Brushless e-maxx - new setup questions

[ozdave]

Hi guys, great forum, very helpful and it has provided me with just about everything i need to place my order for an upgrade to brushless :)

Ok so I have an e-maxx with with a few upgrades, rpm shock towers, a-arms, and skid plates. MIP drivetrain. 3.3 diffs. Pro-line steering kit. Traxxas Big bore shocks. ACNCM bulks. Pro-line Velocity 6 wheels (standard size) with Pro-line masher tyres. Not a particularly light truck fully loaded with 14 cells.

I am planning on going brushless and would like to hit 40mph. After reading lots the top of my list is BK warrior 9920 controller and Wanderer 8xl motor with a UBEC.

I'm will ony be typically running 12 - 14 cells but would lke to have a play and maybe run 16 cells, all NiMh (GP, IB) I bash the truck around a bit and like to do jumps so am not going to go lipo

So my questions are....
Is there another motor I should consider with these goals in mind?
Do I need the UBEC with this setup? Will it make that much difference?
How about a fan? just for the ESC? I'd like to keep it all running cool and prefer safe than sorry.
I realise I will also need to make some gearing changes. Will I be be able to make the changes I want without changing the slipper setup?

What else is a pretty sure thing to go in the first few runs?
diffs? should i just change the cups now given how fast i want to go and the way i use the truck? or shim them? or both?
Steel idlers?
Will the standard transmission hold up ok? I realise first gear will be useless.

Last but not least is there anything i have missed that I need to consider to make this thing a nitro beater :)

[BrianG]

Welcome to the forums!

The 8XL is a very solid performer, especially for the price. You could go higher-end for a more efficient motor, like the Lehners or the Neu (but can't use the 9920 with the Neus), but the XLs are definitely good bang for the buck motors.

Yes, with anything over 10 cells (8 cells IMO) you should use a UBEC. Your ESC will thank you for it. It doesn't alter truck performance per se. They are a few bucks, but well worth it.

Personally, I don't like fans. Others do. I feel that if something is overheating, something isn't geared right or you need better heatsinks. None of my setups use a fan and they run just fine - and I am a stickler for not liking anything over 130*.

The stock slipper simply won't hold up under brushless power - those pegs will melt in no time. I would get the Strobe slipper setup. That also lets you use Mod1 gears, which seem more durable.

You're gonna want the steel idler gears for the tranny as they will go. And once you see how much power there is, you won't need first gear, so I'd also get the locking hub to lock the tranny into second. This hub eliminates the slop from the dog gear.

I'll let someone else comment about the diffs (I don't have an emaxx, but have used the emaxx tranny in a revo conversion). You may want new driveshafts too. Again, others can comment on what will work best.

[ozdave]

Thanks for the quick reply Brian.

For gearing i've used your tool and the forums and come up with 51T Spur, 18T Pinion. Thoughts?

I cant find the locking hub you mentioned to lock me into second?

So my shopping list so far...
9920 Warrior
Wanderer 8XL
Heatsink/clamp (L size)
External UBEC
Strobe slipper kit
ofna 51 tooth spur gear
5mm bore, 18t pinion
Steel idler

oh i forgot to mention i already have deans on too

[BrianG]

51T spur sounds good, but the 18T pinion sounds a tad high. I'd go 16T personally. But again, I've never run an actual emaxx, so someone else may pipe in.

The hub isn't listed in the store, and the Gmaxx site is down right now so I can't even get you a pic of it. It's like a $12 part. If you email Mike, he might have it or be able to get it.

The rest of the list looks good, although I would get the XL size clamp (not the L).

[ozdave]

ok cool, XL heatsink it is.

So back to using your tool again and I drop down to a 16t pinion and its predicting a top speed of 35mph. Good, but not quite the 40mph i was hoping for to compete with the nitro guys I run with.

