84" twin electric Eastern Airlines DC3, 12 pounds

[blnk00]

I currently purchased this model from a member at the club. I removed the two .40 nitro motors and am setting it up brushless.

The motors are two turnigy 400kv motors spinning 11x7 3 blade props. Battery is a 6cell 8000mah 10c pack. I have two 70amp speed controllers, one for each motor. Seperate lipo and BEC for receiver. My problem is the following:

When I run one motor, I get 550 watts on either one. As soon as I run both motors, I lose 100 watts on each motor. This is irrelelevant of what prop I use. I've tried different sizes, I always lose 100 watts per motor when they are both running in sync.

My first suspect would obviously be the capacity of the battery. However, the motors are pulling on average 25 amps each, 50 amps total, well below the 10c, 80 amp capacity of the battery. If I prop up to 11x8 3 blade props, the amp draw is 30 amps per motor, still below 10c. However, I get the same 100 watt loss per motor when they are running in sync. Doesn't matter what prop I use, I lose 100 watts per motor when they run together. This has me stumbled. Has anybody experienced this phenomenon before? Please help.

Vic

[Heather]

Do you have a watt meter? You need to measure the voltage of your battery pack under the two different loads.

Even though your pack is rated at 10C you are still going to get a voltage drop between a current draw of 25A versus 50A, its just ohms law.

By second guessing your voltage under one motor is roughly 3.66v per cell and under two motors - 3.4v per cell - still quite acceptable for a 10C pack. Modern high C packs will hold a higher voltage but you can of course just prop up a bit.

Heather

[earlwb]

I think in your case that the 10c battery pack is unable to provide the 50 amps or more for very long.
If possible, you should try a better grade pack.
The other possiblity is to run two battery packs, one for each motor.
Use a 4000mah pack for each one and you keep about the same weight as the single pack. Considering how much lift the wings on the DC3 has, running two 8000mah packs probably isn't a big deal.
Now the power wires is another gotcha, I have seen guys try to run motors with wires that can't handle the current and it keeps the motor from getting that extra oomph.
The silicon covered wire that the RC race car people use is good for this. Especially the extra fine stranded silver plated wires.

[blnk00]

I appreciate your help and the quick response! Well, I used 12 gauge wire so I know this isn't the bottleneck. However, you both bring up a very good point with the voltage and the 10c rating. The pack probably can't hold up the voltage like a higher c rating pack can. I'm pretty sure that this is the problem!

It just so happens that I do have two 4000mah packs that I can test. But the reason I was feeding off of one battery is that I am guaranteed that both speed controllers will have exactly the same voltage at all times. I don't have to worry about one pack giving me different output, motors running out of sync, etc.

I will test this tonight to confirm. I'm pretty sure the c rating is the culprit. At the end of the game, I think it is better if I prop up and keep the single battery so that I get the same rpms from both motors at all times. The last thing I want are motors whose rpm's oscilate during a flight.

Thanks so much for your help!

Vic

[earlwb]

Did you use wire like this?
http://www.shopatron.com/product/part_number=5512/135.0
or
http://www.wsdeans.com/products/wire/index.html
12 gauge with maybe 665 copper strands in it or the better 1660 strand version. The stuff can handle over 100 amps.
I was reading about some of the newer car motor ESC's rated for 400 amps forward and 200 amps braking. Sheesh the RC car people are getting dangerous.

years ago I remember having trouble with a couple of motors and it was the wires weren't able to handle the current load. I since then use this type of wire on all my larger motors or the smaller wire on the smaller motors. I also remember burning out a few cheap power connectors like Tamiya used, before I wised up and switch to the good low resistance connectors.

[GuppyG]

I appreciate your help and the quick response! Well, I used 12 gauge wire so I know this isn't the bottleneck. However, you both bring up a very good point with the voltage and the 10c rating. The pack probably can't hold up the voltage like a higher c rating pack can. I'm pretty sure that this is the problem!

Regardless of the C rating you are still going to see less than double the single motor watts when you run two since the increased draw will result in decreased voltage. With a stronger pack the effect will be reduced, not eliminated.

Also, on my Lancaster with four Medussa 28mm in-runners I see variance in the rpm of about ~100rpm across all motors. It could be better or worse solder connections somewhere for a particular motor, slight differences in the speed controllers/motors despite being the same brand. I didn't stress about it and the model flys fine.

Finally, the fact that you have a shared power source does not prevent one motor from shutting down in the low voltage case before the other. In fact, I can guarantee that one will shut down first and the other will continue to run, since the voltage will increase when the first motors load is removed. I choose to disable the low voltage cut off (set it to the minimum) and measure my flights to ensure I never hit it. The other choice is to use a Dimension Engineering "SmartBec" or similar item to have one device do the LVC decision and control the throttle input of both ESCs. (Disable the ESC LVC in this case as well).

scott.

[blnk00]

I use the 1050 strand type. This one here to be exact:

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idproduct=5156

I have it on my large Sukhoi which is running on 13 a123's so I figured if it could handle 42 volts with 50 amps then it should be able to handle 22 volts. In fact my worry was that it was too thick and heavy, 4 ounces just in wires but I'd rather be safe then sorry.

