Why do Motors Get Hot When Undergeared?
 

Hi,

I've been wanting a definitive answer to this for ages, I gather it's to do with efficiency but I'm finding it hard to proove to someone.

I'm having this argument with some guy on YouTube, yes I know there is no point but it's fun :P

Basically it all started from this video

[YOUTUBE]http://www.youtube.com/watch?v=AkSmbVdyYhM&lc=ObAeBxswFuGpIboWkKDnUjEfRXy Wzt4JUiByIGyyWE4&feature=inbox[/YOUTUBE]

I made a comment saying it was undergeared, and for months now I keep getting people messaging me saying I'm wrong, and undergearing doesn't make it hot etc.

However I've learnt that

Hot motor + cool esc = Undergeared
Cold motor + hot ESC = Overgeared
Hot motor + hot esc = Way overgeared
Warm everything = Just right

Of course it varies a bit with the terrain and your driving style but as a general rule of thumb that's it?
Or am I wrong?

I want to know if and why a motor gets hot when it's undergeared?
I thought it was to do with a motor operates most efficiently when under a certain load, so least energy is lost as heat.
However this guy on YouTube is saying it's most efficient under no load, which I disagree with..

Basically, who's right, and why.

Thanks

You are right. No need to explain why.

On the face of it, that is in obviously untrue statement (which you are right to disagree with) because:

efficiency = power-out / power-in

At no load, the motor produces no power (power = torque * rpm) since it is producing zero torque at the output shaft (if it was still producing torque it would speed up, duh!).

Therefore power-out = 0 [zero] and thus efficiency at no load is zero.

If you extrapolate this down the rpm curve a little bit, you will see that when the motor is operating at very light load, it will have lower effeiciency than the max that it is capable of. And so it end up hotter than you would otherwise expect for the work that it is doing.

[Rant: on]

It is really hard to win an argument with someone that has faith in their position because they don't understand the science behind what they are talking about. It is rarely worth trying to educate such a person because they are usually pretty far down on the learning curve. It could be they are a youngster who hasn't had the opportunity to learn yet, or it could be another failure of our education system.

Arthur C. Clarke said "Any sufficiently advanced technology is indistinguishable from magic."

Unfortunately, for too many people today, current technology is magic.
[Rant: off]

Love the rant. "Technology is Magic"

Just the explanation I was looking for, thank you!
Loved the rant bit lol, and yes it's sad but true.

The guy messaged me saying "I give up with you" :lol:

Another message from him

Oh the irony

All of the above assumes* that the motor has enough power to move the truck at the desired speed and handle the load. For example a vxl motor will not get an emaxx to do 50mph without getting hot. It may produce enough power to do the job, but will be operating past its ability to disapate the heat it it making due to the fact it is ocverlaoded by the weight/gearing. Correctly sizing the motor will allow you to then apply the info listed on cold/hot motors and escs.

Plus battery type and capability are a huge factor in keeping the heat down in a system. If the voltage does not sag the amp draw will be lower for the same output - watts = volts x amps.

So without more knowledge, checking temps does not really give you an insight into why the system is making too much heat.

I will say that I have setup alot of rc cars with brushless, and have never had an issue with heat produced from undergearing... I always geared for 40mph and used what appeared to be a correctly sized motor. I think cheapo 2 pole motors may have more issues than good quality 4 pole motors.



* makes ass of of You

Interesting... I'm in 9th grade now and we are studying about electricity( motors, efficiency...) and I'm realy interested. I think this should be sticky. Very good info here on how to set up your system, but off course some knowledge is still needed.

It's not only electronic principles in play here, there are some basic laws of physics which prove the argument true as well.

Unfortunately many people make assumptions about how things work without actually understanding the science behind them. Whether regarding as "magic" but said individuals I will not speculate.

The thing is that it's really futile and pointless to argue with said individuals over the internet. Believing you are right with no other possibilities is the epitome of ignorance.

Me personally, I don't believe anything anyone posts on youtube and don't bother posting there myself.

It depends on the driving style too, but generally, when a motor is undergeared, the driver is almost all the time at full trottle, making the motor spin at full RPM.
And at high RPM, there is a lot of magnetic losses (directly linked to RPM). The no load power corresponds to the air drag and magnetic losses.

that is a little ignorant as well. not everything on youtube is a lie. there are some very good, professional documentaries on youtube that use factual information and not opinionated and biased garbage.

sorry, i'm not meaning to call you out or start anything, i am just trying to make a point :angel:

I bet if it was written in a 2000yr old book most people would believe it :lol:

I was referring to comments, not videos, which is what this discussion is about. :whistle:

I believe it because i don't want to go to Hell.

oh, in that case, not all comments on youtube are garbage.....just 90% of them are:lol:

Do you think they'd let you in anyway?.. :lol: :rules:


I'm going to hell where all the drug dealers, hookers and free-thinkers are.. :yipi:

I had a little back & forth with one of the guys commenting on that video, think I managed to silence him with just 2 posts. If in doubt, refer him to the Castle & Tekin CEOs on this forum who will say the same thing we have; can hardly tell the people who designed and built the motors that they are wrong or lying can they? :yes: