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[murphy1570]

Hello folks

 I have fitted a Graupner speed 600 BB motor  as recommend in an  earlier question I asked on the site prior to the great "crash" of the site (thanks to all who got it up and running again), I am a relative beginner and am hopless at all things electric I kid you not!!, the model is of the Vosper MTB 379 as featured in the April 2011 issue of Marine Modelling. I have fitted the prop shaft, motor etc and everything turns freely by hand no problem, I am using an Mtronics Viper 15 amp ESC, and a 7,4 volt 3300 battery pack. When I apply power via the transmitter everythig works okay for a couple of seconds then stops, on further investigation ie 2 blown 10 amp fuses later and much rather coulourful language!! that the shaft was locked solidly within the tube, but on turnimg the coupling a few times by hand a few times everything turned freely again, but on repacing the fuse and appling power BANG the same problem occured ie complete seizure and a blown fuse. again after turning both the coupling a few times all was fine. I am at my wits end perhaps I should revert to the old clockwork trains of my youth!!

I would be grateful for any advice on this subject before I destroy the motor and the ESC  and consign the model to the fire even after for months work on it.

Thanks folks to all who may respond I am obviously doing somethig wrong,
All the best John.

[philk]

have you locked the nut on the shaft to the coupling and the nut on the other end of the shaft to the prop. if you don't lock them tight to each end they can tighten up when turned by the motor and lock onto the outer shaft then if you turn the coupling the other way it unlocks
hope that makes sense bit late

phil

[derekwarner]

  .... murphy1570

I think Dr Phil     may have provided the correct answer....... or at least a step in the right direction.......

Derek

[DickyD]

It does sound like the lock nut tightening up on the outer tube of the shaft,

Check that your lock nuts, where you have them, are tightened against the coupling and the prop.

[essex2visuvesi]

As a side note do you guys use threadlock on the propshaft nuts?

[DickyD]

As a side note do you guys use threadlock on the propshaft nuts?

Normally just the locknut

[barriew]

As a side note do you guys use threadlock on the propshaft nuts?

Only after I have lost the first brass prop


Barrie

[baloo]

I have been told that what ever esc you use always use 5amp fuse higher than whats on the esc eg,15amp esc 20amp fuse to protect your esc.Also leave a 1mm gap when locking up your nut to the tube.baloo

[cos918]

I have been told that what ever esc you use always use 5amp fuse higher than whats on the esc eg,15amp esc 20amp fuse to protect your esc.Also leave a 1mm gap when locking up your nut to the tube.baloo

Hello I think you have that the wrong way around. The fuse should be lower that the max rating of the ESC. SO for a 20 AH ESC use  a 15 AH fuse.

john

[rsm]

I would go the other way if I was you and use a fuse rated lower than the esc (i.e. a 10amp fuse for a 15amp esc) to protect the esc from damage.

[malcolmfrary]

I have been told that what ever esc you use always use 5amp fuse higher than whats on the esc eg,15amp esc 20amp fuse to protect your esc.Also leave a 1mm gap when locking up your nut to the tube.baloo

Very definitely the wrong way round.  The ESC should be capable of living longer than the fuse, and it is the fuse that protects the ESC, not the other way round, since fuses are usually cheaper than ESCs. 
The 1mm of play seems a bit generous.  I prefer "barely perceptible movement", but the locknuts do need to be locked against whatever they are locking, otherwise the nut will travel along the shaft and lock itself against the end of the shaft outer.  When the shaft spins suddenly and violently, the mass of the nut has inertia, and is reluctant to spin.  It therefore travels along the shaft until something stops it.  If it is the inner end, the shaft seizes.  If it is the outer end, the chances are that in one direction the prop will unwind itself.  Since more force is exerted on it in water, it will work perfectly on the bench, but will only decide to fall off when in six feet of muddy water.  This is in full accordance with Murphy's Law.

[GG]

Oil?

[malcolmfrary]

Oil?

Always a good idea, but even a really unlubed shaft would take more than a couple of seconds (as in the OP) to stick, especially if, as stated, it "turned freely by hand".

[baloo]

Sorry folks,i did get it round the wrong way,not with it today.Baloo

[nemesis]

Hi, This is a sympton of Nylon/ Plastic bearings which are sometimes fitted in the Tube. They have a tendency to lock up. I would still go for the nuts not being done up correctly.  Nemesis

[murphy1570]

Hello folks

Thanks for all the responses to my question all sounds like sound advice and I will check out if I have locked the nuts to both the coupling and prop, I suspect I have not knowing me!! to be honest I did not know this was so important!! i do now. thanks folks I will let you know how I get on.

All the best John.

[irishcarguy]

Yes it would nice to know what the cure was, thats how we build forum knowledge. I think it is the nut too. Mick B.