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How To: Keep Your Brushless Motor Cool

How To: Keep Your Brushless Motor Cool

Heat is the enemy

Here’s a fact: a cool motor is a happy motor (unless it isn’t being run). With the efficiency of brushless motors and higher LiPo battery capacities, run times in the 20-minute range aren’t uncommon. But during extended runs, heat build-up can affect your motor’s performance, or at worst, cause total system failure. And even in short five-minute runs, things can get plenty hot under the stress of race speeds. Here are some ways to keep heat away from your motor and let your electronics run their best.


Take a look at a pro’s car or truck and you’ll likely see the wires from the speedo to the motor just long enough to reach. Excess wire puts more resistance in the system, which turns into heat, especially in high-current applications like with brushless motors. Leave an extra centimeter or two of slack on each wire for gearing changes or chassis flex.


Passive solutions, like a heat sink, can be really effective in drawing heat out of the motor can. Clip-on heat sinks work great and usually don’t take up much room; remove motor labels or stickers to increase the contact area to wick heat away.


The “cheapest” way to cool your motor is to give it some airflow. Even if there are no cooling cutouts in the body, air does still move around under that shell. If at all possible, position the other electronics so they don’t block the motor from getting air. You can also use a low-profile speedo or receiver. You can also cut out holes in the front of the body to increase air flow.


If you can’t get airflow naturally to the motor and you have the space, use a fan such as the Castle Creations CC blower to do it. Most plug right into an empty channel port on your receiver (if they are all full, use a Y-cable to split the power with another component). The little current they draw is easily offset by the benefits of a cooler motor.


Every car and motor has a gearing sweet spot-the gear ratio where the motor works most efficiently. Gear it too tall, and the motor will struggle to pull the load. Gear it too short, and the motor will be revving at max rpm for most of the track. Either case will generate more heat than you want, so start off with the car manufacturer’s recommendation for the right gearing range. Better yet, log the temp of your motor at the end of each run to find the sweet spot of 150 degrees.


Charlie Suangka from Team Novak clued us in on what some creative spec class racers are doing; because of the milder winds used in spec classes, some racers use the optional speed control fans to blow air on their motors instead of on their speedos. This lets them gear slightly taller so they can pull away from competitors on the straights.


Keeping your brushless motor cool should always be a priority; that is, if you want your car to run its best and want your gear to last. Plus, you really don’t want to know first-hand what a burnt-out motor smells like.

Updated: July 22, 2015 — 5:23 PM
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  1. I have a question is a 4800kv on 3s faster than a 7200kv on 2s ?

    1. Jean, all else being equal, no. Kv is a measure of RPMs per volt. A 2S LiPo produces 7.4v while a 3S LiPo produces 11.1, or 3.7v per cell. Both of your mentioned setups will theoretically spin the motor at 53,280 RPMs (4800 x 11.1; 7200 x 7.4).

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