why would same kv motors perform so different?

[pmdevlin]

Hi all,

bit baffled by this, I have a large boat, with castle creations hydra 120 esc, running 6 cells, eagle tree data logging has 23mph, using a turnigy t600 880kv motor, through a gearbox with 1.14:1 ratio, and a 50mm 3 blade cleaver prop.

The motor is I know budget end, and is quite hot after 10 mins, so I treated myself to a scorpion HK4025 890KV, not expecting any extra speed, but more efficient running and hopefully cooler.

THe motor was a direct swop in, all settings and power supply identical, but the speed has dropped to 13mph!

Any suggestions would be appreciated as to why same kv motors should produce such different results, everything was double checked, and data was from eagle tree with gps, I would have thought tyhe scorpion would be miles better than the turnigy is every way, as it is 4 times the price!!

thanks

[martin]

Most outrunners like long timing anthing up to 30degrees but Scorpion recomend 5degrees, Dont know what timing you have your esc set at though.

[Fluid]

First off, apples and oranges comparison. Kv is not everything when it comes to power delivery. The T600 is 58mm in diameter, the Scorpion is just 40 mm. The T600 is also heavier. Both can add up to more torque with the T600 and the ability to swing a larger prop faster. Since you have an EagleTree, what was the amp draw of each motor? Voltage drop at full throttle?

IME the Scorpion 4025s like 15 degrees of advance.



.

[Make-a-Wake]

Hmmmmmmm, being that they are almost identical in size i'd be curious about the logging data as well, maybe you got the lower kv scorpion by accident....................the 630 or 540kv............

T600 specs on left....................Scorpion 4025 on right.

[martin]

The Scorpion is 49mm o/d its the stator thats 40mm & yes the T 600 should be 49mm o/d. Martin.

[pmdevlin]

thanks for replies, I too wondered if the scorpion is the correct one, but its stamped on the box, and the motor itself, so I can only assume its correct.

my understanding is kv would be revs per volt, so if the set up is identical for both motors, and the kv is almost identical, I would expect the scorpion to at least match the turnigy, as you can imagine I am really disappointed given the cost of the scorpion in relation to the turnigy, which when compared is technically and build quality a far inferior motor.

Unfortunately I have deleted all the recorded sessions for the scorpion, but the approx max readings from memory, speed was 14mph, amps 29,
most recent max turnigy readings, which are pretty typical for this boat, where, gps 23.67, amps 88.91, watts 1684, after 10 mins running the motor was quite hot, on other runs, particularly warmer days calm conditions and batteries charged immediately before running the gps can be over 24mph amps and watts pretty much the same. Over 24mph the boat is becoming unstable due to torque roll, so ideally with the scorpion I was hoping for 24mph to match the turnigy, but a slightly longer run time, 15 mins would be great!, and lower amp draw.

To eliminate the possibility of a faulty scorpion motor, I have refitted the turnigy, leaving all set up exactly the same, and weather permitting will run again tomorrow to comapre readings, what is the likelyhood of a dud scorpion motor?

With regard to timing, Im really getting out of my depth! The scorpion is stated to be 5 degrees, the turnigy is unknown. Motor timing on the esc is the default of normal, I have never changed this as I dont really understand it. The throttle curve is linear, again I have never changed this, its a hydra 120 if anybody has any idea
Takne from esc instructions:

4) Timing Advance 1) Low Max runtime, slightly lower
power.
*2) Normal
Best balance of power
and efficiency.
Recommended setting.
3) Race
Slightly more power
(possibly in the 5% range
on inrunners, less than
10% on outrunners) at the
price of significantly higher
heat (30% or more!)
generated due to lower
efficiency.
Use at your own risk! 4) Extreme Max power. Most smoke.
No warranty.

its not very specific regarding timing unfortunately,

thanks

[bigwaveohs]

How well a motor can "pull" a given size prop depends more on the power output than anything else. I run a UL-1 motor and an ARC ducted fan motor. Both are around 2000Kv, but the ARC is 2000+ watts compared to the UL-1 which is probably only about 600 watts. The ARC will pull a much larger prop and is much faster. At 746 watts per horsepower I think you can see where this is going...

[pmdevlin]

ok thanks bigwaveohs,

but then at 2700watts for the scorpion, (cannot find the watts figure for the turnigy, but testing figures state it was doing in the region of 1700watts), with what you are saying would it be correct to say the scorpion should easily out perform the turnigy with same set up, or are you saying the scorpion is under performing as it now needs to either be a different gear ratio, or bigger prop as its not working hard enough?
thanks

[BHChieftain]

You mentioned that your turnigy motor would get hot-- how about the scorpion? If everything is running cool then you should have headroom to increase prop (or rpm).

Chief

[pmdevlin]

yes I was thinking that, maybe I am not working the motor hard enough? I was going to try the turnigy again today, just to eliminate the fact that the scorpion might be faulty, and just my luck! I decided to get the latest download on my castle creations esc, and since then, now the esc will not initialise, so now waiting for CC to help me!

[6BOOST]

If you have eagle tree like you say you do you really need to spend more time getting familiar with it, otherwise you'd be able to tell us a lot more information to help you. Motors sometimes get stamped incorrectly, I have a few castle motors that were then restamped, of you knew the rpm's of each from the eagle tree you could roughly work it out from the rpm.

6s is imo pretty low for the kv you are running, sometimes less rpm with a bigger prop is less efficient than more rpm and a smaller prop. You also have highly underestimated the T600, EDF guys have run this motor on 10s and 4000w continuous power for over 12 months in the same plane without failure, and have done sporadic testing on 12s and nearly 5kw, they are a severely underestimated motor. As far as heat goes, is your motor mount water cooled? 10 minutes is a pretty long run time without any form of cooling, I'd expect the scorpion to be about the same, I don't think it's the motors inefficiency causing your heat but your application and run time.

More info (read eagle tree data) might help some of the muhc more experienced members like fluid help you, that is after all why you purchased the eagle tree in the first place of imagine, for the data.

6BOOST

[pmdevlin]

thanks for the info 6boost, yes I dont fully understand the eagle tree! I use it primarily for gps speed, and amp draw, when I was testing various props. The mount was not cooled for the turnigy testing, but is for the scorpion, I suppose I thought spend more money get better performance. The prop testing was quite extensive, over 12 months, and various gear ratios, trying to achieve the best overall performance of run time, efficiency and speed. I could go slower with a smaller prop and run longer I suppose. When I arrived at the sort of performance I was happy with on the turnigy, it was then I looked for what I believed to be a superior motor, in the scorpion, thinking similar spec would give a equal comparison, what I didnt expect was for the scorpion to be so much slower!

I decided to refit the turnigy and run itr back to back with the scorpion, if performance was better, then it could point to a wrongly stamped, or faulty scorpion motor. Unfortunately, as I was preparing the boat this morning, the esc started playing up!! and now will not set. I have tried to reset via the castle creations usb link lead but nothing happening, so until that is sorted I am stuck! THe max cells on the esc is 6, so I cant up the voltage, would you say that the turnigy was working harder than the scorpion, which is under volts?

[Jesse J]

I may have missed it, but what boat? I was startled to hear :

big boat, >25 mph = unstable ??

Interesting using a gear box; was the ratio gearing up or down? and what other prop sizes?

[pmdevlin]

Hi JJ,

I wasnt sure where to post really, in scale, or here, I thought here as you guys are familiar with fast brushless setups, however, my set up is pedestrian compared to your boats, here it is, the picture is the motor previous to the turnigy, align 600l, as is the video, but it gives an idea what I am talking about
Align motor was 1260kv, and ran on 1.25:1 ratio, I have considered gearing the scorpion the opposite way to make it work harder but until the esc comes back from castle (posted today) I am now well stuck sorting this motor issue!

[pmdevlin]

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