The ultimate Mini JRX2 thread

[Frankentruck]

Nylon is more durable than ABS. I wouldn't bother with ABS.

[RogueIV]

Nylon is more durable than ABS. I wouldn't bother with ABS.

I need to upgrade the printer before I can really do nylon. It's something I have been looking into though. Really though I want to eventually get a 2nd printer so I don't have to constantly change setups to work with different filament types.

[RogueIV]

ended up changing the scheme of my stock class Mini JRX2 to match my JRX Pro.


Decals are 1/14 scaled JRX Pro decals from MCI which fit quite well. I should have move the side decals forward more on both the bodies but I didn't feel like fighting with the decals to get them to conform to that more complex geometry.

In other. somewhat older news, I did manage to actually win a point series with the little guy a few week back (this is a first for me) and have been having a great time racing these in the stock class. I don't really need to think about this car, just toss the batteries on the charger and go, it's almost therapeutic. The lap times of these are on par with stock Mini B class which I think is pretty cool considering how old the JRX2's design is.

I did some experimenting with the mini B tires on the this buggy as well.

I know I mentioned it in the past and I had mounted this set a while back but I finally got time to run them on carpet after the race last Thursday. Turn in was improved a bit and overall the car felt a lot more consistent going around turns.

I now plan on picking up a 3rd car and try that one in the mod class with these tires and see how it works out since I took apart the 2nd car for the Mini LXT project.

[BattleTrak]

Those matching buggies look great! ..you’re giving me ideas..

[limestang]

ended up changing the scheme of my stock class Mini JRX2 to match my JRX Pro.


Decals are 1/14 scaled JRX Pro decals from MCI which fit quite well. I should have move the side decals forward more on both the bodies but I didn't feel like fighting with the decals to get them to conform to that more complex geometry.

In other. somewhat older news, I did manage to actually win a point series with the little guy a few week back (this is a first for me) and have been having a great time racing these in the stock class. I don't really need to think about this car, just toss the batteries on the charger and go, it's almost therapeutic. The lap times of these are on par with stock Mini B class which I think is pretty cool considering how old the JRX2's design is.

I did some experimenting with the mini B tires on the this buggy as well.

I know I mentioned it in the past and I had mounted this set a while back but I finally got time to run them on carpet after the race last Thursday. Turn in was improved a bit and overall the car felt a lot more consistent going around turns.

I now plan on picking up a 3rd car and try that one in the mod class with these tires and see how it works out since I took apart the 2nd car for the Mini LXT project.

Matching paint scheme - looks Awesome!
-limestang

[RogueIV]

Well I started having ideas and really wanted to run a Mini JRX2 in Mod class. I went and bought a 3rd car, which unfortunately had abysmal build quality so I abandoned it for the time being so I can return it and get one that isn't put together wrong.

For this I took apart the Mini LXT for the time being and went through the process of returning the parts back to the JRX2, but this time with the Pro shock towers, and a Dynamite 2 in 1 Brushless setup. The replacement 3rd car will end up being the replacement donor car for the mini LXT

The buggy still retains the 5 link in the rear because I don't trust the printed H arms to survive, especially at this power level. I'm using the Pro rear tower. It seems to work OK I have it currently set to use the bottom outside shock position, I added a spacer to the front of the top links to give a little bit of extra room for the spring as it was slightly hitting the link during travel.


The Pro Front tower requires that I use rear shocks up front. I limited the travel a bit in both directions to keep the suspension from over traveling. I also used front axles from a first gen Mini T, this widens the front track a little.


The Dynamite setup is quite a bit heavier than the stock motor and esc combo and it's all behind the rear axle. On the bright side I no longer have that big ESC/Rx box taking up space so to fix the weight balance issue I made a new battery box that spins the battery 90degrees and pushes it all the way forward right up against the servo. This gets the weight balance close to the stock setup. My stock buggy is 33/67 f/r split and this buggy is 35/65.


The body is a bit hacked up but it'll suffice for now.


I haven't tested it on the track yet but hoping to get some track time tomorrow night and see how well it holds up against the Mini Bs.

[RogueIV]

I tested it out on Thursday and it wasn't too bad. The sprint tires didn't work on the grey carpet nearly as well as they did on the black carpet. I instead went back to the stock step pins in the rear and kept the front proline wedges. Traction was actually quite impressive.

My main issue was power delivery and admittedly me completely botching up something. All night I was chasing issues trying to get the car to start off smoother. No ESC settings seemed to help. I'd have issues accelerating out of corners or recovering from crashes because the car would immediately want to wheelie (not what you want went trying to turn). 2nd heat I installed a MIP slipper which helped a lot but still had issues reigning in the power.

