E-revo Motor "ARG CONFUSED"

[Rcbros]

So many choices. So many choices. What to choose.


I'm going to be running an E-revo, Stock chassis, E-maxx Transmission with G-maxx single speed.

I plan to Run 14 cells and/or Lipos. (lipos soon, nimh for now)

I want maximum runtime, yet race worthy speeds. I will be racing this truck against nitros and need to stay competitive.

Price range under $100 and would like it to work fine with the Warrior 9920.

Rather not deal with heat issues.

What motor do you think would be best for me? and what gearing should I consider?


Thanks so much guys. Please, if you list a motor, tell me why you chose it. This helps me alot rather then basing my decision on the motor that was picked the most lol.

Thanks!!

for 100 bucks i would say a feiago 8xl 9xl or 10xl.
do know blacked out revo? thats me on youre web site

[Serum]

On 14 cells, the 8Xl would be my favorite.

or choose the smaller L motor if you want to go for a lighter setup!

[crazyjr]

If you want max runtime while still getting good power i think a 9XL would be very good. Thats what i'm thinking for mine

[Finnster]

For under $100 your only choice is a XL motor.

I have a 8XL, its really great, altho my be a bit hotter motor than you are asking for, but prolly ok for heat. Perhaps go with a 9xl then. I would think mid to high 30s on 14 nimh. Power vs heat/runtime are competing issues, so you will have to decide on the balance. A 7xl will run fast/hot/short. A 10xl will run cool/long/ and slower. 8 & 9s in between.

Depends on what your track is like and how long the races are.

[Serum]

not necessarily. You need to find the sweet spot.

My 7XL stays rather cool on 14 cells. meaning it's running rather efficient. if you put your epa on 70 percent, you will have good runtime, and you'll be able to drive fast if you set it to 100 percent. Something to think about.

[Finnster]

Originally Posted by Serum

not necessarily. You need to find the sweet spot.

My 7XL stays rather cool on 14 cells. meaning it's running rather efficient. if you put your epa on 70 percent, you will have good runtime, and you'll be able to drive fast if you set it to 100 percent. Something to think about.

That's a good idea w/ the EPA. Would give alot of flexibility of different tracks or conditions. Do the efficiencies really change that much on the XL motors just by going up/down a turn, given the same number of cells? I haven't seen their charts.

Playing with the motor calculator on the Neu motors website, when comparing a 2700 kv (1D), a 2200 kv (1Y) and a 1700kv (2.5D) 1515 motor, all on 14 cells, the efficiencies run:
91.9%, 93.3%, and 92.1%.
The current draw runs 111A, 75A, and 57A.
Motor RPMs; 46K, 38K, and 30K.

I understand this is just a calculator and there a huge number of other things that go into this, but perhaps I'm missing something?

Generally the advice above is also given to 1/10 scale systems (say all running 6 cells or 2s.) If you want the the fastest, go a low turn, say a 3.5R or 7700, but heat and runtime will suffer. If you want more runtime and don't need lots of power, go with a 6.5R or a 5700. If you go too low, I would think the extra current load would overshadow any changes in eff, if you are talking within a narrow range of turns.

[Serum]

Please get that current thing out of your head. these are not 'standard' values. the current a setup takes depends on the gearing, weight and quality of the batteries.

A motor that can take 200A can run more efficient than one that can take 100, while the one that can take 100 can take peaks of 250+ (if the batteries deliver the juice)

there is not such thing as a constant current draw with rc cars.

[Dafni]

Originally Posted by Serum

there is not such thing as a constant current draw with rc cars.

Word!

[Serum]

Look who's back!

Cool to have you around Daniel.

[Dafni]

Thank you!

Never been far away, though. Still read most every thread here, watching all your posts ;)

RCBros, for under 100 bucks, you'll have to go with a wanderer XL. For 14 cells I'd choose an 8XL too.

[Serum]

You did quite some reading then.. LOL

[Finnster]

Originally Posted by Serum

Please get that current thing out of your head. these are not 'standard' values. the current a setup takes depends on the gearing, weight and quality of the batteries.

A motor that can take 200A can run more efficient than one that can take 100, while the one that can take 100 can take peaks of 250+ (if the batteries deliver the juice)

there is not such thing as a constant current draw with rc cars.

I'm sorry, but I think my post was misunderstood. I hate to make them any longer as they take long enough to write as is. I have never claimed current draw is static. Its a silly idea. Plus the values posted were also related to RPM. Cars by definition are dynamic (speed (rpm), accel, load, resistance, etc) and so then is current draw. If you were pulling 100A constantly you would have no throttle control (by definition) and would drain the batts in a min or so (assuming nothing caught fire first.) OTOH, I wonder if you just like to argue w/ me... :o :P

The data above was demonstrative only. At a point in time (or static load) a higher turn motor will pull lower amperage than a lower turn. Since voltage is ~fixed, total power output is lower (and so runtime longer.) Over a cumulative period of time, the net amp draw is higher, yada yada yada. OTOH, the efficiencies were very close to each other, at least for that fixed time period (all on 14 cells) that the calc generates (values listed as @ Max Eff.)
What I was wondering is eff that great of concern when talking within a range of motors of a turn or so, or at least a bigger factor to offset the gains in heat and loss of runtime (the OPs stated criteria) when going to a lower turn motor. IE, are there large eff differences in a lower turn motor running at a lesser throttle than a higher turn motor running at a higher throttle? Hopefully that clarifies my point. or maybe not. Maybe its just moot. Whatever

Either way I stick with my rec of an 8xl (I gear mine at 15/51 w. same setup OP is considering) and perhaps a 9xl if runtime/heat is a major concern (altho my 8xl only heats up to ~160F+ after several packs.) Maybe a 7xl would run cooler, just seems counterintuitive, but I just haven't seen controlled data either way.

[Rtsbasic]

Another vote for the 8XL. I ran a 9XL in my Emaxx/Savage for a few months, and it was fine, but I wanted a tiny bit more oomph so picked up an 8XL. Not arrived yet, but my 9XL would run 130-140F in my Savage, and gave good runtime. 180F is the recommended limit on these motors so the temp was fine. On 14 cells its hard to get more than 35mph out of it, part of thats because you run out of gearing.

[BrianG]

From the many setups I've seen here, it seems to be:

- For a light vehicle (3-5lbs), an S size motor is used
- For a medium weight vehicle (5-8lbs), an L motor is used
- For a heavy vehicle (9lbs+), an XL motor (or larger) is used

Of course, there can be some overlap, but the motor and vehicle weights tend to fall this way.

Then, you figure out the voltage you want to use.

Then, figure out the working rpm based on ~80-85% of the max recommended rpm for whatever motor brand you want to use. Example: for the Wanderers, 40k rpm is the absolute max rpm. 80% of that is 32k rpm.

Then, just divide the working rpm by the voltage to get the approximate kv value. Just pick a motor of the size you figured earlier, with the kv value you just figured (preferably using the loaded kv value if possible).

Then, taking into account of all the various gear ratios (diff, tranny, etc) gear up/down for the speed you want, while keeping the motor/ESC/battery temps at a decent value.