Prop Size and Pitch

Discussion in 'CineStar FAQ - Tips and Tricks' started by Josh Lambeth, Sep 1, 2012.

  1. Peter Gøthche

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    Hmm well if you already have them then try them out and take it from there
     
  2. SteveWilson

    SteveWilson Member

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    We generally fly the APC 13x6.5 on our CineStar 8s - we run pretty heavy with 4 batteries and we've found that we are slightly over-propped with the APC SF 14x4.7 - especially in the summer - our esc temps just get too high when parked in a hover. Constant flying around keeps everything nice and cool though.

    We've done extensive tests and our results were the opposite of spyde. With no load - just a CineStar 8 and one battery we get about 10% more flight time using the 14x4.7s.

    When we are fully loaded, 4 batteries and a gimbal, etc the 14x4.7s loose some of their advantage - we were only getting about 7% more time over the 13x6.5s.

    Bottom line - if heat isn't a problem for you I think the 14x4.7s are the better choice.
     
  3. Peter Gøthche

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    Maybe its the shape of the propeller
     
  4. SteveWilson

    SteveWilson Member

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    Bigger props are just more efficient.
     
  5. Dave King

    Dave King Well-Known Member

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    Great thread. Anyone else do any more testing?
     
  6. Peter Gøthche

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    I got great results with thes, 15 min on 6000mHa 6s image.jpg
     
  7. Peter Gøthche

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    And alot better Wind performance
     
  8. kjetil tønnesen

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    I only use 13x6,5 carbon and 5cell on cs 8 and nothing else
    i have tried them all ,but i think 13x6,5 is a class off it self,big differenc in fligt and also in wind from the other props
     
  9. Dave King

    Dave King Well-Known Member

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    How heavy is your C8? What camera are you using? Just trying to get an idea so I have something to compare to.
     
  10. kjetil tønnesen

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    i fly with 360 gimble and sony 730
    my cs 8 is about 5,5kg when i fly it
     
  11. Gary Kaplan

    Gary Kaplan New Member

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    Hi Josh,

    I just wrote this dissertation :) for another member. I come from the R/C Heli and fast plane world (125MPH+). This comes from my EE background but also most importantly from my experience with how these parameters matter to RC heli's and planes. The answer to your question lies in the combination of motor you are using, the battery and the prop. Only use a wooden prop on a motor that has a high pole count and therefore a lot of torque to turn the heavier prop (as compared to a plastic APC SF (slow-fly) prop. A motor with a small number of poles (and windings for that matter) are not efficient and as it tries (but can't) turn the prop the wasted energy is turned into heat in the motor. Let me know if this helps. If you want some bad ass motors to give you some real power look at these. They are not cheap but you will be amazed at what they can do.

    http://www.neumotors.com/Site/Welcome.html

    There are many different (important) electrical and physical parameters regarding brushless motors and batteries like those used on all electric heli's. It takes a little explaining so please bear with it. :)

    Principle 1.) Kv = The motor will turn (the propeller) 1 revolution per 1 volt (V) of the battery that you use.
    In the case of a LiPo (Lithium Polymer) battery each cell is 3.7V (volts). The term "S" is used to describe the battery pack. So, a 3S battery has 3 cells and is 11.1V (3.7 volts per cell x 3 cells). A 4S battery is 14.8V (3.7 x 4), a 5S battery is 18.5V (3.7 x 5), and a 6S battery is 22.2V (3.7 x 6). Using what Quadcopter calls their "heavy lifting motor", the QC-3328; it is rated at 700Kv (but they call it "no load speed"....I'll explain in a minute). So, if you use a 6S battery for your heli (22.2V) and a 700Kv motor you get 22.2 x 700 = 15,540RPM out of the motor under no load, meaning "without a propeller attached to the motor. Just the motor shaft spinning by itself. If you used a 4S battery instead of a 6S you would get 14.8 x 700 = 10,360RPM under a no-load (no propeller) condition.

