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Old Dec 20, 2001, 12:03 AM
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Muah's Avatar
Singapore
Joined Jan 2001
736 Posts
cobalt or speed 400?

Hi everyone...
I am rather confused......most of the planes i have are driven by Speed 400 6volts motor, and they are cheap to come by. Recently my LHS started carrying the Promaxx Cobalts..and i am tempted to buy some to try out, but it seems that in every article or postings i read, they require more cells, somewhere in the figure of 10 cells. hey that is no problem if i am getting 10 cells worth of power, but looking at charts, the motor only dish out nothing more than 60% efficiency, that isn't a lot compared to the relatively much cheaper Speed 400s....in short, if i go cobalt, i need to buy bigger cell packs, pay more for the motors, and change brushes, for only a very marginal power increase! Help me understand the rationailty of paying for Cobalts, when Speeds are just that little less better, on the other hand, i am sold on brushless....just waiting for my skills to get better and then i will be more comfortable with my investment!
thanks all for commenting...
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Old Dec 20, 2001, 04:17 AM
Single-task at best...
tim hooper's Avatar
Telford, UK
Joined Feb 2000
7,509 Posts
Muah,

From experience, it's my opinion that these little cobalts are far more powerful than the S400 6v units, and on the same cellcount too!

The downside (there always has to be one, doesn't there?) is that the usual 500/600 size cells just wont deliver the amperage that these motors need to perform properly. So then we need to carry the extra weight/bulk of an 8x800AR or CP1300 pack, in order to deliver the 18-22 amps that these motors pull.

Sooo...then we also need an ESC capable of dealing with this current....

Oh yeah, you'll need bigger props too - the Aeronaut 6.5x4 is a good match for a 4014 on 8 cells.

Conclusion? From a Zagi point of view? It's not just a simple motor swop, but the difference in performance is quite astounding!

tim
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Old Dec 20, 2001, 08:13 AM
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Muah's Avatar
Singapore
Joined Jan 2001
736 Posts
mmmmm..so Tim
more current, larger cells, and bigger prop for MORE power but less duration? or would it be like brushless set up where i can throttle back and get the same power as Speed 400s, and thus fly longer? that would also be because Cobalt have better efficiency..?? right? but on charts seen on SE modeler magazine, the best eff is about 60% and that is only 10% more than the normal Speed 400s.......correct if i am wrong...alternatively, i could use my same 600aes cells and save up for brushless, use the same prop and run on lower current!
mmmm.....
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Old Dec 20, 2001, 08:59 AM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
6,761 Posts
Muah

Having owned Speed 400s, a brushless Mega 22/10/6 and a Promaxx Cobalt 4014- let me make the following observations.

1) Tim is quite right. Think about overall power systems. The Speed 400 on an 8 cell 600AE pack is a very different overall system than either the Promaxx cobalt or Mega brushless on a 7 cell CP 1300 pack (effectively the next battery upgrade.) Only the Hacker motor can deliver more on the 8 cell 600AE pack in practical terms, and it sounds like that's out of budget.

If you have decided that you need a significant power increase from a Speed 400 system and can tolerate the additional 3+ ounces in power systems, then you have two choices-the Promaxx cobalt or the Mega brushless.

2) The brushless motor is much more rugged and doesn't need maintenance. If you dork, it's easy to bend the shaft on the Promaxx motor- I know this firsthand.

3) The brushless and cobalt have similar power levels in the same airframe using the same batteries. (A 7 cell CP 1300 pack)but some brushless motors can swing a larger prop.

4) When you add up the total cost of the power system, motor, mounts, ESCs, batteries etc. the brushless is maybe 25% more expensive than the cobalt.

Sam
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Old Dec 20, 2001, 10:13 AM
LJH
Moths do not fly inverted
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Greenwich CT.
Joined Sep 2000
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I have 30-40 flights on my Pico Jet combat with a 4014. The performance is MUCH better then the P480 that came stock. I have tried a bunch of diffrent props ranging in size from a 5x5 to a 8X4 APC E-prop. When I first got the motor and tried the 5X5 I checked the AMP draw and the RPM. Much to my amazment the motor turned the prop at just about the same speed as the P480 with a significant increase in AMP draw. After doing a little reading I relized this motor needs more prop. I thin found a 7X3.5 COX prop at the LHS and tried that. Vertical was MUCH better but the speed was about the same. I ordered a couple of props from APC in the 6" range with more pitch to see if I could speed the PJC up a bit. Well they where all pulling around 25 AMPS and I though that was a bit much for this motor. I also had a the 8X4 E-prop which I tried which was great in the vertical but pulling 28+ AMPS static. Fun for me but not the motor. I just got a CAM 5.5X5.5 which I have tested and has shown around 23 AMPS static but I have not flown it yet. I will let you know after the weekend. All these test where done with 8X800ar's. These are really the smallest cells you can use though I have flown the 4014 on 8X1600 Nimh RS cells. you can not keep the throttle punched with these cells but after launch if you throttle back she will stay up for 9+ mins. I really hope that the 5.5X5.5 works since I am hoping to use two in my Twinjet and I want it to go fast . Sorry for being long winded but I have spent a fair amount of time playing with this motor. Hope this info helps.

