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  1. #76

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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    I have a richmodel yak 54 that has a 30 amp esc and a r-28 rimfire engine on it however I don't know what battery to use can you help me out with a very simple , non-teck way to size my elect planes for batteries??? It seems that all the batteries that I am using on the yak 54 are causing the esc to get real hot in just a couple of seconds. The motor is what is recomened and so is the esc but they don't give any information on what battery to use . I have tried a 1500amp 3s 15c on up to a 2000amp 3s 20c but everything is heating up the esc to a very high tempeture and then the motor wants to quit on me . Help anywhere without the tech-no stuff . I is just an old country boy.??

  2. #77
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT


    ORIGINAL: dancingeagle

    I have a richmodel yak 54 that has a 30 amp esc and a r-28 rimfire engine on it however I don't know what battery to use can you help me out with a very simple , non-teck way to size my elect planes for batteries??? It seems that all the batteries that I am using on the yak 54 are causing the esc to get real hot in just a couple of seconds. The motor is what is recomened and so is the esc but they don't give any information on what battery to use . I have tried a 1500amp 3s 15c on up to a 2000amp 3s 20c but everything is heating up the esc to a very high tempeture and then the motor wants to quit on me . Help anywhere without the tech-no stuff . I is just an old country boy.??
    I can see from your question that you have not read the e-book. If you go back to the first post you will see that Chapeters 3 &4 address your question.But let's see if we can help.

    Batteries can not cause your ESCto get hot as long as the cell count or voltageis not higher then the ESCis rated for. The amperage draw of your motorcancause your ESCto get hot.

    You say you are using therrecommended ESCfor that motor. Are you also using the ecommended propeller for that motor? Which motor do you have? If the prop is too big or too deep it will cause the motor to draw more power. This puts more strain on the ESC.


    What prop are you using?

    Looking at Rimfire motors Idon't see a model R-28. However I do see a series of Rimfire motors in the 28 range here. http://www3.towerhobbies.com/cgi-bin...RCH=Rimfire+28

    Which one do you have? Each would take a different prop.

    If you had a watt meter you could measure how many amps the motor was drawing and tell immediatly if you were over working the ESC and/or the motor.

    Here is the watt meter that Iuse.
    http://www3.towerhobbies.com/cgi-bin...&I=LXLMV0&P=ML





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  3. #78
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    This Electrifly website allows you to choose between outrunner and inrunner, and shows the specs, battery size, etc. for all their products:

    http://www.electrifly.com/motorsgears.html

    The only thing I really don't like about it is that all of the inrunner applications are shown with reduction gearboxes. They don't show any direct drive at all. Dumb.

    Do what the boss says: get a wattmeter. You plug it in series with your battery leads to the ESC and it allows you to measure the current and voltage at any throttle setting. All of the maximum allowable currents and voltages are shown on the Electrifly website, so it's easy to tell if you're exceeding the recommended valuesif you have a wattmeter. This is the wattmeter I've been using, comes with Deans connectors on both ends so it's a snap to use. (The page says it has Astro Flight zero loss connectors on it, but it doesn't)

    http://www3.towerhobbies.com/cgi-bin...&I=LX3605&P=ML

    Compare the specs on your ESC to the specs on your motor. I like to size ESCs so that the constant current rating on the ESC exceeds that of the motor by a healthy margin, usually 10-20 amps, so that I can use the BEC feature without worrying about over amping.

    Bob Hunt

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    -Gen. Chuck Yeager

  4. #79

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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    Ed,

    Thank you, thank you, and thank you. Your posts have been very valuable to everyone. I know this must have taken alot of personal time and I really appreciate that. Being a member who lost a field to development, then finding another one where only electric flight is permissible, I really do appreciate all the information. I know it's all published throughout the internet, but it's real nice to have it all in one place. You have definitely answered a boat load of questions and made the light bulb alot brighter with other topics.

    Thanks again!
    Pat
    One day, I stopped to think then forgot to start again!

  5. #80
    Moderator aeajr's Avatar
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    Pat,

    Thank you for your kind words. I am glad you found this e-book helpful.
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  6. #81
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    I would like to bring to the attention of the readers of this e-book the work of Ken Myers, President EFO. Ken has taken this e-book, added some editorial work to it and has produced it in .pdf format so it can be downloaded.


    Ken has reorganized some of the my chapters. In doing so it shifts the focus of the e-book from the electric power system to an overall guide for the new and experienced electric pilot. While the content is 98% the same as here the content order is different. Thanks for your contributions Ken.

    This is the reason I published this in e-format rather than paper. The electronic format allows us to work together to take the work of one and build upon it.

    You can find the .pdf format here. It is 49 pages.

    Ken, on behalf of the electric community, we thank you for your time, effort and your contribution.
    http://theampeer.org/everything-e-power.pdf
    ( direct link to the pdf updated 7-2012)




    edit: The .pdf continues to be a useful reference document but it is not updated on a regular basis, so you may find some minor variations between the .pdf articles and the on-line articles. However the basic information is sound. Updates are mostly to refresh links, make adjustments about cost or perhaps add some additional information. However the articles in the .pdf are sound and useful. Enjoy them.
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  7. #82
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    Thanks for this thread; it is really helping me with the basics as I convert from wet power. I am currently trying to decide on the voltage for the system in my new plane - either 8S or 10S lipo power.

    People are running 8S or 10S setups on the plane I am about to get, yet they are both spinning the same 18x10 propeller (different motors, of course). I found this to be confusing (wouldn't you want to spin a bigger prop with the higher voltage system?) but this is what I hypothesized: by using higher voltage you are drawing less current from the battery to do the same job, and thus have a more efficient system. Therefore you can use batteries with less capacity, or you can deal with the extra weight and increase flight times. Is this correct?

    Also, I now understand that ESC's just send pulses of full charge/current to the motor to regulate RPM. Is a lipo C rating supposed to be the constant discharge of the battery?
    Joe Marri
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  8. #83
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    ORIGINAL: gaRCfield

    Thanks for this thread; it is really helping me with the basics as I convert from wet power. I am currently trying to decide on the voltage for the system in my new plane - either 8S or 10S lipo power.

    People are running 8S or 10S setups on the plane I am about to get, yet they are both spinning the same 18x10 propeller (different motors, of course). I found this to be confusing (wouldn't you want to spin a bigger prop with the higher voltage system?) but this is what I hypothesized: by using higher voltage you are drawing less current from the battery to do the same job, and thus have a more efficient system. Therefore you can use batteries with less capacity, or you can deal with the extra weight and increase flight times. Is this correct?

    Also, I now understand that ESC's just send pulses of full charge/current to the motor to regulate RPM. Is a lipo C rating supposed to be the constant discharge of the battery?
    First, the C rating of a lipo is the MAXIMUM constant current drain it sustain without serious damage. So, if you have a 2000 mah pack, which is the sames as saying a 2 ah pack, and it it rated at 20C, then that pack should be able to handle 40 amps max. In practice we like to run our packs at a somewhat lower rate than max so as to put less stress on them. So, for example I would probably prefer to run this pack at about 32-35 amps max.

    Some packs also have a BURST rating. So you might see a pack rated 20/40C rated. That means it could handle 20C constant but could handle a burst of 15 seconds at double that level. I never use these burst ratings but if you have well understood need for very short bursts of power, then it might be helpful.


    Power

    Watts is the electric equivalent of horsepower. Watts = Volts X Amps

    And just like cars, where we talk about HP per pound, in electric RC airplanes we talk about watts per pound. So if I have a 2 pound plane, I can achieve 100 watts/pound by using a higher voltage running at a lower amperage or a lower voltage at higher amperage.

    So you can use a 10V pack delivering 20 amps to reach 200 watts.

    Or you could use a 20V pack delivering 10 amps to reach 200 watts.

    So, how could we have the same prop in both cases? Well we are going to deliver 200 watts to the prop and we are going to turn it at about the same speed in both cases.

    If you look at the specs of a brushless motor, you will see something called the kV rating. That tells us how many RPMs we will get per volt applied.

    So if the motor has a 300 kV rating and we apply 20V the motor will turn at 300X20 = 6000 rpms.

