E-Maxx Help - RC-Monster Forums

GT4X · **E-Maxx Help -** 06.24.2006, 10:31 PM

Hi Guys,

I'm new to RC-Monster however i've been doing quite a bit of reading trying to find any information on the right brushless set up for my E-Maxx. Listed are what I would like out of this set up:

1. At least 45mph
2. 30min run time
3. Run with T-Maxx 3.3

I don't know if the above is far fetched but it is what I would like to have, I have loaded and emptied my "cart" on RC-Monster so many times because I just don't want to make the wrong purchse.

Pics:

Regards,
Kurt Knight
Knight's Auto

squeeforever · 06.24.2006, 10:35 PM

How many cells?

BrianG · 06.24.2006, 10:42 PM

Welcome to the forums!

About how heavy is your truck? Have you done anything to bulletproof your tranny (you'll need to if you want to run brushless). You'll also want to change the stock slipper to something a bit more robust like the strobe slipper.

I'd say a BK 9920, BK 12020, or Quark 125B for the ESC. The brushless motor you select will depend on type of batteries, how many batteries you want to use, and how much you want to spend. Lehners are superior motors but a little pricey. The Wanderer XLs are quite a bit cheaper but still run very well.

GT4X · 11:58 PM

Quote:

Originally Posted by squeeforever

How many cells?

As is i'm running 14cells.

Quote:

Originally Posted by BrianG

Welcome to the forums!

About how heavy is your truck? Have you done anything to bulletproof your tranny (you'll need to if you want to run brushless). You'll also want to change the stock slipper to something a bit more robust like the strobe slipper.

I'd say a BK 9920, BK 12020, or Quark 125B for the ESC. The brushless motor you select will depend on type of batteries, how many batteries you want to use, and how much you want to spend. Lehners are superior motors but a little pricey. The Wanderer XLs are quite a bit cheaper but still run very well.

Thanks for the welcome! She is about 12lbs. and I was looking at the Hardened steel idler gears, the CVDs are changed since I was twisting the stocks.

squeeforever · 06.24.2006, 11:59 PM

If you dont plan on adding cells, I would go for the 8XL however, you won't get 30 minutes runtime. I can barely get that on 14 IB 4200's with a 10XL. Top speed with my setup is right at 40.

BrianG · 12:07 AM

Yup, you'll need those steel idlers. Also, you won't need first gear anymore, so you might want to either lock it in second gear, or get the single speed conversion which also locks it in second and removes some weight. Even without second gear, you'll have wheelie popping torque and high speed.

I imagine you are using a receiver pack for the servos and Rx? If so, you might want to pick up a UBEC (sold here). It is small and lightweight and lets you do away with a receiver pack (and the weight associated with it). It will take power from your main batteries and digitally convert it to 6v @ 3A for your receiver and servos.

If you are using 14 cells, want tons of torque and speed, and want to stay a little cheaper on the brushless motor, I'd say a BK Wanderer 7XL motor. If money is no object, those Lehners are great and a bit more efficient. I don't personally have experience with them, but someone else should be able to tell you what will be equivalent.

The tough part might be the 30 minute runtime. Brushless is more efficient, but it still needs some juice. If you are just bashing, you might be able to get 20-30 minutes if you use some of the higher capacity (4200mAh) batteries. Racing is more demanding so runtime will be lower if that's what you are planning.

To get an idea of the speed you'll have, try this. Your actual speed will probably be a couple mph better than what it says, but it'll give you an idea anyway.

squeeforever · 01:00 AM

Yup, Brians exactly right. I would however, go with a 8XL for somewhat of a compromise with the speed vs runtime that you want.

