-27-2016, 01:35 AM   #11
Tech Master
 
fyrstormer's Avatar
 
Join Date: Mar 2014
Location: Maryland, Near DC, USA
Posts: 1,817
Default

Ah, interesting. I didn't think of short-wheelbase shells. There's such a limited selection to choose from, but I suppose that doesn't matter if you've found one you like.
fyrstormer is offline   Reply With Quote
Old 03-27-2016, 10:35 PM   #12
Tech Regular
 
firefoxussr's Avatar
 
Join Date: Oct 2013
Location: Naples FL
Posts: 342
Trader Rating: 4 (100%+)
Default

Quote:
Originally Posted by fyrstormer View Post
Ah, interesting. I didn't think of short-wheelbase shells. There's such a limited selection to choose from, but I suppose that doesn't matter if you've found one you like.
I love it when they do that. The cars are far more realistic. Currently I own a Lancia 037, 911 GT1 and GT2. All run the 236-239mm wheelbase setup.

I'm a fan of adjustable wheelbase cars. I own a Cup Racer to run it exclusively in short setup (for the Lancia Stratos shell).


Sidenote:
There's also a Toyota Rally car and a Peugeot WRC as front-engine short wheelbase (TA03F-S). I just might get one eventually, the Pug is beautiful.
__________________
Parking lot heroes: M06, TA05sw, XV01, XRay T1, SC10B
Partially disassembled: HPI Cup Racer, FGX, M04, TA02, TA05 IFS
Newest acquisitions: A210SS Exige, HPI MX-5, Tamiya F40
firefoxussr is offline   Reply With Quote
Old 05-01-2017, 06:59 AM   #13
Tech Adept
 
Join Date: Jun 2016
Location: Prague, Czechia
Posts: 159
Default

fyrstormer, would you be so kind and share how exactly you have mounted the TA-06 one-way pulley? I'm really interested in this setup, so I have tried to apply it to my car today. However, I have realized, that XV-01 gearbox doesn't work with the installation procedure suggested in the manual that came with the one-way.

BTW - 3racing is making 19T one-way, which is absolutely identical with the 18T from Tamiya. So if I can figure out mounting, I can use standard 18T pulley in the front, and 3racing's 19T in the rear to get this done.

Thanks!
haplm is offline   Reply With Quote
Reply



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 12:30 PM.


Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net