    Principle 2.) Propellers create a load on the motor (see above)! ;-)
    Once you put a propeller on the motor everything I just said above goes out the window! The theoretical RPM you calculated using the motor Kv and battery voltage goes way down. The reason is the motor is now loaded up with the effort needed to spin the propeller. The diameter of the propeller and its pitch (the angle the blades) will affect how fast the motor can turn. Increasing the propeller diameter will make the motor work harder (which generates heat) as it tries to reach (but can't) its theoretical max RPM at full throttle/power input from the transmitter (calculated in principle #1 above). Motor manufacturers will tell you about "recommended prop size" to use because they have tested a bunch a sizes for you and found which ones give maximum RPM (thrust or "lifting power") while staying within the boundaries of voltage (and current), and heat the motors can tolerate.

    Principle 3.) Motors have different number of "poles" and "windings" (the number of turns of wire wrapped around the pole inside the motor housing). Each one of these spec.'s affect the motors torque ("horse power") or it ability to turn the propeller under load. A motor with a small number of poles (like a 6-pole motor used in a regular R/C helicopter or Jet "ducted fan") will product less torque than a 14-pole motor used in a airplane or a hex-copter. In a regular RC heli the 6-pole motor turns a gear which in turn spins the rotor shaft that spins the rotor blades. The gearing system steps up the slow turning motor RPM into higher "head speed" of the rotor blades. A 14-pole airplane motor has a propeller mounted directly to the shaft of the motor in the same way a hex-copter or oct-copter does. The motor has enough torque to directly spin the propeller by itself.

    Principle 4.) Max Current (A): is the maximum amount of current that the motor (and speed controller) can handle going through the windings of the motor. Pull too much current through the motor and the too much heat is generated and the windings burns out, the motor stops turning and your helicopter crashes. The size of the propeller affects the amount of current taken from the battery (making the battery hot) and put through the speed controller and the motor itself. If you keep putting a larger and larger prop on the motor and run it you will find this limit (something you don't want to do). So, you have to stay within the maximum current rating of the motor by using the proper size propeller for the type of motor that you have installed.

    Principle 5.) Max Voltage (V): is the maximum battery voltage the motor (and speed controller). Manufacturers will specify maximum voltage (usually. Sometimes they don't and they just give max current and power input and you have to figure out what prop to use to stay within the recommended range) for the motor. They will state something like "Voltage Range 11.1~14.8V (meaning a 3S~4S battery), or 14.8~22.2V (4S~6S).

    Principle 6.) Power into the motor (mechanical power) = Voltage of the battery pack (V) x current through the motor (A). You have to stay under this power rating of the motor to avoid burning it out. If you go up in battery voltage (like from a 4S battery to a 6S battery) the current will go down and the motor will run cooler. You can then keep increasing the propeller size until the current reaches the maximum level. Conversely, if you keep the battery pack constant (say you are using a 6S battery) you can raise of lower the current coming out of the battery and through the motor by increasing or decreasing the propeller size. So you again will see a recommended propeller listed. The smaller diameter propellers will have a smaller load on the motor and will increase the RPM and give more speed to the heli but will suffer less thrust and therefore less "lifting capability". This is good for a shoot if you want to fast and you'll be carrying a small Go-Pro or DSC. A large diameter propeller will turn slower (lower RPM) and will not go as fast but you will have more lifting and can carry heavier loads. A heavy wooden prop also creates a larger load and will generate too much heat for a motor that isn't meant to drive that kind of prop as compared to a light weight plastic APC Slow-Fly (SF) prop with a large diameter but very little pitch.

    Summary: So you take upgrade your motors to something that has a high pole count (like 14 pole) so you can spin a large prop, can take a good amount of input power (W) and current (A) and high voltage (such as 6S) and decent Kv for speed (RPM). Then you can use a variety of propellers to suit your needs at the time.
     
  12. Jose Luis Ocejo

    Jose Luis Ocejo Active Member

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    Thanks Gary for your time to write this detail explanation is the best I have read
    Thanks
     
  13. Chakradhar Raju

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    Very detailed and easy to understand explanation.....true EE Guy.....
     
