This was raced at VONATS in 2019, but I made changes since then. The car had quite a lot of steering and in that sense is quite similar to the Lazer ZXR, both of which are narrow compared to their contemporaries such as the CAT 2000 and YZ10. Using offset front rims helped, but still I wanted the chassis to be wider. This is where it really helps to use modern Kyosho CVAs (65.5mm front, 62.5mm rear, using LA59 front caster blocks to widen the front and increase caster), so you can then use a wider wheel hex to push the width out. 10mm wheel hex up front and 8mm in the rear, with modern Kyosho rims, gets you very close to the YZ10 and CAT 2000 in width. There isn't much thread left on the wheel axle, so you have to switch from lock nuts to serrated nuts to keep the wheels on.
Although I did find a way to "seal" the front and rear gear diffs, the method I chose didn't withstand the rigors of racing and the diffs started falling apart during Q3 and the A-main. So I had to slow down and drive easy to avoid grinding the gears too much. I was using the metal gear diffs, which are quite loud (very good for intimidating others with their fragile XX-4s
), but since then I have switched to Duratrax ball diffs, which are plastic, lighter, and quieter, as much as way easier to adjust without having to tear the car apart. The real trick here is with the center gear diff. It's also unsealed, and it would be quite a lot of work to incorporate a modern ZX6-like center slipper and layshaft. I had originally had it locked by simply adding o-rings to the inside to bind up the gears, but really I needed a bit of give to preserve the drivetrain. So what's in there now are some shims (I think ~ 1mm total, if I remember correctly) to generate some bind. Not quite enough to lock it, but enough to slow it down and make it feel like an oil-filled center diff. Motor and battery layout was tricky. I first considered mounting a shorty pack, but there isn't enough room for a 4.2 Ah shorty (too long), so you'd end up having to use an ultra-shorty. I don't like small capacity batteries for 4wd buggy, so I went instead for a saddle layout, which is still tight but possible. I used B44.3 saddle cups/holders, which work quite nicely. Had to mark out where to drill the holes and then countersink them on the bottom of the chassis (this goes for all screw holes on the underside. Nothing was countersunk, so I had to countersink everything). I also had to cut some of the upper deck on the left side of the chassis to make enough room for the left saddle to slot in, and also make a hole in the upper deck over the negative terminal of that saddle, so I can make an actual connection. This gives you basically no room to mount an ESC, so I made a little Kydex plate to go over the upper deck, to make enough surface area to mount the ESC. Anyway, this setup basically forces me to mount the motor on the front right of the chassis, which is fine except for the fact that the diff gears are mounted in such a way that the car goes backwards unless you have an ESC that can run in reverse mode (you can't flip the diffs, as they ride a little bit into openings in the bottom plate, so they have to sit where they are unless you cut the chassis again, and I'm not doing that). The Trackstar 120A does have reverse mode, and I generally love that ESC as it's only ~ $70, is very tunable, and works quite well.
Steering setup took some work as well. I don't like the stock Inferno 10 rack, which is actually rather similar to the Lazer ZX/ZXR rack, so instead I installed a ZX6 rack. The carbon fiber drag link I had custom made by Brian Marquez, which basically follows the ZXR drag link geometry, but is widened for this chassis (the bellcrank mounting holes are further apart here than on the ZX/ZXR). Brian and I also worked on some revised shock towers, which he made for me, plus upper and lower decks. Those will go into a different build, but anyway...steering servo normally mounts upside down from the upper deck, but I wanted to keep CG low wherever possible, which meant drilling new holes and making sure the steering link was straight and didn't run into the front center driveshaft. It's a tight fit, and I decided on a low profile servo for this. Trackstar again! TS-D99X servo is seriously good for the money. Small and very fast with plenty of torque for this application. Front steering knuckles are aluminum units from Jazrider. Again, using LA59 (ZXRR) caster blocks, which widen the front and increase caster, both of which help settle the car down.
Rear swaybar is from the Kyosho TF5. There is no way to take a "conventional" swaybar and mount it from the back of the rear tower, because the rear gearbox juts out in such a way to make that impossible. So I needed a shallow swaybar that I could mount to the front of the rear tower and not get too far ahead of the ball joint on the arms that the swaybar links to. The TF5 swaybars fit the bill pretty nicely, and they come in various thicknesses. I use 1.6mm at the moment. Rear hub carriers are aluminum units for the ZX5. Very similar geometry as the ZX/ZXR/Inferno10 carriers, but can more finely tune roll center. The hinge pin mounts on the upper hole to increase rear droop. I was previously using Jazrider Optima aluminum universals in the rear. I figured they're lighter and so it would save some weight, but dogbone pins do seem to wear more than those on steel CVAs, so I switched back to modern Kyosho 62.5mm CVAs. If you do run those Jazrider universals, though, put some red threadlock on the pin that slots into the universal joint and make sure to move it around a lot so that the joint doesn't lock up from the threadlock. You just need enough to lock that pin in there, because out of the package, that pin is just pressed in there with some weak serrations to hold it in place. I've had a few break apart there.
I forget the part number for the motor mount. It's a Kyosho part, but it's not made anymore
I think I was for the DBX. Undertray is hacked/modified from a spare TBG YZ10 870C undertray.The stock front bumper is rather large and extends past the chassis by quite a bit. I had used that bumper at VONATS and it was okay, but really I needed a shallower bumper. So I just made one from Kydex (I know, it doesn't look perfect, but it works), which pulls the leading edge of the bumper back in, behind the front wheels. This gives you a larger approach angle on jumps and will help keep the car from nosediving off of steep jumps.
Ride height set to 22-23mm. Kyosho RB5/ZX5 front/rear shocks with Losi blue/Kyosho gold front/rear springs and AE spring cups (need to choose the right spring cup to avoid it hitting the front arms at full droop). 2C/2B front/rear pistons with 45wt/35wt AE oil. This is a setup for hard packed dirt. Not exactly what I ran at VONATS, but what I arrived to afterwards as something that should work much better, especially on jump landings where the car was previously not jumping very well.
This all adds up to a pretty significant departure from a stock Inferno 10, which by no means was much of a "racing" chassis. However, in its current state I can say with confidence that this is a SERIOUSLY GOOD chassis, certainly to the point where it really does feel/drive as good as my YZ10. It's definitely a little heavier than the YZ10, but from testing so far, it corners great, jumps great, and lands great. I look forward to racing this at VONATS again, this time being able to drive it harder and faster without worry of nuking the drivetrain.
