Lifting Equations...?

[Sephern]

I'm one of those people that don't like to buy things. I have a little experience with RC cars and such, but I've never been into RC planes and helicopters until I've learned about quadrotors/quadcopters. I'm incredibly interested in the lifting capabilities (I'm sorry if I use terminology wrong like lift if I mean thrust, that's why I'm posting in the newbies section so people can correct me) of quadcopters. I keep looking at equations and things online, but they're generally talking about static thrust of RC planes. I'm not sure how to translate things like that.

Basically what I'd like to know is this : If I were to make a quadcopter from scratch (please don't cling to thoughts of how, it's hypothetical), is there an equation I could use that would tell me how much mass I could lift with my quadcopter if I plug in things like the size of the propeller, the Kv of the electric motors, and the voltage of the batteries?

I'm really just looking for equations based around lifting and how to find out how big a quadcopter would have to be to lift objects. I've taken physics classes, but they never went over stuff like that, so if you wouldn't mind explaining the variables of the equations, that would be great, too! Thank you to anyone that replies with help!

 

[IanB]

Hi,

I appear to be in a similar position to your good self. I am also looking at building a quad copter from scratch. There are dozens of questions already and my drawings are still on the back of a fag' packet!

I think that there may be an equation or calculation to complete that would give us ( both ) some idea as to size, power and so on. It must, by default, include the size, pitch, and rotation speed of each rotor. I found the following page which, sort of, confirms what I suspected. It also confirms that I am too thick / dumb / numb to understand it all!....

http://www.heli-chair.com/aerodynamics_101.html

Ferociously complex stuff huh?

Would this scale down to our size of project? One can only assume that 'yes' would be the answer. Which leads me to another question... Why only 2 blades on each rotor? When I replace fan blades in some HVAC applications, the number of blades sometimes exceeds 10. Surely 10 blades provides more thrust that 2? Drag? Air resistance?

I look forward to reading your thoughts and those of others here. I also hope that we can move to completion on our respective projects.

Best regards.

Ian.

 

[Sephern]

I, too, found that site. I thought it was interesting and I began playing around with a calculator I made for it in a Microsoft Excel spreadsheet. I also found this site : http://personal.osi.hu/fuzesisz/strc_eng/ which I found helpful, though I'm not sure if it's very good for what we want. Is static thrust the same thing for us as lift would be? If I had (let's stick to 2-blade props because it's hard to find large props with 4) four 26"x10" propellers (using inches, sorry, American, looks like it comes to be about 66cm x 25.4cm) we could lift like 400lbs or a little under 190kg...But then what kind of motor would we need to turn those props? I used 9000 RPMs in my calculation, but what would we need in terms of a motor to turn that prop 9000 times in a minute?

 

[IanB]

Hello again,

Hmmmm - Even more confused now. I am sure that lift is different from thrust. More force is required for lift I am sure ( I may be wrong - perhaps others can confirm? ). Motors can be readily bought as many others have already proved to the both of us. I need to spend some more time looking both here in the forum and on the " googleness ". Lifting 400lbs is going to require some really, really, really, heavy duty battery power and motors..... frankly, I doubt that can be done without spending some serious money!

I keep playing with the calculator and my anticipated total load. I feel that I may actually be making some progress too. I will keep you posted on progress.

I have found a good source of nuts and bolts too. A local guy here sells them by the shovel load. I can pretty much source anything from M1 right up to M16 in stainless and other nice stuff. Let me know if you need any. They will be for postage only!

Regards again.

Ian.

 

[Sephern]

You're definitely right about the motor and battery. Looks like for really heavy lifting you have to get into some serious money or go for gas. The heaviest I've seen anyone lift with a quadcopter so far was 33kg, and it wasn't really a quadcopter, it was an X9.

Pretty cool video. also ecalc seems to have a good calculator if you're looking to build. I honestly was just looking to design, I don't have the money or space to build right now. Also, from other forums I've found that the general rule of thumb is if you do a thrust to weight ratio of 2:1. Good luck! Let me know if you end up try to do some heavy lifting, and if you build I'd love to see your results!