Cheers,
Jim
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Old Dec 20, 2001, 06:22 PM
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Muah's Avatar
Singapore
Joined Jan 2001
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THat is exactly what i mean, more money for Cobalt, higher amperage draw which means less duration, and SAME RPM. Larger prop is allowed, so dare i say that the Cobalts are much better for gearboxes and larger props, not for speed like pylon. Therefore it would be more efficient for me to buy 4 promaxx cobalts 4014 and plug it into my Cargo, and get better thrust, longer duration if i throttle back, using the same cell count of 8, then with the equipped Speed 400 motors? As for pylon or the twinJet, brushless is the way to go yah?
thanks all for listening!!
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Old Dec 20, 2001, 07:32 PM
LJH
Moths do not fly inverted
LJH's Avatar
Greenwich CT.
Joined Sep 2000
4,195 Posts
It depends on what you want to do. If you want to spin a 4.75X4.75 really fast then use the 4011 motor. I am thinking that I should have really gone with a 13 turn motor since I am looking for more speed then vertical. I will let you know about the 5.5X5.5. There is a HUGE diffrence in performance over a P480 though it comes at a cost of less duration.

Cheers,
Jim
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Old Dec 20, 2001, 07:42 PM
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Dorme's Avatar
United States, NJ, Manchester Township
Joined Dec 2000
1,058 Posts
You'll be amazed at how fast the Cargo flys just with the stock 400 6v motors(I've added 7+oz of lead to the nose and it still climbs like a homesick angel, although it is easier to fly level. Next is to add an additional 1/16" of downthrust to all the motors. The problem really lies in the way the wing is to far fwd. It needs to go back approx 1/2", I'm guessing, to balance that large heavy tail.)
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Old Dec 21, 2001, 09:48 AM
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Muah's Avatar
Singapore
Joined Jan 2001
736 Posts
thanks all for replying...
still not convince about the 'value' of Cobalts. it would seem that if a system was started off with CObalt, meaning more cells, high capacity and larger ESC, i would get more power compared to a measly Speed 400s.

Promaxx cobalt = 70
BAtteries 10xCP1300 = 35
New C50 ESC = 50

Total of $155

Hacker brushless B20 S for 90
ESC (Jeti 18-3P) for 70

Total $ 180

mmmm....for another 25 dollars i get to use back my old cells but get MUCH better efficiency and duration!!!!

DUH!!!!


thanks Dorme for sharing with me about the mod you did to your Cargo....any pics??? i still haven't decide on how to paint my Cargo and should i build it first or glass it and paint it first before building it. 7 oz weight in front!!! whoa...
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Old Jan 15, 2002, 05:35 PM
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GaryB's Avatar
Topeka Billard, Kansas, United States
Joined Feb 2001
612 Posts
...i spoke to Sean, the proprietor @ Aero-Model (US distributor for Hacker brushless motors) about my PJC w/MPI Speed 400 Cobalt vs. Hacker B20 setup...
...he told me that he had seen the Pico Jet fly with both and that i would have a hard time beating the performance i was getting with the 13 turn MPI Cobalt - he said the PJC has too much drag to run the Hacker B20 direct drive...and that it was more for pylon type designs...

...to really beat the performance with a Hacker, he said i would have to go with the B40 direct drive with 8-CP1700's - which would add 5 to 5.5 oz. to my PJC AUW...
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Old Jan 15, 2002, 07:29 PM
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Malaysia
Joined Jun 2001
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MPI cobalt price in SGP

Hi Muah

Are you sure the price of that MPI cobalt is $70. I believe it should be about $52 after conversion($95 SGD)

The great planes C50 esc should be less than that. I just bought one C20 for only $24($44 SGD). The C50 should cost no more than $50 bucks based on the C20 estimation.

Not sure about the batt price.

So you now have about additional 20-30 dollars differences. I believe the same shop selling the Promaxx also carried the Kontronik brushless, but a bit stiff(about $550 SGD full set).
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Old Jan 16, 2002, 06:25 PM
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Muah's Avatar
Singapore
Joined Jan 2001
736 Posts
hi Magna...
i do believe you travel to Singapore often then to buy stuff yah? i was just comparing prices that i found in the e-flight magazines advertisements...i know they are cheaper here in singapore but still i just cannot justify the costs and hasssles of going cobalts, when i could just save up longer, wait longer and get a brushless set-up and forget about it for a long time....what do you think? and i believe i am tempted to get a Kontronic set up as they are only about SIN$330 here, about US$183...not too bad would you say? do you have any experiences with Promaxx cobalts?
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Old Jan 16, 2002, 09:30 PM
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Malaysia
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Kontronik

Well you do need to get the brushless esc which will cost you another $200 SGD?

All in I was told abour $550 SGD.

OK on the Promaxx cobalt vs the Jeti 30/3. I tested it with my buddy. He is using the Jeti 30/3 with 12x7, and I'm on Promaxx 2006 with 12x7. He is using 8 2400 mah cell, and mine on 9 2000mah cell. He got about 7700 rpm, and mine about 6700 rpm. The jeti run direct and mine is geared 2.7:1. However, he is running about 27 amp while mine is about 23 amp given the run time over batt amp when the esc cut off.

The brushless will have better eff % than the cobalt but with the gearbox, I'm not too bad. I advanced the timing and got about 7000 rpm. This is with the batt not that fully charged. So the amp may have reached 27 amp and, technically, I would have about 220 watt on the prop after minus some 20-25% for losses. With 4 lbs AUW, its about 55w/lb. I can run it up to 35 amp if I need to but that will be over kill.

So I will more run time given the lower amp drawn so I may match his total flying time. Beside his glider is about 6 lbs.

I will go to brushless later this year, but the promax should satisfy my need. I only need it for climb and then off for soaring/thermalling. The Jeti brushless is one of the best you can get for its price. Cost about 170 Euros, which is about $280-290 SGD. This is with controller.
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