  14. Chris Odom

    Chris Odom Member

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    Clear and concise. Even though I understand the principles on their own, individually, your explanation helped me put them all together into a system.

    One question I have is how does pitch relate to all this? Is there a baseline pitch number that is a standard? If you increase the pitch you are increasing the amount of lift generated=greater load on the motor=greater load on the battery. If I am using a 15x5.5 prop, what would be the cost/benefit analysis of changing it to say a 15x8 or a 15x4? Conversely, how would a 13x6 or a 14x6 affect this in relation to the othe prop sizes?
     
  15. Gary Kaplan

    Gary Kaplan New Member

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    Chris,

    There is no standard spec for a prop that is used for any type of multi-rotor helicopter. The prop used is based only on the capability of the motor to turn it (while staying within its voltage, current and heat limits), the batterys ability to provide (source) the current required, and the ESC's ability to take in/pass (sink) the required current to the motor. The motors # of poles determines its turing strength (torque) and the # of windings determines the speed (Kv) that it turns (per voltage of the battery.

    You can think of prop diameter and pitch in terms of a car or motorcycle engine. The amount of torque of the engine will determine how fast the car can pull away from a dead stop (this is the diameter of the blade). The amount of horsepower (HP) of the engine determines its top speed (this is the pitch of the prop).

    A car with lots of torque and and little HP would be able to pull away from the line quickly but will soon reach its top speed. Its like having an awesome 0~60MPH time and then finding out that it takes a long time to get to 70MPH and then wont go any faster.
    Conversely a car with little torque but a lot of HP will leave the line slowly when you step on the gas but as you hold your foot down the car will continue to slowly go faster as faster until finally reaching lets say, 150MPH.

    Both increasing prop diameter and increasing pitch will cause the motor to draw more current from the battery, and depending on the efficiency of the motor you will increase the acceleration of the helicopter, the top speed of the helicopter and/or heat in the motor.

    Lets assume your motor is capable of handling more power (Watts) than it is producing now: If you keep the diameter of the prop constant (15") and just increase pitch you will have the same amount of thrust (lifting capability) but you will
    get more top speed if you keep it at full throttle for a bit longer. If you keep pitch constant and increase the diameter your top speed wont change but you will have more thrust (lifting capability or acceleration from a dead stop if you havent added more weight).

    There is no direct relationship between diameter and pitch with regards to increasing current. Like I explained earlier the increase in current you see will depend on the design of the motor that you use (pole count and winding count).

    You have no choice but to try one, land, look at your flight data (current and/or Watts), decide if you want more speed (pitch) or acceleration/lift capability (diameter), then change the prop accordingly, fly again, and read data again. Then adjust the prop again until you get what performance you want or need. Fly, read data, change prop, fly, read data...its a simple as that.

    Keep a log book and record the data for that specific motor you are using so you can change props based on the flight you need.
    For example, carrying a small camera but following a fast moving car, or carrying a large camera while hovering and slowly moving from place to place.

    If you are not carrying a camera and just flying for fun the maximize both diameter and pitch for quick take offs and fast top speed.

    Did that help?
     
    MIke Magee likes this.
  16. Chris Odom

    Chris Odom Member

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    Thank you again Gary for such a concise and clear explanation. I believe I understand-mostly...

    So, if I am understanding correctly, if I wish to maximize my flight time within my given tested parameters (payload, battery, motor and prop configuration) could I simply lower the pitch?

    For example, under my current tested configuration I am able to swing (6) 15x5.5 in carbon fiber props on tiger navigator 4014 kv400 motors with dual 6s 5200mAh batteries for 13 mins landing at 21.0 (3.5v per cell). I am maximizing my lift (15in prop) and by changing the pitch up or down, could I extend my flight time by sacrificing my top speed? Or, if I lower the diameter to say 14in at the same pitch (14x5 or 14x4.8) would this extend my flight time at the sacrifice of thrust?

