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[Biggles]

Hi Everyone

I was browsing Ebay and saw a Sea Queen for sale powered by 2 MFA 850's in tandem, what is the benefit of mounting the motors this way?

Thank you for any help received.

Biggles

[john44]

Hi Biggles, do they run off 1 speed controller or is 1 motor used for forward and the
Other for reverse through separate 1 way speed controllers?


John

[Biggles]

Hi John

Here's the information from Ebay...

... fitted with tandem MFA 850 brushed electric motors (drive thru rubber flex coupling) and fitted with Tornado 50 AMP speed controller with forward and reverse controls, Raboesch heavy duty UJ coupling and 2 blade 55mm sport propeller Complete with correct Jotika custom made support stand Lively performance and easy planing as seen in the photos without the complexity of brushless or noise restrictions of IC power set ups ...

Only one speed controller!

Biggles

[Calimero]

I guess someone had too much time on their hands.

[Netleyned]

I might be looking at this from the wrong angle,
but the motors will only rev at their design speed.
Would the torque be doubled?
A seaqueen would go quite well on one 850
with adequate volts and a beefy esc.
Probably get shot down by the experts .

Ned

[Stavros]

Ned you are 100% correct a single 850 is enough to get it on the plane especially on a 55mm prop but the run time is around 1o mins on a lead acid batt....WHY on earth would you put a pair in tandem Baffles me
 
Dave

[inertia]

WHY on earth would you put a pair in tandem Baffles me
 
Dave

Perhaps ten minutes is too long for the guy? Short attention span? Who knows (and who cares)?
I'm with Calimero on this one. I can't see any advantage at all other than the "Wow!" factor.
WOW probably stands in this example for Waste of Wonga.
DM

[Time Bandit]

Not such a bad idea (despite the weight of the motor), I have no datasheet of the motors, but there is definetly a point where you have less Amp consumption with 2 instead of 1 motor.

Itīs a matter of calculation since the wire losses (which can make 90% of the losses depending on current drawn) in the motor increase squared with the Amps, while other losses stay constant (at constant voltage).
If 1 motor is running somewhere way above itīs efficiency maximum and the second motor is attached the wire losses are only 50% (1/4th x 2) of the losses of 1 motor.

So lets say 1 motor is running @ 20A with an efficiency of 60% it produces an output power of 144W.
If we attach the second motor the power consumption of the boat stays the same @ 144W.
If the efficiency of the motors at 8A is then 75% the motors will only draw 192W or 16A out of the battery, which is again 144W output power.

If we now calculate the added weight of the motor with an additional 20W power consumption and 73% efficiency (higher amps --> less efficiency) on the 2 motors theyīll take 224W or 18,6A. Still makes sense and produces a lot less heat out of the electric energy in the battery.

That is by the way the basic principle in all electronics to reduce losses. Itīs often better to use 2 (weaker) MOSFET instead of 1.

For sure if 1 motor is running in the area of itīs best efficiency itīs absolute "xxxxx" to add another one 

[david48]

Could this be a generator !!!!!!!!

[Andyn]

Stupid looking things happen when you've got nothing better to do, like Greg's water cooled engine mounts...


Retirement seems awfully boring to me

[inertia]

Retirement seems awfully boring to me

Yep - it can be at times, Andy. As my mate Irish Dave said the other Friday, "All I have to look forward to now is a good death". He can be a right miserable old ^Ģ$$(*&! sometimes, especially after four pints.
The worst part is admitting that you're old enough to qualify.
Don't rush, dude - it'll happen soon enough, and you'll know when it has because you'll start doing odd things - like making water-cooled engine mounts..................
DM 

[derekwarner]

Guys...I know less about air cooed model internal combustions than I understand about motors driven by a path of electrons , however seeing the example of a water cooled internal combustion engine mount in a model boat is far from questionable

1. the natural air flow over the engine in the model boat would be of far lower velocity and spread of distribution than in a model plane
2. neoprene elastomers have an operational limit bordering 100 degrees C, however its flexural resistance is greatly reduced above 60 degrees C

So this is a little of thread track, but in defence of the concept of water cooling drive components that may suffer from overheat......  ......it would be interesting to get my new Chinese digital pyrometer [AUD$12.00 including APP] and ascertain the actual component temperature without burning   my fingers  .....and Derek

[Biggles]

Hi All


I'm happy with the answers, its time to close this thread!


Thank you all for all your help, very useful as usual.


Biggles

[malcolmfrary]

There have been cases where two motors have been connected to one shaft via a gearbox, presumably to increase available power without using a bigger, fatter/longer motor but still fit in the space available in the model.  Whether there is a point to this example is an open question.  It certainly would give whatever advantages the two motors - one shaft gearbox would give without the racket associated with gearboxes.


Somebody in a thread, possibly in a forum far, far away, wanted to use a coupled motor as a generator.  While it was pointed out that this would just be a novel way of flattening the battery a bit faster, a thought wandered in.  A small motor (brushed or brushless) could probably be used as a signal generator for a sound unit.