Brushless motor for Chris Craft 19″ racing runabout

[JeremyParticipant @jeremy15845]

I have read John Parker’s article on brushless motors and, as he says, it all falls apart when it comes to the actual choice of a motor!

 

I would appreciate a specific recommendation for a brushless motor for the Dumas 28″ model of the Chris Craft 19″ recing runabout.

I will be using a 7.2V NiMh battery pack and the motor is to drive a 34m twin bladed prop. If I were to go brushed, I would probably use the Graupner 600 Race 7.2V motor which I use on my Slo-mo-shun model of about the same size.

 

I would like to use an in-runner motor with built in water cooling. I will use a Hobbywing Seaking ESC (I have the 60 amp version in my Bluebird) as this can be programmed for forward/reverse operation and for NiMh or Lipo cells (detailed operation instructions available on the Hobbywing web site are a definite bonus). The 35 amp version is smaller but there is plenty of room for the 60amp version if required.

 

Advice as to a specific motor and source of supply would be very helpful.

 

Jeremy

[JeremyParticipant @jeremy15845]

Alternative to brushed Graupner 600 Race 7.2V

[Mark Beard 1Participant @markbeard1]

Can’t advise a particular motor, but I do concur with your preference for a water-cooled in-runner. By far the best solution to cooling!

[ashley needhamParticipant @ashleyneedham69188]

There are a million motors out there but wanting water cooling will cur it down a bit, however if you have decided to use a 7.2V battery, then you will need a motor of sufficient KvA to drive the prop at a speed not exceeding the design limit, and then developing the sort of power you think you might need…offhand cant remember how much a Gp600 develops.

 

So… decide the KvA required and then find a motor of suitable current draw .

 

I suspect that at this stage of the brushless game, there are no hard and fast motor choices.

 

Ashley. Armchair expert.

 

[Mark Beard 1Participant @markbeard1]

The Graupner Speed 600 7.2V, Pt No 1793, does 18,200 rpm no load, so has a Kv of about 2,500 rpm/V.

[JeremyParticipant @jeremy15845]

Hi Ashley and Mark

 

Thanks for your help. I wish I could say that I understood it all! The Graupner 600 Race 7.2V has a no load rpm of 22,635 = about 3,150 rpm/v. It’s current drain at maximum efficiency is 17.7 amps. How do I find a motor “of suitable current draw” and how would this be defined? How should the amperage of my ESC relate to the current draw of the motor? Is it some multiple of the motor’s current draw at maximum efficiency? I use a 40 amp ESC with my Graupner 600 Race 7.2V, so 2.25 times the motor’s optimum current draw. Any thoughts to get me closer to the selection of an actual motor?

 

Jeremy

[ashley needhamParticipant @ashleyneedham69188]

Sorry….”suitable current draw”  read…amps drawn and hence power developed  P=I x V.

 

I have in front of me a fantastic catalogue from “J Perkins” .. the “JP catalogue” no less.

 

There are 4 pages of motors from various manufacturers , in tableture form giving every statistic and also average current and for most, max current (before burnout I suppose!!!)

 

One caught my eye, as it is labeled “brushed 600 equivalent” one presumes for aircraft use,but nonetheless..

 

It is a JP EnErG brushless in-runner,mini-torque i/r 1000 (A28-15) ref 4445100

 

spec.. 6-12 NiMh, 228g, working current 5-30A,shaft 5mm, 36mmX54mm, 35A esc recommended (however this would be on an aircraft where stalling of the motor is not usually an occurrence)… 52 quid.   I suppose it is 1000Kv  sods law that this particular chart doesn`t mention the Kv as such.

 

Just as an example..

 

That`s one of the dearer ones mind, I think that perusal of a copy of this weighty tome may be in order. They also do heat-sink motor mounts. See the JP website.

 

If not using water cooling it seems to me that out-runners may run a bit cooler than in-runners due to the greater area or motor moving about.

 

I can only reiterate my own experience of one motor, an in-runner “speed 280-370” replacement….which at 11v develops 100w-ish at about 38,000rpm and is a tiny 20mm diameter by 30mm long.Awesome. useless on a boat unless geared of course.

 

Ashley. Even MORE of an armchair expert now!

 

 

 

Edited By ashley needham on 18/07/2011 19:34:17

[JeremyParticipant @jeremy15845]

U-tube link to the Chris Craft in action at Black Park. With its Turnigy 2000kv motor it is fast and almost silent.

Jeremy

[steamer briParticipant @steamerbri]

got a brushless motor in front of me water cooled 8.3 v 2.2 amp 11,717rpm 2 pole 1,428kv what size speed controller is req dimensions 5mm shaft 63.08 mmlong 54mm width thats all the info got on it thanks brian

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