How true is this statement regarding ESCs
- Thread starter Quinton
- Start date
Debian Dog
Old Heli Guy
Somewhat. You want your Prop, motors and ESCs maximized for your load but taking you big camera rig up with no camera mounted is not "unheard of". We run RC helicopters all the time at 80% (or so) in idle up 1 and 50% (or so) for a hover. I have never smoked a speed controller. Then again I do not skimp when buying them.
http://www.castlecreations.com/support/faq/faq-general.html
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Perfect thanks for that.
No6 on that link actually answers a few questions I had.
One thing I was thinking of looking to expirement with was upping the prop size by an inch, but then seeing e-calc it showed my motor was rated @30W at maximum, but e-calc showed at full throttle it would be using 34A for that prop, so I wondered if it would be OK to limit the end points to not go above 30A would it be OK.
I would rarely go full throttle, but probably not the best of idea.
There is just so much you have to think about, its a constant learning curve.
No6 on that link actually answers a few questions I had.
One thing I was thinking of looking to expirement with was upping the prop size by an inch, but then seeing e-calc it showed my motor was rated @30W at maximum, but e-calc showed at full throttle it would be using 34A for that prop, so I wondered if it would be OK to limit the end points to not go above 30A would it be OK.
I would rarely go full throttle, but probably not the best of idea.
There is just so much you have to think about, its a constant learning curve.
Partially true, but it depends on serveral external factors. First, lightly loaded ESCs are a non-issue. There is nothing in the design of an ESC that could be damaged by a low-load or no-load condition. High-load, yes, low-load, no. Second, flight stability and ability to adapt to a light-load condition, is purely up to the FC design and state of adjustment. Some FCs, in some set-ups, will be very OK with a low-load flight, some will be less so. I doubt that any would be dangerous or unflyable with a low-load state. If you know you want to do this regularly, it is possible to tune most FCs so it's less of a factor.
Debian Dog
Old Heli Guy
Yes and on that note: I typically will pick combinations others are already using with no issue. I have learned over the years that unless you have a lot of time and money it seldom pays to be first.
Yes and on that note: I typically will pick combinations others are already using with no issue. I have learned over the years that unless you have a lot of time and money it seldom pays to be first.
Wish I would have read that last year, I would be a lot better off
Now this opens up more questions from the link you provided, does it mean that it is actually bad to have an ESC larger than you require, as it would always require full throttle half of the time?..
6. Can I control how much current passes through my speed controller by limiting full throttle travel on my transmitter with endpoint adjustments/trim? In other words can I use a 25 amp speed controller with a motor that will pull 45 amps but lower my top throttle endpoint on my transmitter so my watt meter only shows 25 amps at full throttle? Will this be OK?
NO!!! A speed controller controls power to the motor by turning full throttle current on and off really fast, 11 to 13 thousand times per second (Pulse Width Modulation or PWM). The percentage of each on/off pulse that is off compared to the part that is on determines how much power the motor sees. I.E. With a pulse that is 50% off and 50% on the motor will see 50% power*. Because each on pulse is 100% of full throttle current, a system set to pull 20 amps at full throttle through a Phoenix 10 will not last if you are throttled back to the point where you only see 10 amps on a wattmeter. The ESC in this case is still switching 20 amps, which it can’t do for long. Actually it is worse than the simple example above. Because an electric motor will always to try to pull as much power as is available to get to its rpm (volts times Kv), when you are running the motor below its Kv speed by switching power on an off, each on pulse will actually be way over the full throttle amp draw. That is why ESCs work harder at partial throttle than full throttle and why we underrate our ESCs. We underrate not so they can handle more current than their rating at full throttle, but so they can handle extended partial throttle operation with no problems.
Debian Dog
Old Heli Guy
You're reading it backwards I think if you are pulling 20 amps though a 10 amp controller it won't last long. But a good controller will allow for those > 100% bursts once in a while.
Think of it this way If you have all 10 amp ESCs and you are all up weight with all the stuff you want to fly with... Each speed controller controller should be pulling near 10 amps on a climb out. If you replaced all you 10 amp ESCs with 30 amp ESCs you would be constantly running at 33% max and the ESCs would be hot as crap because each one has to buffer/hold ~70% of the power from the motors all the time. That is "bad".
Without variable pitch (like a RC heli) there is no way to run the speed controller at 100% all the time (because the individual motors have to sped up and down to turn, deal with wind, fly, everything a multicopter does really) but, you do not want to much more speed controller than you need.
Think of it this way If you have all 10 amp ESCs and you are all up weight with all the stuff you want to fly with... Each speed controller controller should be pulling near 10 amps on a climb out. If you replaced all you 10 amp ESCs with 30 amp ESCs you would be constantly running at 33% max and the ESCs would be hot as crap because each one has to buffer/hold ~70% of the power from the motors all the time. That is "bad".