Vic

[blnk00]

Interesting Scott, thank you. After reading your post I am starting to lean on flying these motors on separate 4000mah packs instead of a single 8000mah pack. I get the advantage of an additional 200 watts and if the motors vary by 100 rpms or so it should not affect the flight characteristics greatly, you are right. In the case it does because one battery is depleting faster then the other for whatever reason, I can lower the throttle a click or two so they will even out and take this as a sign that's it's time to come in for landing. I will disable the LVC like you mentioned. Thanks.

Vic

[GuppyG]

Interesting Scott, thank you. After reading your post I am starting to lean on flying these motors on separate 4000mah packs instead of a single 8000mah pack. I get the advantage of an additional 200 watts and if the motors vary by 100 rpms or so it should not affect the flight characteristics greatly, you are right. In the case it does because one battery is depleting faster then the other for whatever reason, I can lower the throttle a click or two so they will even out and take this as a sign that's it's time to come in for landing. I will disable the LVC like you mentioned. Thanks.

Vic

I actually have two batteries in my Lancaster, but they are wired in parallel. This way all ESC/motors get the same voltage. I thought of wiring the two inner motors to one battery and the two outers to the other, but I thought my setup would decrease the difference in RPM's since one battery could be slightly weaker or have a slightly different discharge curve and the voltage would "average out".

Lets see how my ascii art turns out:

/---ESC0----\
battery0---\ |---ESC1-----\
|-------| |--rcvr
battery1---/ |---ESC2-----/
\---ESC3----/


The safest solution in a parallel battery setup connected to a SmartBec. As the voltage drops towards the setting in the SmartBec it will retard the throttle setting on both motors at the same time. At this point you should have landed a minute ago... ;)

scott.

[blnk00]

Yes I'm going back to my original design of running both speed controllers from one battery. I connected two separate batteries for each speed controller but I get different rpm's, no good.

I went ahead and set the timing on both speed controllers to high to offset the lower voltage of running from one battery pack. Now I get roughly an extra 150 watts. 1050 watts total when fed from one battery, should be enough to fly this 12 pound bird. The DC3 has plenty of lift on the wings, especially in the center section right around the motors where the prop wash does the most good.

I could put 11x8 3 blade props to get the wattage in the 1200-1300 range but I noticed that the motors warmed up quite a bit with the high timing so I don't want to push it. With 1050 watts I should get a fairly scale flight and with a good 8 minutes in the air, what else can you ask for.

Thanks for all the help!

[earlwb]

if it helps any, I don't think having perfectly matching RPMs is really needed all that much. I remember flying my multi-glow engine powered models and at first I was concerned about it a lot. But trying to get two or more engines to sync up perfectly was a major effort. eventually I found that even if they were off, it only mean a little extra trimming at the worst. So I just tuned each engine to run its happiest. Never had any problems as far as I can remember. Electrics make it so much nicer though for matching up engines better.

[ezrydr]

uh kind of off topic but.....PICTURES!?

please - I'd love to see what this looks like!

Thanks,
Steve

[rcfun33]

You could connect the two packs in parallel so they look like a singe pack connected to the 2 controllers.

[blnk00]

She flew great. Today I put in another 3 flights; 4 total. Super happy with the setup. Decided finally on 11x8 3 blade Master Airscrew props. Getting 1200 watts average, 1300 initially for take off. Plenty of power. Takes off on 3/4 throttle, good lift on those wings.

At 12 pounds she's pretty quick on landing, flaps are essential. 12% down elevator mix on full flap deployment for level approach.

If anybody decides to build a DC3 kit at this scale, follow this guaranteed setup:

-two 50-55a turnigy 400kv motors
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idproduct=2102

-two 60 amp Hextronic speed controllers
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idproduct=2062

-11x8 3 blade Master Airscrew props

-one 6 cell lipo of atleast 5000mah 20c to feed both speed controllers

Everything is available from hobbyking.com for peanuts.

I set the timing on my speed controllers to high but it is not necessary, plenty of power with normal timing. I'm using an 8000mah lipo on mine and my flights could easily extend 10 minutes. My longest flight was 7 minutes and I only used up 4100mahs on the battery. I will probably be replacing the battery with a 5000mah for a lighter bird and slower flight. There is plenty of room in the nose to move the battery forward and keep the cg in check.

Don't be afraid to set up maximum flaps, I wouldn't land without them. She reacts very well to them on approach. The more the merrier, with a bit of down elevator mix.

All in all, I am one happy camper.

[ezrydr]

now that's what I'm talking about! Wow - beautiful airplane!!

Thanks for the pictures!

Steve

[sarg96]

She flew great. Today I put in another 3 flights; 4 total. Super happy with the setup. Decided finally on 11x8 3 blade Master Airscrew props. Getting 1200 watts average, 1300 initially for take off. Plenty of power. Takes off on 3/4 throttle, good lift on those wings.

At 12 pounds she's pretty quick on landing, flaps are essential. 12% down elevator mix on full flap deployment for level approach.

