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Old Aug 10, 2004, 10:32 AM
God is good
Viper Pilot's Avatar
Banjul
Joined Jan 2001
4,246 Posts
Question
Three Speed 400s in series ???

Ok, I've never tried multi-motor planes, and I'm not entirely sure of the setup.

Tell me if I have this right.

Speed 400s draw about 10 amps for good power. I want to use three 6 v. S400s. A singe motor seems to run fine with an 8.4 v. battery.

With 3 of these in series, the voltage needs to be about 24 volts, which would deliver 8 volts per motor.

Is the current draw on all three still 10 amps??

Please, someone, tell me if I have this right??

With a plane with AUW near 48 oz. work with a 20 x 1100 battery pack??

Viper
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Old Aug 10, 2004, 11:44 AM
Mad Max meets the Thinker
Cyberman's Avatar
Pittsburgh, PA
Joined Apr 2004
569 Posts
Quote:
Originally Posted by Viper Pilot
Ok, I've never tried multi-motor planes, and I'm not entirely sure of the setup.

Tell me if I have this right.

Speed 400s draw about 10 amps for good power. I want to use three 6 v. S400s. A singe motor seems to run fine with an 8.4 v. battery.

With 3 of these in series, the voltage needs to be about 24 volts, which would deliver 8 volts per motor.

Is the current draw on all three still 10 amps??

Please, someone, tell me if I have this right??

With a plane with AUW near 48 oz. work with a 20 x 1100 battery pack??

Viper
I'm not sure you want to do this, unless the motors loading is VERY equally matched parallel is MUCH better. Use a 7 Cell GP3300 with a high current ESC, using a BEC with it will work better because it has to drop a lot less voltage (that will save you weight).

Series is tricky because what WILL happen is if there is a slight imbalance in the loading of any of the motors (IE it runs a TINY bit slower because of the prop), the other motors will see a higher voltage and begin to spin a bit faster it's a rather interesting but anoying situation, especially with 3 motors. Your other option and just as good is use 14.4V (or if you can find them 18V) this will drop your amp draw per motor. One thing I have noticed is higher voltage motors tend to operate more efficiently so this might be a much better option as you can run it with 16 or 17 cells and get your current at about 12.5A not a big draw. And you loose some weight.

If you hae the motors already though... I would go with a higher current ESC and GP3300 battiers.

Cyb/Stephen
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Old Aug 10, 2004, 10:05 PM
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vintage1's Avatar
East Anglia, UK
Joined Sep 2002
29,705 Posts
IF you are gearing them, use 10 cells or 3S LIPO, connect in parallel and prop for about 7A apiece. You will get more power out of them at 10v and 7A than 7v and 10A....

If you want to do direct drive use big 2s LIPO pack or big 30A capable 7 cell pack.

Since one speed 400 adequatly flies a 20oz plane it seems reasonable that three would easily fly a 48 oz plane.
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Old Aug 10, 2004, 10:22 PM
CD-ROM Junkie
Art Newland's Avatar
United States, WA, Bellingham
Joined Apr 2001
13,976 Posts
Quote:
Originally Posted by Viper Pilot
Ok, I've never tried multi-motor planes, and I'm not entirely sure of the setup.

Tell me if I have this right.

Speed 400s draw about 10 amps for good power. I want to use three 6 v. S400s. A singe motor seems to run fine with an 8.4 v. battery.

With 3 of these in series, the voltage needs to be about 24 volts, which would deliver 8 volts per motor.

Is the current draw on all three still 10 amps??

Please, someone, tell me if I have this right??

With a plane with AUW near 48 oz. work with a 20 x 1100 battery pack??

Viper
you are correct, you will need an esc that can handle that kind of voltage, and a UBEC or an onboard receiver battery. I've run twins in series (never a trimotor) and it worked great.
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Old Aug 11, 2004, 06:49 AM
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vintage1's Avatar
East Anglia, UK
Joined Sep 2002
29,705 Posts
Theoretically it works BUT the RPM synchronisation is NOT great. Motors run from the same voltage (paralell) tend to try and run at teh smae RPMN, whereas motrs run from the same current (series connected) tend to run at the same torque.

Small differences in loads or friction can send the motors quite far out of synch.

3 speed 400's could be no more than 20A on a suitable 3s LIPO or 10 cells pack. Its a heck of a lot simpler than series connecting them to use a 20-30 cell pack.

30A capable 3s LIPOS or 10 cells packs are also very easy to obtain. Its usually a 3s 2p pack or 10xsub C of some sort.
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