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Electric Motors-Controllers-ESC
Other › ESC for dummies
09-10-2007 03:09 PM  10 years agoPost 1
RunNoob

rrNovice

Canada

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Can someone tell me what are the differences between a ESC for brush and brushless motors?

Are all ESC with the same specs equal? (probably no!) What differentiates them then? Things like the ability to stay cooler or something?

What does a 20 ESC mean? 20 amps is it?

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09-10-2007 03:10 PM  10 years agoPost 2
RunNoob

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Canada

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oh if anyone knows of a good tutorial on the basics of ESC (what they are, what they do, etc) that would be great!

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09-10-2007 05:47 PM  10 years agoPost 3
Rob_T

rrElite Veteran

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A brushed motor ESC is basically the solid state equivalent of a variable resistor. It just takes the battery voltage and provides a controlled voltage to the motor. As you know, a brushed motor will run just fine if you connect it to a battery.

A brushless motor is totally different, they are in fact an AC motor! If you take a brushless motor and try and hook it up to a battery with no ESC, it wont run, in fact it will probably just burn out. (The 3 wires on the brushless motor compared to the 2 wires on the battery should also tell you they're not meant to be connected!)

So what the brushless ESC has to do is 2 things. First it has to take the DC from the battery and generate the AC waveforms that the motor needs (and it even times the AC to the rotation of the motor to get the best efficiency- that's what the term "timing" in some ESC instructions is all about). The other thing the brushless ESC does is to vary the voltage going to the motor to control it's speed- similarly to the way the brushed ESC does.

As well as the basic specs like voltage and current capability, you need to look at the "features" of the ESC too. Helicopter ESCs usually have a governer mode that can help you maintain a constant rotor speed, and they usually dont have low voltage cutouts (although some do) or brakes. An airplane ESC will not usually have a governer, but it will often have a brake (helps to get folding propellers to fold) and usually has a low voltage cutout too.

Castle Creations make some ESC that have a lot of features and can be setup for plane and heli use. Kontronik also makes a good line of ESCs. Both of these brands have a great reputation. There are other good brands too, but sometimes you'll find that some of the cheaper brands also have a reputation for "smoking" without too much reason. Do a search here on RR (use terms like ESC and smoke).

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09-10-2007 06:37 PM  10 years agoPost 4
RunNoob

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Canada

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wow, great explanation!

so a low voltage cutout is what exactly?

Does it mean that below a certain voltage, the ESC won't turn the motor?

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09-10-2007 08:22 PM  10 years agoPost 5
Rob_T

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so a low voltage cutout is what exactly?
A way to make the motor stop suddenly, giving you surprise opportunities to practice auto-rotation landings

Seriously, when ESCs and BECs are used in motor gliders, the low voltage cutout stops the motor from running the battery all the way empty, so you still have some battery power left for the BEC (Battery Eliminator Circuit, that powers the radio gear from the motor battery, without using a separate battery for the radio). So for motor gliders, low voltage cutoffs make perfect sense.

For helis, you will usually be able to tell when the battery is running down, and so you'll land anyway before there is any danger of the battery not having enough power for the radio gear.

There are some people who will tell you that you can use the low voltage cutoff to protect your expensive lipos battery from being over discharged. That's sort of true, but it's much better to get in the habbit of using a timer and land after flying 10 minutes (or whatever the time works out to be for your particular setup). Even the "soft" cutoffs that reduce the motor speed at first (rather than stop it completely) can make the heli hard to control- I find they tend to make the tail lose control.

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09-11-2007 08:39 AM  10 years agoPost 6
ROSSM

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UK

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ESC Explanation

Well done Rob..those were two damn good explanations you gave there.

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09-11-2007 02:54 PM  10 years agoPost 7
RunNoob

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Canada

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Yeah that was excellent.

Ok if you so desire, can you go over how one matches a motor and battery pack with a given ESC (thinks to look for, what has to go with what etc).

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09-11-2007 07:12 PM  10 years agoPost 8
Rob_T

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Picking a motor and gearing it correctly can either be done scientifically with a lot of motor performance calculations, for example see KC's spreadsheet, or it can be done by reading the forums and seeing what works for other people.

Once you have picked the motor, you can make some guesses about current draw (again read the forums to see what other people get) or you can take a guess based on the weight of the model. As a rule of thumb, a well setup 3D heli will draw about 250 watts of power per pound of weight. So for a model like a TRex 450 which weighs about 1 1/2 pounds, a good guess would be 1.5 X 250 = 375 watts. Most people use a 3S lipo for the TRex, so the current draw is going to peak at about 375 / 11 or just under 35 amps. So I'd say a 35A ESC would work great!

