Note that when I discuss Active Freewheeling I talk about what's happening in the motor. The active freewheeling is actually taking place in the ESC. At partial power, each power pulse is cut up into a lot of little segments, with the FET transistor turning the current on and off many times during each pulse. Every time it turns it off, the windings are trying to keep the current going, and if nothing was done, there would be a voltage spike that would cause damage. So, they 'dump' the current through a diode, allowing it to go back around the 'loop' that it had just gone through. The diode has resistance, which makes it heat up and waste energy. By replacing the diode with another FET, the transistor can simply open up that 'channel' for the current to go through when needed without significant resistance, allowing the current to 'freewheel' around that loop of the circuit.
That's a good idea. I'll think it through and see what I can do. In the meantime, check out this related article on our website: rcjim.com/2024/01/05/electric-power-selection-for-planes/
Thanks again. With your calculations I made a quick and dirty excel spreadsheet to plug in some numbers and jumped in and ordered a motor and ESC. We'll see...@@RCJim
Great info, but when it comes to conversions and ARFs over the years the first thing I do now is check and see how much room do I have to install a battery can the plane handle a large 6s or a medium size 5s or a small 4s once I determine the battery or fuel tank then I look at the weight of the plane and how much thrust and minimum speed Ill need to fly it , choosing motor is I like to cross references the engine wieght that was designed for it, all helps me to determine the motor size ,wieght , watts amps requirements for a given prop size..and then its test on the bench after I picked everything thing and try different props to target thrust that I need without over amping the motor. it's a fun process. 😊
Excellent job on the video Jim!! I have been wondering what are the benefits of electric motors? They obviously have benefits but, I am going to stick with the nitro engines! The sound the smell and the power they produce is just not replaceable. Thank you for the information!
A internal combustion engine power output is effected by a number of things such as barometric pressure, temperature, humidity etc. Most HP ratings are based on perfect conditions which almost never occur. While certain extreme conditions can effect electric motors generally under normal conditions they can and will put out there max rated HP. This is the reason for the power disparity. A interesting exercise that shows this is portable generators most of which have IC engines with 2 to 3 times the HP ratings of the output of the generator.
1. Longer props aren't necessarily more efficient. They may produce more thrust, but will be harder for the motor to turn. You can use the energy in the battery to move a lot of air slowly or a small amount of air quickly. What you need is somewhere in between. So, pitch speed is just as important as thrust. 2. A prop might generate enough thrust to pull a locomotive, but if the prop doesn't pull the plane through the air faster than about 3 times its stall speed, it won't be much fun to fly. Thrust without enough pitch speed is useless. You might can hover, but will it pull the plane fast enough in horizontal flight to keep the wing from stalling. 3. Manufacturers use one of two measurements to specify the motor size - the outer dimensions of the motor can or the stator size. With a 4250 motor, they're usually specifying the outer dimensions of the can whereas the 4120 motor is usually the dimensions of the stator. They can't be compared directly by using only their dimensions. 4. Battery manufacturers lie about the C-rating. Since there's no standard test to determine the C-rating, they can't be caught in a lie. And besides, they are made in China.
Thanks again for your insights. Clearly thrust produced with the plane on a bench isn't telling the full story. Unfortunately, I don't have a wind tunnel!
@@RCJim Power loading (watts/lb) is a good indicator of performance. If you look up propeller-driven WWII fighters in Wikipedia, they usually have power loading in the specs. Since the rpm of an electric motor is predictable, we can choose a pitch that’ll give us the approximate speed we want. Using the formula for the power required to turn a prop, we can use the rpm and pitch to find the diameter that will load the motor to its power limit. If the prop has an appropriate D:P ratio, we should be good to go. If not, we need a motor with a different KV rating or a battery with a different number of cells. I can do the calculations on my cellphone, but a spreadsheet makes it easier to make changes and see the results. Watts = 5.3E-15 x rpm^3 x diam^4 x pitch.
@@RCJim Also, if the level flight speed isn’t at least 3 times the stall speed, a plane won’t be much fun to fly. There are formulas to estimate the stall speed based on the weight and wing area. Wing loading and power loading (power-to-weight ratio) can give you a good idea of how a plane will fly.
