Rogue's JJ Ultima retrofuture edition

[RogueIV]

So after building the JJ I decided to do a bit of tinkering to it to better suit my home track, RCM, which is high grip grey carpet.

I used the Turbo Scorpion wheels with JC fuzz bite tires. Front wheels i cut off the inside bead and left the inner rib to fit the skinnier front tires.

From the factory, the front track width is way narrower than the rear. While NVR makes longer axles to fix this I went a different route. Back when I bought one of my Losi JRXs it had these, incorrect, Andy's front arms. They were too tight for the losi and didn't have the right geometry but they happen to fit this Ultima perfectly and widens the track to just about where i want it. Original arms are 56mm. Andy's arms are 62mm. Increasing track width by 12mm. The down side is I lose the ability to use the optional front sway bars without modification.

I ordered up some P.A.P. Towers from Factory works, did a little surgery to the body so it would fit, I already messed it up a bit anyway by not understanding how the rear transmission mounted wing worked. Note that this rere Ultima uses 3mm hardware in place of the original smaller hardware used for the camber links. I still need to fit the front but the rear one offers a lot of tuning options.

Springs I might have to do some fiddling with after testing. Rears are the stiff gold ones that are supposedly for the Scorpion, but I found to be too long to use on that car at the ride height I wanted. The fronts are a pair of LC racing ones I had in my pit box. both are a bit stiffer than the originals.

Alignment time - starting off with -2deg camber all around and 1deg of toe out up front.

Electronics I went with a basic Hobbywing Justock ESC. I would have used a Tekin but both of my Tekins are dead right now and awaiting repair. For the motor I picked up a used Trinity Monster Max 17.5t at least it's still a Trinity Monster right? Radio gear is the same stuff I use in my other rides Spektrum DX5R with a Blue MX SR3100 Rx.

Servo is a Savox SC-1258TG with a front cover from a 1268SG. Front cover on the 1258 is prone to having the center bushing area break out and causing the servo to lock up. The 1268 cover is much stronger in that area and fits without modification.

I use shorty lipo batteries and mounted this one fully forward. While the supplied Kyosho straps are pretty, the rough side of them is exposed on the button of the chassis and I really don't want velcro grabbing onto the carpet if it bottoms out. So i went with a cable management velcro strap so the fuzzy side is only exposed and not prone to catching onto things and there's no buckle to break. I may make some hold down tabs later and remove the strap altogether.

I also added some lexan tabs with velcro to help keep the body on and straight. Rear wing is actually a JRX-Pro wing that I had laying around and decided to make some clear endplates for it to emulate the original replica.

Ready for some testing and tuning

[RogueIV]

Mounted up the front tower today. had to get some longer turnbuckles. Might buy some titanium ones later after i do more driving with it.

[RogueIV]

Crappy video of me driving the car at the track for the first time.

https://youtu.be/9ILZuEcreV0


I didn't have a way of holding the camera so it was just propped up at the corner of the track. Also part of it is muted because apparently Speedwagon really gives a crap that their music is vaguely in the background obsured by motors wirring and compressors going... Yes I'm sure people would have flocked to my video to steal your music.... anyway I digress.

Considering I shot from the hip with my setup the car handled amazing! Turn-in was great and you can really swing the back around tight corners. Very predictable handling. I was under geared and running an older Trinity Monster Max 17.5 and was only half a second off my B6.4's lap times without touching anything. No traction rolling either! I felt more consistent with this car too and I kinda regretted that I didn't use the car for the race earlier that night.

Only issues were the wing endplates immediately flew off (those were cosmetic anyway) and it bottoms out if I don't land the jumps perfectly, but that can be remedied fairly easily.

[RogueIV]

I ran a club race with it last Friday in 17.5 Stock buggy. I had to add a lot of weight to it to get it above the ROAR regulations. Tried to give it a little more droop to help with landing but it was still prone to bottoming out even with fairly heavy oil (45wt f 60wt r). If I don't land perfectly on the down ramps it slaps the chassis. It just seems the pistons supplied just aren't the right fit for these conditions.