Without variable pitch (like a RC heli) there is no way to run the speed controller at 100% all the time (because the individual motors have to sped up and down to turn, deal with wind, fly, everything a multicopter does really) but, you do not want to much more speed controller than you need.
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gtranquilla
RadioActive
A valid statement for the most part.... A RTF or ARF is developed for a specific all up weight which includes the payload weight.
And changes to the payload weight also affect the z parameter setting for C of G on the vertical plane. If not re-adjusted your FC will not be able to adequately level the MR on the horizontal plane.
Reducing the payload weight increases flight time but also create a need to re-adjust Basic and Attitude PID loop tuning to re-optimize flight control.
And in some cases where the payload weight is too low, the MR will take off when it should be idling on the ground and/or the motor speed range will be narrowed toward the lower rpm end etc.
For greater insight try loading all the required data into eCalc for Multirotors. It is a a handy tool for circumventing most of the multi-discipline engineering skills that would otherwise be required starting with motor speed/torque curves.
And changes to the payload weight also affect the z parameter setting for C of G on the vertical plane. If not re-adjusted your FC will not be able to adequately level the MR on the horizontal plane.
Reducing the payload weight increases flight time but also create a need to re-adjust Basic and Attitude PID loop tuning to re-optimize flight control.
And in some cases where the payload weight is too low, the MR will take off when it should be idling on the ground and/or the motor speed range will be narrowed toward the lower rpm end etc.
For greater insight try loading all the required data into eCalc for Multirotors. It is a a handy tool for circumventing most of the multi-discipline engineering skills that would otherwise be required starting with motor speed/torque curves.
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Hmm the way I am reading it is, if you are using a 50A ESC and you are at half throttle, it is pulling 50A, 11-13000 times per second, even though your watt meter shows that it is only pulling 25A...no?
What it says that you are always pulling max Amps on the on pulse, and the off pulse equals it out to your throttle position.
No wait..after reading again..its not your ESC, its what power you actually require in your setup..ok I think its sinking in
If the "motor" requires 50A then it would be the case, it doesn't mean that it would always be 50A on the on pulse.
What it says that you are always pulling max Amps on the on pulse, and the off pulse equals it out to your throttle position.
No wait..after reading again..its not your ESC, its what power you actually require in your setup..ok I think its sinking in
If the "motor" requires 50A then it would be the case, it doesn't mean that it would always be 50A on the on pulse.
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PeterLester
Member
IMHO - Its not quite so simple as PWM is used in different ways for different purposes. Also if you look at a PWM signal on a high quality Oscilloscope you will see a high voltage spike on the leading edge of each square wave and that spike tends to break down motor winding insulation by poking holes in the motor winding insulation especially in the first few windings. Search for H bridge in the attached for info specific to Brushless motors control.....http://ebldc.com/?p=48 There are ways to minimize that leading edge spike but it usually requires a hefty capacitor to integrate the volt spike over time or a heavy power transistor and these are too big for model aircraft.
A mechanical analog style watt meter needle does not have time to jump up and down with each pulse of the square wave and will typically fall between the two extremes based on the relative time at at top versus bottom. A motor will respond in a similar manner due to inherent mechanical momentum. To simplify the motor circuit from the perspective of ESC output an norton or thevenin equivalent circuit can be modelled. http://en.wikipedia.org/wiki/Thévenin's_theorem
But in the case of motors the circuit elements include inductors and capacitors not just resistors. It is simplified parallel series capacitor/inductor/resistor circuit representing all the possible electrical characteristics of the motor regardless of speed and torque......
Getting scared yet!!!
A mechanical analog style watt meter needle does not have time to jump up and down with each pulse of the square wave and will typically fall between the two extremes based on the relative time at at top versus bottom. A motor will respond in a similar manner due to inherent mechanical momentum. To simplify the motor circuit from the perspective of ESC output an norton or thevenin equivalent circuit can be modelled. http://en.wikipedia.org/wiki/Thévenin's_theorem
But in the case of motors the circuit elements include inductors and capacitors not just resistors. It is simplified parallel series capacitor/inductor/resistor circuit representing all the possible electrical characteristics of the motor regardless of speed and torque......
Getting scared yet!!!
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I would be more scared if I did not find out how something 7-9kg flying in the air works.
Thanks for the link it was very helpful.
It is a lot to take in, but everything you read helps fit the jigsaw parts together, and hopefully it will all slot into place.
What I have learned in this process is knowing a little bit about everything can be quite dangerous, its trying to find out as much as possible about the most important things which hopefully makes it less dangerous (and less expensive).