Sep 02, 2011, 11:29 PM
Registered User
Prineville Oregon
Joined Jan 2007
309 Posts
Quote:
 Originally Posted by NoMatta Now that I like. Always wondered about the Fox gassers. Always loved my glow engines. American made??? Don't think I could get in my Camaro, though
Just strap it on the roof after you have the rest of the car filled lol
 Sep 02, 2011, 11:36 PM 3d NOOBular United States, NV, Las Vegas Joined Aug 2010 9,421 Posts wow guys I totally missed your posts about your new planes. Congrats!
Sep 03, 2011, 12:25 AM
A trail of smoke is GOOD!
USA, TX, Springtown
Joined May 2008
7,356 Posts
Quote:
 Originally Posted by NoMatta You do fine, Wayne. I presume you have either self educated yourself on electrics, or have a background in the subject. I'm an electrician of 45+ years as well as an instructor for 18. I know that sometime it seems we deal in witchcraft, but your on-off switch analogy is dead on for BLDC motors. I think some run into a confusion with brushed motors where speed is voltage (and load) determined, since the commutation is by the brushes, where our brushless motors are electrically commutated and the speed is controlled by the speed of the pulses from the ESC. Probably won't have a new prop for the Edge tomorrow, so I'll likely fly the eYak and my T150. Go by the hobby shop on the way and pick up the prop, but won't be able to drill it without coming home to the drill press. Later on
I have an AS in electronics, Extra class Ham ticket, completed an extensive communications electronics program, and have worked in test set design for telephone systems.

The watts is average and simply multiplies Voltage X Current for you.

Yes, the windings are inductive and they do create a counter voltage. In fact, the ESC uses the counter voltage to determine motor position. If you have ever heard of a sensored motor, it uses sensors in the motor to detect the motor position. Most of the ones we use are sensorless and use the counter voltage.

When you apply a voltage to a coil, a magnetic field starts to expand. The coil resists this expansion by creating a counter voltage. The same thing happens when you turn the voltage off. The coil creates a voltage in an effort to keep the field expanded.

Essentially, this means you don't have a neat square wave when you apply a pulse to an inductive (coil) load as you would with a purely resistive load.

I left all that out because is is a bit harder to swallow in one chunk.

Like I said, I will try to set up a demonstration with three traces on an o-scope next week.
 Sep 03, 2011, 12:39 AM 3d NOOBular United States, NV, Las Vegas Joined Aug 2010 9,421 Posts sweet... Now for a little more application... I was just wondering... since the amps/watts are averages... even though you can get a surprisingly high current as it goes along heat is the main concern. So if I'm at 10% throttle and the motor is only firing 1/10 as often as at full throttle wouldn't I also get 1/10 the heat creation as well? My point is... if heat is the main concern I'd think the motor would function heat wise similar to a normal brushed motor. Even though one is drawing constant current and the other is pulsing the average amount of heat created should be similar. In fact the brushless motors, being more efficient should be better at NOT losing a lot of energy through heat. Can I just figure something like limits in calculus and treat the average amps/watts my esc is pulsing to the motor as though it ISN't pulsing since it is happening so fast anyway and revert back to the basic electrical equation? A*V=W?
Sep 03, 2011, 05:50 AM
Registered User
winston mo
Joined Oct 2006
9,050 Posts
Quote:
 Originally Posted by NoMatta Now that I like. Always wondered about the Fox gassers. Always loved my glow engines. American made??? Don't think I could get in my Camaro, though
Your Fox gassers are based off the sachs engine. Knowing Fox they are no doubt a fine engine. You could always do like plowboy and strap it to the top of your camaro LOL
 Sep 03, 2011, 06:11 AM Registered User winston mo Joined Oct 2006 9,050 Posts Well said Wayne, it is a very compilcated subject. AC theory can be quite in depth and the math daunting especially when we start talking about impedance
 Sep 03, 2011, 06:17 AM Registered User winston mo Joined Oct 2006 9,050 Posts Last edited by kerwin50; Sep 03, 2011 at 06:54 AM.
Sep 03, 2011, 07:59 AM
A trail of smoke is GOOD!
USA, TX, Springtown
Joined May 2008
7,356 Posts
Quote:
 Originally Posted by brathanke sweet... Now for a little more application... I was just wondering... since the amps/watts are averages... even though you can get a surprisingly high current as it goes along heat is the main concern. So if I'm at 10% throttle and the motor is only firing 1/10 as often as at full throttle wouldn't I also get 1/10 the heat creation as well? My point is... if heat is the main concern I'd think the motor would function heat wise similar to a normal brushed motor. Even though one is drawing constant current and the other is pulsing the average amount of heat created should be similar. In fact the brushless motors, being more efficient should be better at NOT losing a lot of energy through heat. Can I just figure something like limits in calculus and treat the average amps/watts my esc is pulsing to the motor as though it ISN't pulsing since it is happening so fast anyway and revert back to the basic electrical equation? A*V=W?
First, let me say I am not a motor expert and definitely not well versed in thermal dynamics.