    If the motor has a 600kV rating, and we apply 10V to it, then the motor will turn at 600X10 = 6000 rpms

    So, that same size prop, in this example, will be turned at 6000 RPMs. The prop will deliver the same thrust and the same pitch speed in both cases. We would just match up our voltage with the kV rating that would give us 6000 rpms, or whatever RPMs or pitch speed we wanted.

    Same RPMs using two different voltages, the watts, the power is the same in both cases. We just derrived them in different manner.

    Look at multispeed bicycles. You have a set of gears in the front and a set in the back. If you want to change the speed, or the effort, you can change the back gear you are using or you can change the front gear, or you can change both.

    So the back is the kV rating of the motor and the front is the voltage of the battery pack.

    I used to be involved in drag racing, years ago. We would match the rear end drive ratio to different gearboxes and differnt size tires to get the kind of torque we wanted to get the best hole shot from the starting line. All the same thing.


    I hope my analogies and my examples don't confuse you. Keep asking questions.
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  9. #84
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    Your analogies are great, actually

    In practice we like to run our packs at a somewhat lower rate than max so as to put less stress on them.
    How do you regulate the discharge of the battery?
    Joe Marri
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  10. #85
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT


    ORIGINAL: gaRCfield

    Your analogies are great, actually

    In practice we like to run our packs at a somewhat lower rate than max so as to put less stress on them.
    How do you regulate the discharge of the battery?
    By properly matching the motor/prop and teh battery. You don't regulate, you select the right motor/prop combo.
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  11. #86
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    I think I'm getting this:
    Let's say I have (to simplify) a 30 volt battery, 2000mah, rated at 10C. If I use a motor with 250kv, the motor will spin whatever prop is there at (250x30=) 7500rpm. How many amps this will draw from the battery depends on the resistance supplied by the prop; the bigger the prop, the more resistance, the more amps need to be drawn to achieve the 7500rpm. So, I need to choose a prop that will draw no more than 20 amps (probably 15 or so?) to be safe.

    Is this correct so far?
    Joe Marri
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  12. #87
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    By George, I think you've got it!

    So, how do you know what prop?

    You use the MFG calculators, like the one I used for AXI. There are several others listed in the post on sizing power systems.

    You can also look at the spec sheets included with the motors. For example Max Pro motors come with great documentation. Take a look here. You can read it right off the chart.
    http://www.maxxprod.com/pdf/HC6332-230.pdf

    Reading the chart, if we use a 10 cell pack, approx 37 volts, and we use a 17X10 prop the motor will draw about 60 amps yielding about 2200 watts. If you put his motor in your 11 pound plane you would have about 200 watts/pound. That would be unlimted verticle and would likely hover.

    If you used an 8 cell pack and the same 17X10 prop, that would be about 1200 watts or 109 watts per pound. That would be an excellent sport aerobatic plane, but maybe not unlimited pattern. Uplines might be a bit weak.

    An 8 cell pack, turning a 20X10 prop would yield about 1800 watts. ON your 11 pound plane that would be 163 watts/pound.

    That is how I would work from a MFG chart.

    Battery Duration.

    A 2000 mah pack can sustain 2000 ma/or 2 amps for one hour. So it can deliver 20 amps for 1/10 of an hour or 6 minutes.
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  13. #88
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    Wow, a couple hours ago I had no idea why things would work, and now I'm tearing through data sheets and totally understanding why people are choosing what they're choosing and how it would work.

    You are just a step ahead of me, too. Next is to look at props and flight times as I've got the battery and motor stuff down pretty good.

    So a 2000mah battery can put out 20 amps for 6 minutes...that's 10C. A 20C battery could put out 40 amps for 3 minutes and still be relatively safe.

    Thanks so much for your help! This just turned in to a lot of fun
    Joe Marri
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  14. #89
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    It is good to understand how things work, but if you plan to select your own power systems on a regular basis, an investment in one of the commercial calc programs is a good idea. It will let you play "what if" and will give you a list of motors, props and batteries that will meet your needs. This is one of them.

