hyflyer9

Hi
I am currently Scratch building a DC3 and the out runner motor's both call for a 70 amp speed controller ! Would I have to use a separate controller for each motor or is it better to use just one large amp speed controller say maybe a 150 amp?
hyflyer9

Dr Kiwi

Typically one needs a separate ESC for each brushless motor. There are a few dedicated (Kontronik) ESCs which can run two motors... but with anything else it is one ESC, one motor. Failure to start together (or, at all), uneven running, differing RPM.... none of these is good in a twin!

You will be better off with one battery pack... since that will ensure that each motor gets the same juice.

spalex

I too am working on a DC-3 electric project and would like to know if a Y connector is used to plug both ESC's into the receiver? I would imagine so, but just want to know for sure.

Thanks, Steve

Dr Kiwi

You've got it, Steve. Typically you will need to sever the red wire on one of your ESCs (I use a 3" servo connector and sever the red wire on THAT, rather than disfigure an ESC I might use on its own for a future project!).

hyflyer9

Ok I am using the type of ESc's in my twin DC3 build that requires a separate Battery pack for the Receiver would I still have to sever one of the live wires from the ESc to the Receiver .
Thank you
hyflyer9

mdlflyer

I have purchased 4 BP A2814-6 Brushless Outrunner Motors and have tried to use BP 30A Brushless ESC for each but they only rock back and forth and do not even try to run.  I tried another 40A ESC with no luck either.  Also, the ESC's do not seem to arm (No sound).  I use a transmitter W/ receiver and plug ESC in #3 terminal of receiver and use a LiPo 11.1V for power.  What else may I do to get the motors to run?

Glacier Girl

My Feedback: (4)

hyflyer you are using opto style esc's, no built in bec, so no you don't need to disconnect anything.

p.s. I never cut the wire. Just pop it out and heatshrink the terminal and then heatshrink the lead to the rest of the harness. That way I can easily reinstall it if I use the esc in something else.

mdflyer,
In yours you need to disconnect at least three of the bec leads, to start with. Though I'd recommend doing them all and go with a stand alone bec, or an rx pack.

First thing I'd look at is every solder connection you made. Cogging back and forth like that is a sign of one leg of the motor wires not getting a good connection.

If you soldered the ends on the motor wires and esc's check everyone for a cold joint. More then likely it's on a motor since swapping esc's didn't change it.

As for arming tones, Maybe try adjusting your throttle trims or end points and see if that helps.

mdlflyer

Thanks much!  The motors came with connectors, but one leg was bad.  Now they work as they should.  Thanks again.

hyflyer9

Ok here is my motor set up and specs my question is what kind of power do you think I will need to run both motors and still have good power and is it best to run just one very large lipo pack or go with two separate packs and also the ESc has no BEC built in and is rated for 80amp + 85amp burst also I will be using twin 8x7.5 3 blade props as I need clearance for the DC3 .

TURNIGY AerodriveXp SK Series
AerodriveXP SK Series motors are designed for those who want the very best in outrunner technology for their R/C plane. Typically an efficiency improvement of around 8-10% can be seen over similar classed motors. This is in part due to the following;

Stator Laminations: .2mm
Magnet Type: N45SH
Bearings: Dual oversize


Model: SK35-48 1100
Kv: 1100rpm/v
Turns: 3
Resistance: 25mOhm
Idle Current: 3.5A
Shaft: 5mm
Weight: 171g
Rated Power: 770w
ESC: 70A
Cell count: 3~5 Lipoly
Suggested Prop: 12*6, 12*6.5, 13*8
Power equivalent : .25~42 + glow engine

Thank you
hyflyer9

Dr Kiwi

That particular SK motor doesn't get very good write-ups... but if you get lucky and receive good ones, they might be okay with your 8x7.5x3 on 4s. I doubt you'd want to pull more than into each motor than 40A on 4s. I'd run one large pack to ensure that you get exactly the same voltage fed to each motor as the pack wears down.

hyflyer9

So a 4s or 5s pack at 5000 mah would work ok to run both I guess?

Glacier Girl

My Feedback: (4)

If Doc says 40 amps on 4S, 5S is going to be a lot higher. And you are pulling 40 amps on each motor, so 80 amps on your pack.
Will give you 3 minutes at full throttle. That's using 80% of the pack capacity, best for long life.

Not a lot of flight time. Even backing off to 1/2 throttle after take off maybe 5 or 6 minuets flying time.

On 5S it's going to be shorter. As your volts go up so too do your amps.

If you can't fit one big pack, you can use two smaller ones. Hook them up in parallel. Will double the capacity of the single pack value. So 4s5000 and a4S5000 in parallel would give you 4S8000.



How big is this DC3? Looking at the motor calcs, your set up is going to produce around 7.5 pounds of thrust, and have a pitch speed of 94 mph. So real world roughly I'd say flight speed around 70 mph.

I'll be happy to run the calcs on the airframe with your power system for you. Might find you don't need that much pitch, and then your amp draw would drop.

hyflyer9

Hi Glacier girl
The problem is the prop size as you can see the motors are rated for a prop any where from 12x6 to 13x8 but my DC3 will not handle a prop any longer than an 8 inch . Any longer and the prop will tear into the side of the fuselage . If you would like to run the calcs please go ahead . The DC3 is not the big I am planing for it to be some where in the 7 to 8 LB range . I built this DC3 before but with twin 25 nitro's and it was a very good fly'er .
Thank you Again .
hyflyer9

Dr Kiwi

As Glacier Girl says... you probably need 4s or 5s to get the right amount of power, but at such high RPM you might be better off with less than 7.5" pitch. We are all guessing as to what these motors would draw with 8" 3-bladers...I think you need to test a few props on 4s to get a handle on it [if it isn't enough then you need to test 5s]. Your twin 25 glow motors gave you the equivalent of ~1000W.... so 4s or 5s @ 40A (x2) is well above that!

Re-calculating.......I might be well out in my estimates... after looking at amp draw from a Suppo 2820/6 1040Kv motor with 8x4x3 GWS HD... that only drew 10A on 3s.... an 8x7.5x3 will obviously draw more but maybe no more than 30A on 5s... you might need 6s!

hyflyer9

Hello Glacier Girl
I am having a problem trying to figure out how to wire up the harness to run twin lipo's in parallel to twin esc's
i too a guess on it is it a double Y set up connected to each other with two male on one end and two female deans connectors on the other end. the two male going to the twin lipo's and the two female going to the esc's
cheers
D

bassmanh

My Feedback: (5)

hyflyer,

check out these from tower hobbies, i use them and they work very well. link below...


http://www3.towerhobbies.com/cgi-bin...?&I=LXPTT6&P=7



hope this helps


bass