One interesting thing is the durability of electric motors with permanent magnets ,edies currents in rotors has no restrictions so it is heating the mass ,for 1 kW with 0.7 efficiency it is 300W heater destroying the strength of magnetic field among natural degradation over time ,5 years old unused motor has about 45 % strength output.
That's an interesting thought. I might just start a long term test on given motors with given props on my test rig over a long period of time. It would be good to know how bad the degradation is.
Did you find out manufacturing date on most mainstream motors ,especially the mass produced bargains ? Just a hint ,spinning motor by fingers give you feedback as the poles pass each other ,yes the humps .
I have noticed the difference on various motors regarding feeling the magnetic pull as you spin the motor with your hand. I'll have to start looking at manufactured dates.
Good job mate, don’t you think it’s a shame these days everything seems to be foam and comes out of a box when you go back to the 1980s we used to build them out of the Balsa kit not with standing foam flies very well - it has its place sure thing just seems to make it more of a toy, than a hobby….. I learned a lot about structures and engineering and glueing and support and bracing and aerodynamics. Some of the young fellas. These days have got no idea. They smash these things and go back down to the hobby shop, the next day and buy another one. …..
Understood! And those foam things can get a bit pricey! I still have my good ol’ Great Planes Trainer 40 that I got started on over 25 hrs ago. Smashed and repaired more times than I can count!
Excelente video. Informacion precisa. Me ha aclarado muchos conceptos. Muchas Gracias JIM. Saludos desde Argentina!!!
Gracias por tu coraje. ¡Disfruta de tu vuelo en Argentina!
Note that when I discuss Active Freewheeling I talk about what's happening in the motor. The active freewheeling is actually taking place in the ESC. At partial power, each power pulse is cut up into a lot of little segments, with the FET transistor turning the current on and off many times during each pulse. Every time it turns it off, the windings are trying to keep the current going, and if nothing was done, there would be a voltage spike that would cause damage. So, they 'dump' the current through a diode, allowing it to go back around the 'loop' that it had just gone through. The diode has resistance, which makes it heat up and waste energy. By replacing the diode with another FET, the transistor can simply open up that 'channel' for the current to go through when needed without significant resistance, allowing the current to 'freewheel' around that loop of the circuit.
Thanks for this excellent video!
Glad it was helpful!
Awesome videos truly helps me grow in understanding how to get set up for my DIY builds!
Glad to hear it!
Thank you so much for this clear and comprehensive explanation. I'm beginning to see the light. 🙏🏼♥️
fantastic! Glad it was helpful.
great video jim very informative ty
Glad you enjoyed it
Thank you for this detailed explanation. I would like to see a flowchart type procedure. I may have to watch this several more times and take notes.
That's a good idea. I'll think it through and see what I can do. In the meantime, check out this related article on our website: rcjim.com/2024/01/05/electric-power-selection-for-planes/
Thanks again. With your calculations I made a quick and dirty excel spreadsheet to plug in some numbers and jumped in and ordered a motor and ESC. We'll see...@@RCJim
Jim, Thank you so much. You answered a ton of my questions regarding..just getting into some foam rc atm. Small park flyers.
Glad to hear that!
Thnx … very useful
Happy to help
👍👍👍💯💯💯Thank you so much for this clear and comprehensive explanation. I'm beginning to see the light. 🙏🏼♥💯💯💯👍👍👍
Glad it was helpful!
Great info, but when it comes to conversions and ARFs over the years
the first thing I do now is check and see how much room do I have to install a battery can the plane handle a large 6s or a medium size 5s or a small 4s once I determine the battery or fuel tank then I look at the weight of the plane and how much thrust and minimum speed Ill need to fly it , choosing motor is I like to cross references the engine wieght that was designed for it, all helps me to determine the motor size ,wieght , watts amps requirements for a given prop size..and then its test on the bench after I picked everything thing and try different props to target thrust that I need without over amping the motor. it's a fun process. 😊
Yes, it is a lot of fun!!