    MotoCalc
    This program will tell you everything you need to know: Amps, Volts, Watts, RPM,
    Thrust, Rate of Climb, and much more! It is a popular tool for predicting
    the proper motor, prop, battery pack for electric planes.
    http://www.motocalc.com/
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  15. #90
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    Is there a resource for information as to how a prop will affect a generic motor, or doest this only come from the motor manufacturers? Some of the motors I've been looking at say nothing about props.

    As for motocalc, I already have it. I'm from the school of thought that says not to get too comfortable with a computer program until you understand the basics behind it. I want to know if the answer I get back is reasonable before I trust it, or trust the values I entered are correct.
    Joe Marri
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  16. #91
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    WebOCalc is the package I use to do generic modeling.
    http://flbeagle.rchomepage.com/softw..._imperial.html

    You can play around with voltages, kV, Max prop size, target speed, target thrust, max amps and see what it spits out as recommendations for props. It really works from the motor out, rather than the prop in.

    Once you feel you have some grasp on these concepts, WebOcalc can be a great way to test your understanding. I use it all the time.


    For example, if I use it to model a plane similar to the one we have been discussing:

    180 ounces
    800 sq inch of wing
    80 inch wing span

    I set a max prop size of 20 inches - Perhaps ground clearence would dictate something less.

    I set speed target at around 80 mph

    I set a thrust target of around 160 oz

    I clicked the voltage wizard and it gave me a range of choices. I chose an 8S pack, it filled in the voltage and the target amps

    I used the kV wizard to suggest a kV for an outrunner. I used 300

    It suggests a 17X12 prop yielding a pitch speed of 72.9 mph and a prop thrust of 186.6 oz.

    Now, I can vary the voltage, max amps, kV, and see what happens to the prop recommendations, the pitch speed and the thrust. Also take a look at how it evaluates the set-up.

    Change the kV motor rating to 320 and see what happens.

    If you were building a Pylon racer, you would optimize for speed. So set a high speed target and play with KV and voltages.

    If you are building an e-glider or a 3D plane, you would optimize for thrust for fast climbs or hover. So set your speed target lower and make your thrust target higher. Watch what happens.

    This is fun!

    This is a "roughing out" tool. No brands, just general specs where you can do "what if". I like it a lot and I find it an excellent first step in selecting a power system. Now I know what to look for in terms of motor specs across brands.
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  17. #92
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    Awesome link! It actually just made me feel a lot better about my 10S decision. People have been saying the plane is 'floaty', and at 9.25lbs and 10S (or 8.5lb and 8S like stock) the program said it would fly like 'a glow trainer'. I bumped it up to close to 10lbs and I got 'fast aerobatic' - more like the pattern plane that it is. The extra cell weight should be just fine.

    Thanks again for all your help. I can't believe how much I've learned from this thread in 24 hours!
    Joe Marri
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  18. #93
    Moderator aeajr's Avatar
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    Glad to help, and our conversation here will help others as they follow our conversation.
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  19. #94

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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    Hi,
    I've just started electric flying this year and it's great. My first electric plane is the Super Cub. But, flying is pretty much done for winter, how do I store and maintain the NI-Mh and Li Po batteries over the winter ? What would be the proper way ?
    Thanks in advance.
    Wayne

  20. #95
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    I have read that Lipos are best stored at about 1/2 charge.

    Nimh can be left fully charges as they will self discharge over time.
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  21. #96

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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    Ed,

    I have been looking for something like this for well over a year. Myself and several club members will enjoy going back to school.

    Thanks,

    Ken

  22. #97

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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    Ed,
    thanks for all the input educating me on the motor. i saw a kit plane ( micro telemaster ) in hobby lobby. this one need to get my own electronics. well, this seems good learning experience from what i've read from your post.

    Following is the brushless requirement for this little plane ( 10 oz in weight), prop size 7*4, i am planning to fly with 2 lipo ( 7.4volts) name of motor reconmended by manufacturer :AXI Gold 2203/52 . 12 Amp Brushless Controller -12 amps continuous, for use with 6-10 NiCad or NiMH, 2-3 Lithium cells. BEC can run 4 servos with up to 3 Lithium cells, or 3 servos if 10 NiCad/NiMH are used.

