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Old Aug 14, 2011, 12:07 AM
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Four Motor Wiring Diagram

I just purchased a B-17 ARF but need to add the electronics. It calls for 2 batteries--one for the inboard and one for the outboard. My question has to do with wiring this with the 2 batteries and one receiver----how does that Work? Is there already a resource that explains this?

Thanks!
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Old Aug 14, 2011, 12:34 AM
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Chances are you will be running brushless motors. Test/set up your motors and ESC's separately if you have to do any programming. It is usually much easier to make sure each ESC programs right, separately. Make sure they are set up to spin the right way, have the same settings so you don't have thrust differences between motors, etc. Take notes if you get fancy, having 4 motors can get messy if you are not organized. If you are using fancy motors and props and need to know exact amp draws, better to test rig one motor up and make some measurements than to have to test 4 props at a time, it's cheaper and faster if you have one or two dog props that you can eliminate right away as you'll just have the one dog prop for each rejected type, not 4. Again, take notes that you can refer to, you'll thank yourself later.

So once everything is in the airplane, wire up your inboard motors/ESC's to route the power lines to the location of the battery packs. You will have #2/#3 motors (inboard) power lines coming together and wired in parallel. Two black wires soldered together soldered onto the negative plug and the two red wires soldered together for the positive plug of your choice of battery plugs. Route the ESC wires to a "Y" lead where your power lines join, and disconnect the BEC wire from each ESC before the Y lead. Another Y lead will join the motor "sets" to a single lead into your receiver throttle control channel.

Wire up your outboard motors in the same way. Same thing with disabling the BEC's on those ESC's.

With a 4 motor airplane I would not bother using any sort of BEC. I'd use a separate battery pack. A 1500 nimh pack weighs not much more than a SBEC and reduces wire runs considerably in such a wire mess like this. Single engine is one thing, but this is different.

Another advanced question is: Do you run the 3 wires from the motor all the way to the ESC in the fuselage? Or run the 3 wires to the ESC in the nacelle and run two wires (long wires) to the battery in the fuse? There have been many arguments about this and all I can say is research yourself and see if guys have compelling arguments either way. I have done a lot of research on this. If I were running two long DC wires I'd have a few capacitors wired along the way to absorb voltage spikes as long DC wires create havoc at the ESC. If you want your ESC's in the fuse and want to run long AC wires tot he motor you won't have voltage spike issues but you'll have heavier wire runs and your motor KV will artificially drop a tad as the 3 wires are effectively part of the motor winding. You may need slightly more prop to compensate if you want a hot setup but it will be a small difference.
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Old Aug 14, 2011, 03:02 AM
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Of course if they're brushed motors it's a LOT easier....so which are they ? And what size model are we talking about ?

Steve
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Old Aug 14, 2011, 07:47 AM
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Good point, Steve. They are brushless--BP2212-10 motors. I have one of the B-17 ARF kits sold by General Hobbies. The wing span is 65". Thanks!
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Old Aug 14, 2011, 08:16 AM
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Flimnar, I used a similar power set up on my Wowplanes B24. First off, you will need a separate bec, preferably a switching bec. Then you disconnect the center red lead from your esc's. In other words, don't use the esc's bec circuit, b/c with 4 of them hooked together you will have problems.

I made some enquiries in the power forum and technically, you should keep the battery leads short and extend the motor leads. For ease of installation and cooling I put all my escs in the nacelles and extended the battery leads. Most of us building the B24 did this, and no one had problems.

Unless you have separate throttles for the inboard and outboard motors, there is really nothing to be gained by putting them on separate batteries. If you want to use two flight packs, (I do in my Mosquito) parallel them to all 4 motors.

Hope that's clear enough. If you run to any other specific issues, I will try to help. There is something just too cool about 4 motors droning away on a model.

Regards,
Jeff
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Old Aug 14, 2011, 08:37 AM
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This came up the other day at the club. I have the first version of the HK B-17 and another member just got one of the latest versions. I'm pretty sure the power lead from 3 of the esc's are clipped on mine. On his all are still intact. Like me, he had always been told to remove the power lead from the extra esc's or all of them if running an rx pack.
Then we started thinking about it for a second and both figured since they are all hooked in parallel it would be better to leave them. If one of the bec's dies then you still have three to power the rx.
Both planes work the way they are, so what problems could be caused by leaving the power leads intact from all the esc's?
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Old Aug 14, 2011, 08:54 AM
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Quote:
Originally Posted by V2rider View Post
Both planes work the way they are, so what problems could be caused by leaving the power leads intact from all the esc's?
I can't give you the technical answer, but apparently the "cross-talk" between esc's can cause problems. I flew my HC Mosquito stock with both esc bec's live and it was okay but apparently it's a bit of a crap shoot. It must be less of a problem with better electronics, but a few years ago, people were losing multi's b/c of interference between the esc's.

For larger (more expensive) planes with lots of servos, the consensus is that a separate bec or a separate flight battery are a good plan. These days I pretty much install a separate bec from the get-go, cheap insurance.

FWIW,
Jeff
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Old Aug 14, 2011, 12:02 PM
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Thanks Jeff. I figured there was some reason, but couldn't really think what it would be. Makes sence that newer and supposedly better esc's should eliminate those kinds of problems. But, I like the better safe than sorry approach. One of the guys in the club likes to build twin, multi motor planes and he always runs a seperate rx pack. He's been dealing with electrics for quite a while so I'm sure he has run into these problems and just decided to run a pack and take the esc's out of the equation.
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Old Aug 14, 2011, 01:32 PM
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Quote:
Originally Posted by V2rider View Post
Both planes work the way they are, so what problems could be caused by leaving the power leads intact from all the esc's?
The BECs are more likely to die. Basically they're all likely to be working at slighty different voltage and that can confuse the voltage regulation. Most manufacturers will tell you not to do it, one or two, like Castle Creations, are fine with it. But it has nothing to do with how new they are, it depends on exactly what components and circuit design they choose to use.

Steve
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Old Aug 14, 2011, 03:29 PM
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I can see why guys flying ARF's might chance using a BEC on a speed controller, to save money and hassle of charging a separate pack - if anything goes wrong, a new airframe is just a click away. My experience has been scratch building multi-motor scale electric models, two and four motor airplanes, for the last eleven years. I've always been a bit more conservative coming from that perspective. I've only recently risked using BEC's on large models with anything more than 4 servos, most others still having a separate switching regulator (external BEC) or just using a separate battery or even two batteries and a dual power bus for giant models.

Today there are so many options. The key is to use the options that are proven and reliable. Many are, some are not!
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