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Time for me to step up a gear in electric flight


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Forgive me for jumping in halfway through a thread but how are you feeding electrical power to the ubec? Via the standard switch & connector shown in the picture above? Given that the ubec is rated at 20A I'm guessing you are intending to use some fairly serious servos......will that switch/connector cope with the expected current?

IMHO you might like to consider uprating both the switch & the connector & the wire gauge too.....

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Adrian, looking good. I wondered why you didn't dispense with the EC5 connector at the termination of your Y lead. Just have two 5.5 mm bullets (one male one female) and plug to the ESC 5.5 mm bullets. Why use an additional EC5 connector which seems redundant to me. Or, am I missing something?

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Steve, Peter please feel free to advise /criticise as this is my first step up from the smaller electrics and any direction is helpful.

Steve.

The 20A UBEC may be overkill as I am using Hitec 5645 MG digitals (x5) and using the jumper on the UBEC to regulate the voltage at 6v. The battery for the RX/servos is bog standard 6.0v 2500mAh Nimh which is mainly because that's what I have to hand. I use them on my I/C petrol jobs too. However, I am open to suggestions on that as the Nimh may cause a weight issue rather than using a smaller 2S Lipo for instance.

Peter.

I don't think you are missing anything. The only reason for wiring it up in series the way I have is on the basis on this video clip for wiring Lipos in series for a 12S set up -

**LINK**

I am sure there are other ways, but my knowledge has not stretched that far! I think you might explain to me a bit more as I am a bit dense, not quite following what you are saying. Thanks for the input chaps, very grateful.

yes

The other thing is this is going to be an out and out aerobat and NOT a 3D machine so some of the crazier moves will not feature in my routine!

 

Edited By Adrian Smith 1 on 30/07/2017 08:43:33

Edited By Adrian Smith 1 on 30/07/2017 08:44:16

Edited By Adrian Smith 1 on 30/07/2017 08:45:18

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Posted by Adrian Smith 1 on 30/07/2017 08:40:52:

Peter.

I don't think you are missing anything. The only reason for wiring it up in series the way I have is on the basis on this video clip for wiring Lipos in series for a 12S set up -

**LINK**

I am sure there are other ways, but my knowledge has not stretched that far! I think you might explain to me a bit more as I am a bit dense, not quite following what you are saying. Thanks for the input chaps, very grateful.

Adrian - it just seemed to me that the final EC5 connector that you then broke with a bullet connector to fit the Jeti spark arrestor was a "plug too many". If you terminate the final output without the EC5 but 2 bullet connectors (one male and one female to avoid confusion) you will reduce your plug count. You also need to keep the leads from the ESC to the motor to those shown and the power leads also need to be kept as short as possible.

I use 2 x 5S LiPos for my F3A aircraft. I fit 4 mm bullet connectors to the LiPos. When I want to charge I charge them in parallel and when I fly I use them in series. I plug one black connector on one battery to a red connector on the other and so don't use an intermediate harness that the Link you provided advises. If you use those types of connectors then you do need those types of harnesses. However, using 4 mm bullet connectors, or 5.5 mm for more than 90 amps, you can cut out the need for a separate harness while retaining the ability to charge in parallel.

If that's still not clear, let me know and I'll post some pictures to show what I mean.

Peter

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It did cross my mind about that, Rich. On my small electrics where the power train is straight to motor, to ESC to lipo with the servos being controlled and regulated through ESC, an anti spark connector is all that's needed to power up. However, with the bigger set ups where a separate UBEC unit / small battery controls just the RX then a switch is necessary as I understand it. This is because of the large voltages going from ESC to Lipo power source and from which the Rx needs protecting from. However, I am learning as I go along so scrabbling in the dark afraid.

Peter,

Thanks for your explanation it was very helpful. Once I have found where the lipos will sit for the CoG them I will probably have to re-shorten the leads from the ESC to the lipo power source. They are the length they are purely until I establish that. As far as charging the Lipos I will probably charge them separately rather than charge in parallel.

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Hi Adrian...my comment was based purely on what I saw in your pic...namely a 20A capable regulator that looked to be supplied with connectors & wires capable of taking 3A or so absolute max. In electrical circuits it's good practice to match the components current carrying capacity throughout the circuit otherwise you might find that one item is sat there quite happily whilst another is being forced to pass more current than it can cope with.

What is your plan generally BTW? To supply the radio from the main flight battery via the UBEC?

Servo power supply is an area that I often find myself wondering about....at what point does the power bus within the Rx become overloaded.....?

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Steve, as I am using an OPTO ESC, the RX/servos have to be powered by a separate RX battery (in this case an Eneloop Nimh battery) via the UBEC, hence my question about upgrading the switch. The main flight power from the 6S x2 lipos is delivered separately from ESC to motor. The only connection between the two circuits is into the throttle CH3 from the OPTO ESC. Having tested the set up on the ground, it all seems to work okay, but then I am no expert.

