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    Motors  used in model boats are called DC motors,  i.e.  the motor rotates  when  a Direct Current is applied.  You don't need to know the "WHY'S  and  WHEREFORE'S",  just  take my word for it.  Batteries supply Direct Current  and  so  are the most suitable power source.    DC motors  have  permanent  magnets  and  a  central rotor called an armature.  When  the  current  is  supplied  to  the armature,  it produces an electro/magnetic  field  which  reacts  within the permanent magnet's field causing the armature to  spin.  DC  motors  are  designed  to  spin faster and  more  efficiently  in  one  direction,  usually anti-clockwise looking from the output shaft end.  You  can run these motors in two different modes.  Mode 1) Motor run at maximum  efficiency  which  is  optimum  speed or torque for  the  minimum  current  consumption. Mode 2) Motor run at maximum possible speed within the motors  current  limit.  Mode 1 is for "scale"  boats and mode 2 is for the  speed  merchants. There you are, a complete physics lesson in  two minutes.   

   There are two basic types of DC motors,  'slow' ones and 'fast' ones,  I'm  not  going too fast for you am I?  Both types may appear identical but the  internal  construction  and  set-up will determine it's speed but  all  DC  motors  use  the same basic components.   Slow motors are used  in  scale boats, tugs, merchant ships, warships etc, any boat that is required  to  run  at a relatively  low speed.  These slow motors commonly have  low  current  consumption  which enables them to run for a long time from  each  battery charge. What they lack in RPM they make up for in torque, they can  propel  large  boats,  drive  multiple  prop shafts  and  can  turn  large  propellers.  A  larger propeller is usually more efficient than a  smaller  one  but requires more torque to turn it.  A reduction gearbox will reduce  RPM from any motor but increase it's torque. This applies to slow and fast  electric  motors  and  IC engines so reduction gears are not  uncommon  in  model boats.

Size of a motor is commonly an indication of it's output power but  not of  it's  speed.  There  are all sorts of numbers associated with the size  of  model motors, eg. 380, 540, 550, 750, which are Macbuchi numbers, probably  the worlds largest producer of electric motors. (For more details on these  motors,  see  'The power game'  RCMB Nov/Dec 1992).  Motors can also  have  names such as Milliperm,  Monoperm, Decaperm and Hectoperm, these are high  quality and high priced slow motors. Other terms connected with motors are  poles  and windings which refers to how the armature is constructed.    Of  course  you can also use electric motors from other sources such as  video  recorders,  tape decks, computer equipment, car heaters etc,  even from an  aeroplane  wing in one case!  These motors are usually chosen because  the  builders availability to them.  With these motors you will obviously be on  your  own  when it come to testing them for suitability.  You can use  any  sort  of  electric motor to power your boat but if in doubt all boat  kits  give a recommended motor names or sizes.














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 A fast boat requires a fast high revving motor. Some of these  motors  can be really fast,  50,000 RPM (yes fifty thousand) and handle up  to  100  Amps.  These motors can break world records as well as your  bank  account.  But unless you are using an efficient prop and running gear (the  motor, couplings & shafts etc.) you could be wasting a lot of that RPM and  power.  We'll  come  back  to  this when talking  about  installation  and  upgrading.  There  are  number of really high power  fast motors  such  as  Ultra,  Astro,  Keller & Hecktoplett,  these are specialist motors used by  people that just want out-&-speed. Most sports boats kits use 540, 550 and  750  sized  motors or SPEED 500,  600 & 700 motors according to   GRAUPNER  numbering. The range of fast motors is staggering and choosing the "right"  fast  motors  is a highly debated subject.   I've used  a number  of  fast  motors  and  personally I like the Robbe EF 76 II,  Graupner 7022 and  the  Graupner SPEED 700 BB TURBO.  The first two are 550 sized and the  third a  750.  You  will see these motors and others used in various kits over  the  following months.  These motors are from the cheaper end of the market but  are good enough for most sports boats and club racing.

