Project Losi JRX-2

You know how it all goes... see a pic of a cool RC car... google more pics... search forums for more info... and before you know it, you're spending hours working on the same cool car yourself!

Been about a week since my last post with the picture of that cool Losi JRX-2 buggy and guess what I've been working on? lol!

I bought 2 used JRX-2s a long time ago and I basically cleaned one up to be a shelfer and built the other one intending for it to be a runner. Back then I couldn't find a shell for any of the two cars and after hunting on ebay for the longest time for one I finally gave up and the cars were left aside.

I've since discovered wonderful resources for vintage cars like Mr Lexan's cool repro shells and I've also acquired my Sherline CNC setup and it was finally time to build my own JRX-2 with some personal touches!

Starting Off...
The first thing I wanted to do was to use some modern shocks on my buggy and in my opinion Kyosho makes one of (if not the *best*) shocks available today so their velvet shocks were the shocks of choice. Their 3" front and 3.5" rear shocks seemed the exact length needed for the car so I picked up a set.

On the JRX-2 rear, the lower end of the shocks didn't use traditional spring retainer and rodend due to the unique 5-link suspension of the car; instead the spring retainer features a unique "C"-shaped bottom end to attach it to the lower suspension link. While the setup works and is undoubtedly cool, I wanted to work out a way to use the standard shock end. After all, I intend to run this car and it would be unfortunate if I was sidelined because I damaged a shock end. :)

Here's the new lower link which I machined. It allows me to use all the standard shock parts and it "wraps" round the rodend so everything's nicely protected. It is identical in length to the stock lower link and the shock mount positions are maintained too so geometry is retained.








Shock Towers...
After mounting up the rear shocks everything looked good, but it seems that this setup resulted in a bit less droop than the standard shock mount would've provided. To solve this I designed a new shock tower with revised upper shock mount positions to drop the shock down by 3.5mm to regain the droop I lost. The tower is made from 3mm thick carbon fiber sheet so it should last a long time.




Since I was going to cut stuff anyway, I cut out a front shock tower at the same time. While it retains all the stock holes, I added one more upper shock mount hole and 2 more upper camber link holes. One of the camber link holes is there to allow me to swap to a RC10B4 upright with minimal changes to the upper camber link angle of the car. The 3mm towers should work well - not to mention CF always looks good!




Batteries... where do they go?
I started this project with the intention of using lipo stick packs in standard configuration but I when I tried to fit even my smallest 4000mah lipo packs into the car they were a very tight fit in the rear battery retainer. The newer lipo packs are also longer than the ni-cad packs this car was designed for... back to the drawing board.

After much thought, I decided to go for a slightly more unique setup on this vintage car... saddle packs! The idea is simple - the car was designed to fit a much heavier ni-cad battery lengthwise towards the rear of the car. Swapping to a lighter stick lipo in the same position would move the weight balance further front in the car. Using a pair of saddle batteries in the rear will move the weight bias backwards, thus bringing the balance closer to that of a JRX-2 running a standard ni-cad.

I don't like cutting new holes in vintage car chassis unless I really have to, so I designed the lipo trays to mount where the 5-link suspension block mounts to on the chassis. They fit the saddles nicely in the rear of the car and also feature 3 different sets of mounting holes so I can adjust the position of the batteries forward or aft to fine-tune the weight bias of the car.




Next problem... what's going to hold the batteries in place? I needed a battery strap and some way to mount the strap on. After a variety of designs scribbled on paper, I ended up re-designing the suspension mounts to incorporate a battery mount on it. Now I can fit a battery strap down with thumbscrews so I can accomodate batteries of different heights.




Wheels & Tires...
I wanted to run current tires on this car so wheel and tire testing began. Front tires weren't much trouble as standard B4 fronts worked fine. The rears were more of an issue... Standard B4 tires had too much offset and would not even fit on as they would hit the suspension links. I had a pair of Duratrax Evader and CRT.5 wheels with less offset but although they fit, they made the rear end far too wide for my taste.

I finally decided to drill holes on my axles to move the axle pin outwards to allow me to run B4 rear wheels while maintaining rear width. Now I have a full selection of my current tires to run on this car.

As she stands now...
Here are a few pictures of my JRX-2. I've still got to paint up a shell but she's almost there!



Hope you like the build-up so far!