On a side note, Brian, could you explain as to why the speed calculator is so far off on my old setup. I was running a Lehner XL3100 on 12 cells in a E-maxx with 13/66 and it says only 30 something MPH....I know it was at least 50....

neweuser · 06.25.2006, 12:55 AM

Brian G hit it on the nose. I run a 10xl though with 16 ib3800's and get about 28 min, thats bashing, but i put a lot of top speed on that most of the time. If you want to keep up with the 3.3, GO LIPO! You lose tons of weight, also, dump four shocks and first gear, so you may as well do the conversion to single speed. It cuts you tranny in half! Steel idler a must! CVDS, MIP or UE are great. Remember, Nitro generally is already lighter, so the more cells you run, the more weight you add, the more weight you add, means less speed and could mean more damgage when you crash. Also, in my opinion, get better than the 9920....20120 maybe? Depends on the motor...I personally would get a lehner....
Squee, calculator...grearing?

squeeforever · 06.25.2006, 01:01 AM

Stock E-maxx in second gear, with 13/66. Gearing was up there^^

neweuser · 06.25.2006, 01:04 AM

Hmmm, maybe you just built a better machine than they predicted? LOL, or is it worse than what it says?

squeeforever · 06.25.2006, 01:07 AM

It said it would be like 30 somthing MPH, but I know for a fact that it was at least 50...It would fly by my modified Revo no problem and Revo's run 40+ stock. And mine is far from it. Maybe its because it calculates in a bigger RPM drop then really was...

neweuser · 06.25.2006, 01:17 AM

Could be, but I just think you "out built" the calculator!!!! LOL. Seriously, i agree on the RPM's part....

BrianG · 02:11 AM

Quote:

Originally Posted by squeeforever

On a side note, Brian, could you explain as to why the speed calculator is so far off on my old setup. I was running a Lehner XL3100 on 12 cells in a E-maxx with 13/66 and it says only 30 something MPH....I know it was at least 50....

Well, I'm not sure, but these are some possibilities:

- My "program" assumes 1.2v/cell for NiXX and 3.7v/cell for LiPo. As we know, these batteries have more voltage at a full charge: ~1.35/cell for NiXX and 4.2v/cell for Lipo. That does make a difference. Of course, we assume that the voltage will drop under load, but once the vehicle is no longer accelerating as heavily, that load is reduced. Plus the motor is running at higher efficiency at high speed requiring less current. So the voltage sag will be less pronounced.

- There might be some discrepancy between the motor kv ratings published versus the real world values.

- BK Wanderer motors are listed with their "loaded" kv values. Exactly how much load? I dunno. I generally use the unloaded ones for best case speed. Vehicle weight definitely has some say here.

- Tire diameter can make a large difference. Even duct-taped, there has to be some expansion, although small. Even .1" ballooning can account for 1.5 mph.

For example, if I have an Emaxx, in second gear, with 51/15 gearing, using 5s lipos (3.7v/cell), an 8xl motor (loaded kv=1875), and 5.5" wheels, I get 34mph.

Now, on the same emaxx with the same gearing, using 4.2v for the lipos, unloaded kv value of 2084 (according to the Feigao chart), and 1/2" of tire balooning, I get 50.78mph.

Quite a difference! The latter is best case, while the former is more conservative. The real speed is somewhere in the middle.

Edit: I forgot to add that the calculator simply takes the total battery voltage, multiplies by the kv value, divides by the total gear ratio, multiplies by the tire circumference (which changes based on ballooning factor), then converts inches per minute to mph. That's it. Nothing magical. I've checked it numerous times and everything looks correct. You can check the source code if you want - it's just javascript. Math doesn't lie, so there's gotta be something different in the motor specs or something. If anyone can see a mistake, by all means please let me know and I'll fix it.

coolhandcountry · 06.25.2006, 08:20 AM

Nice truck.
I was noticing you still have the stock diffs.
If you go with alot of power the diffs will fail.
If you want speed and runtime you need more voltage.
I you go 6s lipo on a 9xl or 10xl with 3800 or so mah.
You will be able to meet your goal or be extemely close.
As for the single speed. I like the two for a bashing setup.

sjcrss · 06.25.2006, 10:02 AM

I agree with everyone...you definately need to upgrade the diffs...to atleast the UE 6 spyder, but for a few bucks more you can get the 8 spyder setup, with has the aluminum diff cup over the 6's plastic cup...if these diffs are setup correctly , you will be set..also you need to lose the aluminum bumper mounts..and put stock on there...you need a give point ( or flex point)...at the speeds you want to run..if you hit something....that will transfers the damage elsewhere....bumper mounts are cheap and easy to replace. Also get a steel idler if not a set of the Ultramaxxed tranny gears, which are hard to find, but once in awhile you can find them....