Brushless Motor Confusion

Question:
Hey, Doc-
I currently own a Traxxas Rustler VXL and I love it (it is my first hobby-grade RC, mostly because I found this hobby at the old age of 26). So now I am looking into buying or building another vehicle but I haven’t decided much other than I want it to be brushless like my Rusty. As I look at all the options for brushless motors out there, I realize that I am not completely informed about all the terminology surrounding them. I would love to see a general run-down on terminology surrounding brushless motors, such as can size, kV, turns, etc. I want to make sure I get the appropriate motor for whatever I buy.

Thanks, and keep up the great work!!
Darren

Answer:
Hey Darren.
I could definitely spend quite a bit of time talking brushless stuff, but since we have limited disc space I’ll cover the basics. The most important things you’ll want to recognize in a brushless motor setup is exactly what you’re asking about; motor size, kV (or turns) and output shaft size.

Motor Size
There are many sizes of brushless motors but the two that are the most common in 1/10th scale is 540 and 550. Between the two, 540 motors are slightly smaller than their 550 cousins and, in comparison, build alot more RPM than the 550’s. Consquently, 550 motors tend to build more torque, lending themselves better to heavier vehicles like 4×4 Short Course trucks. The downside to the larger 550 motors is sometimes speed and the size of the output shaft (see below).

Output Shaft Size
As mentioned above, the side of the motor also dictates the size of the output shaft. 550s usually have a 5mm output shaft will the smaller 540s have a smaller 3.2mm shaft. The smaller shaft is the ‘normal’ size and most people (and hobby stores) will have replacement pinions that will fit this size shaft. The larger shaft requires a larger pinion (with a larger, 5mm through-hole) but since these motors are not as common finding pinions might be a little more difficult. Of course, there’s always the art of purchasing online…

kV, or Turns
The kV of a brushless motor is similar to what the turns were in a brushed motor. While some people will tell you that a xxxxkV brushless motor is equal to a xx turn brushed motor, there is a little more involved in it than that. My suggestion is to stick with brushless motors that ‘are already figured out’, meaning purchase ones that state what turn they are; iec, 10.5t brushless motor. This is much easier to deal with and should really be the norm as far as RC brushless motors go.

I hope this helps with your question. In fact, I think I’ll be working on a more in-depth article in the near future so keep an eye out!

The Doc