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|The nose of the Lulu with the new 2S LiPo. The folding prop improves the glide performance, and is at minimal risk of damage during a belly landing.||Lulu flies very well with a simple brushed 400 motor. There's plenty of power for this delightful model.|
The main issue here is that of LiPo safety. To avoid damage, LiPo batteries must remain strictly within the voltage range of 3.0V to 4.2V per cell (Vpc). If these limits are exceeded, the cells can puff up or even catch fire.
For your 2-cell battery, this safe voltage range means your battery needs to be kept between 6.0V and 8.4V at all times. The upper voltage limit (8.4V) should be taken care of by a suitable balancing charger. Normally, a suitably set up LiPo capable ESC should ensure that the battery does not become discharged below the safe limit of 6.0V after a flight.
However, in this case you wish to use an ESC which is not specifically designed to work with LiPo batteries. This poses an interesting question about the cut-off voltage. This function of the ESC is often referred to as the low voltage cut off (LVC) or power cut-off (PCO) function.
If you are able to set your ESC up manually, then the cut off voltage may be set to a suitable value. For this relatively low power model, I’d suggest starting with 6.0V. You may be able to locate some instructions by searching the internet, but if not, then you will have to work with the controller’s existing programming.
Almost all ESCs automatically detect the battery voltage, and select a suitable cut-off voltage based on this voltage. Often, a value of 0.8 or 0.9Vpc is used. For example, if a well-charged 7-cell Hydride (NiMH) or nicad (NiCd) battery (nominally 8.4 V) is connected, the ESC might select a cut off voltage of between 5.6V (7 x 0.8) and 6.3V (7 x 0.9).
Coming back to your model, a fully charged 2-cell LiPo has a voltage of 8.4V. When this battery is connected to your non-LiPo ESC, the question is what the automatically selected cut off voltage will be. Since a fully charged 7-cell NiMH or NiCd battery will be around 8.4V when fully charged, so the ESC may well detect this as a 7-cell nicad and select a cut off voltage of 5.6 – 6.3V. If its the higher figure, your battery will be protected, but if the lower figure applied, your battery could become over-discharged in flight. Also of course, there would be a risk of a loss of control due to a flat battery as the RC is also powered from the flight battery.
|The Lulu design is 50 inches (1,270 mm) in span, and was designed as a free flight glider. Click to see an enlarged plan.|
The conclusion is that the safest course of action is to assume the ESC will not protect the LiPo from excessive discharge. For this reason, you should time your flights so that there is never less than, say, 1/3 of the battery capacity remaining in the LiPo. Build up flight time slowly, starting with a short flight. By measuring the amount of charge that is required to recharge the battery, you can arrive at a safe flight time. Make sure that you always start with a fully charged battery, otherwise this method won’t provide the required margin of safety.
In any case, for all battery types (and especially LiPo examples) it’s always best to end a flight when there is still some charge remaining in the flight battery.
I hope this helps, and I wish you many enjoyable flights with your charming Lulu!
|Lulu technical data|
|Span||1,270 mm||50 inches|
(800 mAh 2S LiPo)
|Wing Area||0.00 sq m||0.0 sq ft (000 sq in)|
|Wing Loading||00g/dm||00 oz/sq ft|
|Battery||2S 800mAh LiPo|
|Motor||Speed 400 (000 Kv)|
|Propeller||6x3 folding prop, 0,000 rpm|
|Power Loading (at maximum power)||000 W/kg||00 W/lb|
|Average Power Loading during flight||00 W/lb|
|Control functions||Throttle, elevator & rudder.|
Note: For safety, it is extremely important
that LiPo batteries are maintained within their safe range
of 3.00V- 4.20V. If this range is exceeded, the battery
will suffer damage and the risk of a fire will increase.
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