bauerbach

ok, so first number the big one amps, what is this related to? what does it mean what does it do? I know what amps are, but is this a number that should be matched to the battery or the motor, or both? does it need to match exactly or is more ok?

IE if you take a 20amp motor and attach a 30amp ESC, what happens? does the ESC just work with a lighter load then it could handle, or will it burn out the motor?

As I understand it, all the ESC does is switch the phasing on the 3 wires to turn the motor, current draw is a factor of resistance from the load, so with that said, is the AMP rating just a factor of how much load the motor puts on it? How would one know what the load on the motor will be to adequetly know what ampage is going to be needed? isnt this all a factor of not just the motor, but the prop?

how does the ESC know how fast to switch the phasing? do all brushless motors(and thus ESCs) turn the same RPM? or will some turn faster, how does the ESC know? is this a factor of programming your ESC depending on your motor? what if you dont know the maximum RPMs of your motor?

how do batteries factor into this? does the voltage of the batteries your running affect the RPM of the motor and factor into the amps drawn since it would be part of that calculation?

answers are fantastic, but a good link would also be much appreciated, Ive tried searching for a good ESC explanation page, but have come up short so far.

bauerbach

1 more question, BEC, I know what it is, I saw a thread on it, read all that. so it seems most all ESCs are 5v as thats what servos/rec need, some cases that need more would require a standalone BEC. but there is also an ampage to this, is this the number that relates to just how many servos it can power? most seem to be 2-3amps? that seems like an aweful lot for a few micro servos, does this really even matter 2 vs 3? is both overkill for most applications?

mjsas

The amp rating can be simple or complex. In your case it would be like the current rating of wire, 14 gauge is good for 15 amps and 12 gauge is good for 20 amps. Usually the current between the ESC and battery is measured and the ESC rating should be twice that reading.
The complex answer is the ESC's ability to carry current, dissipate heat and handle the flywheel current or whatever the manufacture thinks it should be.

Switching the phases is a complex subject. The result is that the motor responds the same way an internal combustion motor would, more throttle = more power. More power = more RPM.

The BEC rating is how much current can be drawn. This is the peak current so 2 amps is not much. Most if not all BEC's have a built in current limiter, even with a short current load the current will not be much more then the rated current. Overloading the BEC, even for an instant, can cause many strange and wonderful things to happen.

bauerbach

hmmm so 2 and 3 amp are not interchangable... the one Im trying to replace is 3AMP and Im having a tough time finding one that is both 20Amp and 3amp bec, most seem to be 2amp.

what do they do for these things that are talking about 100-120amp? this seems silly high... but youd need like 00gauge wore for that... and it sure doesnt look to be that thick hah.

DaveFlynn

The battery should be the weakest link, for best results don't exceed 80% of the batteries current rating. Build the setup to protect the battery, they're expensive.

Many of the answers you seek depend on the firmware and hardware of the ESC which differs considerably by brand.

I recently put together a small plane, 51"WS, and used what I had on the workbench to get it flying. 11x5.5E prop, 2614-830 Kv 25 amp motor, Thunderbird 18 ESC and 3S1P 2100mAh battery. Works great, nothing gets hot, WOT is 15 amps and flight times are in the 14 min range. However, if you try this with one of the cheap, "20 Amp", ESC's you'll burn it out.

Flypaper 2

The motors are rated by how many amps they can handle safely. So your motor is rated at 20 amps. You use a wattmeter to pick a prop that the motor will handle without going over the 20 amp draw. The ESC needs to be over the rating of the motor by at least 20%, so the 30 amp would work fine. The BEC needs to be rated at over the amp draw of all the servos combined under load. On the smaller planes I like them to be at least 2 and happier with 3. With the batts. you go by the C rating. For instance a 10C rated batt. can handle 10 amps safely. For the motor in question, a 1200ma 2C batt. would work fine as at 2C it can handle 24 amps safely. Mind you, using that motor you would fly mostly at half throttle cruising around so the motor would only average 10 amps being used while loafing around and only use full power in bursts for aerobatics.
Have fun.

el_xero

My Feedback: (2)

Great info guys thanks!

bauerbach

yes excellent info!

ok, so I checked out my battery, it is a 15c 11.1V 1500mAH

so I should not really be drawing over 15amps based on the 15c part? the difference in the cost of speed controls is all but insignificant, so I can easily pick up a 30amp ESC to make sure Im in the clear.

see if I have this clear though, the battery and ESC need to exceed the pull of the motor, which cannot really be calculated without testing the motor with a given prop?

motor says 1200KV, but I have no clue what the draw of that is with the given the prop to be used, any rule of thumb? hows it work for double motors ? does that not add together being in parallel? each ESC is 20amps or so, presuming thats pushing each motor that hard, isnt that potentially 40 amp draw? I know I dont know the draw on the motor, so all of this is guessing. but any thoughts anyway?