    No. of cells 2 Li-Poly
    RPM/V 1525
    Max. efficiency 74%
    Max. efficiency current 2 - 5.5A (>69%)
    Current capacity 7A / 20s
    No load current 0.4A
    Internal Resistance 390mĪ©
    Dimensions (Diameter x Length) 27.5 x 21mm
    Shaft diameter Carbon 3mm
    Weight with cables 18.5g

    now the math part for my lesson
    10oz plane will be 0.629 pound. if i want to park fly ( 75Watt), then the motor requirement is 75Watt*.0629pound and it will be 4.7175 watt. So i round to 5 watts motor. Am i correct so far?

    then i go to maxxprod and found few motors there. I am picking one HC2808-0860kv.

    HC2808 - These 100 watt motors are for small models weighing 9-12 oz for 3-D flight, up to 16 oz for aerobatic flight and up to 20 oz for leisure flight

    this is spec of that motor
    Part No. Dia mm Length mm Weight g Shaft Dia Prop Size* ESC Rating Kv Rm Io
    HC2808-0860
    Learn more 28 25 52 4mm 9x5-12x6 10 860 .255 .36

    efficient operation cuttent=2-7A, 11A max 15 seconds



    These are my questions. diameter, and length is not a big issue( i have good background on fixing my nitro buggy every few weekends).

    1. what am i suppose to do with my 5 watt motor requirement in math above? or how do i apply that 5watt calculation to choosing motor? My guess will be wattt= volt*amp, so 5watt = 7.4volts *amp. Amp will be 1.48. In the AXI Gold 2203/52 motor spec, it said max effieiency current 2-5.5A. so my 1.48A will be less than 2-5.5A requirement? so i won't fly too efficiently or safe to go lower that 2-5.5A limit?



    2. the Kv value in the required motor AXI Gold 2203/52 is 1525, but that HC2808-0860 is only 860KV. so the HC motor will have lower rpm with same voltage input ( 2s- 7.4volts)?


    3. what are the meanings of ESC rating, Rm, Io suppose to mean in that HC motor?

    4. what is meaning of current capacity (it said 7A/20s)on that AXI Gold 2203/52. does it mean 7A and 20 cells ( 74volts ( 20*3.7volts) is maximum current and volts this motor can run without burning or overheating? and what is that internal reistance suppose to do in any math equations used in flying ?

    5. for the lipo, it is 910mah. i will have 0.91A in an hour. if i am drawing 1.48A as my calculation above, then i will have 0.61 hour of flight time ( 0.91/1.48), about 36 mins? it seems too high of a number, isn't it? Am i suppose to include the servo amp in this equation, too?

    6. if my calculation is correct, 1.48A for motor. then that 12amp ESC will be too high for this application? what am i suppose to look for in choosing ESC. or what brand is good and budget?


    7.i know this HC motor might be higher than the require of the kit plane. so if i don't go full throttle, the plane won't fly crazy? but this plane will be capable to go faster when i am ready? I know brushless ESC is not variable resistance. it is on and off to create the difference in speed.


    Hope hearing from you. happy holidays. mike

  23. #98
    Moderator aeajr's Avatar
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    ORIGINAL: pontiac6000le88

    Ed,
    thanks for all the input educating me on the motor. i saw a kit plane ( micro telemaster ) in hobby lobby. this one need to get my own electronics. well, this seems good learning experience from what i've read from your post.

    Following is the brushless requirement for this little plane ( 10 oz in weight), prop size 7*4, i am planning to fly with 2 lipo ( 7.4volts) name of motor reconmended by manufacturer :AXI Gold 2203/52 . 12 Amp Brushless Controller -12 amps continuous, for use with 6-10 NiCad or NiMH, 2-3 Lithium cells. BEC can run 4 servos with up to 3 Lithium cells, or 3 servos if 10 NiCad/NiMH are used.

    No. of cells 2 Li-Poly
    RPM/V 1525
    Max. efficiency 74%
    Max. efficiency current 2 - 5.5A (>69%)
    Current capacity 7A / 20s
    No load current 0.4A
    Internal Resistance 390mĪ©
    Dimensions (Diameter x Length) 27.5 x 21mm
    Shaft diameter Carbon 3mm
    Weight with cables 18.5g

    now the math part for my lesson
    10oz plane will be 0.629 pound. if i want to park fly ( 75Watt), then the motor requirement is 75Watt*.0629pound and it will be 4.7175 watt. So i round to 5 watts motor. Am i correct so far?

    then i go to maxxprod and found few motors there. I am picking one HC2808-0860kv.

