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Old Aug 11, 2008, 09:06 AM
Airplane crasher
CapMike's Avatar
USA, CT, Shelton
Joined Jan 2008
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Question
Power System setup

I am building a new plane that will have 4 motors. I will be useing the Dynam 2208 motors and speed controlers. Now then I have plans of supplying power to each wing set through one battery. ie two batteries one for each side of the plane. I know I will need to add in a bec due to servo count. Should I link the batteries join in the bec and then split off again? I want this to be right so I wont puff the batteries or make the smoke rise. Any suggestions would be appreciated
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Old Aug 11, 2008, 01:54 PM
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Letchworth, Great Britain (UK)
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One advantage of parallelling all your batteries is that all ESCs will get the same voltage, so you're less likely to have one set of motors stopping before the other due to a battery not fully charged, or something like that. So, parallel the batteries in the battery bay, tap off for your BEC, and then split the leads to go to the four ESCs. Come to think of it, there's probably no good reason why you shouldn't tap off for your BEC anywhere that's most convenient along any of the main leads, because they'll all be at the same voltage.

If the battery leads to your ESCs are more than about 8" long, you probably need to put an extra capacitor across them, close to the ESC. Jeti recommend 100-330uF capacitor, of suitable voltage, for their Spin ESCs; I've read that other manufacturers recommend similar.

With a multi-motor setup it's even more important to fly to a set time, rather than waiting for lvc to kick in, because it'll kick in on one ESC before all the others, due to manufacturing tolerances. Then all the others will keep running because the battery voltage recovers a little bit due to some of the load having been lost. Probably not so important on a 4-motor model, compared with a twin, but not worth risking anyway ...
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Old Aug 11, 2008, 03:45 PM
Airplane crasher
CapMike's Avatar
USA, CT, Shelton
Joined Jan 2008
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I will keep the lead length in mind as I am hooking everything up. Thanks for the info on the time vs lvc. With luck and barring any mishaps I will hopefully debuting this model next month at NEAT.
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Old Aug 12, 2008, 02:14 AM
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There is a way to make all four ESCs shut down at the same lvc: You get a Liposhield http://www.dimensionengineering.com/LipoShield.htm and insert it between your Rx and your ESCs (assuming your ESCs are all Y-leaded into the same throttle channel), then program the lvc in your ESCs to a lower-than-normal value, and the lvc in the Liposhield to the value you really want.

The Liposhield will then stop all motors when it hits its lvc, which should be long before any individual ESC hits its lvc because you've set their lvcs so much lower

In another thread some time ago someone else contacted Dimension Engineering to confirm that this works with a twin. It may be worth contacting them about using it with 4 ESCs, just to be sure.
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Old Aug 12, 2008, 03:39 AM
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East Anglia, UK
Joined Sep 2002
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One of Dimensions BECS - smart BEC? - also has this function built in.

I'd definitely go that route, and I would also add in some low ESR electrolytics on the battery wires to the ESCs if these get a bit long.
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Old Aug 12, 2008, 07:05 AM
Airplane crasher
CapMike's Avatar
USA, CT, Shelton
Joined Jan 2008
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This plane is going to be the prototype, so length of flight is not all that critical. Knowing that she flies well will be enough for me. I will keep in mind the length of wires going to the motors. Adding in the Smart BEC I think will be the best for all the servo's Then I do not need to be so concerned with numbers. I will most likely go for the 6 volt instead of the 5 just to play it on the safe side. With luck and the Gods smileing I will have it finished up in the next three weeks.
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