    Which  motor  you  choose to use is not the most  important  consideration  however, the motor / running gear alignment is much more crucial. In every  case  the  motor  to prop shaft or shafts MUST line  up  perfectly.   Good  alignment  will  mean less load on the motor therefore less current  drain  and  enabling   higher speeds.  Bad alignment could damage the  motor  and  running  gear  bearings,  overload the speed controller or just shake  the  boat  to  pieces.  What you are trying to achieve is a perfectly  straight  continuation  of the motor shaft  down through the coupling and prop shaft  to the propeller. Use a longer prop shaft and a solid sleeve to check that  shafts meet parallel and dead centre. Alignment is purely a matter  of  the builders skill but even a novice can do a good job if he takes the  time to get it right.  While installing or generally working on your boat,  it's  an idea to tape up the motor's vent holes to prevent the ingress  of  dust and dirt.

     In direct drive boats,  i.e.  motor in-line with a solid prop shaft,  some  sort  of flexible or universal coupling must be used to join the motor  to  shaft.  The coupling compensates for any slight changes in  alignment that  occur  as  the  motor load varies.  There are lots of different  types  of  coupling  but the plastic and brass HUCO or RIPMAX couplings are the  most  popular and provide good service. If you buy a straight middle section for  this  type of coupling and install the motor and shaft around this "solid"  coupling,  (swapping it for the jointed type when complete) this will make  for  'straighter'  alignment.  The exception to this rule is 1) the  flexi  shaft were you must use a solid coupling to prevent the shaft whipping and  2)  when using a gear reduction in which case the gears provide the  shaft  alignment.  In  all  cases  the running gear  should always be  very  free  turning  and   very quiet.  If it's easy to turn the running gear in  your  fingers  and it makes hardly any noise,  it indicates a good installation.  Always check that the coupling is secure before running your boat. If it's  seems  to wearing quickly during the boats life your alignment is out  and  needs to be corrected,  a coupling "should"  never wear out in most normal  situations.

    The motors need SMALL drop of oil on the shaft bearings from time to time.  The  armature's  copper commutator also needs cleaning,  model shops  sell  cleaning sticks for this which makes the job easier. Most low cost 540 and  550  motors  have  sealed cans so cleaning or replacing  worn  brushes  is  difficult  if not impossible,  try meths on a cotton bud through the  side  cooling  slots and turn over by hand.  Of course you can completely  strip  down  and overhaul a motor,  but only if you've got a major problem.  I've  read in several publications that motors must never be washed out with any  sort  of spray but there are a number of reputable motor cleaner sprays on  sale  in model shops so make your own choice but if water does splash into  your motor,  you will need to wash it out and lubricate it with something.  For  more  information  on  electric motors,  read any of  the  model  car  magazines which often feature such matters.


Bad 540 Motors!!

These are pictures of the rogue 550 fan-cooled motors which have caused several members some grief over the last year. They are available on E-Bay as well as at shows and from certain retailers. The legend on the can says simply “Johnson”; there is no further ID except the numbers around the flux rings (which mean nothing to me). These are three-pole motors with an internal plastic cooling fan which can be seen through the slots in the case just in front of the brushes. The backplate is a dark grey metal casting as opposed to the usual 540-style white plastic moulding or silver-coloured steel pressing. The case is substantially longer than a stock 540 – some 65mm from end to end, and the motors have two steel flux rings pressed around the forward half of the case.

We have found that the motors are not suitable for “normal” scale models if run at anything over 6 volts. For example, one member has two of these things fitted into a Graemsay ferry and has discovered that he has “low speed handling difficulties running from 12 volts” – probably the understatement of 2006. Another member reports that the stalling current is astronomical and I can personally vouch for the high current consumption, even at relatively low speed on 7.2 volts. They also get very hot very quickly and should be water-cooled for all installations.

In short I wouldn’t recommend anyone to buy one of these unless they are very familiar with all aspects of operating high-speed DC motors. Indeed, the only reason I have one to photograph is that it was given to me. Personally I wouldn’t install it in anything but a wheelie bin………
but what do I know!


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 Well  all  of this is just my opinion,  but what the hell do I know!

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