Excellent job on the video Jim!! I have been wondering what are the benefits of electric motors? They obviously have benefits but, I am going to stick with the nitro engines! The sound the smell and the power they produce is just not replaceable. Thank you for the information!
Thanks Jim, that makes sense when you are already set up with everything you need, and if you are in a place where the fuel is affordable.
A internal combustion engine power output is effected by a number of things such as barometric pressure, temperature, humidity etc. Most HP ratings are based on perfect conditions which almost never occur. While certain extreme conditions can effect electric motors generally under normal conditions they can and will put out there max rated HP. This is the reason for the power disparity. A interesting exercise that shows this is portable generators most of which have IC engines with 2 to 3 times the HP ratings of the output of the generator.
Good thought. And with both the generators and electric motors, there is a matter of efficiency. Input power drawn is always greater than the output.
1. Longer props aren't necessarily more efficient. They may produce more thrust, but will be harder for the motor to turn. You can use the energy in the battery to move a lot of air slowly or a small amount of air quickly. What you need is somewhere in between. So, pitch speed is just as important as thrust.
2. A prop might generate enough thrust to pull a locomotive, but if the prop doesn't pull the plane through the air faster than about 3 times its stall speed, it won't be much fun to fly. Thrust without enough pitch speed is useless. You might can hover, but will it pull the plane fast enough in horizontal flight to keep the wing from stalling.
3. Manufacturers use one of two measurements to specify the motor size - the outer dimensions of the motor can or the stator size. With a 4250 motor, they're usually specifying the outer dimensions of the can whereas the 4120 motor is usually the dimensions of the stator. They can't be compared directly by using only their dimensions.
4. Battery manufacturers lie about the C-rating. Since there's no standard test to determine the C-rating, they can't be caught in a lie. And besides, they are made in China.
Thanks again for your insights. Clearly thrust produced with the plane on a bench isn't telling the full story. Unfortunately, I don't have a wind tunnel!
@@RCJim Power loading (watts/lb) is a good indicator of performance. If you look up propeller-driven WWII fighters in Wikipedia, they usually have power loading in the specs. Since the rpm of an electric motor is predictable, we can choose a pitch that’ll give us the approximate speed we want. Using the formula for the power required to turn a prop, we can use the rpm and pitch to find the diameter that will load the motor to its power limit. If the prop has an appropriate D:P ratio, we should be good to go. If not, we need a motor with a different KV rating or a battery with a different number of cells. I can do the calculations on my cellphone, but a spreadsheet makes it easier to make changes and see the results.
Watts = 5.3E-15 x rpm^3 x diam^4 x pitch.
@@RCJim Also, if the level flight speed isn’t at least 3 times the stall speed, a plane won’t be much fun to fly. There are formulas to estimate the stall speed based on the weight and wing area. Wing loading and power loading (power-to-weight ratio) can give you a good idea of how a plane will fly.
One interesting thing is the durability of electric motors with permanent magnets ,edies currents in rotors has no restrictions so it is heating the mass ,for 1 kW with 0.7 efficiency it is 300W heater destroying the strength of magnetic field among natural degradation over time ,5 years old unused motor has about 45 % strength output.
That's an interesting thought. I might just start a long term test on given motors with given props on my test rig over a long period of time. It would be good to know how bad the degradation is.
Did you find out manufacturing date on most mainstream motors ,especially the mass produced bargains ? Just a hint ,spinning motor by fingers give you feedback as the poles pass each other ,yes the humps .
I have noticed the difference on various motors regarding feeling the magnetic pull as you spin the motor with your hand. I'll have to start looking at manufactured dates.
Good job mate, don’t you think it’s a shame these days everything seems to be foam and comes out of a box
when you go back to the 1980s we used to build them out of the Balsa kit
not with standing foam flies very well - it has its place sure thing
just seems to make it more of a toy, than a hobby…..
I learned a lot about structures and engineering and glueing and support and bracing and aerodynamics.
Some of the young fellas. These days have got no idea. They smash these things and go back down to the hobby shop, the next day and buy another one. …..
Understood! And those foam things can get a bit pricey! I still have my good ol’ Great Planes Trainer 40 that I got started on over 25 hrs ago. Smashed and repaired more times than I can count!