Mamba Max getting too hot?

[viperx07]

I was using a 5700 setup with my b4 and using gp 3300 and 3700 cells and some 3000 stick packs. My pinion was 21 tooth. Sometimes i turned the epa for throttle to 70% especially for the 3700 and 3300 packs because it was too much power. I noticed that the motor/esc were getting pretty hot. I dont kno if thats hot or not because I never ran it before but if I put my finger on it for 3-5 seconds it was pretty hot. I wasnt using 12 cells or any high powered motor so Im wondering if this is normal. Sometimes I didnt wait much between runs so maybe thats why it was getting hot but I dont think it should matter much since the MM can handle so much more without problems.

[pinolelst]

Running at 75% throttle epa is generally not considered good for esc's and motors.They're really happy when all the switches are wide open at least part of the time....running at lower end points creates heat due to the inefficiencies....maybe gear down if it's too fast.Also castle has said elsewhere not to worry about heat below 200 deg...best to run cooler of course but the equipment can take it apparently.

Have fun

pinolelst

[viperx07]

isnt 75% throttle epa same thing as having it at 100% but only throttling at 75%? I dont see how going 75% speed is hotter then going full blast..

[ElectricThunder]

isnt 75% throttle epa same thing as having it at 100% but only throttling at 75%? I dont see how going 75% speed is hotter then going full blast..
Switching losses in the FETs. That's how the ESC works; it's a bunch of little switches turning on/off really fast. They turn on/off slower when throttle input is lower, thus you have a slower spinning motor, and the vehicle moves slower. If you hold WOT, the switches are basically 'on' and so the motor spins as fast as it can, thus the vehicle moves at max speed. Apparently, switching on and off really quickly means there's a loss of current or whatever in the process of going on-off-on-off....etc. That generates heat. That was the abbreviated "I forgot exactly how it all works, but just don't do it" version.

So anyways....try using a smaller pinion and see how that works.

Just for reference though, I gear my Rustler (heavier than your buggy) at 20/87 with IB4200s. After one full run (maybe 20ish minutes), the motor is at around 150F-160F. Castle says don't go above 200 on the motor. For my ESC (I run a fan; I'm paranoid), it comes off the same run at around 95F-100F. Without the fan, it came off at roughly 135F (well within the system's operating temperatures).

[viperx07]

that doesnt explain why runnin it at full with 75% epa makes it hotter then running it at 75% with 100% throttle epa.

[CRASH3]

that doesnt explain why runnin it at full with 75% epa makes it hotter then running it at 75% with 100% throttle epa.

When you turned your EPA down to 75% did you re-calibrate your radio to the esc?

The motor and speedo will run warm, if you can touch it for 3-5 seconds you are fine. But I do believe a 21T pinion in a B4 with a 5700 is a little too tall, try gearing down to a 17-18T pinion.

Hope this helps, :)

[viperx07]

the lowest one that can is a 21 :) I will need to buy a bigger spur gear I guess

[glassdoctor]

that doesnt explain why runnin it at full with 75% epa makes it hotter then running it at 75% with 100% throttle epa.

This is one and the same. When you turn the EPA down to 75 it does exactly the same thing as if you only applied 75 throttle... the esc sees 74% either way.

And YES, this does tend to create more heat in the esc.

I don't thing a 21T is too tall for a 5700... do you run a stock (81) spur?

You will be much better off gearing down since you want less speed anyway... why can't you use a smaller pinion?

[ElectricThunder]

that doesnt explain why runnin it at full with 75% epa makes it hotter then running it at 75% with 100% throttle epa.
It's the same thing; however, when you limit your EPA to only 75%, that's it- that's the max amount of throttle you can have (so when you mash the trigger down, you're really only at 75% of max throttle). You can never go truly WOT where the FETs are just straight 'on' with your EPA limited. When you have it at 100%, you are allowed to go WOT then, and thus, the FETs will be fully 'on'.

Edit- Glassdoctor beat me to it... :eek:

[glassdoctor]

Ha! scoreboard, hee hee....

