Friday, February 6, 2015

Building a QFO - That motor situation.

The QFO is a fiberglass shell, 250 class, quadcopter frame.  The bare shell is about 65 grams. HobbyKing claims 47 grams.. but I think that's without any landing gear, or magnets installed.  "My QFO, ready to install motors" was 65 grams.

Speaking of motors, that's the subject of today's blog post.  They say the frame is designed for 1506-2208 motors.  If you look closely, you'll see that my motor is an 1806.  It will not fit in that hole. 

I mean, that "really" does not fit.  My Turnigy 1704's will fit, but these DYS 1806's are a no go.

The material that makes the frame is very nearly paper thin.  It's thinner than cereal box cardboard.  So running a dremel around in the hole very quickly takes care of the hole size. 

If you're sharp eyed, you'll see that's not actually a dremel.  It's a $9 "multitool" from Harbor Freight.  It's DC, quiet, and I expect it to last all of say.. one project. 

What I really like about this airframe, is that the motors end up recessed.   I think it's a really neat look.  I'm also wondering how you'd get a 22mm motor on there.  As you put in bigger motors, you're going to have less and less fiberglass to mount to.  I think putting 22mm motors on there would probally just lead to them ripping off in the first crash.  I wouldn't try mounting anything bigger than a 18mm motor internally.

I found that mounting the motors to the bottoms of the arms is a valid mounting solution, and while they don't end up recessed, you get around the prop clearance issue, and you retain all of the strength of the arm.  And with the additional prop to frame clearance
The QFO doesn't have a whole lot of internal space.  Stuffing this airframe is going to be a challenge, especially since I plan on getting some reasonable endurance out of this, and hanging an 808 based camera underneath it.  

Here I have all the motors installed, a 1500mah 3s battery, a 200mw 5.8ghz transmitter, a LED power supply, an OrangeRX reciever, an ESC, and the Flip32+, are all in the frame. 

The only way to get the 1500mah 3s battery in there is across the X.  It will fit longitudinally, or transversely if you rotate it after you install it, but having to rotate it after it's put in the airframe means I can't use the corners to hold the VTX or reciever, or LED power supply.  This does make me wonder how it will fly, as the big battery is going to make the polar moment very different across one axis than the other.  It will induce a diagonal pitch movement every time it tries to tip to go forward, or slide left and right. 

We'll need to see how that works out. 

Getting good flight time from an airframe has a lot of factors.   You need raw watt hours to power the motors.  You need lift to get those watt hours into the air.  You need to not waste energy.  Not wasting energy, really means having an aerodynamic frame, and efficient props.  The QFO is "designed" for 5x3 props, which aren't exactly stellar when it comes to turning motor watts to thrust.  So I decided to try a 6x3. 
It fits!  But only just barely.  That really is just 3mm of clearance under that blade tip.  But "any" clearance is enough to make this work.  Hopefully it won't induce to much airframe noise.  I plan on mounting the FPV camera through a hole in the side of the frame, without any vibration damping, so I may be forced back to 5x3 props in the end.  
5x3x3's always have looked good to me.  So I threw that on a motor to see how it looked.  Sadly the extra x3, while it does produce more lift, you also get 50% more tip losses.  I think 5x3x3's will lead to reduced flight time versus 6x3s.
 So that's it for the first night of building.   I still need to relieve each motor hole just a little.  And then I can get to figuring out how the ESCs will mount.  I think they're going to get foam double stickied tape to the inside top of the airframe.

No comments:

Post a Comment