The things to watch when selecting an ESC are the maximum current the ESC can handle- this needs to be the same or greater than the maximum current the motor will draw. Also make sure the ESSC is rated for the voltage of the battery when it's fully charged. Most ESC manufacturers make this easy by telling you a maximum number of cells the ESC can handle.

Match the battery to the peak current drawn by the motor. Sticking with the 35A TRex example, most people fly with a battery of about 2000 mah (which is the same as 2AH, just using different units). So you can estimate the 'C' rating needed as 35A / 2A = 17.5. (that calculation is motor current divided by battery capcity). So I'd look for a battery that can handle a peak discharge of 20C. This confirms what most people who fly TRexes have found!

Finally, one important point to watch when selecting the ESC is to make sure that the BEC (if the ESC has one), is rated for how you'll use it. Most BECs on ESCs work by turning the extra volatge of the battery into heat to drop the battery voltage down to the 5V needed by the radio. The more battery voltage you have or the more current the radio gear needs, the more heat gets created. Many ESCs will give you some limits based on the number of servos and the battery voltage. Usually, once you get to 4S or more for the battery (about 16V when fully charged) the on-ESC BECs cant provide enough current for the servos. So this can force you to use an extra radio battery, or use a high efficiency (switching) BEC instead of the one built into the ESC. Note that some Kontronik ESCs come equipped with a high efficiency BEC which can make installation easier. For high voltage setups, a simple BEC just isn;t going to work. If you look at the high voltage ESCs from Castle (eg Phoenix 45HV) you'll see they don't even have a BEC because of this problem!

Other things to look for in an ESC are governer mode (not essential, but it can make setup easier), fixed throttle end points, no (or programmable) brake, no (or programmable) low volatge cut off. Ease of setup is also important. Castle ESCs that can be setup with a laptop computer, or ESCs that come with a programming card can be much easier to set to the right mode than ones that program using the radio (is the brake the 5th or the 6th setting??, oops I made a mistake, got to start all over again...)

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01-16-2008 12:12 AM  9 years agoPost 9
knockers

rrNovice

Orangefield, TX

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Just a little more info on ESC's

Here's a little more info on brushless motors and esc's. A brushless motor though not exactly like a 3 phase industrial motor it works essentially the same. The ESC is a Variable Frequency Drive (VFD). The DC power is converted using SCR's Silicon Controlled Rectifiers into a stepped AC waveform. It also creates 3 wave forms that are 120 degrees out of phase from each other. This give you a very efficient and high starting torque motor. The VFD takes the stepped wave forms and VARIES both the frequency (how fast it switches directions) and the voltage (how high the wave is) if both are not varied the motor will sustain damage after a short time. The whinning sound you hear from the ESC are the SCR's switching. The faster they switch the higher pitched the whine is and the faster the motor runs. Maybe this adds confusion or maybe it makes sense, but there it is.

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01-17-2008 01:00 AM  9 years agoPost 10
kenneysme

rrApprentice

blgs. mt.

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Great info.

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01-17-2008 02:19 PM  9 years agoPost 11
MikeC

rrKey Veteran

Mosinee, WI

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The DC power is converted using SCR's Silicon Controlled Rectifiers into a stepped AC waveform.
Very good explanations except for the part about the SCR's. ESC's and VFD's don't use SCR's. Rather they use some form of transistor.

Industrial VFD's (also called Inverters) use IGBT's (Insulated Gate Bipolar Transistors) and ESC's use MOSFETs (Metal Oxide Semiconductor Field Effect Transistors)

Old generation VFD's did use SCR's, both on the Converter side (changing AC to DC) and on the in Inverter side (changing DC back to AC). Industrial DC drives still use SCR's except for DC Servo Drives which use transitors. Industrial AC Servo Drives work very much like our ESC's except they obviously need diodes on the front end to change AC to DC.

But otherwise very good explanations of ESC's.

Mike

Century Swift, TREX 450, Blade MCX, Spektrum DX7

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03-18-2008 11:28 PM  9 years agoPost 12
mikeflyz

rrApprentice

Westlake Village, CA

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I sure like reading Rob's posts over the years! Thanks!

Found these nice animations of brushless motors in action. These look like "sensored" motors with Hall Effect Devices (unlike sensorless used today in models) to determine the rotor's position for commutation purposes.

http://users.tinyworld.co.uk/flecc/brushless_motor.html

http://www.townbiz.com/wd/clients/e...bldc_motor.html

Mike
MA Fury Extreme, JetCopter SX

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