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Hi Adrian...I spotted the opto ESC so understand the reason for the separate Rx supply....thumbs up

I'm just wondering why you would use a UBEC attached to a separate NiMH battery...? Would it make sense to draw the power from the main battery via the UBEC or to plug the NiMH battery directly into the Rx & do away with the the UBEC all together perhaps?

The fewer components you have the less there is to go wrong wink 2

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I'm with Steve on the UBEC. No one I know of in F3A uses anything other than a battery and switch to power the Rx and servos. The most popular switches are the Powerbox ones which provide a regulated voltage output between 5.5 v and 5.9 volts. That means you can use a 2 cell Lipo. I use an 800 mah 2S LiPo and that's good for 4 x 8 min flights, although I usually change batteries after 3 flights. The Emotec magnetic switch is also a popular choice. Not many use mechanical switches. There is also the Optiguard back up battery which some are now using to guard against Rx battery failure. I have to say that I don't use that particular back up.

Keep the component count down and the wires as short as possible. I can only speak for F3A models but I've always seen short battery leads and standard length ESC leads used. If the model has been designed for electric power then the battery position will have been chosen with lead length in mind.

Hope that helps.

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Thanks for the input chaps. There's me thinking I had got a handle on all this - now I am not so sure!

In answer to your question Steve, as to why do I need to attach a separate Nimh battery to the UBEC, this is what I understand:-

According to an advisory sheet on why you need a UBEC, produced by 4-Max, "When using an OPTO (optical isolated) ESC, OPTO ESCs do not have any built in BEC and therefore you will require a separate power source for your receiver and servos." A fuller explanation is shown here.

**LINK**

As I am using a ZTW Mantis OPTO ESC I am aiming for a wiring diagram as shown on page 2 of the manual as shown here.

**LINK**

Unhelpfully, there is nowhere in the diagram that shows that a switch of any sort is incorporated. Presumably using the PowerBox route is just a more modern way of doing it.

I take your point fully on board, Peter about the wire lengths. The CoG is correct with the 2 Lipos sitting just behind the "firebox" so my leads can be shortened somewhat which is a simple soldering job.

I must admit if anybody has a couple of pictures to post here of their actual wiring set up for this type of application it would help no end. Any step I take now is one step nearer fully understanding what is required for the job! Thanks again chaps.

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The UBEC is not mandatory Adrian.....we are all very used to ESCs having a BEC built in & by plugging in the ESC to the Rx hey presto it all just works. Lets not forget what BEC stands for....a Battery Eliminating Circuit & the clue is right there in the name....by drawing off a small amount of power from the main battery the need for a separate battery is eliminated. In the early days of electric flight every ounce mattered so the removal of a separate battery to power the radio was a great help

With an opto ESC there is no BEC built in to the ESC so the radio needs a separate power supply in order to function. This can come from either a stand alone battery pack OR from using a separate BEC (more correctly called a regulator really) drawing power from the flight battery.

Of course you might choose to use say a 2S LiPo as the power source. A 2S Lipo is rated at 7.4 volts & up to 8.4V fully charged & this is too high for most servos. In this case we would use a regulator to reduce the voltage from the 7.4V of the battery to the 5-6V required by the radio.

Using a regulator on a 4 cell NiMh battery makes little sense IMHO....it's just another failure point.

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Hi Adrian,

Here's what I use for connectors. They are HXT 4mm bullet connectors which I separate into 2 separate connectors by cutting through the plastic joiner. That allows them to be used to plug together in series for flight and in allows them to be charged in parallel. You can buy them here.  They, the wiring and ESC are good for 90 amps.

2017-08-02 12.05.05 sml.jpg

The batteries connected in series look like this. I just plug the anti spark lead into the battery positive plug and then the ESC +ve plugs into the spark arrestor itself.

 

2017-08-02 12.16.38 sml.jpg

Edited By Peter Jenkins on 02/08/2017 23:33:59

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The wiring setup for the ESC to battery connection is below. The ESC is a Jeti Spin 99 Opto with no BEC output. It is almost universally used in F3A as you can programme in the amount of braking in the downline using the Jeti Box to set up the parameters.

2017-08-02 12.09.40 sml.jpg

For powering the Rx and servos I use a 2S LiPo of 800 mah which is good for 3 flights - usually more than 50% remaining at that point. The battery is plugged into a Powerbox Digiswitch which provides a regulated 5.9 volts to the Rx and servos. I have 3 standard BLS servos (rudder and 2 ailerons) and 2 mini servos (elevators). In my biplane I have the same set up but with 6 mini digital BLS (one per aileron and elevator) and one standard BLS (rudder). The standard servos are 11 Kgcm while the minis are 5 Kg cm. Again, a standard set up in F3A, The aircraft are 2 mtr standard F3A weighing in at 5 Kg with batteries. The photo below shows the Rx battery setup.

2017-08-02 12.12.13 sml.jpg

Hope that helps.

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