Author Topic: New build - RCME Bambina  (Read 12277 times)

angry_muppet

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Re: New build - RCME Bambina
« Reply #15 on: January 18, 2018, 10:56:15 AM »
The prop will be a 6x4, as recommended.

Not sure of the all-up weight, but electronics are about 200g. I guess the airframe will be at least 300-400g?

angry_muppet

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Re: New build - RCME Bambina
« Reply #16 on: January 18, 2018, 22:06:58 PM »
Seems my guess-timation is way off! Design weight is 300g (10.5oz in real measurements  ;)) with a wing loading of 9oz/sqft.

Spec is:
31" wingspan
189sqin wing area
10.5oz weight
9oz wing loading
24" long
2050kV 2321 motor
6x4 prop
350-500mAh battery
11A peak power
Power/weight: 189W/lb

Happy Days

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Re: New build - RCME Bambina
« Reply #17 on: January 18, 2018, 22:30:11 PM »
Ha!,at full throttle she'll be very fast I'd say.
It'll either put a smile on your face, or something less welcoming in your pants! :)
Try not to run out of airspeed, altitude and ideas....... all at the same time.

angry_muppet

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Re: New build - RCME Bambina
« Reply #18 on: January 21, 2018, 13:36:13 PM »
I'm making loads of mistakes...  :-[

Power is 120W, but that's 189W/lb!  ??? I can see visions of underwear filling moments already!

I got the recommended motor delivered yesterday... The mounting bracket is MUCH too big for the firewall. Thankfully the screws are long enough to mount the motor directly to the firewall.  Downside is that the cowling I'd already made won't fit around the motor. Today's job!

Quick question; is it sufficient to just secure the control snakes as is, or would another retainer at the end of the fuselage be recommended? I'd be of the tendency to over-engineer and add additional support...

angry_muppet

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Re: New build - RCME Bambina
« Reply #19 on: January 21, 2018, 16:19:13 PM »
After a frustrating afternoon, I finally got the 2mm motor and battery connectors soldered to the ESC. Even with a pair of crocodile clip "helping hands", it's damn fiddly!

Motor is mounted and it's now a matter of trying to figure where the battery will fit to keep the CoG on the spar so I know where to place an access hatch. The model was designed to remove the wing to replace the battery - not my preferred method! It's busy inside the fuselage at the moment, but there's room to place the ESC and battery side by side just ahead of the LE. I estimate the CoG should be approximately correct with that.

Happy Days

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Re: New build - RCME Bambina
« Reply #20 on: January 21, 2018, 19:13:45 PM »
All looking good David. :D
Points to note
Speed controller: I see the ESC is only rated to 12 amps. Too late to change it now as you've already bought it but if the motor is going to draw 11amps it would have been safer to have an ESC rated to about 14+amps
At high power levels the ESC will likely get quite warm/hot, as will the motor. They will need some cooling so place them where there will be an inrush of air. (And allow for an outrush as well because if the incoming air can't escape then no air will flow.) The battery can also get warm BTW. So bear these facts in mind when you're deciding where to locate them.

Question: Is the diameter of the wires from the Red (so called) BEC connector, (the one that will connect your battery) the same as the diameter as the black & red wires from the ESC?
I didn't think BEC connectors were rated to 12 amps, though I might be wrong. :-\

Little Keith
Try not to run out of airspeed, altitude and ideas....... all at the same time.

angry_muppet

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Re: New build - RCME Bambina
« Reply #21 on: January 21, 2018, 21:22:01 PM »
You and I both know that this won't be flown at full chat... At least for a long time!  ;). The ESC has an additional 16A (10s) burst capability, so hopefully will be ok.

SBEC is rated to 1A, so I hope that's sufficient for 4 9g servos... If not, I need to order clevises, nylon wing bolts and a few other bits, so could still replace the ESC with something a bit meatier.

Have been wondering about the cooling; I'd like to keep it aesthetically pleasing rather than just functional.

EI1638

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Re: New build - RCME Bambina
« Reply #22 on: January 22, 2018, 13:38:03 PM »
Soldering Bullet Connectors (either gender):

OK, I know it would have been useful to know this before hand, but for the next time...

I use a scrap of MDF that is drilled to take the bullet connectors I want to solder.
Ideally the connectors are a sliding fit into the holes (not too loose).
Just whack the scrap of MDF into a vice on the bench, or clamp it to the bench (the fewer things to move the better), insert the connectors you want to solder (cup/bucket/wire end up), tin the wire ends and solder.