    HC2808 - These 100 watt motors are for small models weighing 9-12 oz for 3-D flight, up to 16 oz for aerobatic flight and up to 20 oz for leisure flight

    this is spec of that motor
    Part No. Dia mm Length mm Weight g Shaft Dia Prop Size* ESC Rating Kv Rm Io
    HC2808-0860
    Learn more 28 25 52 4mm 9x5-12x6 10 860 .255 .36

    efficient operation cuttent=2-7A, 11A max 15 seconds



    These are my questions. diameter, and length is not a big issue( i have good background on fixing my nitro buggy every few weekends).

    OK, let's walk through this together. We are going to look at power first, then we are going to look at kV, prop size considerations, motor mounts and weight. The fact that we have a reference motor, the one that HL recommended will provide us with some insights that we might not normally have, so let's see how to use that information.


    First of all, since Hobby Lobby recommended a specific motor, the easiest thing is to buy that motor, prop, esc and battery combo. We can be pretty confident that that will work well. Hobby Lobby does an excellent job of matching up motors and planes. They like the AXI line and AXI has a great reputation.

    But even if we are not going to use the AXI motor we can use it as a reference point, as a check against any other motor we decide to get. We could, for example look for another motor of a simlar kV, amps/volts/watts ratings that is similar in size and weight. If we did that we could be fairly confident of a good outcome, assuming the motor is of good quality.

    I am going to post a link to the motor in case we want to reference it during the discussion. Any time you ask about motors, planes, etc, I suggest you post links.
    http://search.hobby-lobby.com/psearc...Gold+2203%2F52


    I am also going to add a link to the micro telemaster, again for reference. This is a kit, so you will have some building to do.
    http://www.hobby-lobby.com/micro_tel...QueryId=317840
    35-1/2" wingspan, 24" long, 192 sq. in. wing area, 6-8 oz. flying weight, 6 oz. per sq. ft. wing loading.


    So my first concern is that you feel the plane will be 10 oz, but the HL listing says 6-8 oz. So I think we may be looking at a different plane. This is why I always recommend you post links. Or perhaps you are planning to have a heavier overall set-up?

    HL considers 6 oz to be a light set-up and 8 oz to be a heavy set-up. Going from 8 oz up to 10 oz is a 25% weight increase over their heavy set-up. Why so heavy? But take this into account as you do your build. That is a significant weight increase.


    Also, you are looking that the Himax 2808-860 so let's post a link to that motor for reference. Looking at the brief specs, if we can get it to draw 7 amps on a 7.4V pack that will give us 51.8 watts which is close to your 45 watt target so the motor can handle the power you need. We will look later to see how it matches up in other areas.
    http://www.maxxprod.com/pdf/HC2808-xxxx.pdf
    HC2808-0860 Kv = 860, Rm = .255, Io = 0.36, Efficient Operating Current = 2-7A, 11A Max 15 seconds

    Since Himax provides wonderful charts for their motors we can see that this motor would need a 12X6 prop to hit that power level. So, if you plan to fly the plane from a runway, you would need to check to see if you have enough ground clearence for a 12" prop. If I look back at the HL specs I see that they are matching up with a 7" prop. So I am doubtful that you will have the ground clearnece for a 12" prop. However if you will only hand launch, then this might work. Still, that 12" prop is going to be heavy by comparison to a 7" prop and huge on that plane.

    I would probably look more at the kV 1160 verson of the 2808 motor and match it with a prop in the 8X6 to 9X5 range. If nothing else it might look a little more in proportion to the plane and be lighter, though you might still have a ground clearence problem, even with an 8" prop.

    I check all my custom set-ups with a watt meter just to be sure the prop I chose does not over burden the motor.

