Motor Mystery

[Bill-SOCAL]

So here's one for you. My 32" DF Storm P mono has a Nemesis 10XL (1668 Kv) in it. Runs very nicely and clocks in at 48 to 50 mph running m445/m447/x646 props. Good temps too, never anything over 120 or so.

But the FE NATS are coming up so I decide to install a Feigao 9XL I had sitting here. Figured I'd get a little extra punch from the 1853 Kv over the 10XL.

Now here is where the mystery enters. Ran the 9XL yesterday and it is on average 5 to 7 mph SLOWER!!! Temps were a touch higher, by about 5 degrees over what I normally see.

Same set up. Same ESC (Hydra 120, no firmware updated), same batteries (4S2P 5,000 25C Poly RC), NO changes at all to the boat.

So can anyone explain to me how a motor that is 185 Kv higher (11%) can run slower by so much using the same props??

The 9XL turns over silky smooth, no binding. Everything is as it should be mechanically. I am mystified to say the least.

I can think of only 3 possibilities:

1) the 10XL was miss-marked and is a 8XL or higher Kv

2) the 9XL is miss-marked and is a 12 XL or lower Kv

3) the 9XL is defective

Any other ideas??

[Doby]

I would go with the mis-labled theory
All other things being equal, it sounds like the only expanation!

[SJFE]

I would have to say you have a miss marked motor Bill. You need to run some type of kv test to figure out what one. How thats done is beyond me.

[Mich. Maniac]

just outta curiosity what do you have hydra timing set at?

[Bill-SOCAL]

Same settings as the 10XL, which was the "normal" setting in the Hydra. Like I said, there were no changes made except the motor swap/

I could use a drill press with a known RPM and run the motor at that RPM and measure the voltage produced. A motor run that way is essentially a generator. But I don't have access to a drill press with a known and verified RPM.

[SteveReesor]

Try an prop with less pitch say an X442...or even an ABC 42x55.

Increasing motor RPM by dropping a wind or two...drop down in pitch slightly to keep the RPM's up an let it wind out.

[Bill-SOCAL]

I'll give that a try, although I am hard pressed to believe that a m445 was too much prop for it. It has that much less torque??

I have a x442 I can try and a 42x55 and a 440/3, which I use on my SV - which is much smaller than this boat. I can also go all the way down to a x637 if I have to.

[ReddyWatts]

Mount an airplane prop on the motor and get a laser prop tach for checking the RPM/KV difference of the motors. Maybe one of your buds has one you can borrow.

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5609

[Eyekandyboats]

what was the condition of the motor before it went into the boat?
did you buy new or used, or ...

[Jeepers]

Bill my P mono ran great on a X442 4s1p 9XL 45 to 50 mph.

[Bill-SOCAL]

In order:

I have plenty of props and a tach. Not sure it's worth that much work

Motor was brand new, never mounted or run

I'll give the smaller prop a try. Maybe I was expecting too much. Seems like a m445 should not be too much prop, but maybe it is.

I want the 9XL to be faster than the 10XL. If it takes a smaller prop to go faster, then I am OK with that.

Jeepers, which hull did you have??

[properchopper]

re :

Prop down ! You've seen my 9XL Titan rip, completely aired out with a X442 & not any faster with the modded M445 . Your boat , at 32.5 inches with the Delta-like hull runs waay wetter then the 29" Titan. Methinks the 9XL isn't unwinding !! My 2.3 cents anyway.

[Bill-SOCAL]

Like I said, I plan to go small. In this case maybe size does matter, but in the other direction. I thought your Titan had an 8XL?? Guess I thought wrong!!

[properchopper]

re :

Titan's got a 9XL/Hydra 240. Been in it over a year now & still pumpin'. Drifter's got the 8XL; much less running surface, OM 26 's got an
8XL for fun running [ & embarrasing nitro SV 27's ]

[domwilson]

Yep a smaller prop might be your best bet. I have a 9XL in my 30" Skunkworks cat. With a X445 it was kind of slow. Maybe about 25 mph. Changed the prop, to a X637 and a X640. Big, I mean really big, difference. Beats my SV27 with a X642 on the same batteries. 4S1P lipos.