Flypaper 2

If it were a 15C 1000 batt., then it would be 15 amp, so being 1500 it would be 22 amp draw. Only difference in using the bigger ESCs is the weight goes up as they get to higher amp rating. The motor we were refering to above was a 20 amp motor. The KV rating is the RPMs per volt, so a 1200kv motor would be drawing a certain amps on a certain prop. If you were to go to a 2400 kv of the same motor it would draw double the amps, so you would have to put a much smaller prop on it to get it down to the required 20 amps. Does that make sense??

bauerbach

how do you know what a motor is going to draw? only way to test it or find someont thats run it with a given prop and see what they drew from it in use?

and still curious what dual motors result in, do they add together?

Flypaper 2

What is needed is a wattmeter. Goes between the batt. and ESC and tells the batt. voltage, amps and watts while the motor is running. One of those tools you can't do without. You try a prop. If it goes over the amps of the motor specs, try a smaller prop. Most of the motors on HK give a recomended prop to start. Go to the search in Hobby King website for Turnigy Wattmeter.
http://www.hobbycity.com/hobbycity/s...dProduct=10080
Here you go.

jdetray

bauerbach -

Most of your questions would be answered if you read the sticky at the top of this forum:

[link=http://www.rcuniverse.com/forum/m_7100376/tm.htm]EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT[/link]

It covers all the basics, as well as more advanced topics.

- Jeff

bauerbach

I am embarressed that I have somehow overlooked that thread, thank you for pointing it out, I have much reading to do. and Ill pick up that wattameter too.

Flypaper 2

As far as dual motors goes, each with its own ESC, only the batt capacity would need to be doubled as the amp draw would be doubled to 40 amps.

bauerbach

kinda makes you wonder how this is working then... 22.5amps on the battery, each motor would have to stay under 10amps or so. though I dont know what the amp draw on the motors are.

Im a bit worried that the motor might be fried, when I got it off the lake, it was kind of sizzling, probably just water making a short that probably didnt affect anything... or maybe it did, so I might just rework the think with a new motor, new battery, new ESC to be 100% sure everything is paired correctly, if shipping takes a while, Id hate to get ESCs only to burn out my battery on the next flight or find out one of the motors was also damaged.

Flypaper 2

The motor should never get hot enough to sizzle. Shouldn't get hot enough that you can't hold it in your fingers. Very warm is fine. Go to a smaller prop to cool it down. What plane, motor, ESC and batt are you using.? For the twin, you need to go to a bigger batt. About 3000ma 20c would be capable of 60 amps. Dropping the motor amps down because of the batt. means that the motors aren't able to put out what they're capable of or may not have enough power to fly the plane.

bauerbach

oh no, it wasnt heat that was the issue, it was a short. there must have been water crossing wires in the motor and whenever current was applies (which I stupidly did thinking the crash was nothing serious, as there was no physical damage, only wet electronics that I couldnt see from a distance), it sizzled. the motor was not hot at all, hardly had the opportunity to be hot as the crash was after maybe 3 or 4 minutes of use and took me another 5-10minutes to retrieve. I have not had much flight time being winter and all, so I dont know how the battery would have held up to prolonged use. this was only the 2nd flight, the first just being to trim the plane and didnt last long or fly hard.

everything Im using, or was using, was part of the kit. presumably matched, as I have not read any reviews indicating component failure. I have to presume the motors are drawing 10amps given the battery rating. I have not noticed any issues, acrobatic flyer it is not, but it takes off from water with half throttle and flew well before I stalled it out.

I did find another post on here from someone else that has swapped the motor and battery, given his positive review, I will follow his lead.

jdetray

Getting a wattmeter is a smart plan. Without one, you must depend on others who are running exactly the same package, or worse, you are merely guessing!

And by the way, it is certainly possible for a motor to become overheated after 3 or 4 minutes of use. Never assume that because you flew "only a few minutes" that the motor can't overheat! In fact, a motor can overheat to the point of destruction in a few seconds if drawing excessive current.