The reason for all of this is quite embarrassing and I figured out my entire reason for my woes last night, I had misread the EXP graph on my radio and set it in completely the opposite direction then I should have, meaning I had turned my throttle trigger almost into an ON/OFF switch at starting travel. I figured this out only after my following changes.

To help combat the front lifting and add a little more stability I lengthened the wheelbase to be the same as a Mini B. It's about 6mm longer than the stock JRX2. Now I really do have a Pro replica just with a 5 link rear. I ended up using the mini LXT chassis as a drill guide for these new holes then countersunk them.







During this I noticed that I had to clock my Motor differently because the signal cables were getting chewed up by the rear pivot block, This unfortunately meant I have to move my receiver back so the cables could reach and also had to extended the battery cables. I also put some adhesive lined heatshrink over the chewed up ends of the signal cables just to ensure they wouldn't get worse.



The switch was mounted to the transmission as well making it a lot easier to prepare for the night as I can have the body clipped on and still be able to turn the car on and off. It may not seem like much but when you run heats back to back you kinda want to just grab the car from the bench and go. the other thing of not is I can unplug from here as well.



With extending the car the body holes no longer matched up, and the rear shock tower hit the factory wing mount. So I decided to make use of those wing tubes in the rear bulkhead! Note if you do want to use these I suggest putting some CA on the outside of them as they don't grip into the bulkhead nearly as well as the 1/10 car they're based on. I pushed the wing mounts all the way back and then straightened the wire then rebent them further back. This has an added bonus as not the wing can't really get tilted if it gets hit like it does with the factory mount.



Hears some comparison shots of the slightly longer car next to my white Stock class car





I have some stick on weights to play around with the weight balance. I do think I can get this platform to be competitive against the Mini Bs especially now that my remote is set right. I also may make the 3rd car into a mid motor conversion based on what I've seen people do with the 1/10 scale cars.

I think the best part of these little cars is they're fairly cheap and I don't feel bad experimenting with them.

[RogueIV]

The mod version worked fairly well with the proper transmitter settings. Still need to figure out the traction rolling issue, might need to put more spacers inside the shocks and fool around with the front camber link positions. The major mod is on myself, I need more practice, driving a car with this much power is much more difficult, this thing is an absolute rocket.

I also made this thing. I'll go into more details on it later though.

[BattleTrak]

Mid motor? I hadn’t thought about doing that to one of these minis..

[RogueIV]

Mid motor? I hadn’t thought about doing that to one of these minis..

Correct! Unfortunately you can't swap the top shaft in this transmission as easily as you can on the original LRM transmission so it's running an old Mamba mini motor in reverse. I really wanted to try it with the dynamite motor but that doesn't have a reverse rotation option. The weight balance at the wheels didn't change as much as I thought The stock one has 33/67 split with the battery forward. My mod JRX mini with the new battery box has a 35/65 and this mid motor version is 37/63, granted this is with a much lighter motor.

It feel like it flies a little better than the other mod Mini JRX2, unfortunately I broke a rear link pretty early in testing and didn't print spares, I have since revisited the design of that part to use the original link instead. Keep in mind this design is not ideal as it twists the link with how the shock is mounted and a H arm would be a better solution, or figuring out a way to mount a shock tower further forward to use the original trailing arm mounting holes.



My Factory Work order came in. I went with the A&L style towers on this one.



Another issue is the slipper just isn't working right, the outside disc isn't properly coupling with the inner disk so it starts to unscrew the tension nut during use unless and crank it down all the way. I might run a slipper eliminator or upgrade to the MIP slipper to fix that issue. I also need a sensored mini motor that I can reverse since this Mamba is way too twitchy and inconsistent to race with. I might switch back to the stock ESC and put a mod brushed motor in for the time being.

[RogueIV]

BTW if anyone has a Mini B and a food scale, could you measure the f/r weights preferably in grams?

[RogueIV]

Mild update today.

Mod Class JRX "Pro" car

Did more racing in the Mod class against Mini Bs. Handling is great, jumps can still be bit of a challenge but I'm getting used to it (this might not be the cars fault but more of me getting used to the smaller scale handling). I almost feel like the car handles the flat portions of the track better than the Bs, most of the issues I have is flying the car over jumps and repressing the urge to get greedy. More wheel time on this and I should be able to hang with the others.

Biggest weak point of this platform is that way too thin motor mount and it's extremely weak threads. My mount is battered, the previous week a 1/12 4wd nailed it pretty bad during practice, I straightened it out but during racing this time the threads started to let go. At least it held together for the Main.