This way the only heat loss is through the wire as the MDF isolates the connectors from the vice/clips, and whilst it would help to have a third hand, it's not absolutely necessary, as only the soldering iron and the wire can move.

Depending on the size of wire being soldering I use a lolly stick and rubber band tweezers to hold the wire. Thicker wire sizes can get un-comfortably hot to handle during the soldering phase. No need to ask how I figured that out...

All told, the time spend cutting/drilling the MDF is more than compensated for in the much faster soldering time (and generally much neater soldering finish)

Chris

angry_muppet

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Re: New build - RCME Bambina
« Reply #23 on: January 26, 2018, 22:14:51 PM »
I've a few offcuts of MDF and more soldering to do, so I'll take that advice for the next batch!

Latest few nights have been frustrating and not exactly productive... The rear of the fuselage is covered with either curved balsa or planking; I chose planking... I'm not sure if trying to cut and curve the balsa wood have been easier.  :-\ The practice was required for the next build planned, so had to make a try at it.

There are a few gaps, but as quite a bit needs sanded off, I'm hoping that won't matter too much.

The cowl is being a serious pain. A square profile isn't easily rounded given the lack of clearance around the motor.

angry_muppet

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Re: New build - RCME Bambina
« Reply #24 on: February 02, 2018, 20:10:07 PM »
After a week of not getting near the bench, I've had about an hour. Enough to sand the rear planking, which I think has turned out ok. Some discoloration in the wood from the laser (I used scrap from the laser cut parts), but no gaps that I can feel...

Started putting the necessary top on the fuselage front with a gap for a hatch.

Also went back to my first attempt at a cowl for the original (too small) motor and hollowed out out with a dremel.  It fits, but cooling may be more difficult.

angry_muppet

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Re: New build - RCME Bambina
« Reply #25 on: February 11, 2018, 22:26:21 PM »
After a mental week where I couldn't even think about planes... I finally ordered the blind nuts and polypropylene wing bolts to allow me to fit a wing mounting plate. Unfortunately, said plate is installed below the servos (as per plan), so they needed fitting first. Perhaps I might be able to cut a slot for a screwdriver to fit through should the servos need accessed.

I've left a section of the upper forward fuselage so I can (hopefully) access the battery without removing the wing if the CoG and access permits. Failing that, I can just glue it closed and take off the wing.  :(

Happy Days

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Re: New build - RCME Bambina
« Reply #26 on: February 12, 2018, 06:49:40 AM »
You could always recharge the battery in situ, between flights David. Save having to "dismantle" the plane! ;)
Try not to run out of airspeed, altitude and ideas....... all at the same time.

angry_muppet

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Re: New build - RCME Bambina
« Reply #27 on: April 13, 2018, 20:28:19 PM »
After not having a lot of time to spare, I finally got a bit more done.  It's a much slower build than it should be, but the journey is almost as much fun as the destination.

Belatedly discovered I mis-built the fuse and put the firewall in to far forward...  For better or worse, I decided to cut it out and reposition it to the correct location. By my measurements, it appears to have remained square. I want it to be, so I acknowledge that may be due to "confirmation bias"!  :-[

Anyway, I have the hinge slots cut on all control surfaces; only the ailerons remain to profile for smooth operation. Everything fits perfectly, so I must have done something correct?

I've dry fitted most of the electrical gubbins to try and find the positions to achieve CoG on the main spar.  Man is it fickle! Move the battery a little forward and the nose drops like a ton of lead. Move it a little rearward and the tail goes!  More perseverance required.

Need to order more film covering, so the Director of Finance suggested a yellow wing with navy flashes... Not sure of what colour to do the fuse.  She protests at the concept of a "fleet scheme" of white and red.  ;)

angry_muppet

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Re: New build - RCME Bambina
« Reply #28 on: April 14, 2018, 21:30:11 PM »
And the firewall is not square.  >:(

It's angled right at perhaps 1 - 2° but is square in the vertical plane.  I hope that as right thrust angle on a CW prop is claimed to improve something, it won't matter too much and I can claim it was deliberate.  :-X

The forward upper fuze is detachable for battery removal. Otherwise I can still glue it shut.  :)

There is a plywood ring to close off the front, but I've added a vent on the underside to aid cooling.

angry_muppet

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Re: New build - RCME Bambina
« Reply #29 on: May 26, 2018, 15:15:40 PM »
It's taking it's time...

But finally started to get the covering on.