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[guitar man]

Hi all
    Just been reading about gearbox drives on here. What would be the disadvantage of gearing up a motor to produce a faster speed? Does it draw more load from the motor,burn a motor out,  just not done. I was only wondering as pillar drills etc are geared to produce a range of speeds. I was not thinking of any more than two gears one one the motor one one the prop shaft.This is only an interested thought at the moment as I have a large boat that runs acceptable but was just thinking if I ran it on 6 volts instead of 12v to cut the weight down then geared it up etc. Also another thought do more props produce more speed, I do not mean more motors but say two props driven off one motor. Thanks in advance for your thoughts

Regards Tony 

[Shipmate60]

If the motor is overpowered for the prop you can gear up.
Gearing up puts more load on the motor which increases the power required (Amps) which can overheat the windings and burn the motor out.
A bit more information on the model, size, prop size etc would produce more specific information.

Bob

[malcolmfrary]

Motors usually spin at least as fast as it is feasible to have the prop turn, and direct drive is fairly loss free.  If a large prop needs to be turned by a small motor, gearing down works - the motor can use its speed, the gears convert that to torque, but do lose some power.  Gearing up, on the other hand, the gears soak up the power, losing lots of torque.

[dodgy geezer]

Hi all
    Just been reading about gearbox drives on here. What would be the disadvantage of gearing up a motor to produce a faster speed?...

You gear down to produce a slower speed but with more torque. You gear up to produce a faster speed but with less torque. The small electric model motors we use in our boats usually spin at high speeds but with limited torque, and if forced to spin at low speed because the load is high they will be operating in a very inefficient part of their envelope.

So it's common to gear them down under these circumstances - they run better and turn a bigger prop.

I can't think of any modelling application where you need to spin an item faster and with less torque than a direct drive. If there was one, you would certainly gear a motor up to perform this task. But I think the real reason you don't see it done is that there is no need. It would not work well for driving a prop, as the initial speed would be faster, but the torque would be pretty non-existent, and the prop would practically stop when it was put in the water... 

[irishcarguy]

Hi Tony you have just had some of the most knowledgeable modellers on the forum answer your question & no doubt answered it for a lot more of us too,me included thanks guys. Mick B.

[guitar man]

Yes thank you all. Its all clear and understood 

Regards Tony

[Circlip]

I can't think of any modelling application where you need to spin an item faster and with less torque than a direct drive.

  Car alternators are spun faster than engine revs allbeit with a belt drive.

  Regards   Ian.

[Andyn]

modelling application

  Car alternators are spun faster than engine revs allbeit with a belt drive.

 

[dodgy geezer]

Hi Tony you have just had some of the most knowledgeable modellers on the forum answer your question ......

Hey, don't forget me! I answered as well.......   

[Shipmate60]

Car alternators are run by a slightly more powerful engine than a model electric motor.

Bob

[irishcarguy]

Hi Ian, car alternators turn at less than engine revs on racing motors in general, otherwise they would fly apart @ high revs. Mick B.

[Circlip]

O/P asked about "Gearing up" and was given examples of gearing down, my own was an application in general use, not a Le Mans 24hr type. Another exampule of Gearing an alternator up is the showmans traction engine driving the alternator to supply the various fairground rides of the past. The crankshaft flywheel doesn't do 20K but still has quite a large drive ratio.

 

   Quote from: dodgy geezer on June 05, 2012, 09:43:55 PM
modelling application


Quote from: Circlip on Yesterday at 04:24:27 PM
  Car alternators are spun faster than engine revs allbeit with a belt drive.


 

   A typical modelling application would be a steam engine driven generator, there are other drive sources than lecky motors.

  Regards   Ian.

[Andyn]

A typical modelling application would be a steam engine driven generator, there are other drive sources than lecky motors.

Then why didn't you say that in the first place?