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Grasshopper
02-14-2006, 03:47 AM
Hello to all,

I'm new to the electric sport and also to these forums. I used to fly gas but it's been some time ago. I have recently taken the easy way out and purchased a PZ J3 Cub to get the feel of it again. So far so good, three flights and plane is still in one piece. I have also purchased a PZ P-51 which should arrive this week. I'll put it back till I'm good and comfortable with the cub.

I have a lot of questions but would first like to know how I can tell when the batteries are getting low and I need to land? Do I just do some trial and error (hopefully more trial than error) and time it with a stop watch or will the motor start to slow down? Or, do I always just stay three mistakes high in case it dies?

Any help here would be appreciated.

__________________________________________________ ________

The older I get, the faster I was.:confused:

Twmaster
02-14-2006, 05:56 AM
You should be able to listen to the motor and hear it slow down. It's also good to time the flights too. You don't really want to run it till it's hit the cut off if you can avoid it. Deadstick on some planes is kinda interesting. :)

Time your flights to get a feel for how long you can go on a pack. When you think it's time to come in you'll have some power left in the event you need to go around again.

MountainFlyer
02-14-2006, 06:01 AM
Wingswithwatts,
First off welcome, The BEC (battery engine cutoff) thats built into the ESC (electronic speed control) have a Low voltage cutoff or "LVC" that is set to turn off the power to the motor when the battery voltage drops to a selected voltage level.( it does NOT disable the power to the RX and servos though ) so the plane remains flyable
for example if your ESC is setup to use a NiCd or a NiMH the LVC would be set to 5v so when the voltage reaches 5v the motor would be turned off ( some ESC's have an option for soft-off this causes the motor to "throttle down" rather than just turning off .. but don't worry you can normally restart the motor by just moving the throttle level to idle then reapplying it. Also you can tell when the battery is getting low because the motor will start to feel slugigsh and down on power. Most smaller electrics fly fine in a dead stick situation even the GWS warbirds ( i always land them deadstick since there belly floppers )

most if not all "newer" Burshless ESC's that are designed for LiPoly batterys have an Auto detect for the LVC it makes it a bit more user friendly im sure other will beable to explain it better , but i hope this helps

M

rr turtle
02-14-2006, 06:24 AM
the cub has a great feature in that when it cuts off all you have to do is cut the throtle off then go back 3/4 throtle and it will give you about 30 seconds of power to the motor and it will do a few times.

Vintauri
02-14-2006, 01:41 PM
With the stock nimh batteries you will know when to land as the power will drop off and it will be harder to keep the plane in the air with the same power settings. Once you go Lipo they keep more consistant power till the end and I find myself landing well before that when flying my mustang on lipos.

But when all else fails if your using the stock setup correctly the BEC will cut off power before the battery gets too low.

Steve

phat23
02-14-2006, 01:55 PM
Just to clarify things.

The BEC (battery eliminator circuit) does not cut power to the motor. The LVC (low voltage cutoff) feature does that job. The BEC only supplies the Rx with it's operating voltage.

Grasshopper
02-14-2006, 10:12 PM
Thanks a lot for all the info. This is good stuff.