Small UAV motors?

[jtprouty]

Hi All,

Anyone have any idea what motors they're using in the Raven or the Evolution UAV's? I'm not really up on electric power and need to start thinking about what motors to use for a twin motored UAV with an all up weight of around 7 pounds. Want to go with brushless motors and a single speed control. Endurance is also a consideration.

Happy flying,

Jimmy

[DiveBombDave]

There are a ton of answers that would work for you, but I'll take a shot.

At 7lbs AUW, you need (ballpark) somewhere between 50 and 100 watts per pound. So at 350watts (175w per motor), you would have sedate performance with maybe 600 ft/min climbouts. On the high side of 100wts/lb, you'd need 700 watts total (350w/motor), and you'd have very steep and fast climbs. Endurance is a whole 'nother subject. Download a free trial version of motocalc (http://www.motocalc.com) and you can pick different motor setups for a given airframe, and be told climbrate, angle, airspeed, and duration info.

Typical outrunner motors in the 175-200watt range would be stator sized (width, length of stator) 2217 or 2808. To get 350watts or better into each motor you'd have to step up to a 2814 or at most a 2820 motor. Look at Axi's as the standard, but clones lose a little efficiency for a huge money savings. Some clone motors will list their sizes as overall, instead of stator size like the Axi's mentioned above.

But if it were mine, and assuming that 7lb ship wasn't expected to fly fast (had a light wing loading, 15-20oz/sqft), I'd use an Axi 2808/24 equivalent pair, or at most a 2814. There are different "winds" of each size motor that determines whether it's power is better delivered into a smaller or larger prop (more or less). This is the KV rating, but I'm not going into all of that here. Get motocalc and do so reading over in power systems, get some finites worked out about wingspan, area, airfoil, max prop size, and AUW, and then maybe we can narrow down some choices for you.

I've really just touched on the subject, so anyone can feel free to add or criticize.


Dave

edit - forget using one speed control with BL motors. People have done it, yes, but I wouldn't.

[CenTexFlyer]

Need to look at your controller too when trying to squeeze out efficiencies. A Kontroniks controller is more efficient than say a Horizon Hobbies, but you pay for it as well. You should also look at motor efficiency at part throttle settings, because even though some motors ballyhoo great efficiencies, they may be at throttle settings that are unuseable. Try to find a motor that is most efficient at the setting you will spend the most time at.

G

[DiveBombDave]

I'll complicate things even more by adding that the specific prop will play into the duration/efficiency math. So you are looking at a specific prop turning a specific RPM to keep a specific airframe aloft (at a specific airspeed) - play with motocalc, it will get you in the ballpark and show you things like how a slow flying plane "likes" a larger prop over a smaller one, etc.

So logically I start with what prop I want for a given model, then how fast do I need to spin it for nominal power, and then LAST is what motor will spin said prop at said RPM for the least amps.

But the more money you spend on the motor/ESC, typically will get you a few more effiency points across the board. Axi, Kontronic, Neu - all top quality and top money.

Dave

[lvspark]

Get ahold of Hacker Motors. I cant remember for sure, but I think his name was Doug. Either way, they have a division that deals with this subject.

Edit: found a google page that indicated the Raven had a Aveox 27/26/7-AV electric motor.

[jtprouty]

Thanks for all of the responses. I have MotoCalc but have problems with finding all of the information for the motors that I'd like to enter. I've heard that the Neu line of motors are extremely efficient and are well worth the added expense.

I'll keep researching and post what I find out.

Jimmy