A tale of two Javelins...

[ahenderl]

If you give me your tires outside diameter, I can calculate a theoretical close-to-ideal pinion gear size with an Optima gear & rollout ratio calculator I made in Excel. Motor power doesn't really have any bearing on ideal rollout ratio because all motors have the same diameter and therefore rotational distance. All else being equal--spur/pinion, tire diameter being constants--one rotation of the motor will always rotate the wheels the same exact distance, regardless of motor. (Unless of course you slap in a 550-size or anything non-540-can size.)

It looks like the tires measures right at 3.5"

Not to question your expertise, but I've had several different brushless esc's & each has had a chart that suggested different gearing ratios depending on what turn (or kv) motor being used. They also had different recommendations for 2wd vs 4wd, etc. Do you think one final drive ratio works for any brushless setup regardless of the power of the motor? I appreacite your input.

I used the suggested 51t brushless spur gear and a 25t pinion (think I mistakenly said 15t in a previous post). Neither the esc or the motor get very hot so it may be fine. I don't need any more top end speed so I don't think I'll need to gear any taller. The low end torque is great so I don't think I'll need to gear any lower.

[Coelacanth]

Interestingly, with a 51T spur and 3.5" tire diameter, the theoretical optimal pinion gear for a rollout ratio as close to 1.00 is 14T, with a 15T being my second choice. Both are within +/- 10% (i.e. 0.90 to 1.10). A 14T pinion yields a rollout ratio of 0.996; a 15T gives you 1.068.

The calculator checks out almost every time. Although rollout ratio is much more important with on-road cars, the same principle is valid for offroad cars...they're just a tad more forgiving of incorrect gearing. And yes, I do believe that an optimal gear ratio exists totally independent to motor output. The one thing that stays constant regardless of motor is motor can diameter, and therefore rotational distance for 1 RPM.

[Coelacanth]

To add to the previous post, if you compare your numbers with the aftermarket 51T spur and 25T pinion to stock Optima gearing and rollout--and I believe the people who engineered the Optima knew what they were doing--the stock 41T:12T spur:pinion ratio, with the stock 3.248" tire diameter, had a rollout ratio of 0.986", right in the +/- 10% sweet spot. My aforementioned recommendation is even closer to this theoretical ideal.

Your current 25T pinion, with that 51T spur, gets you a rollout of 1.779". My take on it is you're way over-geared. Certainly today's motors and ESCs can handle the abuse, but it doesn't matter which motor or ESC you throw in there...a 14T or 15T pinion will result in the most efficient work-load for any motor. If your motor is very powerful, that'll probably mean back-flips and spinouts galore, but it's still the most efficient ratio for the Optima/Javelin gearbox.

[ahenderl]

To add to the previous post, if you compare your numbers with the aftermarket 51T spur and 25T pinion to stock Optima gearing and rollout--and I believe the people who engineered the Optima knew what they were doing--the stock 41T:12T spur:pinion ratio, with the stock 3.248" tire diameter, had a rollout ratio of 0.986", right in the +/- 10% sweet spot. My aforementioned recommendation is even closer to this theoretical ideal.

Your current 25T pinion, with that 51T spur, gets you a rollout of 1.779". My take on it is you're way over-geared. Certainly today's motors and ESCs can handle the abuse, but it doesn't matter which motor or ESC you throw in there...a 14T or 15T pinion will result in the most efficient work-load for any motor. If your motor is very powerful, that'll probably mean back-flips and spinouts galore, but it's still the most efficient ratio for the Optima/Javelin gearbox.

I agree that the good folks at Kyosho know what they are doing. In fact they recommend 30, 31 or 32 tooth pinion gears along with the 51 tooth spur gear when going brushless:

In fact, based on their recommendations...if all 540 motors use the same gearing then I am waaayyy under-geared.

[ahenderl]

I looked at the Javelin instructions as well as the brushless spur gear recommended pinion instructions and did a little math.

Both give final drive ratio with various spur & pinion gears and the internal gear reduction of the transmission is determined to be 3.79:1.

So, for an Optima / Javelin... Final Drive Ratio = (Spur Gear divided by Pinion Gear) x 3.79

This puts the final drive ratio of the 30 to 32 tooth pinion gears recommended by Kyosho between 6.04 & 6.44.

The following chart was provided by Novak and recommends final drive ratios for various turn brushless motors on various platforms. Even though it skips 15.5 turn motors, it looks like Kyosho is right in the sweet spot of what Novak would recommend for a 15.5 turn motor in a 1/10 4wd buggy.

[ahenderl]

So, it looks like Kyosho is spot-on if one is using a 15.5 turn motor, but I'm running a 8.5 turn motor.

If Coelacanth is right that all 540 motors can use the exact same gearing, then I'm actually fine. However, most motor manufacturers have final drive recommendations for their motors and they recommend lower gearing (higher final drive ratio) the lower the turn count (or the higher the kv rating).

Based on the Novak chart, I should be shooting for a 9:1 final drive ratio. The adjustment on the motor plate will not allow me to go any smaller than a 24 tooth pinion with the 51 tooth spur and that gets me to 8.054. Currently, I have a 25 tooth pinion installed & it gives a final drive ratio of 7.732.

I could put the kit supplied 61 tooth spur gear back in & use a 25 tooth pinion and take the final drive to 9.24 which is almost optimal...just slightly under-geared. A 26 / 61 set-up would be 8.892 which is pretty close, too.

However, take a look at the picture below. The 51 tooth OTW126 is on the left and the 61 tooth kit gear is on the right. There is an obvious difference in the composition. I am wondering if the 61 tooth gear is weaker than OTW126.

FWIW, after about a 15 min bashing session last night consisting mostly of speed runs straight up and down a 350 ft driveway I checked both the motor and esc temperatures with a laser thermometer. Both were right at 120 degrees f and it was about 85 degrees outside.

[XLR8]

This is interesting.
It seems to me that the ideal gear ratio depends upon your goal. For instance, is the goal to attain the best possible performance (acceleration and top speed) or is the goal to achieve a reasonable balance between performance and heat/run-time. If you were to run an extremely high FDR, current draw would be relatively low so motor and ESC would remain cool and run times would be very long but the car would perform like a crawler and how fun would that be. Conversely, with an extremely low FDR, the car might perform like a rocket for a short time until it disappears behind a thick cloud of smoke.
I guess I'm just stating the obvious.
Looking at Novak's chart, my cars are under-geared (i.e. high FDR) so I'm probably missing out on some of the performance potential from my equipment.
Regarding the material difference with the spurs, that's a very good question that Kyosho should be able to answer.

[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

[Coelacanth]

I have a question for anyone who is familiar with either the Optima/Javelin re-re and using brushless power.

The stock spur gear included in the kit is 61 tooth. I've read a review at BigSquid.com of a re-re Optima using stock gearing with an 8.5t brushless motor and their review stated that they felt it was almost perfect. With the included stock spur gear & 15t pinion gear, the final ratio of factory set-up is 9.24. However, the Kyosho instructions suggest Kyosho part number OTW126 51t spur gear for brushless set-ups.

I am installing a Reedy 8.5t Sonic 540 M3 motor. I am curious which spur gear would be better. I've looked at the OTW126 on the Kyosho website and it appears to be made from a different material that the stock 61t gear. The stock gear looks to be black plastic white the 51t brushless gear (which is also plastic) is blue and obviously a different material or a different composition. Is the OTW126 made of a more durable material?

Secondly, if I do use the 51t gear with the 8.5 brushless motor, would anyone have a recommendation for the pinion gear. I know I can play with different gears and check motor and esc temps, but I was wondering if anyone was running something similar and had an opinion about what works well. I'd rather learn from others' real-world experiences than run countless packs with every conceivable pinion gear constantly checking temps.

FWIW, my re-re Javelin is for bashing on dirt, grass, concrete & asphalt. I have a set of front & rear Proline Dirt Hawgs and will use 2.2" wheels for running...I was hoping to use the Turbo Scorpion re-re rear wheels in satin chrome but they are on backorder right now. Kyosho says FAH203BK (front) and FAH204BK (rear) will work on the Javelin, so I may go that route so that I can start playing.

ahenderl, I'm trying to update my gear ratio calculator to include re-re Optima gear info. I see that the re-re spur gear is 61T and has a 21T inner cluster gear inserted into it. What I don't have is the counter gear specs; the one with the slipper. How many teeth is that gear? The original stock Optima counter gear is 28T but that slipper gear looks like it has a lot more, finer pitch teeth than that. That would completely change my calculator's output.

I assume the internal gears are the same as the original Optima; i.e. internal diff gear = 37T and internal final pinion gear = 19T. Thanks!

[XLR8]

here are gear teeth counts for rere javelin. assume optima is the same. hope this is helpful.

[Timmahhh]

I'd definitely run the larger spur. The ratios listed on the novak chart seem more applicable to older brushed motors, and most current motors will require more reduction than what that shows. As an example, I used to run about 34/69 with an older 17.5, and in the same car and on the same track, but with a new 17.5 I run 26/75 now and hit the same temps. For what its worth, I run high 20's for pinion on the rere optima with an older tech 17.5. Its still plenty fast for the car. to me, 8.5 seems waaaay too fast for an optima/javelin unless its just a huge wide open area with no jumps or things to run into, but I'm also much more conservative than bigsquid, whos upjective is to "send it" as far as possible without regard for consequences for the vehicle.

[Timmahhh]

Heres the motor im running

[Coelacanth]

here are gear teeth counts for rere javelin. assume optima is the same. hope this is helpful.

That's excellent, XLR8...just what I needed. The re-re Optima gearing is completely different, outside AND inside, so my gear calculator's results will be way off for a re-re Optima. I'll update my calculator with the new gearing. Should be interesting to see how the new rollout compares with the old.

[Coelacanth]

Okay, here's what I got, plugging in the new stock re-re gear numbers, and comparing to the original Optima, Turbo Optima, Optima Mid and Lazer cars, and some observations:

You'll notice with the stock original Optima and Turbo Optima and even Optima Mid, Kyosho was aiming for a rollout ratio "sweet spot" of 1.00 inches, give or take 10%. All of these cars, with the originally-included gears, had a rollout between 0.90" and 1.10". I don't think that was a coincidence. In all my modded cars, I selected spur & pinion gear ratios to match that "sweet spot" rollout ratio to get as close to 1.00" as possible, factoring in the very different tire diameters I used with some of those cars; the Barney Optima using larger 2.2" wheels & Proline Caliber tires and the CYANide Optima on-road project car, that has smaller-diameter HPI Vintage VTA wheels & tires installed.

EDIT: I assume the re-re Optima tire diameter is 82.55 mm, is this correct?

Even the later Lazer models, with different gearbox gearing and finer-pitch spur/pinion gearing, ended up with rollouts very close to that 0.90" - 1.10" optimal range.

The re-re Optima, with stock gearing, has a final drive ratio of 8.03 vs. 10.35/9.78/9.74/10.06 (orig. Optima/Optima Mid/Lazer ZX/Lazer ZX-R), which is a significant departure. When you rotate the motor one revolution, the car's tires will roll forward 1.272", about a quarter-of-an-inch more than most of the vintage cars. My guess would be that the taller gearing is acceptable since all of the gearing is stronger than original, the car has a functional slipper gear, and you can easily adjust "punch" acceleration settings in modern ESC's these days.

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?

[ahenderl]

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