    Sorry for the noob questions. This has been one area that I haven't fully explored due to so many questions and possible configurations. In my last build, I went with the suggested prop configuration, tested it for my application and just kept it there, mostly due to the fact that my gimbal limited the size of camera I could place underneath. Now with so much flexibility with my CS 360 gimbal, I want to fully understand the relationship and trade offs for different prop sizes.
     
  17. Gary Kaplan

    Gary Kaplan New Member

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    Chris,
    No need to applogize for the "noob" questions. I jumped into this thread to provide some information because of posts from others who obviously dont understand their system and how everything is interrelated. Those misinformed posts are from veterans, pros, "experts", whatever you care to call them. Either way they dont know what they are talking about. Your noob questions show you have the ability to grasp the concepts, understand them and then ask a good follow up question. So again, dont applogize. I like to help those such as yourself who are willing to learn and open to assitance. Its funny how I dont get asked questions from the "experts" because they think they know what they are talking about but in fact they do not. Study these basic concepts because if you can understand them you will be able to properly apply the knowledge with every heli you build from now. The same rules apply to airplanes if you end up getting into those for aerial work or just fun.

    Now with regards to your question: everything you do to reduce your helicopters current consumption will increase your flight time (assuming you dont change the voltage, capacity and discharge capability of the battery you use). If you change anything with regards to the battery spec you have to start the analysis all over again. But if longer flight time is what you are looking for here is the list of things you can do. Reducing the amount of current consumption of the (total) system is just one of them. I will also assume you will be using your heaviest camera and the weight of the batteries is not going up (meaning you dont go up in capacity, mAH, and you stay at 6S).

    To increase flight time the goal is to either reduce the amount of current consumed OR more efficiently use the the current you are already consuming (these are in no particular order in terms of cost or level of impact because you will have to look at your flight data to tract current (A) consumed or power (Watts) produced). Also, remember that heat produced in the motor is wasted power. Always monitor motor heat. It will tell you a lot about your heli's performance. Buy a simple infrared thermometer to monitor motor heat. Look up your motors maximum heat spec and adjust prop to stay below the maximum temp. Check motor temp immediately after every flight to keep on top of potential failures. With that in mind also keep you motor bearings lubricated with bearing oil. This will keep the motors running cooler, will extend motor life and will help avoid inflight (fatal) motor failure. People make this mistake more than all others. Motors need regular maintenence to keep them working properly!

    1.) Reduce prop diameter (amount of current reduction will depend on motor design spec)
    2.) Reduce prop pitch
     
    Chris Odom likes this.
  18. Gary Kaplan

    Gary Kaplan New Member

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    Continued...
    3.) Reduce weight of the heli
    4.) Use same capacity battery but with higher discharge capability (C rating). Use 65C batteries if budget allows.
    5.) Use motor with higher efficiency. Current is used to turn the prop and doesnt turn into heat.

    Hope this helps.
     
    Chris Odom likes this.
  19. Chris Odom

    Chris Odom Member

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    Again, all makes total sense to me. I feel I am starting to really understand the dynamics of how they all relate to each other.

    Here's my thoughts on further prop testing... considering that I can not go up any further in prop diameter (15 in is my max) so that part is settled. As for pitch, I know enough about my consumption to at least have a base line from which to judge. My thoughts are that I will be able to get longer flight times and more stability if I go with a 14 in prop and keep my pitch about the same (14x4.7 seems to be close enough). I think the tiger 4014 400kv will be able to handle the payload just fine and without increasing the amount of heat generated. In relation to my batteries, I am using a 60c/75c burst rated 6s battery so I feel that I have maximized all the parameters. I do wish I would have used a 50-60A ESC in retrospect but so far my maytech 45A ESCs have not been close to hot (temps stay constant around 40.5-41C).

    Considering your list of suggestions, these are the only parameters I can change.

    As for motor maintenance, do you have a recommendation for a particular brand of bearing oil? What about intervals or suggestions of warning signs (besides an increase in motor temps?) to keep a eye on? Any other motor maintenance tips? I was under the impression that there wasnt much to do beside keep the poles clear.
     

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