    ORIGINAL: pontiac6000le88
    1. what am i suppose to do with my 5 watt motor requirement in math above? or how do i apply that 5watt calculation to choosing motor? My guess will be wattt= volt*amp, so 5watt = 7.4volts *amp. Amp will be 1.48. In the AXI Gold 2203/52 motor spec, it said max effieiency current 2-5.5A. so my 1.48A will be less than 2-5.5A requirement? so i won't fly too efficiently or safe to go lower that 2-5.5A limit?
    Using your 10 oz target, this plane will be .625 pounds. If we want a 75 watt/pound power to weight ratio, then you are targeting ( .625X75) a 46.875 watt motor. Let's say 45 to 50 watts for convenience. If you go back and look at your original post you will see that you got your decimal point in the wrong place. Also, if we look at the recommended HL motor it is a about a 40 watt motor, so that would have been your clue that your calculation was off.

    If you are going to use 45 watts as your reference and your 2 cell lipo (7.4V) then your battery will need to be able to supply 6 amps. Again, looking at the HL motor we would have picked the error in your calculation.


    ORIGINAL: pontiac6000le88
    2. the Kv value in the required motor AXI Gold 2203/52 is 1525, but that HC2808-0860 is only 860KV. so the HC motor will have lower rpm with same voltage input ( 2s- 7.4volts)?
    That is correct.

    ORIGINAL: pontiac6000le88
    3. what are the meanings of ESC rating, Rm, Io suppose to mean in that HC motor?
    Not sure I understand your question. You will need an ESC that can supply at least the amperage that your motor will demand in order to hit the watts you want. You can use a larger ESC but not a smaller one.

    ORIGINAL: pontiac6000le88
    4. what is meaning of current capacity (it said 7A/20s)on that AXI Gold 2203/52. does it mean 7A and 20 cells ( 7.4volts ( 20*3.7volts) is maximum current and volts this motor can run without burning or overheating? and what is that internal reistance suppose to do in any math equations used in flying ?
    This is constant current vs peak. Their specs are a little confusing but as I read it, this motor is rated for 5.5 amps constant current. You can run it at that rate all day long. The 7 amps/20 s means it can handle 7 amps for 20 seconds. After that it will start to bulid up so much heat that it will likely be damaged. This is something you take into account when you consider what kind of flying you will be doing. If you were going to need 7 amps to hover the plane, for example, you could do it but don't keep it at that level for more than 20 seconds. Or, if you were going to power an e-glider where you would climb for 20 seconds and then turn the motor off and glide, you could use the 7 amps as your sizing number. For you, I were using the AXI motor, I would use the 5.5 and select a prop that would run the motor at that level. Chances are that is what HL did.


    ORIGINAL: pontiac6000le88
    5. for the lipo, it is 910mah. i will have 0.91A in an hour. if i am drawing 1.48A as my calculation above, then i will have 0.61 hour of flight time ( 0.91/1.48), about 36 mins? it seems too high of a number, isn't it? Am i suppose to include the servo amp in this equation, too?
    Again, your calculaton was off. to get to 45 watts you would be running about 6 amps. Use that for your calculation if you plan to run at full throttle all the time. Chances are you will run at partial throttle some of the time so your average amps will likely be closer to 4, so you can use that as a second reference point to estimate your running time range.


    ORIGINAL: pontiac6000le88
    6. if my calculation is correct, 1.48A for motor. then that 12amp ESC will be too high for this application? what am i suppose to look for in choosing ESC. or what brand is good and budget?
    Based on 6 amps, any ESC of 7 amps or greater would work and leave you a little extra margin. The Maxx Pro 040 package uses a 9 amp ESC, for example. Also be sure that your ESC is lipo friendly and has a LVC that can be set for a 2S lipo. This wil protect your battery packs from being overly discharged.


    ORIGINAL: pontiac6000le88
    7.i know this HC motor might be higher than the require of the kit plane. so if i don't go full throttle, the plane won't fly crazy? but this plane will be capable to go faster when i am ready? I know brushless ESC is not variable resistance. it is on and off to create the difference in speed.
    All the ESC that I know, for model airplanes, use a pulsed power model to control the speed. That includes brushed and brushless.


