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[scoobster]

After your thoughts

Took my Krick WSP Police boat out for it's first voyage yesterday  and I was using my usual 3300 Nimh 7.2v stick packs which I have used in my other boat which is a triple motor 1 meter long PT boat and they perform as expected in that.

The Krick is using the small kit motor, prop and shaft etc so lets just say its no power boat but there was a noticeable drop off in performance after only a few minutes. I thought it might have been an issue with the battery pack and so changed it out for another and the same thing 2 or 3 minutes then a drop off in power, and when I got home and put the packs back onto charge they were almost full and took no time at all to re-charge. To be honest they had left what capacity I would have expected for the time they had been used for. So my question is for such a small prop and motor combo what could cause such a drop in power?

[chas]

From what you describe, it's not a battery issue. That leaves the motor, ESC and shaft / coupling. Could something be tightening up after it's been running a while?  I've never heard of an ESC that would do what you describe apart from very old resistance types. 
  Just for interest, what motor, ESC and prop is in the model. 

[grendel]

is the prop shaft binding, on one model I doubled the performance, just by realigning the motor and prop shaft.

[unbuiltnautilus]

My gut feeling is that you have a duff motor. It would be useful to know if the motor got hot to the touch when it started to slow down.
The other option mentioned, that the shaft could be locking up is also worth checking into. Check you have enough play, you are usually looking for about 1mm of movement once the prop and coupling are locked off against the lock nuts...I still suspect a cheap motor!!

[malcolmfrary]

A dud motor out of the box in not unknown (try it uncoupled), but the usual culprits are either a locknut not properly locked allowing clearances to tighten or a shaft not as straight as it should be giving excess friction.
Not sure about having 1mm of end play in the shaft - I usually just go for "perceptible movement" and a couple of thrust washers at the outer end.

[chas]

I've known bad Hugo style couplings start to lock up, quality can vary a lot. I agree with Malcolm about the 1 mm being rather a lot of free play, just enough to allow free rotation, no more.
 I would check the motor directly on a battery, ( assuming a brushed motor) if possible put a light load on it, a pulley or similar would do. Check for any sparking. If you have an ammeter, see if the current changes significantly over a few minutes running.
All this is assuming that the prop shaft, lock nuts, alignment  etc are fine.

[Tug Fanatic]

..................... If you have an ammeter............................

Watch the readings for the model held in the water & see if it changes over a few minutes at the same time seeing what, if anything, gets hot and whether there are any nasty vibrations etc. It should all be silky smooth and sound it!


A 3300mah 7.2v battery should have few problems with a 400 sized motor (I am guessing brushed?)


The 1mm end float does sound high but as we fly models with all the thrust load on the motor bearings I would not have considered it the most likely problem source


I am assuming that your wiring and connectors are up to the job. You don't use Tamiya style connectors do you?


What prop are you using?


If you have a voltmeter (in a multimeter?) keep an eye on that as well!

[scoobster]

Thanks for all the replies

Not sure what motor came with the kit it looks like just a 380 size motor with no marking etc. and the kit didn't come with an ESC but the shop sold me a Hobbywing 1060 waterproof esc for it

The prop shaft seems to turn freely so as mentioned above it could be the motor so I think I will order another one and swap it out just to be sure.

Any recommendations for a 380/400 size motor?

[Tug Fanatic]

Well that is an ESC for a brushed motor.


Before anyone recommends a motor I think we need the prop (make, diameter, number of blades etc) that you are using.

[scoobster]

Hi Tug Fanatic,

Yeah its a brushed motor don't know the make of the prop as it came with the kit but its 3 blade 35mm diameter

[Tug Fanatic]

Hi Tug Fanatic,

Yeah its a brushed motor don't know the make of the prop as it came with the kit but its 3 blade 35mm diameter.

I would not jump at changing the motor until you know that there is something wrong with it. Have you done the tests suggested?

[scoobster]

Not tried running the motor uncoupled yet will try to get that tested later tonight and don't have an ammeter but I have been out today with the PT boat so know for sure now its not the battery packs as they were fine.