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Motor Chat: Cheetah vs Turnigy Motors

Old 05-20-2016, 08:03 PM
  #26  
solentlife
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Originally Posted by Billyg View Post
Ok- So I am going do do my reading. I understand the matching of battery to esc to motor then prop importance. What I am trying to get is where to start. So I have a plane... about 30 oz. Where do we start? I am reading a lot and understand adding a lipo cell increases voltage which will push up amperage to motor. So you have to change the prop and make sure ESC handles it. But what is the biginning question to answer to start to solve the equation of "what to put on the plane"?

Thanks
One of the best tools after the Wattmeter is online :

http://ecalc.ch/motorcalc.php

For just a few cents you register and fill in the general data of your model / motor / prop / ESC (don't bother changing the 'engineering data' - just leave as default) ... it will tell you all basically you need.

The motor list and such is extensive with most models / brands listed.

Nigel
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Old 05-20-2016, 08:23 PM
  #27  
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Well in the first post you said it might take a 480 motor, that would be a 3536 1000kv.

I was reading this thread, http://www.wattflyer.com/forums/showthread.php?t=55611 and they used possibly a 2836 motor, so maybe a 2836 1100kv with a 9x6 prop, 30A ESC and 1500mah 3s lipo.
http://www.hobbyking.com/hobbyking/s...strSearch=2836

http://www.hobbyking.com/hobbyking/s...?strSearch=30a
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Old 05-20-2016, 08:27 PM
  #28  
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If you are talking about peak amps from acceleration, their duration is so short that it is likely still within the ESC's burst rating. I've run my hobbyking 30A ESC hard on my slow stick at rarely over half throttle on 4s and the motor gets very warm, but the ESC is cool. With the prop I'm using I get 15A static on 2s, 25A on 3s. I might get higher amp peaks on 4s, but since I keep the motor speed around what it would be on 3s I'm running the same watts with lower amps and higher voltage.
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Old 05-20-2016, 11:04 PM
  #29  
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Billyg

Maybe this will help but everyone has their own ideas.

The plane I am talking about is a biplane about the same weight as yours, just over 800 grams.
That Turnigy motor you looked at would be quite OK.

The motor I use is this one

I use a 30 amp Turnigy ESC. (Plush are my favourites)

I have tried 3 different sized props on it and the most efficient is a 10 x 6E APC Prop.

I tried a 10x7E APC and it works very well but is heavier on the battery hence slightly shorter flight times. Still very safe to use if you have plenty of batteries.
I tried a 10x5E APC and it was quite OK as well but if there was a head wind it struggled. It was noticeable to me anyway.

You can see it flying here. I have fitted an U/C on it since. In fact I have built 3 of these now. 2 for me and one for a friend.
I use Zippy Flitemax 2200mAh batteries.
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Old 05-20-2016, 11:44 PM
  #30  
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Incidentally, running a motor "hard" at rarely over 1/2 throttle and having it come down with the motor "very warm" is extremely bad practice and even worse to suggest others exercise.

Ok, so we have some plane statistics listed earlier. One of the first questions, in my opinion, is how big of a propeller do you wish to spin and secondly, what type of flight characteristics/style do you wish to achieve?
No need for a system to swing a 12" prop when you only have 5 inches from prop hub to runway. Will a slowflyer prop really do my warbird justice or even get it of the ground? Things like that.

Then you figure from there taking all other airplane specifics into account.
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Old 05-21-2016, 12:35 AM
  #31  
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You are missing my point, I consciously keep the throttle low when using a 4s so I am running it as if I was running it hard on a 3s. It still is using the same watts as it would on a 3s, so it gets very warm as it does when I fly hard on a 3s. I don't let it get finger burning hot though. I wouldn't suggest others do to something that could burn up their plane, I was using a more extreme example as I tend to over power many of my planes. I know what I'm doing when I do it though. I was just mentioning how it is common belief that more voltage means more amps, but it doesn't have to even with the same prop.

Yea, the desired prop size is major, I was wanting to know what you had clearance for all along. Also too big of prop can make hand launching hard if you plan to hand launch it because the torque can roll it over at launching speeds. GWS direct drive slowfly props give good thrust, also normal slowflyer props are a good idea too, but you have to be careful not to spin the GWS ones too fast (you will know it if it starts to make weird sounds), but GWS props are flexible which is good incase it noses over.
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Old 05-21-2016, 01:00 AM
  #32  
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Better to just get the right motor....
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Old 05-21-2016, 05:51 AM
  #33  
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Originally Posted by Nutball View Post
If you are talking about peak amps from acceleration, their duration is so short that it is likely still within the ESC's burst rating. I've run my hobbyking 30A ESC hard on my slow stick at rarely over half throttle on 4s and the motor gets very warm, but the ESC is cool. With the prop I'm using I get 15A static on 2s, 25A on 3s. I might get higher amp peaks on 4s, but since I keep the motor speed around what it would be on 3s I'm running the same watts with lower amps and higher voltage.