I ordered some longer M2x28 flat head screws and I'm going to drill and countersink the motor plate, put the screws through the plate into the trans and have nuts on the other side. I'll also come up with some sort of bumper to put on the rear to keep it from getting tweaked during rear collisions. I may even just use a completely different motor plate, redrilled. Another benefit would be that I could have slots instead of these damned preset screw holes allowing me to used a larger selection of pinions.

The other issue is steering ball cups popping off. Granted this is easily resolved by not hitting things, and I only really had this issue during the first heat. Still, I ended up using some ball studs that were slightly bigger that I had rolling around in a parts bin. Hopefully that helps resolve the issue in the future.

Mid motor 'JRX2m'

I drove this around with a old Reedy brushed mod motor for a few laps it really does handle well and is a little easier to control over the jumps. Didn't really get too crazy with it though as the stock ESC didn't much care for my decision to attach a hot motor to it and thermalled after a couple minutes.

I ordered a new, sensored motor and esc combo for this but while thinking about things I remembered that @clm had made a 3d model of XX retrofit style transmission case. This gives me the ability to just print that case mirrored, allowing me to put the top shaft out the other side and eliminating my need to run the motor in reverse. It'll also keep the slipper from disassembling itself. Hopefully the print comes out OK, My machine can be a bit of a pain sometimes but at least this is a time saver as I won't have to measure and build a model of the original case to mirror.

The mid setup may be my way forward in this class if I can get it all sorted, Not having an easily bent motor plate hanging out the rear is definitely an advantage I just have to hope that my rear suspension is durable enough. If the rear arms still aren't strong enough plan B is to find a way to move the rear tower forward closer to where it was in stock form.

Edit: So I realized I probably won't have the parts for the "Pro" ready for the next race so i went ahead and printed the new trans case for the JRX2m and transferred my electronics over to it. Weight balance is now 40 front 60 rear. Testing it on track soon.

[RogueIV]

Been racing the mJRX2m for a bit now, it's been holding up alright but the major issue with it was the open diff. Trying to go full throttle often leads to the car pulling to the side, not the greatest when trying to line up jumps. Sadly there's no actual direct fit ball diff or cvds available for this car. (Hey MIP are you listening???) I decided to do some scavenging and now my poor Mini T 1.0 is not missing a lot more parts.

The MIP ball diff from the 1.0 is apparently the same as the mini B and T 2.0. It also fits in clm's mini XX retro case. So in it went. This was the easy part. I had just gotten a new SLA printer so what better thing to test it with then a new case to replace the now broken one in the car. I

t came out OK but I messed up when adding my supports so now the top edges of both halves have some gaps, it's fine for now, I'll print out a new case later on, I'm more interested in running the car. I seemingly forgot to take pics of the assembly, but I'll take some next time i have it apart.

Unfortunately you can't use the ball diff with the original sliders. I needed CVD's or a dogbone setup. The CVDs from the Mini B/T 2.0 are too long but the Mini T 1.0 ones are actually the right length. Sadly, the stub axles aren't really right. The 2.0's are closer but the way the bearings are spaced a lot further apart in the JRX2 hub.

you can see there's quite a bit of difference in the stub axles as far as the drive pin location to where they seat on the inner bearing. The hole is only partially visible when the axle is installed. this wasn't going to work. I had to ditch the 5link setup and go with H arms.

I had a set of h arms printed from before, I'm hoping they hold up but if not I'll do a new design instead of the period looking replicas. The hubs were the next problem. The ones I had printed before were far too fragile. Too many holes and not enough meat. Enter the old Mini T turned parts donor. It had a pair of aluminum rear hubs that I decided to repurpose for this. I spaced the hub mostly rearward and also had the arms mounted with the sweep towards the back to give me a little added wheelbase. There is still a slight hurdle left, the regular wheels have a really deep pin pocket and the wheels end up rubbing the hub. This isn't much of an issue on the original setup as the wheels rest on the spacer but I can't fit the original spacer with this. Thankfully the wheel I had made previously have a slightly shallower pocket so I can tighten them on and they don't rub.

Drove it around in the driveway it seems to launch a lot more consistently. We'll see how well it works in Thursday race.

[limestang]

Breaking News- Check Out the 2 page ad on the Feb 2023 RC Car Action issue - Losi Mini JRXT limited edition!!!

Unfortunately the QR link is not showing the vehicle yet.

-limestang

[RogueIV]

Breaking News- Check Out the 2 page ad on the Feb 2023 RC Car Action issue - Losi Mini JRXT limited edition!!!

Unfortunately the QR link is not showing the vehicle yet.

-limestang

I kinda figured this was coming but now I'm happy! Now if MIP would go ahead and make actual CVDs for these I'd be extra happy because 3d printed arms are not working out for me.