Well, after a long time in the theoretical world, I decided it's time to see how APM works in reality, so I splashed some cash and ordered this and a bunch of other parts from Hobby King:
At this point, my MS Excel OCD set in and I felt the need to figure out how I could package everything and still achieve a good CoG position. Taking the front of the launch finger holes as the published "ideal" CoG starting position, and the nose of the fuselage as my zero moment reference, I weighed, measured and calculated* the following:
I was surpised that this arrangement seems to put the battery way out in front - much further forward than I anticipated, which will give me some good headroom to add other, lighter things further forward. I can also double the battery capacity moving the pack CoG back to 345mm, which might be a handy thing!
So, my initial spec will be as follows:
Motor: NTM Prop Drive 28-36 2200Kv
ESC: Turnigy AE-45A
Sensors: MT3329 GPS
MPXV7002DP Pitot-static IAS
MHC5843 remote Magetometer
LV-EZ0 Sonar Altimeter
Servos: HTX900 9g
Radio: Futaba R617FS decased
Battery: Zippy Compact 4S 25C 2200mAh
More to follow as the build progresses.
*after ripping all the stickers off...
RIP Skyfun... If it's any consolation Andrew, it was quite spectacular!
Yes, it was a pretty high-energy crash. I'm finding missing connectors and capacitors here and there on the boards. Designing electronics to survive crash damage is a bit of an art, I'd say...
OK, so Skyfun Mk2 is in gestation and I've got a bunch of new stuff planned, including telemetry and REVERSE THRUST!
Here is my new Turnigy ESC with reversible (SimonK) firmware loaded up and functioning. I am a happy boy right now, having conquered the mysteries of AVR flashing - don't ask me too many questions about it though!
Skyfun UAV build 2.0 is in full swing now with the weekend's work producing a concept for removable wings. This is to improve the transportability and shipping of a fully-built airframe. The main wing spar (5mm carbon tube) slots into a central spar carrier (6mm tube) that passes through the width of the fuselage
The wing incidence is held with forward mini-spars in the same sizes and manner, excepting that they don't pass through the entire width of the fuselage. I intend to make the servo plugs connect directly with the plugging in of the wings by bonding the connectors into the right position. The holding-the-wings-on-tight mechanism is still to be developed. I expect it will be tape at the wing-fuselage join for aerodynamics purposes as much as keeping the thing together.
I use a 6mm main spar on a 600mm wingspan 600g plane that flies much slower than this and have had spar failures and flies with noticable flexing. I'm concerned that your 5mm spars will not be strong enough given the speeds that this flies at. I am also building another one of these for the Ardupilot.
I'm still experimenting with the design of how this will go together, so some changes are likely. Having said that, my original Skyfun ran a 5mm split spar with no problems. On reflection, I don't think it's actually that effective in bending since the EPS foam wing is quite stiff already. I plan on experimenting with laminating the entire airframe with glass/epoxy too to improve general handling robustness. It's worth about 70g in extra weight which I may be able to recover by hollowing out some of the foam in the fuse and possibly wings.
"Fun" project ;) Looking forward to progress on Mk2.
How to polish a turd 101:
Well, never one to leave things well alone, I am somewhere along the homeward stretch on my next Skyfun airframe.
I have abandoned pretensions of making it break down for packing and glued it all together, laminated it with epoxy and random layers of 18gsm woven glass after cutting big holes in various places for electronic gadgets and ze vires.
Here is the current status of the basic airframe, including embedded GPS, magnetometer (together at the starboard wing root), telemetry radio (port fin) and, of course, elevon servos (in the wings, stupid!). All up, this weighs currently 400g - would weigh 260-270g without all the slap.
Projected flying weight with a 2200mAh 4S battery is around the 925g mark - a hundred grams or so more than last time, but with telemetry, which I'm looking forward to using.
Oh, I should add, it's not just the airframe that's put on the pounds. The GPS/magnetometer is much heavier and the servos are metal geared thingies. The proposed ESC is lardy but APM2.5 is at least lighter than APM1.something and I have eliminated or minimized a lot of ze vires, compared to before. I am also adding a APM power module thingy for learning some more about motor operation in operation.
All of this extra weight is to ensure this really is heavier-than-air flight. (of course!)
In the past I used kkflashtool to flash Simonk to my ESC's. However, I can't find a hex file for the reversible version and I don't know how to set parameter RC_PULS_NEUTRAL.
What application is required and how is the reversible version implemented?