Electronic Speed Controllers (ESC's)
Table of Contents
Table of Contents
Introduction
ESC Ratings and Features
Input voltage range
Input AMP range
Low-Voltage-Cutoff (LVC)
Other Features
Introduction
An ESC is the component that controls the power to your motor.
It is the equivalent to the throttle servo on a Glow or Gas plane - so to speak.
There are a number of brands that offer excellent quality,
but always make sure that whatever ESC you chose, it is appropriate for your application.
The three major factors are Brushless vs. Brushed, Input Voltage range and Current
(Amp) range.
Remember to match your ESC to your motor. Use a brushed ESC if
you have a brushed motor and a brushless ESC if you have a brushless motor.
ESC Ratings and Features
Input voltage range:
This represents the voltage range that the
ESC can operate in. It dictates the size of the batteries that can be used with
the ESC. For example, if an ESC has a rated input voltage range for 7V to 12V, you
will be able to use LiPo batteries ranging from 2s (7.4V) to 3s (11.1V). Sometimes,
the manufacturer will specify a cell range instead of the voltage range. In this
case, you can calculate the voltage range from the cell range by multiplying the
cell count by 3.7V per cell. For example, if the range is specified as 2s-3s, the
voltage range will be 7.4V (2sx3.7V) to 11.1V (3sx3.7V) -- assuming LiPo batteries.
On good quality ESC’s, these numbers are conservative and you can sometimes
exceed the recommended maximum voltage or Amps. You must be very careful when exceeding
any recommended limit as you may cause damage to the ESC and possibly cause an in-flight
failure.
Input AMP range:
This represents the AMP range that the ESC
can operate in. If you have batteries that can output 100A, you should make sure
that your ESC can handle that kind of current - assuming your motor can handle it
as well. A properly configured power setup will have a well matched ESC, motor,
battery(ies) and propeller. More on this in the section on selecting your power
configuration.
It is important to pay close attention to AMP draw and to test your setup before
the maiden flight or any time you change a component (ESC, motor, batteries, prop)
in your plane.
Here is an example why this is important. This is something that
happened to me and the resulting crash could have been easily avoided. I was playing
around with the power setup in one of my 26% planes at the field one day.
I was running it with a Castle Creations Phoenix 85A ESC, 6s 5000mAh battery, a
Turnigy 50-65 270Kv motor, and an APC 20x10 electric propeller. At full throttle,
this setup was drawing about 75-80A. Perfect! However, I wanted to see what would
happen if I put an 8s 4000mAh battery (actual 2 x 4s 4000mAh in series). So on
my next flight, I pop in the 8s battery and off I go... without testing the Amp
draw. Well, I’m taking off at a pretty steep angle and then I go full throttle
to test the power and go vertical.... and then the motor completely cuts out... I still
had control of the control surfaces and I managed to point the plane down, gain
a bit of speed but not enough to flare... Pancake!. Landing gear broken, wheel pants
broken, the left wing had a puncture and some wood damage from the wheel pant when
the landing gear bent back, the fuselage had some wood damage as well. Not good!
The good thing was that the damage was repairable and all the electrics and electronics
were fine. Anyway, I got the plane behind the flight line and did a bit of investigating.
When I turned the plane back on, I had throttle control again... hmmm... well lets
try some full throttle again. Full throttle for about 15 seconds and then it cuts off
again... It turns out that the motor was drawing over 100A - I can’t remember
exactly and the ESC was over-heating and cutting off. What did I do wrong... I didn’t
change the prop. That was it. The big 20x10 prop was over-Amping the ESC - and probably
the motor too. Since then, I’ve fixed the plane and set it up for 8s with
an 18x8 prop and all is well. Works perfectly. I want to try it with an 18x10 prop
next.... but this time, I will throw my Amp meter on it and do a test on the ground
before the first take off. Lesson learned :o)
Low-Voltage-Cutoff (LVC)
When a LiPo battery is at rest (actually this applies to pretty much all battery
types), its
voltage is higher then when it is under load. The FULLY CHARGED cells in a LiPo
have a voltage of 4.2V at rest and 3.7V when under load. Of course, the 3.7V under-load
voltage drops as the battery is depleted. To be safe, you never want to drain a
battery less than 3.0V per cell while under load. Most ESC’s have a low-voltage-cutoff
(LVC) setting which will cut power to the motor if it detects a low voltage situation.
Typically, you can set the LVC setting and the type of cutoff (soft or hard). So
if you want to give yourself a bit of safety margin, you could set the cutoff
voltage to 3.2V per cell (so 9.6V for a 3s battery for example) and set it to a
soft cutoff. This is an example and not a recommendation. The soft cutoff will reduce
the power to the motor when the ESC detects that your battery is near or at the
low voltage setting. You will notice that all of a sudden, you just don’t
have full power anymore. The soft cutoff should allow you enough time to make an
“emergency” landing under power. Don’t try to do any 3D maneuvers!
Just land as soon as possible. This is not the best way to end your flight. You
should always use a timer and get to know how much time you can fly your plane
without hitting a LVC situation.
A hard cut-off will cut all power to the motor instantly. Can you say dead stick!
One thing that happens if you pull the throttle back and effectively lower the draw
on the battery is that the battery voltage will go up a little. If you are in a
cut-off situation, the battery voltage could possibly go back up above the cut-off
voltage setting. You will then get power back if you push the throttle up again,
but not for long (if at all).
Avoid LVC situations all together! Use a timer to let you know when your flight
is over. Start with a short flight timer and see how many mAh you put back in the
battery after a flight. If you are using 50% of the battery add a minute or two
to your next flight. Keep adding time to your timer with each subsequent flight
until you get to 75% or so. Keep a 5% margin (see the 80% rule) in case you have
a windy day or need to abort a couple landings. As a side note, aborting failed, or failing
landings was one the best things I’ve learned. I don’t damage my plane
on landings nearly as much any more. Remember, when it’s windy, you will use
more power within the same amount of time so be mindful of your flying conditions.
Other Features
There are other features of ESC’s that are useful but the
above describes the most important ones. Almost every ESC will work out-of-the-box
with the factory settings. However, depending on your application (and your preferences),
you may want to change some of them. Depending on the ESC, there are multiple ways
this can be done. Some ESC’s can be programmed easily by using the sticks
on your transmitter and listening for beep sequences - well not so easily some times
- it can be confusing. Some can be programmed using a programming card or via PC
software and USB cable. Make sure to do your research when selecting an ESC to make
sure you are aware of the programming capabilities of the ESC and which features
can be programmed - not all ESC’s are equal.