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[tonyH]

Hello All,
 
I'm trying to save weight for a possible fireboat and one of the biggest contributors is the motor built into the pump. So, could anyone suggest a lightweight 30/40 watt brushless with a shaft diameter of 2.3mm?
I've found a couple of inrunners but I presume they're heavier than outrunners so can anyone suggest an alternative?
 
Thanks
 
Tony

[AlisterL]

This one? 2mm shaft however... http://www.hobbyking.com/hobbyking/store/__8475__Turnigy_1811_Brushless_Indoor_Motor_1500kv.html


I think the big problem is going to be the Kv rating of the motor - not sure what it should be for a bow thruster, but wouldn't have thought it would have been much.


In my limited experience the bell type brushless motors tend to be lighter and smaller. But this tends to also equal higher Kv.


HTH.

[essex2visuvesi]

I think finding a brushless motor to match your requirements would be difficult and I doubt the difference in weight would be that much

[malcolmfrary]

Fireboat, pump, probably nothing to do with a bow thruster, more to do with flinging water.  Reading the spec, at max voltage its a 35watt motor, equivalent to a 400 motor working reasonably hard once the difference in efficiency is taken into account.

[tonyH]

Thanks for that.
 
I'm trying to utilise a pump which has a 385 type motor inbuilt with a 2.4 (not 2.3 - I've re-checked ) shaft slotted into the pump vanes. It's got the punch but is certainly on the heavy side.
 
I've checked mini/micro pumps on line and the general sort of rating is in the 30-60 watt bracket. Brushless versions are available and a lot lighter BUT with a price tag seemingly in the £150.00 area.
 
I'm contemplating a small (under 1ft) fire boat built around a single Graupner waterjet unit so I need to keep the total weight under 1lb. It would be nice to have a decent water spray to go with it!
 
Tony

[malcolmfrary]

There was a thread a while ago that currently escapes me, but someone clever with search might find, that described making what could have been a centrifuge type water pump, fixing the vanes more or less direct to the motor spindle.  For a given motor of small size but high power, that might be the way to go.  (Brass collar to fit shaft, brass sheet vanes soldered into brass collar.....)
Getting a decent water stream in a small size might be tricky - there was a discussion a long time back where I was muttering about surface tension mucking things up. and somebody who knew what they were talking about said that the critical component was the profile of the exit nozzle.  This to make it look like a fire hose rather than someone doing a widdle.