2S Quadcopter
This is a planning page for a quadcopter using 2S batteries, more exactly 1300 mAh. The reason is that I already have plenty of such for MS Composit Swift II and wouldn't want to get yet another different size only for one device. Something ultrasmall or even mini isn't the target. More likely something using 8" props resulting in around 30-40 cm motor to motor distance. The target flight time is around 6 minutes.
Motor options
Starting with the assumption that using a 8" prop would be the best option, the motor would need to have a KV of around 1400-1600 if the usualy KV for a 3S build is between 900-1100 for the same prop size. One possible problem can be that motors of this size use integrated prop holder that might not be stiff enough.
| motor | weight (g) | size (mm) | rpm/v | current | shaft (mm) | prop | battery | note |
|---|---|---|---|---|---|---|---|---|
| E-Power GC GT2203 | 16 | 28x12? | 1560 | max 6.8A | PH | 8x4.3 | 2S | http://www.flybrushless.com/motor/view/593 |
| Turnigy 2204-14T | 19 | 28x12 | 1450 | max 7.5A | PH | 8x4/7x3.5 | 2-3S | |
| Keda KD2203/41 | 19 | 27x20 | 1500 | max 8A | PH | 8x4.3 | 2S | http://www.giantcod.co.uk/forum/viewtopic.php?f=24&t=1610 |
| C2404 | 21 | 30x10 | 1900 | 9.4A | PH | 9x5 | 2S | that prop suggestion sounds wrong... |
| E-Power GC GT2205 | 23 | 1660 | max 8A (12A) | 3 mm | 8x4.3 | 2S (3S) | ||
| Blue Wonder 1300kv | 25 | 1300 | max 8A | 3 mm | 8x3.8 | 3S | 2S quadcopter mentioned in Giantcod comments, 460g/7.5A hover | |
| Blue Wonder 1500kv | 25? | 1500 | max 7-9A | 3 mm | 8x3.8 | 3S | max current somewhat unclear |
Turnigy and Keda seem to be the best options so far.
Blue Wonder test data: http://www.rcgroups.com/forums/attachment.php?attachmentid=1732731
Weight calculation
These are really only rought approximations.
| item | weight (g) | note |
|---|---|---|
| 4 x motor @ ~20 g | 80 | Turnigy 2204-14T has a prop shaft of 5.3 mm |
| 4 x 1x1x15 cm aluminium square tube @ ~15 g | 60 | |
| 4 x 8" prop @ 5 g | 20 | how about 3-blade prop? flyduino 8" props have a hole of 4.65 mm |
| 4 x ESC @ 10 g | 40 | 10A, 6A could save a little weight |
| MiniWii | 8 | availability unknown, alternatives much heavier |
| FrSky TFR4 | 7 | ppm is a must |
| Turnigy 1300mAh 2S | 90 | |
| Baseplates | 42 | would plywood be lighter? could be smaller than 10 x 10 cm |
| Wires and screws | 20 | just a guess |
| = | 367 | seems a little bit heavy... |
Since I'm not going to change the battery, the most obvious places to save weight would be the baseplates (maybe too sturdy for a light weight quad), the aluminium arms (shorter with 3-blade props?) and the motors (are there suitable alternatives?). It would be nice to have the weight closer to 300 grams. Smaller props might result in smaller current needed during hover with the cost of climb speed but a benefit of longer flight times.
xcopterCalc suggests that using a 7x4 props would provide better efficiency instead of using 8x4 props. The hover time would still be about the same. However, the hover throttle jumps 45% to 62%. The motor to motor distance could also be smaller with 7" props resulting in less weight from the motor arms and a more portable size.
Flight time guestimation
The comments section of Hobbyking for Turnigy 2204-14T motor mentions the following thrust/current values (to be tested myself) with GWS 8x4.3:
| 3.5oz (100g) | 1.50A/8.0v |
| 5.3oz (150g) | 2.35A/7.9v |
| 7.0oz (200g) | 3.40A/7.6v |
| 9.0oz (250g) | 4.70A/7.3v |
This video seems to suggest that the table above might not be totally correct: http://www.youtube.com/watch?v=qlEejY43wsQ
However, another video gives similar result as in that table: http://www.youtube.com/watch?v=WAItgbTUi9M
With the planned weight, the quadcopter should be able to hover with about 100 g thrust from each motor (4 x 100 g = 400 g). As a result, we should be able to assume 4 x 1.5A = 6A as total current required for hovering.
| capacity | calculation | time |
|---|---|---|
| 1.3A | 1.3A / (6A / 60min.) | 13 min. |
| 1.0A | 1.0A / (6A / 60min.) | 10 min. |
| 0.8A | 0.8A / (6A / 60min.) | 8 min. |
If the battery isn't totally drained (like it shouldn't), a 1300 mAh battery can be expected to have something between 800-1000 mAh of usable capacity. That gives a hovering time between 8-10 minutes making a flight time of around 6 minutes realistic.
The GAUI 330X is reported to have a flight time of about 12 minutes with a 2200 mAh 2S battery and a weight of around 500 g.
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