A BEC is short for Battery Eliminator Circuit. The BEC takes the supplied voltage from your battery packs and decreases it to 5 or 6 volts (depending on the ESC) for your receiver to use. If you run a higher cell count than what is rated for the ESCs BEC, then you'll need to disable the BEC(by cutting the center RX wire)and run a separate BEC that can handle the higher voltage. Kool Flight is one company that makes BECs for many different applications. Here is one that is commonly used with our E-conversions that run high cell counts.
http://www.rc-monster.com/proddetail.php?prod=6vubec&cat=21
The Plettenburg Big Maxximum is a good motor but is known to run hot and is less efficient than comparable motors from Neu and Lehner.
Some things to consider when selecting a brushless system is how many rpms are you trying to achieve with your system? Most brushless motors like to be run in the 35-40K rpm range. Any more than that and the motors tend to overheat, mainly because the bearings in the motors are limited to that speed. Neu and Lehner motors are rated for 60K and 65K (respectively) max rpm out of the box. They are also in the $300 range so quality does come at a price. To calculate max motor rpm, take the Kv rating of the motor and multiply it times the pack voltage. This will give you the max rpm that your motor will run. Keep in mind that all batteries experience a voltage drop when under load. High quality packs will drop their voltage less than low quality batteries. The voltage drop varies but expect between 1 to 2 volts drop with high quality batteries.
Once you figure out how many rpm you want to run, then you figure out which motor and cell count. Low Kv rated motor systems that use high cell counts are more desirable than high Kv/low cell counts for a few reasons. The higher voltage system will run cooler and more efficiently than a lower Kv system. There is also more starting torque with a low Kv motor. The drawback is that running a higher cell count means more weight from the batteries. It's also more expensive because high cell count batteries cost more money. Trying to find a happy medium between cell count, weight and efficiency is key to a good system.
Once you have chosen your motor and cell counts, then you select an ESC that will work with the cell count and motor. Don't just look at voltage numbers but also look at maximum amp handling and resistance. Less resistance is better, and more amp handling means there is less likelihood of ESC failure. To figure out how many amps you need, take the max watt rating of the motor and divide it by your voltage. Add 10-20% for headroom and that will tell you how many amps your ESC will be required to handle.
It is not unrealistic to see how the dollars add up quickly to over $1K just for your motor, ESC, batteries. (and new charger/balancer if you decide to run lipo cells). If your budget is $300, the Feigao XL and Mamba Max are the cheapest route. (You will be limited to 4S lipo with the Mamba Max running a separate BEC) You'll also need pinions, and the special mod1 pinions run about 15 a piece. You'll want a few of these to experiment with gearing. That leaves no room for batteries/charger. Or was $300 just for the ESC and motor?
http://www.rc-monster.com/proddetail.php?prod=6vubec&cat=21
The Plettenburg Big Maxximum is a good motor but is known to run hot and is less efficient than comparable motors from Neu and Lehner.
Some things to consider when selecting a brushless system is how many rpms are you trying to achieve with your system? Most brushless motors like to be run in the 35-40K rpm range. Any more than that and the motors tend to overheat, mainly because the bearings in the motors are limited to that speed. Neu and Lehner motors are rated for 60K and 65K (respectively) max rpm out of the box. They are also in the $300 range so quality does come at a price. To calculate max motor rpm, take the Kv rating of the motor and multiply it times the pack voltage. This will give you the max rpm that your motor will run. Keep in mind that all batteries experience a voltage drop when under load. High quality packs will drop their voltage less than low quality batteries. The voltage drop varies but expect between 1 to 2 volts drop with high quality batteries.
Once you figure out how many rpm you want to run, then you figure out which motor and cell count. Low Kv rated motor systems that use high cell counts are more desirable than high Kv/low cell counts for a few reasons. The higher voltage system will run cooler and more efficiently than a lower Kv system. There is also more starting torque with a low Kv motor. The drawback is that running a higher cell count means more weight from the batteries. It's also more expensive because high cell count batteries cost more money. Trying to find a happy medium between cell count, weight and efficiency is key to a good system.
Once you have chosen your motor and cell counts, then you select an ESC that will work with the cell count and motor. Don't just look at voltage numbers but also look at maximum amp handling and resistance. Less resistance is better, and more amp handling means there is less likelihood of ESC failure. To figure out how many amps you need, take the max watt rating of the motor and divide it by your voltage. Add 10-20% for headroom and that will tell you how many amps your ESC will be required to handle.
It is not unrealistic to see how the dollars add up quickly to over $1K just for your motor, ESC, batteries. (and new charger/balancer if you decide to run lipo cells). If your budget is $300, the Feigao XL and Mamba Max are the cheapest route. (You will be limited to 4S lipo with the Mamba Max running a separate BEC) You'll also need pinions, and the special mod1 pinions run about 15 a piece. You'll want a few of these to experiment with gearing. That leaves no room for batteries/charger. Or was $300 just for the ESC and motor?
