School me on brushless

[OldSchoolDude]

I'm building a custom mini monster based on some TLT axles. It'll have a custom chassis, Wild Willy tires/wheels (Lunch Box size), and a wheel base a little over 8 inches. Im using a Stampede transmission and driveshafts. This thing wont be light, but not quite as heavy as a Wheely King. IT IS NOT A CRAWLER. I'm building something more like a scaled down Wheely King or Ground Pounder. I'm tired of trying to cobble together a brushed motor combination, and I like the idea of lower maintenance with the brushless motor, and the combo kits that are available. The problem is there's too many variables. I've searched this forum, and many others, but no one seems to be running anything similar. What I have been able to gleen is I think I need somewhere around a 3000-3300kv motor, and it seems like 13T (which I assume is turns) is a popular rating. The thing I don't get is the amp rating on the ESC.

An electric motor responds to load, and draws the amount of amps it needs to overcome that load. But then I find some forums stating a 35amp ESC is plenty, but the 60amp ESC "will make your car run faster". How does the 60A ESC make the car run faster? Seems to me like the 60A rating would just give the ESC the ability to handle more draw from the motor, based on the what battery pack being used. So if I had a 3000mAh LIPO with a 40C rating, isn't that a 120amp capacity. So how does a 35A ESC or even a 60A ESC handle a battery with a 120amp capacity. What keeps the motor from drawing too many amps for the ESC.

I'm confused! Can somebody put it all together for me?

Thanks,
Mark

 

[joe]

Like with all things electrical, the device will draw what it needs regardless if the unit can handle it!
For smaller cars the 35a is ok, but for bigger or off road stuff I'd recommend at least the 60a.
I'm using a 13t in an m03 mini, but also in a wk.
That motor should be plenty.

 

[william g]

onroad I'd say a 35a would be golden, but offroad or racing offroad the 60a may be a better choice and run cooler. Until you have it cobbled together and know weight and rolling resistance you never know from a brief description.
A 60a won't have a higher top end everything else equal, but would be quicker

 

[OldSchoolDude]

So how does the larger ESC (35A to 60A) make the truck quicker? It seems like the 60A ESC would just be capable of handling a larger battery/motor combination. Is it because the 60A ESC "allows" a quicker harder acceleration from the motor, which calls for more amperage from the battery?

The way I envision it is, there's some max acceleration/load the motor can draw, based on variables like the overall vehicle weight, rotating mass, traction, etc... So does the smaller ESC impose an artificial lower limit to this theoretical max load (when compared to the 60A ESC)? Does it run hotter because it may be constantly having to limit the load it transmits?

I'm also still confused on the motor KV rating. For instance, within the same mfg, I see 3300kv 12T motors costing more than 4300kv 9T motors. Whether it costs more to produce one motor or the other, you would think from a marketing standpoint, the larger kv motor would cost more. I'll also see low turn motors with a kv rating somewhere around 1200 or 1700, but with a 60A ESC. What's it all mean?

So after I've got the proper motor paired with the proper ESC, how do I finally pick a battery? I'm going to use LIPO, and I know the higher "C" rating gives more punch, or basically enables it to deliver quick or sustained high amp draws. I supposed the mAh rating is sort of like the fuel tank, or a way to relate to how long it can power the truck.

Can somebody clarify all of this and sort of put the pieces of the puzzle together a little better?

 

[HawnMT]

To build on your analogy....

mah-size of the fuel tank

C rating-diameter of the fuel line, the higher the C rating the larger the fuel line, meaning you can move more fuel(electricity)

voltage- pressure in the fuel line

esc-fuel pump, how much fuel(electricity) can actually be pumped through the line

motor- kv-rpm(but this is tied to voltage)
size-how large a motor: 1/8th , 550, 540, 380

The lower the kv the slower but you also have to take into account the size of the motor. Larger 1/8th size motors have low kv ratings but use more power(watts) . They also are capable of much higher voltages so they move and use a lot of power so they need higher power escs and batteries. So while it looks like higher kv motors should be more expensive there's more to it than that.

You also have to take into account sensor vs. sensorless. A sensored motor is generally smoother but, in my experience, slower than an equivalent sensorless variant. So if having a smooth throttle is important and you don't mind the extra cost sensored may be the way to go.

 

[william g]

a higher rated ESC will not faulter if under heavy load, can take and allow a harder acceleration because it won't be maxxed out and running cooler.
Hot electronics don't run as well, and if near maxxed out can stutter or stall for a split second.

motors, and pricing
some motors are built with the windings hanging out, these motors are cheaper and if you mess up one of those wires it's toast. A better motor has the tabs so you can replace the wires. Better motors usually have a higher quality core/rotor. Some rotors are cheaply glued too, heat can kill them.
380 core and a finned case make some motors look like a 540. They are not 540's and tend to have less torque due to it's 380 core.

That is not to say those 380 based 540's are lame, just they may not be what a racer wants or a hardcore basher. These are great for a fun bash runner or light weight (wheely king type) vehicle. Clods can use these and be a fun runner, though a true racer I'd be leary of a failure after a while.

 

[OldSchoolDude]

Thanks for the info guys. It's starting to come together better now.