Pinion Size speed and heat

[Rsmith0399]

I installed a new Castle MM2 esc and motor combo in my XL.

I ran it today, and although it runs ok on 2x2s, its no where near the 50mph I hear people talk about. The spur is stock. I believe the pinion is 14.

Is there such a thing as a good all around pinion/spur combo that will give me speed, but not cause the motor and esc to overheat?

[avted]

Are you running 2x2S in series or parallel?

[Rsmith0399]

Like it shows in the manual.

Are there any diagrams that explain wiring options?

[Rsmith0399]

Series

[avted]

You can calculate speed using your battery voltage, motor kv, spur and pinion sizes, transmission gear ratio, differential gear ratio and wheel circumference. Just set up a spreadsheet and adjust spur and pinion size to get the speed you want. Transmission and diff gear ratios are in the owners manual.

50mph is scary fast in the Yeti XL. I'm on 6S, stock gearing, and hitting 41mph, and that is scary. My nitro Revo is much faster, but more manageable at higher speeds, but the Yeti XL is a different kind of fun.

Of course "scary" is relative. I'm worried about hitting things and people (and breaking Yeti parts), and run in my neighborhood, primarily. With more space, courage, insanity, and spare change, I might enjoy 50+.

Do you know what speed you're hitting?

[Rsmith0399]

If your running 41 on 6s, I probably shouldn't expect much mor than 30 on 4s.

Do you use any drag brake?

[Trifish]

If you want to keep your diffs pretty... No drag brake!

[avted]

Here's a table to determine theoretical top speed based on motor KV and pinion and spur sizes. No guarantees that I haven't made mistakes. This is for the Yeti XL kit (I believe the RTR has slightly smaller tires, which will reduce the speed a bit). You'll have to refer to your motor and ESC manufacturers to see if they can handle the voltage, current, and motor RPM. In general higher voltages are more efficient (lower temp) due to reduced current, but you have to adjust gearing to get the right speed. Actual speeds will be affected by drivetrain losses, battery and ESC voltage and current, and tire ballooning. Stock configurations are highlighted. The last four rows are 6S 50mph configurations.

[redsawacs]

I not convinced that moving an 18 lb rig at 50 mph with a Mamba Monster 2 CC2200 combo while keeping it cool and happy is possible. Certainly isnt going to be simple to drive. Let us know how that works out for you.

6s is pretty dang fast and, in my opinion, quite uncontrollable in the stock configuration.

Tell us more about your rig

Dan

[avted]

I'm with redsawacs on this. I'm running a Mamba X ESC with a Tekin 4038 (2000kv) motor. Tekin doesn't recommend 6S in this motor, but thought it would be OK if I keep an eye on temps. On a hot (90-100 F) day, running a fair amount of full throttle (which often means running in grass), and a fan on my motor, I'm getting near max temps (I have telemetry alarms to help manage this risk). A more aggressive driver would run hotter. My truck weighs 17.5 lb (lots of aluminum and big batteries). The speed table I posted doesn't tell you what your system can actually handle. Even with an all aluminum and steel front end (and most of the rear end too), my Yeti XL is a sloppy machine at high speed. Of course, you can run over rather large obstacles at high speed too (curbs, rocks, small animals, children). The large heavy wheels out at the ends of a front suspension that's not protected from impacts (e.g. Mailboxes, street lamps, rocks, sticks) is pretty vulnerable at high speeds too. If you get your Yeti going 50MPH, I'd really like to hear back from you. It sounds pretty cool and would be quite an adrenaline rush!

[Rsmith0399]

Great info! Thanks!

[pro mod steve]

I bash the Castle MM2 and 1515 motor combo with 17T pinion on 4 and 6S (when the truck will behave) with no heat problems. What I have found is I have to drive this completely different from my 1/10 stuff. I like to beat on my stuff and really have fun and tear it up. This thing is a totally different animal the way it acts compared to1/10. So far temps have been good 100 to 140 after a set of batteries depending on where I am at mostly dirt.
Yeah Racing Heat Sink Twin Tornado High Speed Fans Set 1 8 Motor Car Ya 0261BK | eBay
I installed one of these when I built the kit so I have no data with out it.

