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by: morrison
#2449
Brushless Speed Ratings

Unlike brushed motors, springs and brushes will not be a consideration with a brushless motor. However, like brushed motors with many turns and winds, you’ll find a wide variety of brushless motors in various turns or KV ratings. Let’s look at these briefly.

No one standard exists for measuring the speed of the brushless motor. Some manufacturers measure the speed by turns. Other manufacturers use a KV rating. These terms are important to you because they will help you choose your motor’s speed. A sensored motor is marked by the amount of turns it has: 21.5,10.5, 9.5, 8.5 -- the lower the turn count the faster the rotor spins. But a sensorless motor is referenced by KV. With KV, the higher the number the faster the rotor spins. As a comparison, a 10.5 sensored motor is similar to a 4300kv sensorless motor. When you look at specifications supplied by the manufacturers, you will see that they are very close in performance. A 10.5 brushless motor is roughly the same as a 3800-4300 KV motor, depending on the manufacturer.

In summary, the fewer the turns on a brushless motor, the faster will be the acceleration (or spin of the armature). The higher the KV number, the faster it will accelerate.

If you are just going to play on your own and not for racing, then the “need for speed” may hit. If you want the fastest motor, you’ll want to get the motor with the fewest turns or the highest KV rating. Some beginning owners have regretted such a choice for their first motor because it makes driving more difficult. If you are fairly new to RC, you may want to get a motor lower in rating so it’ll be more fun and easy to drive. Get a faster motor when your skills are up to it.

If you are going to race, the decision of which motor to get will probably already be made for you. You’ll need to look at the racing classes offered and decide which class you want to run in. The class will specify the motor used. For instance, if you are going off road racing and you want to run stock, then you will use a 17.5 motor. If you choose to run Pro-stock then you will use a 13.5 motor. For modified you will use motors from 10.5 and lower.

It’s not enough to just get a motor, however. You also need to make sure the speed control will handle the motor. That’s our next subject.



Brushless speed controls

Brushless motors must be run from a speed control designed for brushless motors. They will not run from a brushed speed control. As with brushed motors, different speed controls will only handle those motors which fall into its range. For example, Team Associated's XP SC200 will handle motors from 17 turns and up. Obviously, the speed controls that handle a wider range of motors will be higher in price, so satisfying your “need for speed” will impact your wallet. Running a motor out of range of the speed control can cause damage to both. Be sure to review the manual that came with your speed control to find specifications.

Speed controls determine whether your vehicle can go in reverse. If you are not racing on a track, you’ll probably want to get a reverse speed control. In sanctioned racing, reverse is not allowed, so consider carefully whether you will be racing in the near future.



Sensored or Sensorless

In the sensored system, the motor includes sensors to transfer exact information to the speed control, making the sensor speed control more precise. Sensored systems give the feeling of the vehicle responding accurately to even the smallest changes of speed. These motors are highly prized by experienced racers who are always looking for an edge in the competition.

The sensorless speed controls and motors can only estimate the position of the rotor. Think of the rotor having marks on it like the face of a clock: at one position there is a 12, and 180 degrees from there is a 6 o’clock position. The sensorless speed control doesn’t know how to tell whether it’s at the 12 or 6 o’clock position, so the speed control has to make its best guess as to what is the correct pulse to send to make the motor go forward or reverse when the transmitter trigger is pulled or pushed. Sometimes the incorrect pulse is sent and when you pull the trigger to go forward you actually go in reverse. However, by coming to a complete stop, letting off the trigger, and then applying forward throttle again you will generally then go forward.



Brushless Advantages

• Higher efficiency

• Longer runtime

• More power

• Maximum RPM

• Better acceleration and performance



Brushless Motor Maintenance

Because brushless motors require little to no maintenance, you can simply blow them clean by using canned or compressed air and then use a lightweight oil to lube the bearings and you’re good as new. Brushed motors require complete servicing every seven to ten runs or more frequently when racing to maintain the performance they had when new! Complete brushed motor service means disassembling the motor, cleaning the can and armature, lubing both bearings in the can and hood, re-cutting the commutator, deburring it, reassembling the motor, installing new brushes and springs, and breaking in the brushes. to test different brush and spring combinations for the best performance for the type of racing that you are doing.

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