News from other threads:
1) motors are now 2806.5, 6 per, ganged in sets of 3 per prop.
Props are back to 9x5.
this gives 128 A for static thrust each prop, up from 54.
This seems a bit odd, given the 3 motors are running at a more efficient speed at static loading.
News from other threads:
1) motors are now 2806.5, 6 per, ganged in sets of 3 per prop.
Props are back to 9x5.
this gives 128 A for static thrust each prop, up from 54.
This seems a bit odd, given the 3 motors are running at a more efficient speed at static loading.
<Rambling number spouting follows-ends at next dotted line>
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Minds you, this compares the 1800KV motor that could run the 9x5 at around 13000+ rpm (of 28800, 45%)
The loading sounds odd - normally motors won't go below 65% of KV rpm??? that would be 18720 rpm
Maybe rpm was as that high, with 2016gf, 867w, 54 A.
Assuming 48% efficiency at that point, =416 w real at this loading.
Compared with a single 1300KV, which wouldn't run the 9x5 at all.
further 1800KV specs - drop w div by 1.3 = 320 wats "rated" (by me, 77% point)
amps should be / 1.5 = 36 amps. rated.
a check is the Kv/Kt calculation.
Kv = 1800 x 2 x pi / 60 rad/volt-s = 188
Kt = 1/Kv = 5.3 x 10^-3
and Torque = A x Kt = 36 x 5.3 x 10^-3 = 0.19 N-m
Then power = rev x torque, def 77% rev = 22,176, in rad/s = 2322
pwr = 0.19 x 2322 = 441, so my amp calc may be high or my efficiency calc may be low.
This is higher than my assumed real power at full load! - efficiency may be a little higher, say 52 % at that point.
That can be iterated out, depending on only 2/3 of the amp change being related directly to power;
the rest is due to power factor, or inductance.
(may be more like 77%??)
change from 85 % effy to 48 % effy = .37 (plotting effy change vs rpm drop)
so if power rises from est 320 at 85 % efficiency = 376, to 867 at 48 % - increase by 491, or x 1.3(?)
and the real power increases by 1.3, from 320 to 416, then 416/867 = 48%, as predicted.
However, this leave A at rated being high.
another check is V x (2/3)A = 16 x 24 = 384. -this is in between the two amounts - 320, and 441.
then 1/3 of 36 amps = 12 A, 2/3 = 24 A, 24a x 1.3 = 31.2
add back the 12: = 43. 2A, lower than the 54A maximum overload expected.
If 43.2 is used to calculate rated amps, /1.5 = 28.8,
28.8/32 = 90%, and watts = 441 x .9 also, = 396w, this may be a better estimate overall. - the wheel is going round and round, but
the output estimates seem to be converging.- this depend on my observed amp ratio of 1.3 to 1 holding??
that is not 2/3 , 0.667, it is 0.77 - so that could be factored back into the efficiency loop, to... on and on...
where does it end? nobody knows..
this 77% seems to be coming up a lot though! (rated rpm = 77% nominal max. rpm- my estimate)
<end of ramble>
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2) Prop ducts are removed, to allow for the fatter motor cowls 106mm tapering to 70mmn opening.
3) The main wing is dropped to be in line with the prop thrust lines, and the front wings.
The fuselage is tall enough to mount gear above and below the wing spars.
4)- The 1/5 drawings have been modified to suit.
All my drawing pens are now stuffed by clogging them with whiteout.
I will buy a couple of each .03, 0.5, 0.8. The fine-tipped taper felt pen still works OK. I will see where that came from.
5) Suppliers are tee'd up for motors,-(iflight direct, $260 nz, free delivery-slow boat??), batteries, cowls, collet prop drives, micro belt drive parts.
These will be on my next "to buy" list,
then I had better get some epoxy resin.
(and bearings, shafting, shaft collars, roll pins etc)
6) Next drawing job: break out layers and dimension motor plates. I have a scale drawing.
Note:
In converting DC to AC, 1/3 of the AC amps does not appear at the battery (motors)
so battery A = 100, and a 30C battery is OK.
I have selected 3 batteries:
2 x Leopard Power 2200 4S 30C , 228 g, $70 NZ.
1x 450 mAh Tattu 3S 45C 42g $24.50
Totals : 488g, $164.50 NZD - a little more expensive and heavier than
the original setup, but this one should actually work! (prev = 320g, $99nz)
Motors have gained weight, too, from 100 g to 500g total- assuming 100g
per prop for mechanical parts.
This means overall weight rises to 1968 g.
Total thrust = 2145 x 2 = 4290 g, thrust to weight ratio = 2.17:1
Still OK for a vtol. I now need to recheck wing area and oz/sq ft.
This is now 54 oz/sq ft. - 40 mph stall speed.
A normal RC model plane would need flaps to land at this loading.
With a 92 mph projected top speed, there is leeway for manoeuvres.
A tailsitter-bellyflopper should still be fairly easy to land, with gyro autopilot assistance.
(Auto throttle trim, tail-down transition, attitude, location damping.)
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