P S Captain Sturt problem

[Peter Webster]

Can someone suggest why the motor in my Capt. Sturt burnt out last week and the replacement is running hot after about 10 mins running. The model is 4 ft. LOA powered by a 540 running on a 12volt 7.5amp gel cell a 1inch dia pulley is driving a 3 inch dia pulley on the drive shaft the drive quartering is spot on and can be spun with the belt, a rubber o-ring, disconnected so it is not friction which is the cause of the problem. Could it be that the motor is running to slow as the esc, an Mtronics 15 amp unit, is barely on. I have replaced the 540 with a 550 which still runs hot but not as much I have tried a geared MFA motor 50:1 ratio which ran ok but was too noisy. Any suggestions, apart from converting it to steam, would be greatly appreciated.
Peter Webster

[derekwarner_decoy]

Hi PD's &   Peter that  the motor series 540 & 550 both have a  :?: - I think that they were designed to operate @ say 750 rpm to 3000 RPM & not TOO happy being artifically given reduced voltage which appears to be only a shunt of GO><NO<GO>> VOLTZ multiplied X time & hence your thermal  : motor meltdown :!:

Remember OHMS Law :?: .... & even if you can find an OLD anologue multi meter......these new  :computer electronics speed controllers you may never  understand  

Put the kettle on, put a Twinings Earsle BLACK bag in the cup & a VEGE sanga on the plate & consider steam - you won't regret it -  :bow    :gather  :boom - Derek

[towboatjoe]

It sounds to me like the motor is being stalled from turning too slow and not enough torque.

A small geared motor turning 100 to 150 rpm should be able to power it with no problem. it doesn't take much to push a boat on the water.

[Peter Webster]

Thanks For the replies, it looks like I will have to revert to using the geared motor from MFA Como and put up with the noise. Sorry to disappoint you Derek but this one is staying electric.
Peter Webster

[Bob Golder]

Hi Peter.  Is your geared mtor noisy when running out of the model?  If not you could reduce the noise in the hull by fitting some damping material between the motor and the base plate, rubber perhaps.

[Khephre]

Following up on Bob's comments regarding rubber motor mounts, are you able to tell us a bit more about this.

Slightly off topic - I have a 66 inch long fibreglass hulled long raised quarter deck coaster which runs using an MFA/Como Torpedo 800 with timing belt drive reduction unit. The fibreglass hull seems to amplify what is a normally quiet belt drive and I'd love to deaden that sound. (Yeah I know, screw-drives are heresy, but hey I'm getting counselling for it....)

I know the flyboys sometimes resort to rubber engine mounts but haven't found any small enough for even the bulky 800 motor.

So any suggestions on scratch building rubber engine mounts that are bigger than servo rubbers yet smaller than aero engine mounts? Or are there simpler sound-deadening solutions?

Cheers
Tony

[Eddy Matthews]

One of the easiest solutions is to simply put a flat piece of rubber under the motor mount Tony, it generally works pretty well...

I'm sure that's what Bob had in mind when he posted earlier...

[Peter Webster]

Bob,
       I did use a piece of 3/32 thick soft rubber to soft the noise transmission onto the hull but it still resonates through. I think the hull is partly to blame as it is fibreglassed over balsa skin. The way I normally build is thick walled balsa hull with 5-6 coats of dope progressively thinned  and this still gives a certain amount of flexibility, it's hard to break years of free flight building habits.
Peter webster

[Khephre]

Hmmm...so much for being labelled a Chief Engineer on this forum!!! I think I get the drift of rubber mounts but am still not quite clear on the mount fastenings.

Do you glue the rubber to the hull and then the motor to the rubber or do you still screw or bolt the motor through the rudder onto the "engine bed"? If the motor 'floats' on the rubber without being fastened down, then how's it kept fixed and immobile?

Back to Peter's query - if one is using an electric motor at such slow speeds that it's stalling, wouldn't the speed controller or the fuse be overloaded first?


best regards
Tony

[derekwarner_decoy]

Hi PD's & no Tony - Sir IZCAS Newton [Sandys mate] with his third Law of Motion stated 'if the little wires attached to the comunatator get TOO HOT, they suffer a thermal melt down prior to blowing a fuse  :rant & the simple reason is human nature

  ... if I don't want my vessel to stop in the middle of the lake, I should install a  : HIGHLY  :twisted:  rated fuse -   - Derek

[mjt60a]

....If the motor 'floats' on the rubber without being fastened down, then how's it kept fixed and immobile?....

What some people do is fit a hook (or nail!) either side of the motor and strap it down with a thick rubber band such as the type sold by camping suppliers to attach tent pegs to the bottom edge of a tent...
see this - http://www.modelslipway.com/photo_gallery/kitreview_rescueBrumstead/rescueboat_reviewDB/rescuereview_photos/pic14.jpg
That looks like a very thin rubber band but I guess, with a prop shaft some flexibility is acceptable. For our purposes, a gear or pulley is more likely to be used so the motor needs to be more rigid....(I couldn't find a pic of exactly what I had in mind - though I have seen them in Model Boats mag and at the pond-side  )