If anybody decides to build a DC3 kit at this scale, follow this guaranteed setup:

-two 50-55a turnigy 400kv motors
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idproduct=2102

-two 60 amp Hextronic speed controllers
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idproduct=2062

-11x8 3 blade Master Airscrew props

-one 6 cell lipo of atleast 5000mah 20c to feed both speed controllers

Everything is available from hobbyking.com for peanuts.

I set the timing on my speed controllers to high but it is not necessary, plenty of power with normal timing. I'm using an 8000mah lipo on mine and my flights could easily extend 10 minutes. My longest flight was 7 minutes and I only used up 4100mahs on the battery. I will probably be replacing the battery with a 5000mah for a lighter bird and slower flight. There is plenty of room in the nose to move the battery forward and keep the cg in check.

Don't be afraid to set up maximum flaps, I wouldn't land without them. She reacts very well to them on approach. The more the merrier, with a bit of down elevator mix.

All in all, I am one happy camper.

Beautiful---In mid 1954 I took a flight in one such EAA plane from Greenville, SC to Mobile, AL Thanks for posting the pics.

sarg96

[blnk00]

Thanks guys. She's a pleasure to fly. A bit quick but that will go away when I replace the batteries for a smaller pack since I will save a pound and AUW should be 11 pounds.

[blnk00]

Oh and a couple pointers that can be used not only on this plane but others. Foam the wings! There is no joiner tube in the middle of these wings so the center section takes a large jolt when landing since the gears are on the wings and not the fuselage. You can buy a can of liquid foam at any hardware store for $5. Spray it inside the wings and let the foam expand. It takes about 8 hours for the foam to dry but when it does, the wings are atleast 5 times stronger with a weight add-on of about 2 ounces. Only spray the foam in the center of the wing up to the landing gears, not necessary to spray the inner wing tips.

Second, attach a deans switch between the speed controller and the motor inside the engine cowling on each wing, right above the landing gear mains.

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idproduct=6581

This not only give you the ability to disconnect the battery to each speed controller from the hole above the mains but it also gives you the ability to charge the battery pack externally from any of the switches by simply unplugging the switch from the speed controller and attaching your charger to it. Even if you have two batteries in parralel, they will both charge, simply double the amp rate on the charger. No need to take apart the wings to charge your batteries externally. Very convenient.


Vic

[Scott Morgan]

Blnk00, Is your DC-3 the older Kyosho arf they offered 10 years or so ago? Looks like a nice Gooney Bird.
Scott

[blnk00]

I don't know honestly. The plane was handed down from person to person and looks like nobody knew what to do with it. Finally, I bought it and turned it electric. I know towerhobbies sells a dc3 kit to build but it is not this plane because the fuselage on mine is fiberglass.

[Scott Morgan]

Yea, I'm sure its the Kyosho kit and someone took the decals from the Top-flite kit and used them on your Kyosho kit. It looks good!
Scott

[blnk00]

thanks! Well it's good to know where it came from finally. She flies great, scale.

[realtimerecon]

I currently purchased this model from a member at the club. I removed the two .40 nitro motors and am setting it up brushless.

The motors are two turnigy 400kv motors spinning 11x7 3 blade props. Battery is a 6cell 8000mah 10c pack. I have two 70amp speed controllers, one for each motor. Seperate lipo and BEC for receiver. My problem is the following:

When I run one motor, I get 550 watts on either one. As soon as I run both motors, I lose 100 watts on each motor. This is irrelelevant of what prop I use. I've tried different sizes, I always lose 100 watts per motor when they are both running in sync.

My first suspect would obviously be the capacity of the battery. However, the motors are pulling on average 25 amps each, 50 amps total, well below the 10c, 80 amp capacity of the battery. If I prop up to 11x8 3 blade props, the amp draw is 30 amps per motor, still below 10c. However, I get the same 100 watt loss per motor when they are running in sync. Doesn't matter what prop I use, I lose 100 watts per motor when they run together. This has me stumbled. Has anybody experienced this phenomenon before? Please help.

Vic
You did a super job on the DC-3 :). If u ever run into a problem (w/ only 1 motor running in flight).Don't worry , she will fly for a LONG time on 1 Eng. If its anything like the real thing....Photo 1969 Viet-Nam...RTR

[blnk00]

thanks buddy. Till now I haven't had that scenario and hopefully never will. That's the main reason I decided to make it electric.

[EJWash1]

Photo 1969 Viet-Nam...RTR
PUFF!!!

EJWash

[Darryl Miller]

Blnk,

I havent been on here for a while.......but it was good to see another DC3 around! I just perused the posts..and am glad u worked out the problems with your power system. When I was building mine, I was lucky enough to talk to the reps from Castle Creations and ask some specifics on the set ups..and they indeed recomended to me to use two batteries, but in parralel.
Mine flys well...although I wish I didnt have to fly off grass, it messes stuff up!!!

Happy Landings,
Darryl

[blnk00]

Darryl, that's beautiful man. Sorry for the late reply I hadn't been on here in forever.

And yours has retracts, NICE!

I hate flying off grass also. The landings have to be perfect if not kiss them goodbye.