Electric Conversion  Step 3

Electronic Speed Controls

The third step is to choose an Electronic Speed Control. It is more commonly called an ESC for short. This unit replaces the engine servo in your plane to control the electric motor. It will look something like this.

This unit converts the high current DC battery power into a three phase AC signal that operates the motor. The receiver connection controls the amount of power going to the motor depending on the throttle setting. It plugs into the throttle channel on your receiver.

Don't be surprised if your ESC doesn't come with battery or motor connectors. The matching motor connectors usually come with the motors but you will need to buy matching battery connectors.

The motor connections slip on to the pins of the three motor wires using bullet connectors. The three connections can be swapped at will and won't harm anything. The only thing that happens is the direction of rotation will reverse. If your motor is going the wrong way simply reverse any two of the three connections and the motor will start going in the right direction.

The battery connector can be any high current connector but obviously it must match the battery. Be very careful of the polarity if you need to swap connectors. Reversed polarity usually equals lot's and lot's of smoke and replacing some very expensive parts! Been there, done that!

Also it's a really good idea to put an Arming switch of some type between the battery and ESC to prevent disasters. Remember anytime the battery is plugged in the motor can and eventually will start unexpectedly!

Choosing your ESC

The first step is easy. Since All ESC's are rated in amps you just need a current rating greater than the motors peak current. I usually add 10% for safeties sake. If my motor draws 50 amps peak I would use a 60 or 70 amp ESC. The extra capacity is cheap insurance. If your motor only draws 15 amps use a 20A ESC ETC.

The second step is even easier. The ESC must be rated for the voltage or number of cells you will be using. Up to 3 cells or 12 volts is very common. Above this and you need to be sure your choice can handle the voltage. A lot of the High Voltage ESC's have a HV or OPTO in the part number that makes them easy to spot in a long list.

The third step can be a little harder. Most ESC's have an Battery Eliminator Circuit or BEC built into the ESC. BEC's come in two forms. The analog type is cheaper and therefore popular and then we have the more robust switching type. This was done to eliminate the need for a second battery to run the radio and servo's. It saves weight, especially in small airplanes. Either type BEC regulates the motor battery voltage down to 4.8 to 6 volts for all the onboard radio gear. Of course if you want to you can still run a second battery by disabling the BEC. The switching type is best and you only need to make sure it's current and voltage ratings can handle your servo load. 1.5 amps will run 3 micro servos, but it will take 3 amps to run 4 standard servo's and more for digital or high torque servo's.                                                                                                                                                                                            The problem comes in the current rating of the analog type BEC.  The analog BEC's current rating drops as the battery voltage goes up, so if you upgrade from 3 to 4 cell lipo batteries later you may find the BEC suddenly overheats and fails. It isn't pretty when this happens. If your going to use the built in BEC you need to be absolutely sure it can handle any anticipated load your servo's can dish out.

A lot of the High Voltage ESC's don't have BEC's built in. Also if your ESC can't handle the load there is a solution.  In this case there are lots of stand alone BEC's on the market that can do the same job! I have one switching type rated for 20 amps and it weighs less than an ounce.

The forth and last step is programming. Most ESC's are programmable from your transmitter throttle stick. It is not hard, but it can be confusing. Read the instructions until you understand them. If you can, have an experienced person help you through it the first few times and don't change anything you don't know about. You will normally need to pick the number of battery cells you are using at the very least.. This sets the cutoff voltage so you don't drag the battery so low it fails. When the ESC sees the voltage you set it will kill the motor to save battery power for the radio gear. It's just like running out of gas except most ESC's will reset if you move the throttle to idle and then give it a little gas. Then you will have a little power to limp back to the runway! Try that in your gas plane sometime!