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Old Feb 07, 2005, 09:43 PM
Caster Of Pods
crash-man's Avatar
Waco, Texas USA
Joined Feb 2005
970 Posts
Li-Po's and Brushed Motors

I hope that I am posting in the right place!

Hi, I am new to this forum and have a question.

First off, let me explain that I have been in the hobby for over 20 years and can fly just about anything, so I am not your run of the mill newbie!

My area of expertise is in nitro's, but since the Electrics industry has seen so many advancements, I have now discovered that Electric modeling is actually quite feasable.

I have not flown much in the last couple of years (job, a 3 year old, another on the way, etc.) but, electrics offer many opportunities for 'playing' - both in the front yard and in my factory's warehouse. I am SOOO looking forward to getting back into some 3D flying!!

I now have a few foamies and have been pleased with the GWS 350C(6.6:1). I just bought a new AXI 2208/34 for a new Fore-Play, along with some new Li-Po's.

Back to the question at hand:

If I wanna use these new LiPos with the brushed motors and speed controllers that I have now, should I worry about letting the LiPo voltage drop too low? I read that you should not let LiPos get below 3volts/cell. If I am using a 2 cell 1320 pack with my 350C-B on my SuperFly Delta, and I fly until my BEC cuts out the motor, technically I will have ruined the LiPo, since my BEC will allow for cut off at 4.8 volts, or so - way below the 6 volts that I should be using as my limit.

How do I use what I have without ruining the LiPos? Should I fly for a few minutes, then land and put a volt meter on only to repeat this process to determine approximate flying time? Is there some gizmo out there that will cut the motor off at a higher cut-off rate than the ESC?

Another question - the Brushless ESC I bought for the Fore-Play with the AXI motor was an E-Flight 40 amp unit. I plan to use a 3 cell pack with this combination, but I need to run 4 JR NES-241's. The limited instructions with the ESC suggested the use of only 3 servos (4 servos if I run a 2 cell pack).

What should I do? Will it be okay with the 4 servos?

Thanks for your help in advance! What a great forum!
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Old Feb 07, 2005, 10:57 PM
Pompano Hill Flyers
Miami Mike's Avatar
Miami Lakes, Florida, USA
Joined Mar 2003
8,476 Posts
Quote:
Originally Posted by crash-man
If I wanna use these new LiPos with the brushed motors and speed controllers that I have now, should I worry about letting the LiPo voltage drop too low?
Here's a new thread in Batteries and Chargers where they're covering most of your LiPo questions:

http://www.rcgroups.com/forums/showthread.php?p=3280878

Quote:
Another question - the Brushless ESC I bought for the Fore-Play with the AXI motor was an E-Flight 40 amp unit. I plan to use a 3 cell pack with this combination, but I need to run 4 JR NES-241's. The limited instructions with the ESC suggested the use of only 3 servos (4 servos if I run a 2 cell pack).

What should I do? Will it be okay with the 4 servos?
I'll bet that would work okay in spite of what they say, but if you're worried then two other options are (1) a separate battery pack for your receiver and servos made up of four small NiMh cells such as AAA size, or (2) an add-on switching-mode BEC such as a UBEC or SBEC.
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Old Feb 08, 2005, 12:46 AM
It must have a machinegun
Scaledown's Avatar
Perth, Western Australia
Joined Sep 2004
1,248 Posts
There are some low voltage alarm devices on the market specifically for people with non-programmable ESCs. I bought a Li-saver. Seems to work OK.
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Old Feb 08, 2005, 01:18 AM
Got shenpa?
flieslikeabeagle's Avatar
Los Angeles
Joined May 2004
10,940 Posts
crash-man, there are some brushed ESC's out there that are designed to be lipo-safe (i.e. they have the correct cutoff voltage to keep Lipos from discharging too deeply). I have been using FMA Direct "Super 9" ESC's on my smaller brushed motors, and their "Super 20" on bigger ones. These ESC's can be left on "auto", in which case they use the initial voltage of the battery to decide what the cut-off point should be (3 V per cell is about 70% of the initial 4.2V/cell, so if cutoff is set to 70% of initial voltage, everything works properly), or you can program them to a specific cut-off voltage, though it requires a voltmeter and either a lot of patience or an adjustable voltage power supply. More info at https://www.fmadirect.com/site/fma.htm?body=Store , click on "Motor Controllers".

Dymond Modelsports has some significantly less expensive, Lipo-safe ESC's - check out the 18 amp one, for instance. I haven't used these personally, though.
http://www.rc-dymond.com/order_speedcontrol_dy.htm

Recently lipo safe "Blue Arrow" ESC's have become available at about half the price of the FMA Direct ESC's. I have not used one yet, but Balsa Products cannot keep them in stock:
http://www.balsapr.com/catalog/searc...31525372004498

-Flieslikeabeagle
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