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
Autopilot: APM1.something
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...
Replies
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...
So, now it is pretty much complete and physically ready for test-flying. The thing weighs in, flight-ready, at 826g, which is 67g heavier than I predicted initially, however it does have some thumping great carbon fibre spars that I didn't originally plan on, as well as too much micro-balloon filler and paint...!
The layout of the electronics has taken a little bit of fiddling about. I wanted to make sure that the APM1.4 was located on the CoG. This is "glued" into the airframe with silicone, as is the ESC.
As mentioned in an earlier update, the GPS and Magnetometer are buried into the wing roots and connected via the leads to the front of the APM1.
There is also a hole for a sonar altimeter sensor which I might connect up at some point when things are settling down nicely during the flight test program.
As well as a load of micro-balloon filler used in an attempt to cover up various EPS dings as well as to smooth the wing root gaps, I also reinforced the motor mount with some epoxy-glass and an aluminium spreader plate. There's a layer of glass roving on the belly from the nose back too, to give it some skid abrasion resistance.
The foam airframe is painted in Faskolor polycarbonate-suitable acrylic paints and top-coated with Testors clear lacquer - I think this is where some of the excess grams come from. I chose a high-vis scheme to help with orientation, but also inspired by the Empire Test Pilot School colour schemes. The underside is dark blue, which you can just see in some of the pictures.
So, pretty much ready to fly, save for configuring the APM code/parameters. Flight report to come!
So, then I have been also fiddling about a little with vacuum-bagged balsa-cored elevons. These have turned out quite nicely...
The elevons are hinged with 3M Blenderm tape which is really quite sticky! They are also a little longer chord than the original foam elevons, but this was driven more by the balsa sections that were available than by any aerodynamic advantage.
Well, a few months have passed with little activity here, but in the last few weeks it has been positively feverish! Here's a couple of updates:
Firstly, after a lot of playing around with "optimising" the Turnigy AE-45A ESC, I managed to break it whilst shortening the servo lead by pulling one of the pads of the PCB. This turned it nearly to scrap, so it was off with the heat-shrink in an attempt to rescue it. This proved successful so I had to figure out how I might reattach the heatsink. Necessity being the mother of invention, I decided to mill a new finned heatsink
I then mixed up my patented heat-conductive epoxy (West System epoxy mixed liberally with Calcium Carbonate powder) and used this to glue the heatsink on top of the FETs in place of the aluminium plate and heatsink pad.
Are you really in Melbourne?
I'm in Moonee Ponds and am now on my second SkyFun and SkyWalker doing the same stuff.
Can we catch up?
Regs
Jerry
Thanks Doug!
More progress here. I have installed separate pitot and static ports in each wing. This was an old-style 3DR pitot-static kit, hence the separate elements, but bascially the wing foams are drilled spanwise to accept a 5mmx3mm carbon tube which is both a spar and a sample connection. They are then drilled chord-wise to accept the pitot/static probes. Epoxying this all together has yielded a leak-proof system exiting at the ESC bay in the fuselage.
(note, I've also modified my servo bays - somewhat crudely - to put the pushrods on the upper surface of the wing.)
The fuselage was also drilled span-wise with 10mm holes and cut to allow the GPS and Magnetometer to be embedded in the wing roots. I know this means they are glued in for life, but I checked the functionality before I did this and figure that when I want to remove them next, it's either painful surgery or the airframe will probably be totalled...
It's good for the nice clean, aerodynamic look anyway! :D
By the way, that clumsy hole in the bottom of the fuselage was going to be a perfect 16mm aperture for the Maxbotix sonar until the chuck fell out of the drill press... Oh well!
So that's it for now. I'm currently awaiting more hobbyking deliveries for a replacement motor and ESC as well as sundry hardware bits and bobs to continue the build.
It looks like there is more foam in the shipping crate than in the aircraft.
Good luck on your project!
-=Doug
So, this evening, as well as gluing extra spars-cum-pitot tubes into the wings (more on that later), I had a play about with laying out all the contents of the fuselage. Here's my best guess so far:
As you can see, there's loads of space and CoG spare to add a few things up front, like telemetry and cameras, f'rinstance!
-
1
-
2
of 2 Next