Comments

• 

  Anish February 26, 2012 at 6:07am

  @marco what motors do u have in mind, looks like 450 watt ones (max)
• 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.
• Developer

  Marco Robustini February 24, 2012 at 4:01am

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

  
• 

  Chris Gough February 24, 2012 at 3:45am

  Pay attention, sometimes motors have in their specs the thrust, but it's not lifting thrust but horizontal thrust (for planes)

  ??? I thought thrust was thrust.

  motocalc works well for me.
• 

  Ellison Chan February 18, 2012 at 9:36pm

  Well, 850kv @ 20amp would probably generate over 1kg thrust per motor.  So your flying weight with the gopro is over 4 kg?  That does seem like a heavy drone.  If you're really over 4kg, you should probably be looking at a hexa or octo.  Since if you try to find motors for a quad that can lift greater than 4kg, you're talking about expensive motors and escs.
• 

  Ellison Chan February 18, 2012 at 9:02pm

  Adli, what kv motors come with that frame?  12x45 sounds like they're big for a 20amp rated motor..  Adding another battery in parallel will likely make the lifting ability worse, since there will be the extra weight of the battery added to what you say is an already heavy drone.
• 3D Robotics

  Chris Anderson January 29, 2012 at 3:06pm

  Gage: You'll have to post info on your whole setup. If you're not using the official 900Mhz telemetry kit, I won't be able to help you. (I've never used anything else)
• 

  Kirill December 22, 2011 at 10:50am

  Gage, you can find the info here:

  http://code.google.com/p/ardupilot-mega/wiki/Wireless