RCU - Power System Setup

Power System Setup/Gearing


Perhaps one of the most critical, and unfortunately overlooked aspects of brushless power systems is taking the time to ensure that your setup is geared properly in order to operate without the motor or ESC overheating. A common misconception is that because a certain motor, ESC or combo is rated for a certain voltage battery that it can be run with that voltage regardless of the vehicle or gearing.  Taking the time to monitor temps and adjust gearing when your setup is new will ensure a long life for your electronics.  Skipping out on this important piece of the puzzle can lead to burnt up electronics in short order.


There are many factors that go into the overall gear ratio of your vehicle; pinions/spur ratio, internal transmission ratio (if equipped), differential ratios and tire size.  The easiest of these to change is the pinion or spur gear, so that is where changes are made to your gear ratio.


The reason a motor and ESC can overheat so quickly with improper gearing is because of the amount of load being put on the system.  When faced with increased load, the motor will draw large amounts of electricity to provide the power needed and all that current builds up heat in a hurry.  Just as accelerating a 1:1 car quickly consumes a lot of fuel and raises engine temperature, the same is true in al electric setup.  Imagine trying to take off from a stop in 3rd or 4th gear in your car, the motor is going to struggle quite a bit to get the car going.


Fortunately setting up your gearing is fairly straightforward and does not take a lot of time.  With any new setup, you should start out by driving your vehicle for a less than a minute at moderate throttle.  Stop, check the temperature of your motor and ESC and if it is not overheating you can drive it a little harder for a little longer.  You want to do this several times, driving it a little harder and for longer during each session.  If at any time your motor or ESC are too hot, STOP, let the electronics cool down, adjust your gearing and start testing again.  Once you are confident that your setup is not going to overheat then you can drive your car normally for a full battery pack.  It is still a good idea to periodically monitor temps as varying driving conditions and speeds can increase temperatures, and they should also be checked any time changes are made to gearing.


As a general rule, motor temperatures should be 170F or under, and ESC temperatures should be under 150F.  Motors normally run hotter than ESC’s so most drivers monitor motor temps more than ESC temps which checking their setups.  The best way to check temperatures is with an infrared thermometer/temperature gun, they are inexpensive and take the guesswork out of the process.  If you do not have a temperature gun, you can use the “finger method”.  If you cannot leave your finger on your motor comfortably for at least a few seconds it’s a safe bet it is running too hot.  USE EXTREME CAUTION WHEN USING THIS METHOD AS AN OVERHEATED MOTOR CAN QUICKY BURN YOUR HAND.


If temps are too high, then you will need to gear “down”.  Gearing down means going higher in your numerical gear ratio, and is done by DECREASING PINION SIZE or INCREASING SPUR GEAR SIZE.  Gearing down increases acceleration but reduces top speed, and gearing up (larger pinion or smaller spur) does just the opposite; reduces acceleration but increases top speed.  For example, if you have a 20T pinion gear and a 40T spur gear, your drive gear ratio is 2:1 (40/20=2).  If you decrease your pinion gear to a 16T, then your drive gear ratio is 2.5 (40/18=2.5). Gearing down eases the load on your motor because it gets to spin more times to go the same distance than a higher gear ratio.  If it is only turning 5 times to go 1 foot, it has to work harder to move that distance than if it gets to turn 8 times.


In the excitement of driving a new car or power system, it’s easy to “wing it” with the gear ratio but resist the temptation to  skip this important step and you will be rewarded by a cool-running and efficient power system that will have a long life.