To be honest - why do that ? Surely better to carry that LiPo weight in increased capacity at 3S and benefit from longer flight times.

Second - using full stick travel will give you much better throttle control.

Its like my 540 EPP model ... so much written about flying with 2x 3S 2200 packs in parallel ... why ? I fly mine with 5S 3000 and get more flight time than I ever need. I have full stick travel fine throttle control, motor is cold, ESC is less than the 80A then they need. I still get full 3D and unlimited ballistic vertical ! Again eCalc as the guru on that.

Nigel

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Old 05-21-2016, 05:53 AM
  #34  
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Originally Posted by birdDog View Post
Incidentally, running a motor "hard" at rarely over 1/2 throttle and having it come down with the motor "very warm" is extremely bad practice and even worse to suggest others exercise.

Ok, so we have some plane statistics listed earlier. One of the first questions, in my opinion, is how big of a propeller do you wish to spin and secondly, what type of flight characteristics/style do you wish to achieve?
No need for a system to swing a 12" prop when you only have 5 inches from prop hub to runway. Will a slowflyer prop really do my warbird justice or even get it of the ground? Things like that.

Then you figure from there taking all other airplane specifics into account.
Can I say it again ? eCaLC ?

It really does work ...

I tried Motocalc but got bogged down with 'engineering stuff' ... eCalc came to rescue ...

Nigel
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Old 05-21-2016, 02:42 PM
  #35  
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Using a 4s saved me from buying a bigger 3s. I still have great throttle control, 5s would probably mess up my throttle range. Anyway, being able to use my two 4s lipos gives me 2 extra lipos for that plane without spending more money. They are actually the same size as my 3s, so I probably get the same flight time. 4s 1800mah vs 3s 2200mah.
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Old 05-21-2016, 03:45 PM
  #36  
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Nutball,

This link was posted previously but I dont think you have read it because it is pretty clear that what you are doing is potentially dangerous for your ESC.. sure you might have 'got away with it' but that doesnt mean it's safe:

Question:
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?

Castle Creation tech support answer:
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 canít 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.

* Actually, electric power is not linear as in this example, but you get the idea.
http://www.castlecreations.com/suppo...eral.html#gen6
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Old 05-21-2016, 03:53 PM
  #37  
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Originally Posted by Nutball View Post
Using a 4s saved me from buying a bigger 3s. I still have great throttle control, 5s would probably mess up my throttle range. Anyway, being able to use my two 4s lipos gives me 2 extra lipos for that plane without spending more money. They are actually the same size as my 3s, so I probably get the same flight time. 4s 1800mah vs 3s 2200mah.
Sorry you misunderstood ... the 2 x 3S I quoted for my model is meant to create a 6S pack ... not 2x capacity.
So my 5S draws lower current than the 6S and actually gives more run-time with good performance.

I understand what you are saying about using existing packs ... but in reality you really are not doing your ESC any favours.

I know many of us fly our models at partial throttle for cruise but we still partake of full throttle at times. Your set-up as I understand is to limit throttle to partial throughout.

Nigel
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Old 05-21-2016, 04:59 PM
  #38  
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You mean that stick on the left (or right for you wacky mode1 folks) is more than just an on/off switch?

I do know a couple guys who just leave the throttle pegged and run until a deadstick landing, every flight.
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Old 05-21-2016, 08:14 PM
  #39  
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Thanks for looking out, but I know a bit about that stuff. I had a factory rated 200A ESC, I looked up the data sheet for the FETs and found it's true rating to be 129A, but the heatsink helps some, I'd call it a 140A. Also during some testing I found how partial throttle caused a lot of heating, the throttle and current draw with the motor/prop/and lipo I was using eventually balanced out so the temp would not continuously rise if the Amps were 40A or less. I have a habit anyway of checking motor, ESC, and lipo temps by feel even if I've known them to always be cool on e certain model. on 4s my slow stick ESC is always cool, the motor may get to 125 degrees if I run it hard enough.

TO solentlife; I wasn't talking about your lipos, I was just saying I had one 3s, and two 4s available to fly with and that 5s probably would mess up MY throttle range to the point it is very sensitive, but on 4s I still have very precise control. I fly some 3D and helicopters too, so maybe that helps with my touch. I like hovering my slow stick and need precise throttle control to do it well.
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Old 05-22-2016, 11:07 PM
  #40  
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Cheetah motors are made by Suppo and can be had cheaper at Altitude Hobbies: http://www.altitudehobbies.com/brush...-series-motors
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Old 05-24-2016, 05:06 PM
  #41  
Billyg
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Panther - Thank you - I am very close and have learned a lot about the motor / ESC / Battery / prop set up. I found a motor and will then find a prop battery combo based on watt readings from a watt meter.

I can't thank everyone here enough for all the input!!!

Bill
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Old 05-25-2016, 12:55 AM
  #42  
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Input watts is certainly influenced by prop but not so much by battery anymore. Gone are the days of 5c and 8c batteries. Most batteries offering a decent amount of flight time on a reasonably appropriate motor/prop combo will do just fine.
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