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Using separate battery for servos and motor and how to connect them to Rx

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Russ P11/05/2019 19:55:48
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137 forum posts
10 photos

How do I connect a Lipo for the motor and a Life to power the servos to the rx.

Steve Hargreaves - Moderator11/05/2019 20:43:52
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6720 forum posts
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First question I suppose is why would you want to do this? I assume you have an ESC in there with a built in regulator to supply the radio....why not use that?

To answer your question though simply remove the +ve wire (usually red & nearly always the middle of the three wires in the Rx plug from the ESC). You can cut it but this makes it difficult to use the ESC in future models, or if you look closely at the Rx plug you will see that the contacts are retained by a little wedge of plastic....using a pin you can gently ease this back & withdraw the +ve contact & tape it up out of the way.

You can then simply plug you're separate battery into the Rx for power.

Nigel R11/05/2019 20:44:56
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3051 forum posts
475 photos

Just disconnect the red wire between ESC and Rx.

Either cut it, or, better solution, remove it from the plug and fold the wire back and secure with some heat shrink or similar.

Allan Bennett11/05/2019 20:46:00
1540 forum posts
39 photos

1. The LiPo is connected directly to the power leads on the ESC.

2. The 3-wire lead from the ESC to the receiver has it's red wire (the +5v supply) disabled by pulling its pin out of the plug -- use the point of a hobby knife blade to pry up the little plastic tang that holds it in place, then pull the wire out and tie it back on itself with insulating tape so it can't touch anything.

3. The LiFe battery (2-cell probably) can then be connected directly or, better still, via an on/off switch, to any free channel in your receiver. If it's not specifically designed as an Rx pack you may need to crimp on a standard servo plug, taking care to ensure that the +ve wire (red) goes to the middle pin of the plug.

Frank Skilbeck11/05/2019 20:47:51
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4447 forum posts
101 photos

If the ESC has a BEC, then just remove the +ve pin (the center pin) from the ESC servo plug and plug the plug less the +ve pin it into the throttle channel, I tape the +ve pin back on the servo lead for safety. The LiFe battery then plugs into the receiver like a regular Rx battery.

If the ESC is an OPTO type (no BEC) then it needs power from the Rx just like a servo so leave the +ve pin connected.

Russ P11/05/2019 21:18:12
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137 forum posts
10 photos

Thanks for the replies.

Julian Murch13/05/2019 09:16:46
30 forum posts
1 photos

I am building a Calder Craft Primary for electric power and that has a single battery for both motor and servos. It occurs to me that if the motor drains the battery during flight I will loose all control. How will I know when the battery is approaching critical power.

Dwain Dibley.13/05/2019 09:29:02
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1268 forum posts
1265 photos

The BEC will continue to supply 5v to the servos and the motors power will be cut or reduced.

Some ESC's will respond to closing and reopening the throttle for motor power, but don't rely on this, always set you Tx timer to give plenty of time for a go around for landing.

D.D.

Nigel R13/05/2019 09:29:02
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3051 forum posts
475 photos

It won't, and you won't, as any modern brushless ESC senses when the main battery is very low and stops running the motor. Even if you run the motor right up to this point (which is definitely not recommended and not good for the battery's lifespan) you have plenty of charge left to run the RX/servos for a good while.

Julian Murch13/05/2019 09:38:31
30 forum posts
1 photos

Thanks that is very reassuring. Query to Nigel - Not sure what you mean by set the timer on the Tx

Julian Murch13/05/2019 09:39:25
30 forum posts
1 photos

Sorry should be query to Dwain !!

Dwain Dibley.13/05/2019 10:09:42
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1268 forum posts
1265 photos

Most Modern Transmitters have a timer function, a stop watch and/or a count down. I always set mine to count down from 7 minutes, whereupon a bleeper sounds, this leaves ample time to land safely.

If you have an older Tx or one of the lower end models you may not have this function. If not just take a small wind up kitchen timer with you, it will do the same job.

D.D.

Romeo Whisky13/05/2019 15:15:06
702 forum posts
188 photos

In my view a better way than cutting or removing the red wire from the ESC/RX lead is to use a short servo extension lead and simply remove the centre (red) wire entirely from the extension lead and put it between the ESC and the receiver. That way leaves the ESC RX lead intact for future use if you ever decide to use the built in BEC.

Edited By Romeo Whisky on 13/05/2019 15:15:25

Percy Verance13/05/2019 16:16:23
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8108 forum posts
155 photos

Romeo Whisky

I saw an ad for a widget which plugged in between the ESC and receiver to do just that job. It would save butchering a lead I guess. I just can't remember who was selling them!

Allan Bennett13/05/2019 20:58:54
1540 forum posts
39 photos

The disadvantage of using a modified extension lead is that it introduces another plug and socket into the line -- just another potential failure point.

In my view it's so easy to pry up the little tang and remove the lead from the plug, that it's not worth the effort and money of buying or making up an extension lead.

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