    My suggestion

    Since you like the Himax motors, assuming a 9" prop will work, you might consider the Combo 040 which is rated at 44 watts and is designed for a 2S pack. It comes with motor, ESC and prop all matched up. It comes with a 2212-1280 motor I have purchased their packages and have been very pleased with them.
    http://www.maxxprod.com/mpi/pdf/combo-020-040.pdf


    They suggest an 830 mah 2S pack. Assuming a 12C or higher rating on the pack, anything in the 600 to 1200 mah range would work fine. Select your pack based on weight, size and duration targets. I think 800 to 1000 mah is about the right size target. The smaller pack will be lighter and probably easier to fit. The larger pack will be bigger and heavier so you might have trouble fitting it and then there is that extra weight to consider.


    Other factors

    When you decide to design your own power system there are many things to take into account. Ground clearence is not one I often bring up, but it is a real consideration if you plan to fly off the ground, or if you want your prop to appear somewhat proportional to the plane.

    A 12" prop would be HUGE on this plane, might make it hard to balance the plane, and could produce too much torque on launch, causing problems. I think the 12 is just too big. A 7 to 8 would be more appropariate and a 9" would probably still be OK if you plan it to hand launch.


    Weight, and kV and prop
    Note that 28 grams=1oz

    Again, one of the ways we can select motors is to look at what HL recommended and see if we can find one that is similar in another brand.

    The AXI motor is about 18 grams and 1560 kV, according to the specs you posted.

    The himax 2212 that I suggested in the 040 package is 31 grams. Not knowing whether the plane would need lead in the nose to balance with the AXI motor, the difference of 18.5 to 31 grams, 12.5 grams, about 1/2 oz, is significant, but might be fine. just remember that weight adds up.

    The kV of the AXI, accoring to your specs is 1560. The 2212 is 1180, so we give up about 380 rpms/v or 2812 RPMs. However we would be using a larger and deeper prop so that should make up for the difference, but that larger prop is likely heavier too. Weight adds up.


    The 2802 you chose is about 52 grams, about 33.5 grams, or about 1.5 oz heaver than the AXI motor. That is a very very big weight difference on a plane that is targeted to the 6-8 oz range. Add a 12" prop, comapred to the 7 recommended for the AXI and you have a plane will need a LOT of weight in the tail, most likely, will be very heavy and will probably not fly well.


    Motor mount

    One last point has to do with the mount. The AXI uses a 3 point motor mount. Since HL recommended it, we can assume the plane comes with a motor mount that works well with this arrangement. The two Himax motors we discussed use a stick mount. That does not mean they won't work, it just means that you would have to modify the stock set-up to accomodate a stick mount. Not a big deal but I would not want it to come as a surprise.


    Summary

    My goal here is to bring out the other considerations when we select motors. If HL had not made a suggestion, we would not have a comparision to make. But since they did, we can take kV, weight and motor mount into consideration by comparing to what HL suggested.


    I hope my comments were helpful. I think you will enjoy the buidling of the kit.




    Long Island Silent Flyers
    www.lisf.org
    Eastern Soaring League
    www.flyesl.com

  24. #99

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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    where is the e-book version of this thread?
    I looked at post 90 as the preface stated but didn't see it.
    Also why do lipo battery packs have different connectors for charging?
    If you had a 3 cell thunder power a
    3 cell polyquest wouldn't have the same charge connector.
    I would like to have the same style connectors on all my lipos no matter what brand.

    I found the e - book in post 85 now for the connectors

  25. #100
    Moderator aeajr's Avatar
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    RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT

    Where is the book?


    There are two answers to your question. I think you found one of them.



    One discussion thread IS the e-book. As stated in the first post:

    A number of people have suggested I write a book on the topic of electric flight. I would, but I find the electric field is changing too fast. Paper based books go out of date too quickly. Instead I am going to create a thread that is my version of an e-book on the subject of electric powered flight. This e-format allows me to provide updates and to answer questions, things I can't do in paper form.



    I think you posted that you found the .pdf version as well.


    As to why the balance plugs are not standard, well it is probably the same reason that the discharge/ESC connectors are not standard, there simply is no industry standard, so every created their own. But many of the charger makers created adapters to address it.


    Long Island Silent Flyers
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