We have been talking about the current and so forth in a single winding in a motor. A brushless has three winding and the voltages are fed to the windings 120 degrees out of phase from each other.

As for heat, heat is generated then it has to have a place to go for it to dissipate. The heat builds up in the motor and needs to be radiated for it to be removed. So even though you may not be continuously heating the motor, the heat builds up to high levels if there is no way to eliminate it.

One comment is that heat is an issue and needs to be removed by adequate motor design and cooling air, I don't know if you would consider it the main concern.

Many electronic components are voltage sensitive. They have barriers that can fail catastrophically if the voltage is exceeded. Electrolytic capacitors have voltage ratings for example. If you exceed the voltage, they can break down and explode when they short internally and massive amounts of current flow. Diodes also have a maximum current rating and a peak inverse voltage limit. if you exceed these, sometimes for short periods of time, they can fail and usually open like a fuse. The FET transistors that are used as switches are the same way. You can exceed their voltage limits and the transistor can fail.

Transistors and diodes work on positive and negative barriers to control current flow. They can fail by running too much current through them or by applying too much voltage which causes the barriers to fail.

I see people that say they are using a 5S pack with an ESC rated for 3S. This is asking for an ESC failure. Parts for higher voltage are usually bigger and more expensive. If my design parameters are for 3S, I may design the circuits with voltage ratings of 15V absolute maximum. A fully charged 4S lipo is typically 16.8V so parts would fail.

Years ago, our design parameters in the US were 2x. So if I needed 12V I would build for 24V. International designs may only allow for 10% or 20%. This made US designed equipment more expensive but it lasted longer and could take more abuse.

I am not sure that is the case today. The push for smaller devices limits how much you can over-build.

Also, the circuit boards have traces on them, almost always in multiple layers, that have voltage and current limits. Exceeding voltage ratings can cause arcing in high density boards. This is not a big deal for logic boards but analog boards are a concern since you can't control what a user is going to do on the input/output.

Also, there are a lot of losses in a motor and ESC that don't do anything to help turn a prop.

By the way, I found this website with a lot of rc model information I found interesting.

Last edited by waynemia; Sep 03, 2011 at 08:09 AM.
 Sep 03, 2011, 07:59 AM Registered User Northwest Indiana Joined Feb 2011 1,461 Posts Well, I maidened the Extreme Flight Edge 540 yesterday and all I can is holy crap that thing is fun!!!! On high rates it does everything you can imagine but it is such a stable plane for it's size. It is rediculous how it just keeps flying no matter how slow you get, lol. Even did a knife edge loop with it, lol The combo from EF seems spot on. Right now, I have the timer set at 6 Minutes and after 6 minutes of aggressive flying, the battery comes out slightly warm, and the motor is not too hot to keep your finger on (although it is warm). Hooking the batteries up to the charger generally shows them at 3.82volts per cell - I don't remember how many milliamps though (I am getting old and senile, lol). I could probably go a bit longer on flight time but will stay there for now. On a side note, I did order a watt meter so I will have dfinites soon enough
 Sep 03, 2011, 08:13 AM ProBro, 3D United States, FL, The Villages Joined Jul 2008 946 Posts A little off the 3D or Twisties, but have any of you guys seen this airplane? Can't believe they are selling a plane this size for \$140. Looks like a nice frame for a small gasser, and would make a nice relaxing sport flyer. http://www.advantagehobby.com/103080/SEA5525/
Sep 03, 2011, 08:17 AM
Registered User
Prineville Oregon
Joined Jan 2007
309 Posts
Quote:
 Originally Posted by gregory.da A little off the 3D or Twisties, but have any of you guys seen this airplane? Can't believe they are selling a plane this size for \$140. Looks like a nice frame for a small gasser, and would make a nice relaxing sport flyer. http://www.advantagehobby.com/103080/SEA5525/
my guess is it is now on the discontinued list. Paid about the same at Horizon when I got my twist 1.50 .
 Sep 03, 2011, 09:37 AM Registered User winston mo Joined Oct 2006 9,050 Posts Once again well said Wayne, if people only knew the 1/2 of it would they really stress thier electronic eq that way. Try running your car engine on 1 quart of oil
Sep 03, 2011, 09:47 AM
Flying Half Pound and Down
United States, PA, Bellefonte
Joined Dec 2007
14,845 Posts
Quote:
 Originally Posted by kerwin50 Once again well said Wayne, if people only knew the 1/2 of it would they really stress thier electronic eq that way. Try running your car engine on 1 quart of oil
I really hate aggitated electrons, they dont perform well, they make noise, waste energy, and kill a fella's G Factor.

"Who aggitating my dots?"
Last edited by DaOldGuy; Sep 03, 2011 at 12:05 PM.
 Sep 03, 2011, 09:52 AM Montana Transplant United States, TX, Sealy Joined Aug 2005 2,079 Posts 14 days to DOG's flyin....
 Sep 03, 2011, 11:22 AM Registered User Washougal, Washington, United States Joined Jan 2004 1,390 Posts Texas guys... Low temperature here last night at my house was 48 degrees!