[Kx450]

Thanks for posting that spread sheet that's
So helpful makes it easy thanks

[tonyfalkon]

There is a lot to take into consideration for your 50 MPH target YXL stock tranny ratio is 3.38, diff ratio of 2.91 then factor your spur and pinion gear ratio that will give you final drive ratio then tire circumference + tire ballooning. That is just a third of the equation there is also aerodynamics when you exceed 45 MPH wind resistance and drivetrain drag will slow the YXL down and raise motor temp. Last but not the least batteries, it has to keep up with the motor, C rating will determine how fast it can push 120 amps consistently and continuously as needed by your mamba setup. Don't forget your tranny will pick up heat too even with high temp grease, but RC car action magazine did say on their YXL RTR test reaching almost 50 MPH on 6s, maybe its doable maybe a fib either way I'm sure you'll have fun finding out. Please keep us updated on your progress and video when you reach 50 MPH goal.

[Trifish]

Yeti XL speed run on YouTube.

http://youtu.be/Vr48tt0Hezw

[avted]

I imagine the stock tires and foams donut quite a bit and increase the top speed. I have two rounds of Gorilla tape and CI closed cell foamed on mine, and my calculated top speed (41mph) is about what I see in practice.

[Deckard]

Avted, can you share that spreadsheet?

[avted]

Deckard, I don't see a way to post spreadsheet files on this forum. I did try, but it was not allowed. PM me your email address and I'll send it to you that way. Here are the formulas (units in parentheses) if you want to build your own (and check my math):

Speed (MPH) = Tire RPM * 60(min/hr) * Tire Circumference / 12(in) / 5280(ft/mi)
Tire RPM = Max Motor RPM / Final Drive Ratio
Tire Circumference (in) = Pi() * Tire Diameter(in)
Final Drive Ratio = Tranny & Diff Ratio * Spur/Pinion Ratio
Tranny & Diff Ratio = 5.21
Spur/Pinion Ratio = # Spur Teeth / # Pinion Teeth
Max Motor RPM = Motor KV (RPM/V) * Battery Voltage(V)

*NOTE: This is the calculated max speed the motor will reach at the specified input voltage. The manufacturer rated max speed may be less. Check with your motor manufacturer before running your motor at this speed.

Battery Voltage(V) = Battery Size(S) * Nominal LiPo Batt Cell Voltage
Nominal LiPo Batt Cell Voltage = 3.7(V)

*NOTE: You can adjust this to whatever value you want, based on how you charge and discharge your cells. IIRC, the safe range is >=3V/cell disscharged and <=4.2V/Cell fully charged

[pdxrealtor]

We have a 2200kv motor and momba monster x combo and would like to know what Pinon size tooth is good for a 1/8th scale?

The kit we got came with a 15th tooth pinion gear and we were wondering if that would be okay to run for a while tell we get the bigger tooth? Ps we are running a 6s lipo.

What the best pinion tooth to use for a 6s lipo 1/8th scale, and not over heat? Something safe that we cant destroy while bashing around?


Bump...

[tonyfalkon]

Before you change gears may I suggest starting with motor timing, MMX is equipped with a data logger, start with your data, the MMX/CC220 combo is an adequate pairing both are rated at 120 amps. After full-length run (that's when the battery dies) check the temperature of the motor and ESC, the data should tell you if the motor is getting all the power it needs. If it is your motor temp should be between 155 to 165° (160° is the sweet spot 180° or higher is too much) ESC temp (120 -140°). If the motor is too hot reduce motor timing (too hot the motor loses power, magnets loses strength and eventually fail), too cold increase timing, if that doesn't work then its time to change gears and repeat the whole process. With all that said, it is a tedious, frustrating and mind numbing process also it changes from one track to another compounded by 6s, weather and driving style, take note of those too when comparing your data. If I had done this 2 years ago when I started it could have saved 4 motors in the first 6 months, 6 actually but the first 2 were provided by axial since I bought the RTR brand new.

On a side note, if your taking this route, when checking temps, you might wanna check the battery (I usually pick batteries that have 50% more amps than what the motor needs at the very least)and servo (temps on both depends on the manufacturer), BEC (a must if you have this motor/esc combo, the ESC only has enough power to feed just the motor I use ESC's that have at least 20% more amps, to run the other electronics like the fans or lights on top of that a servo dedicated BEC), transmission and differentials (they should not exceed 110°) too, automatically when you start changing gears. Hope this helps you good luck, stay safe and above all have fun.