- Jeff

bauerbach

fair enough, I dont think I was anywhere near that situation, the motor was only warm to the touch, and I did play with it in my house earlier and didnt have any heat concerns that I noticed

all the same, no more guessing for me. I am having a heck of a time finding a ESC that does 3amps... I found 1 that says 2A/3A peak... thats the best Im finding at hobbyking though. the plane has a total of 4 microservos, cant imagine they are pulling too much, I didnt look though, will the servos have a rated draw on them? is that something typically on the label?

Flypaper 2

2 amps will be fine. Seldom do they show the amp rating on the servos.

jdetray

The BEC in most ESCs will handle 4 micro servos. Digital servos draw more current than analog servos, so if you're using digital servos, it's more of a concern.

If you absolutely must have 3A, one line of ESCs whose BECs are rated at 3A are the 18A, 36A, and 54A Castle Creations Thunderbird series. As you have probably learned by now, there is no harm in using an ESC with a higher current rating than you need. The only downside, and it's a small one, is that the larger ESC will weigh a bit more.

Most servos do not specify their current consumption. However, nearly all servos specify an operating voltage of between 4.8 and 6.0 volts. In case it has not been obvious so far, the BEC (whether built into the ESC or a standalone external BEC) is nothing more or less than a voltage regulator. It regulates the battery voltage down to a voltage that is safe for the receiver and servos, somewhere between 4.8V and 6V.

Some other, random comments.

If something was "sizzling" after getting water in it, that means it may have been hot enough to turn water into steam. If so, that's 212 degrees F, which is hot enough to permanently damage a motor. There are two parts of a motor that are most often damaged by excessive heat. One is the insulation on the windings. Too much heat can melt the insulation, causing a short. The other heat-sensitive components are the magnets. When overheated, magnets can permanently lose a portion of their strength, and the motor will never again perform properly. I don't know if your motor overheated, but it takes a lot of heat to make something (even water) "sizzle."

The "C" rating of a battery lets you determine how much current you can safely draw from the battery. Multiply the battery capacity (in Ah) times the "C" rating.

Example: 1500mAh battery rated at 15C

Step 1. Convert mAh to Ah by dividing by 1000. So 1500 mAh = 1.5 Ah
Step 2. Multiply by "C" rating. 1.5 x 15 = 22.5A

So 22.5A is the maximum current this battery can safely provide. HOWEVER, many battery makers overstate the "C" ratings of their batteries. Or perhaps it is more correct to say they measure the "C" rating under ideal conditions that do not necessarily bear much resemblance to the way we use their batteries! This is why Dave in post #5 suggested never operating a battery at more than 80% of it's calculated current rating. Using this 80% rule, you would not want to draw more than 22.5A x 0.80 = 18A from your battery.

The ESCs used in electric flight are a "sensorless" design. At any given moment in time, two of the three phases are energized, and the ESC uses the third phase to sense the position of the rotor. This keeps the design of the motor very simple and requires more intelligence in the ESC.

Brushless motors with sensors also exist. You have such motors in the CD-ROM/DVD drive in your computer. Here, tiny sensors in the motor send positional information to the controller.

The sounds (beeps) from your ESC are actually produced in the motor, which the ESC uses as a crude speaker. Disconnect the motor, and an ESC will no longer be able to beep.

- Jeff

bauerbach

the sizzle was a short through water, it sizzled when I applied throttle(though the prop didnt turn, just stuttered) and stopped immedietly upon cutting power. in any event, this wasnt something I built up, this is the kit equipment, and from what I can see, it seems that the battery would have been bottlenecked long before the motor.

bauerbach

quick question...

whats the difference between these besides 20 bucks?

http://hobbycity.com/hobbyking/store...idProduct=6380

http://hobbycity.com/hobbyking/store...dProduct=10080

but say watts meter and power analyzer,and 1 says watts up? whats that part?

edit: nm just realized they are different brands... duh

jdetray

They do pretty much the same thing, but I think the Watt's Up is the better of the two.

"Watt's Up" is the manufacturer's brand name for its meter. Here is the [link=http://www.powerwerx.com/tools-meters/watts-up-meter-dc-inline.html]web page for the Watt's Up wattmeter[/link]. I think you get much better service and support by getting the Watt's Up. I believe the Watt's Up remembers its measurements so you can refer to them at your leisure. I don't know about the Turnigy.

Even if you purchase the Turnigy meter, you can learn a lot by reading the [link=http://www.powerwerx.com/techdata/Watts-UP-V2.pdf]Watt's Up User Manual[/link]. It's very helpful.

- Jeff