[TheSteve]

But we're talking brushless so the same rules don't apply. No matter what speed you're going the fets are constantly switching on and off in a brushless controller.

Sounds more like the motor just isn't running in its efficient zone when at partial throttle.

[glassdoctor]

The guys at CC have said it... it's best to not turn down the EPA as a limiter... they said it run cooler at full throttle.

I don't claim to know how or why.

[ElectricThunder]

But we're talking brushless so the same rules don't apply. No matter what speed you're going the fets are constantly switching on and off in a brushless controller.

Sounds more like the motor just isn't running in its efficient zone when at partial throttle.
How would the motor not running in its efficient zone explain the ESC getting warmer than usual though?

I'm with glassdoctor; castle said it!:p:D

[viperx07]

yes i have the stock spur gear. If i use a smaller pinion, I cant bring the motor close enough for the gear mesh. I guess the motor is too big and I cant get the motor mount holes in the right place to mount it with a smaller pinion

[glassdoctor]

I race a B4... I don't recall how small a pinion I have run but I'm sure I've had a 17-18 on it. The MM should fit like any other motor since it's a standard 36mm. Maybe you need to grind off the little screw heads if that's what it hitting the tranny case.

[viperx07]

I think it has something to do with how the wires come out of the motor.

[Chopster]

I've gone round and round with a similar problem when running my 7700 in my T4 on 3S Lipo. I had attempted to turn down the epa to control the rpm under full throttle. Castle told me that it was a bad idea and would cause heat problems, which it did. Something about the ESC always "seeing" the full voltage of the battery pack and having to reduce (or bleed) off the voltage to run the motor at reduced throttle. The voltage (energy) is bled off in the form of heat. The ESC is happiest when it seee full throttle.

In my quest for information with regard to brushless systems, I've found that it is best to setup you car/truck to accomplish a purpose. The right voltage feeding the right motor, with the proper gearing.

If your setup is too fast, first reduce the timing and increase the punch control. If it's still too much, go with a smaller pinion or larger spur. You just want to watch the temps on the motor though. Going to small on the gearing can result in the motor getting too hot. If you get it geared right when the motor and esc are running at an acceptable temp, and it's still too fast, the best thing to do would be to reduce the number of cells you are running.

If you're trying to run the buggy on a track, the 5700 may just be too much. If the track is tight, you will probably be better served with a 4600.

With my system, I like to stay conservative within the limits of the system I am running. What I mean by this is that I gear so that the setup is comfortable. My 7700 system runs at about 150 on the esc and 140 on the motor. This is after running through an 8Ah battery pack.

[vashon10]

You should consider getting a temp gun. I have a MM4600 and even though 180 degrees is within spec, I wouldn't hold my finger on there for 3-5 seconds. And at the limit of 200 degrees ... how long can you hold your finger in almost boiling water ?

In other words, these temps are too high to use the regular finger test.

[tcolesen]

120-130 deg. will feel burning hot, and my guess is most people won't be able to hold their finger on a motor at 130 deg. for more than 3sec.

[ElectricThunder]

120-130 deg. will feel burning hot, and my guess is most people won't be able to hold their finger on a motor at 130 deg. for more than 3sec.
Yeah... I was stupid enough to hold my finger on my 5700 for about 3-4 seconds right after a run... My Flashpoint said it was about 150-155 degrees. :eek: A cursin' sailor ain't got nothin' on me!:D;)

[viperx07]

Yeah... I was stupid enough to hold my finger on my 5700 for about 3-4 seconds right after a run... My Flashpoint said it was about 150-155 degrees. :eek: A cursin' sailor ain't got nothin' on me!:D;)


Lol thats funny... So I gues it wasnt getting too hot, I just thought it was hot

[ElectricThunder]

Lol thats funny... So I gues it wasnt getting too hot, I just thought it was hot
The motors aren't supposed to exceed 200 as per castle's reccomendation. So yeah, they're "within spec". I personally don't like having my motor that hot, but oh well, I can deal with it (at least until I eventually pony up for a more efficient motor..:D)