I have to go to 16 cells to hit 40 with this gearing. I was hoping to do it with 14 if possible but have the option to go to 16 for a bit of fun. Now if I change the motor to a 7xl i can hit 40 with 14 cells but can't run 16 cells as it spins over 40,000 rpm and im getting into the danger of overheating.

Can I drop the spur tooth count safely to up my speed ? If i go down to 44T spur im back in the right range. Does one exist that I can stick onto the strobe slipper? or am i just relocating the problem of a the 18t pinion?

Or should i be considering a different motor to achieve these goals ?

[BrianG]

If top speed is what you're after, then a 7XL on 14 cells, or an 8XL on 16 cells is what I would do.

Yeah, decreasing the spur size is changing the gearing the same as increasing the pinion. Both change the final drive ratio.

I'm sure some of the emaxx people will chime in anytime and they might say 18T is fine. It just sounded a little high to me...

[BP-Revo]

Well, also remember gearing can be increased for more top speed if the system can handle it. If the system is running, say, 35mph but is running at room temp, you could probably get 40mph and the system would never get about 120-130.

But if 35mph is making the ESC constantly thermal, then its probably a good idea to gear down.

16 is a good starting point - you can go from there.

[ozdave]

ok great, so it sounds like i I can work this out up to a point but really need a bit of trial an error with my particular setup inorder to get what im after?

Am i correct in thinking that current draw is what drives up the temp of the ESC? and that at higher revs created by more cells means more current? are there any guidelines that can help me determine ESC temp beforehand?

[BP-Revo]

Originally Posted by ozdave

ok great, so it sounds like i I can work this out up to a point but really need a bit of trial an error with my particular setup inorder to get what im after?

Am i correct in thinking that current draw is what drives up the temp of the ESC?

and that at higher revs created by more cells means more current?

are there any guidelines that can help me determine ESC temp beforehand?

Yes.

Yes.

Yes, given the same motor. If you increase the turns of the motor so that RPM is the same even with more voltage, current is actually reduced. But if you increase voltage on the same exact motor, current will rise.

Generally 160 is the max, some people prefer less. I prefer to be able to touch the motor or ESC for any duration I please, which means that its running no more than 125*

[suicideneil]

Best bet- buy lots of pinions from 15-22 tooth, that way you can have a play as gearing/temp is a tricky thing to get right if you're not all that experienced (including me). As for the gear locker:-





You will have to wait until tommorrow to order it, but to fit it is simple; remove shifter fork and dog thingy, then push this into the face of the 2nd gear, and reassemble the tranny as normal.



If you want the idlers you will only really need one, but you can use two if you still want to use both gears in the future.

[BrianG]

Thank you suicideneil, I couldn't find a pic of the locking part and it is not easy to explain. This little part helps second gear last longer since there isn't that sudden snap from the play in the dog gear.

If you lock second, you can reduce weight by going with only one idler, and then shaving all the material off first gear so only a sleeve is left as a spacer to keep proper bearing placement.

[ozdave]

Awesome! Thanks for the pics and detailed explanation suicideneil. Very helpful.

I think i will do as you say and buy a few different pinions and have a play.

[neweuser]

Originally Posted by ozdave

Awesome! Thanks for the pics and detailed explanation suicideneil. Very helpful.

I think i will do as you say and buy a few different pinions and have a play.

With an 8xl on 16 cells, I probably would not run the 18T pinion unless you plan on running a fan on the esc. A 16 will be about perfect for you. If you are looking for 40mph on 14 cells, go with a 7xl for sure and gear it 16T. I ran my 9xl on 16 cells with an 18T and it ran too hot even for that. That was with using 1/8th diffs as well. So an 8xl on 16 cells with a 16/51 would be about perfect. Or, 7XL 16/51 on 14 cells....

[ozdave]

so if i wanted to go lipo in the future.... how would this setup fair ?

would the 8xl be better with this in mind. I know i said no lipo but you never know :)

[neweuser]

If you are going lipo, you could use 4s on an 8xl. 7xl would be faster though if you are looking for speed and your temps should be just fine.