Planes > Park Flyers / Foamies
Li Po Batteries
Happy Days:
Oh Skyhawk, with out realizing it you’ve walked into a mine field. :cry:
You see, as Aidan said a few postings ago, the power train, (Prop, motor, speed controller, and battery) all work “hand in glove” with each other. You can’t just pick & mix. Here’s the problem I’m talking about.
Your Metal-hydride battery pack has a nominal voltage of 9.6volts. The brushless Electronic Speed Controller that you’ve brought is designed to work with a 3cell Li-po,………which has a nominal voltage of 11.1volts. Doesn’t sound much of a difference does it? But it IS.
To get the speed controller to work with your metal hydride battery pack you would need to fit 2 more cells into the plane to get the voltage close enough for the speed controller to work. But I’ll bet you a pound to a pinch of salt that you haven’t enough room, nor would the plane fly correctly balanced even if there was room.
(It’s a pity you brought these models without asking for some advise before hand.)
I think the best thing you could do is to continue with your brushless conversion, and get some Li-po’s
To safely store and charge them at home get yourself a fire proof Li-Po bag like this one. Much safer that way.
Keith
p.s. Ignore the rubber band in the picture, I didn't see it through the view finder :oops:
skyhawk newbie:
Thanks Aidan....
Just ordered 3x ZIPPY Flightmax 1300mAh 3S1P 20C and 3 charger bags...
will have to look into getting a charger now......
Sean
skyhawk newbie:
For Keith...
I know from reading this... http://www.dmitrynizh.com/tw742.htm
that the Prop, motor, speed controller are the right ones...
I'm just hopeing now that the Li-Po's I've just ordered and bought will work with this combo......
3x ZIPPY Flightmax 1300mAh 3S1P 20C and 3 charger bags...
See Aidan's link.......
Sean
Happy Days:
Put your mind at rest Sean, the batteries you’ve ordered will work in the power train you have got, :D ……….don’t Panic! :lol:
Provided you’ve checked the physical size of the battery to ensure it’ll fit inside the model, all the electrics will work. (I’m just wondering if you’ve also ordered any connectors, to connect the esc to the motor, and the battery to the esc?)
The only slight question will be over the propeller. (As Aidan mentioned.)
From a gliders’ point of view there are two types of propellers.
One type is like that on most planes. The propeller rotates all of the time to keep the plane flying.
With gliders however the propeller rotates for only a short period, just to get the glider up to height. Then the pilot switches the motor off and the glider “Glides.”
From the Pilots point of view, switching the motor on, is like the driver of a car using first gear to get the car to the top of a steep hill,………..then turning the engine off and rolling down the other side!
(If you were thinking that by using the electric motor it would turn your glider into a fast aerobatic aeroplane,……………It wont.)
Anyway, coming back to the question of propellers, the problem with using a fixed propeller is that when the motor is turned off (After the plane has gained height) the propeller blades continue to stick out into the air flow. This acts like a kind of air break (producing lots of drag) and slowing the glider, making it loose height.
To stop this problem, powered gliders normally use what are called “folding propellers”. These work in the following way.
a/ When the motor is switched on the propeller blades stick out and work just like any other propeller.
b/ When the motor is switched off the blades of the propeller fold themselves back and lay against the side of the fuselage. This way the blades keep themselves out of the air flow and allow the glider to fly more efficiently.
I don’t see these type of folding props in the pictures of Dmitry’s web article. If you’ve ordered the fixed props like those you’ve seen in the article it will handicap your planes performance, but it will still fly. ( Replacement props are quite cheap for your type of set up.)
I believe you said you’re going to visit a local flying club today Sean. I’m sure you’ll get a lot of good information there.
Let us know how you get on.
Keith
Ron:
Hi Sean,
Having spoken to Barry from the local club it looks like there won't be any flying at the field today due to the weather.
But might be worth a look as you're close.
Don't think I'm going to manage it today.
But on the subject of LiPo's, they have great advantages and some disadvantages - like most things.
They have great capacity for their weight and can deliver high currents.
But they can be ruined easily, especially by discharging below a certain point. This is why LiPo controllers cut off sharply and don't allow you to run the batteries down in the same way that you can get away with for NiCads.
Also, the max charge point is not easy to detect just from the voltage alone. So chargers have to monitor the voltage curve during charging, and watch for the critical slowing of voltage rise at the top of the curve.
But don't worry, the chargers and controllers take care of all this stuff.
I would just say however, that in general I believe it's better to use LiPos in a regular way. In other words, charge until the charger shuts off, and discharge until the controller shuts off, then immediately re-charge.
Putting LiPos on charge from a 'half charge' state can upset some chargers.
Ron
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