Only issue I really had was my receiver gave up the ghost in the 2nd heat, thankfully I had my other car and just took the Rx from that. Most of my driving issues either stemmed from me messing up or the aforementioned bottoming out but otherwise the car handled great.

[RogueIV]

I'll post more info later, but I've adapted some big bore shocks to the car to fix the chassis slap issue I was dealing with. might be able to use the original shocks at some point but need to find better pistons for my application.

Till then here's some video of a friend of mine down at the track giving it a go.
https://youtu.be/rW4BtDI5ztM

[Frankentruck]

Track tested, definitely approved! Very nicely set up.

[RogueIV]

So more on the big bore upgrade. I've put the option shocks for the Geforce Genova onto the Ultima. GOP106 front and GOP107 rear.

These are well made shocks, easy to build and bleed. went with 45wt front 50wt rear.
Springs are AE red front and yellow rear. The shocks have a smaller top eyelet than the Kyosho meaning I needed to design some new shock bushings, made new units based on the design Kyosho did.

Here they are all installed.

In order to get the fronts to allow me to use less preload I used AE B6.4 +2 eyelets and low spring cups. this does have a bit of an odd interaction with the front arms as they can technically droop more but collide with the spring cup. you can force the arm further down but it pulls the spring perch up on the eyelet. This doesn't seem to really affect handling so i left it, but I could add some internal spacers to stop this if I want later.

The car handles jumps much better now and no longer slaps the chassis on landing.

Next I assembled a gear diff and filled it with 30k oil. this is a bit more free than the Ball diff that i ran a bit more tight for fear of slipping and melting. I haven't gotten to drive it yet but I'm hoping this is more consistent on carpet.

[RogueIV]

Another thing that i've done is cut a new motor guard out of Kydex so I could add a cooling fan, also my original one got a bit bent after someone rear ended me. One thing of note, the bolt pattern for the top of the mount matches the pattern for the fan

Bonus is this shouldn't get permanently deformed if it gets hit again.

[RogueIV]

New lid got painted for it from local painter, Dominators Airbrushing.

The Rear wing looks great but sadly it's not good for racing, spent most of it's time at the last club race bent the wrong way. Will probably go with the Scorpion molded wing, or a JC wing later.

Car has been holding up well. Another racer really tested my rear bumper while I was gridded and he decided to go full send down the straight into me and the bumper and the car were unaffected. The car handles great, the gear diff really helped with consistency in turns. I might start experimenting with using sway bars next and see if I can maintain corner speed and still raise the rear suspension.

I may try some anti squat in the rear too, basically I still have some chassis slap issues that I need to remedy.

I do really wonder what this car could do in more capable hands though.

[RogueIV]

Got some goodies in the mail yesterday from Chimera Model Sport, a brass front bulkhead and aluminum rear pin block this should help getting the car to legal weight.

The bulkhead is 106g heavier than the 13g plastic one. Putting the weight where I need it, the nose.

The rear pin brace is made of aluminum and only a little heavier than the stock plastic unit but should add some durability to the rear, not that I've had an issue thus far.

Something can be said about the durability of the original front bulkhead and the Andy's arms. during installation I noticed that both front hinge pins were bent. No noticeable damage to the bulkhead or arms.

Luckily, I've become good and unbending what was once bent. using a shock multi tool and an aluminum driver handle I carefully bent back the pins to be straight. I've done this a lot with titanium and steel turnbuckles on other cars.

Bulkhead looks good on there.

I need to put a new set of electrics in this car as my poor Quantum2 decided to start malfunctioning and I stole the servo for something else but hope to run the car again soon.

[RogueIV]

Decided to fix the issue i was having with the front spring cups hitting the front suspension arms on droop. Changed the AE eyelets down to 0 form +2s and used springs and cups from the Schumacher L1R. The Schumacher springs are tapered at one end so the spring perch is more around the size of classic non big bore shocks. It now has full range of motion.