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[tt1]

Hello folks could you please help me understand or point me in the right direction whereby I can learn a little more as the title suggests ? 
       Many times I have read posts advising (using hypothetical figures for eg only) a motor of say 7.2volts to be run using a 8.4, 9.6 or even far higher voltage batteries to give (I assume) much more power, firstly does this not go outside of the designed voltage specification for the motor?  Also by 'power', is this speed via increased rpm or torque or both?  I do realise of course, that all set ups are defined by the type of craft to be driven but I'm trying to get a general understanding of how you guys determine this.

      I've read a few basic articles on motors / batteries / props / esc's etc. but finding the right combination is where I'm totally lost. An excellent example is a post by Lord Bungle re his underpowered boat - Spear, this also brings into play the question of weight, as a novice I assumed all craft even the fast (ish) planing ones were built to a waterline, in which case would this not decide the overall weight needed / acceptable, or am I completely barking up the wrong tree?

      May be asking a lot I know but If anyone could help with a basic tutorial, a general overview or even constructive opinion I'd be most grateful, thanks in anticipation and kind regards,

                                                                                                    Tony.

[nick_75au]

Hi Tony,
Motors can be run at almost any voltage but the motor is limited in power (handling),  a 540 for example is about 100 to 150 watts (Watts is power, same as Horse Power) and Watts = Volts times Amps

Under no load.
There is a minimum voltage where friction will overcome power and it wont spin and a maximum voltage where friction and internal losses cause the motor to exceed its power handling capability and overheat or centrifugal force causes failure.

As you increase load to a motor the range becomes narrower.

The speed of a motor is directly related to voltage hence the Kv ratings seen especially on brush less motors, a brushed motor has a Kv rating as well, its not advertised for some reason.

Given the same load doubling voltage doubles speed and amps but power increases 4 fold

Example on a common Graupner,
Speed 700 TURBO   
Nominal volts
9.6v   
Voltage range (practical)
4.8-14.4v   
Nominal Rpm
15000   
Kv
1562   2      
Nominal Amps
12.5      
Nominal Watts
120
 
This motor would be able to handle 150 + watts  push it past 200 and the smoke will be emmitted

Run this motor at 14,4 volts with the same nominal load will increase amps by 66% so will draw 20 amps, 20A X 14.4V = 300 watts exceeding the power handling of the motor, the load would have to be reduced to 8.3 amps to keep the motor at 120 watts, power is the same then but RPM will increase.

I hope this helps as a start
Nick