Comments

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  Anish February 26, 2012 at 6:07am

  @marco what motors do u have in mind, looks like 450 watt ones (max)
• Gerry Mostert February 26, 2012 at 5:57am

  Hi Michael

  Which brands of props in 15" are you looking at?
• 

  Michael Duffy February 26, 2012 at 5:49am

  Jani,
  
  Do you make your thrust test data publicly available?
  
  I am building a large quad, with 15" dia props. It is hard to find right and left handed props at this size so I am stuck with only a few brands.
  
  
  Thanks,
  
  Michael
• 

  Rui Manuel Cravo Marques February 24, 2012 at 7:50am

  Chris, I appreciate the facts ... and yes, I like beeing corrected, since lot of the math, units and facts miss me and I like to learn. I only tryied to put it in not mathematical terms since I've been using some different motors and the lifting and static thrust they can achieve are somehow far from what expected, so I started using ecalc and that was the best thing I encountered to help me. :)
• Developer

  Jani Hirvinen February 24, 2012 at 7:04am

  In generally those calculators and others are always wrong as they miss many important parameters like temperature, humidity, general air pressure, altitude of testing. We at jDrones are testing every week many many motors with different propellers and batteries to find out how to tune motors and how to get bet results out from those. 

  

  Theres one picture of our motor test rigs and Gap (our engineer) is running test runs for some of our test motors. 

  In last month itself we ran different tests more than 200 hours, tests are performed always with same propellers and fully charged batteries to get as accurate results as possible.

  Tests what we run are as close as possible to hover conditions and they give us a lot of good data to tune our motors.

  So far we have been running tests for over 150 different motors (our own custom and reference motors) and 8 most commonly used propellers (for multicopter uses). Based on these results there will be new even better motors coming soon.

  Motor KVs have been from 300kv to 1500kv and propellers from 6" ABS to 15" CarbonFiber, Batteries 3S, 4S and even 5S.

  Besides of technical and scientific data it's really nice to run those motors, as most of you know we are located in hot Asian country so some wind movement is always welcome :)

  Ps. No animals were harmed during these tests but few flowers have gotten hit and several batteries....

  

  jD-main
• 

  Chris Gough February 24, 2012 at 6:27am

  @Rui Manuel Cravo Marques, I agree that motors marked "suitable for a 1 kg plane" are not suitable for 1/4 of a 4kg quad. A 1kg plane requires a lot less than 1kg of thrust to maintain altitude or climb at a reasonable angle, so the motor probably produces less than 1/2 a kg of "thrust".

  Yes I have pushed a car, and yes, I was doing all the work. What's more, I have manually maneuvered an 11 ton boat too. That didn't require 11 million g of "thrust"!

  Thrust is pushing force that can be used to accelerate a mass and/or counteract drag, and is properly measured in Newtons. Measuring it in weight is a OK on the surface earth where counteracting gravity’s force against a 1kg mass requires 9.8 N in the opposite direction. That doesn't make sense somewhere with a different gravitational force though, like in space, weight is relative to gravity but thrust is thrust is thrust.

  When pushing a 2 ton car on the level, the ground is pushing up against gravity, you don't need to supply that force yourself. It would take an extra ~20,000 N to hold it over your head (Aaarg!), but accelerating it along the level ground only requires sufficient force to overcome inertia (accelerate the mass) + rolling resistance (counteract the drag). This is similar to a propeller pushing a plane, where the wings provide lifting force that carries the weight of the plane (but inducing some drag that has to be overcome in addition to the parasitic drag).

  I put it to you that a set of four motors/props that actually produce 1200g static thrust each IS almost enough to hover (but not climb) a quadcopter with an AUW of ALMOST 4800g. Not lift (climb), and only "almost" enough because some spare capacity is required for stabilisation (not all motors can produce maximum output all the time unless the airframe is inherently stable).

  I'm not suggesting anyone should take a quad with a theoretical maximum thrust of 4.8kg, load it up to 4.5 kg and expect it to fly. Given the the need to stabilise and navigate, prop unloading as airspeed increases, operation in a rotating column of air etc. etc. maybe 2kg is a more practical AUW limit for that quad (depending on how you want to use it, prop-speed of the motor/prop combo, etc).

  I think you and I would probably both agree about what constitutes a sensible amount of thrust for any given plane or multicopter. I only got all pedantic and gave you the physics refresher because you said "correct me if I'm wrong" :)
• 

  Ante Vukorepa February 24, 2012 at 6:17am

  The thrust stated in the specs is usually "static" thrust. Meaning, under perfect conditions, with 100% efficiency, you will be able to *prevent* the equivalen load *from falling*, not do anything useful with it. Which is why a hefty margin on top of that is usually a good idea.
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  Ramesh Tahlan February 24, 2012 at 6:14am

  About the issue of thrust, yes, if ur motor has 1000 g thrust, it is supposed to be able to lift a 1000g wt, however, because u never get 100% efficiency, it better to take 80% of that value, so it will lift 800g physically, that is how u calulate the motor thrust u need for a planes. so for a trainer for which u could use a 600g thrust motor for a all up flying wt of 1000g, or 700 to 800 g motor thrust for sport flying of same fly wt  of 1000g or 1200g to 1500g motor thrust for 3D. That is the direct equation and u will never go wrong. There is something called thrust to wt ration, if u have a plane of 1:1 thrust to wt ration, (good enough for sport but not 3D) then if fly wt of plane is 1000g , ur motor thrust is 1000g, but do remember that motor thrust to be 1000g do take efficiency into account so u would actually take a motor thrust of 1200g for 1:1 ration.
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  Rui Manuel Cravo Marques February 24, 2012 at 5:20am

  Chris Gough, yes me too. Correct me if I'm wrong, but have you tryied to push a car ? It has about 2000kgs, are you making that force ? I seriouslly doubt that 1000gr of thrust in spec sheets would be lifting capability but more "suited for a 1000gr airplane model", so it accelerates untill it has a speed where air can sustain the weight. I see spec of motors with 1200gr thrust with a 10" prop... put 4 of this on a quad and see if you can lift 4800gr :)
• Developer

  Marco Robustini February 24, 2012 at 4:01am

  Ecalc work fine, when I designed my X8 got it right: