A tale of two Javelins...

[ahenderl]

What I'd be interested to know however, is if motor and ESC temperatures would decrease a tad if someone were to change the spur & pinion gear ratio to something like 61T/23T, which puts the rollout to 1.017". I don't have a re-re Optima or Javelin but would anybody be willing to try out that ratio and let me know how the car runs?

I can check the temps with 61T/23T and see what I get. I will say, however, that my guess is that the gearing would be a little on the low side. I was running 51T/25T and felt that maybe it was too tall gearing based off the math even though the esc & motor temps were right at 120 degrees F after 15-20 minutes of bashing. So, I swapped to 61T/25T to see how it did. I definitely noticed a drop in top speed and don't think it really helped out much in acceleration.

Even with the taller 51T/25T gearing it made enough torque at almost any speed to stand up straight on its rear tires. The lower 61T/25T gearing may give a tad more low end grunt or possibly better acceleration, but what good is even more acceleration if I have back out of the throttle just to keep it from attempting back flips?

I will double check the temps & for the sake of your experiment will try a 23T pinion with the 61T spur. I'll also get an accurate measurement of the outside diameter of the tires I'm running, too, just in case they are taller or shorter than what you are using for your math.

For what it's worth, I only bash with my stuff...I don't even know where the nearest off-road rc track is. I feel that the 8.5 turn brushless motor is a pretty sweet set-up for the re-re Optima / Javelin. It is very fast and very fun to drive. I found that a high powered brushless set-up to be too much in my Turbo Scorpion and Beetle re-releases. In those I had to dial the power waaaayyyy back to keep them even remotely controllable. However, the Javelin is different. The front suspension geometry is tons better and the car is really fun and easy to drive.

[ahenderl]

After the red Javelin body came in from Japan, I mixed it with the black body and this is what I came up with:

I like the red, black & silver together.

[XLR8]

I agree, it looks fantastic. Very unique.

[keithrc]

Another Javelin fan here, got 2 originals myself but so far haven't gotten around to buying a re release but will in the not too distant future.

Where do you guys buy the new cages from?


Keith

Hey Keith,
I ordered both a black & a red cage off of eBay from hobby_japan. I could be wrong, but I don't think they are offered here in the US, so I waited for them to ship from Japan.

Adam

Hey Adam,

Oh OK, I was looking at their ebay page earlier today, checking out the wings. Do their cages come with the wings, wing mounts and the alloy "roof support piece", (not sure what it's called) I bought some white and green cages a while back but it's just the basic cages without the mounting parts.

Do the new wings fit the original cage mounts?


Keith

[XLR8]

Here's a re-re cage I got from Kyosho mounted on a vintage Turbo Optima. I had to borrow the aluminum "roll bar" from my re-re Javelin shelfer as the kit doesn't include this item. There's no provision for wing mount so you'll need to order the re-re wing mount separately as well. My re-re cage also didn't come with a wing either. I don't recall any problems bolting it on the vintage car; all hardware needed to attach it was included. The decal set is included. You'll drop a c-note to get everything to complete the retrofit. Hope this helps.

[Coelacanth]

After the red Javelin body came in from Japan, I mixed it with the black body and this is what I came up with:



20180812_151001.jpg



20180812_150933.jpg


I like the red, black & silver together.

That does look nice, it reminds me of a Marui Samurai! If that's the car we're going to test temps with, I'll need the diameter of those tires because they're quite a bit larger than stock...and the "optimal" rollout calculation will need to be changed accordingly.

Modern brushless motors are so ridiculously powerful that even when they're over-geared, they'll do insta-backflips on full acceleration. I agree that there's no need to lower your spur-to-pinion ratio when you're already doing backflips, but you're using a modern 8.5T motor...which is over-motored, IMHO. The stoutest brushless motor I put in any of my Optimas is an 11T 3200 kV Tacon motor, and I feel that THAT motor is overkill. I had to dial down the "punch" in the ESC to 3 out of 10 or something and even then, I had to install a Kydex wheelie skidplate under the rear of the car as it would lift the front tires if I punched it even while it was already going half-speed. I'm not a racer either and I find an RC car getting close to 40 mph or faster is practically uncontrollable, unless just doing straightaway speed runs...but that's not "driving", really.

We all have our own idea of how much torque and top speed we like, and too much of either makes the car undriveable, for a particular driver's abilities. That doesn't change the fact that every car's gearbox and spur-to-pinion gearing has an optimal ratio where there's a minimum of energy spent for the maximum output. The drivetrain becomes less efficient the further you go on either side of that optimal balance point. As any 540-size motor rotates the exact same distance, regardless of how powerful the motor is, this particular variable in the equation remains constant. Once you've calculated your drivetrain's optimal spur-to-pinion ratio for a particular car's gearbox and tire size, it doesn't matter what motor you throw in there. You can over-motor or under-motor but that has no bearing on drivetrain efficiency.

I consider the drivetrain optimal "sweet spot" to be analogous to a car's track width. All else being equal, if nothing else changes, widening the track width makes a car steer more (not necessarily "better"); narrowing track makes it steer less. There's a hypothetical balance point where the track width is optimal for the car's controllability, and deviating too much on either side--too narrow or too wide--makes the car steer less optimally. Too sensitive and twitchy or too much understeer--for that particular chassis.

EDIT: Post #5 here pretty much follows this logic:

https://www.rctech.net/forum/rookie-zone/358267-gear-ratios.html

[ahenderl]

The Dirt Hawgs measure 3.55" (90.17mm) and the kit tires measure 3.39" (86.03mm)

[Coelacanth]

Thanks, Adam. When I plug in that tire diameter with the re-re Optima gearing, without changing the 61T spur gear anyway, it would seem either a 20T or 21T pinion would be very close to a 1.0" rollout. 20T = .996"; 21T = 1.014".

That said, the power of your modern brushless motor would already have tons of torque even with a taller pinion gear, enough to do backflips-on-demand...but that's the motor power being excessive more than anything else. I still believe a rollout between 0.9" and 1.1" is probably in the re-re Optima's wheelhouse sweet-spot, but I suppose temperature testing of both motor and ESC, under high-resistance driving conditions (i.e. driving in grass, for example) would help confirm or deny the theory. Of course doing high-speed straight runs up and down a smooth street wouldn't properly stress the gearing/motor/ESC enough for temperature to be a useful indicator.