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Author Topic: Brushless to replace 600 brushed motor and gearbox  (Read 818 times)


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Brushless to replace 600 brushed motor and gearbox
« on: April 06, 2018, 09:02:13 PM »

So, i've got a nice vintage Graupner Scimitar Speed boat (24 inch speedboat, shallow vee), with a horrible original Graupner 7022 setup, Speed 600 8.4v brushed motor with a really noisy 2:1 reduction gearbox.  The motor gear has broken and beinh discontinued, i just cannot find a replacement anywhere.  Performance with this setup, and using a 3 cell lipo is acceptable, but could be better.  According to what i have found online, this motor is good for 15,500 rpm off load, producing 70 watts.  This gives me 7,750 rpm at the shaft, again no load.  The boat is running a graupner x35 prop.

My maths tells me that, eliminating the noisy gearbox, a 1000kv motor using the same 3 cell lipo should give me more final rpm i.e. better performance.  And rather than 70 watts my guess is i need to look at 200 watts at least, on the assumption that the brushless motor, unlike its older brushed ancestor, will do its best to reach its designed rpm.  Speed controller around 50A to be safe.

Are my workings ok here or am I missing something.  I am also tempted to replace the ancient shaft with  better Raboesch water lubricated shaft to do away with greasing, so open to prop suggestions as well.

Thank you

Chris from the little sunny island that is Malta.


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Re: Brushless to replace 600 brushed motor and gearbox
« Reply #1 on: April 06, 2018, 11:03:28 PM »

Hi Chris1
A Hobbyking 3639-1100kv 35mm brushless motor (5mm shaft) on 3S Lipo and a 40mm 1.4 pitch 2 blade prop.
Esc I use the Hobbyking car (HK-60A SL),(handles 2-4S)( nice and small with electric fan ,also on/off switch).



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Re: Brushless to replace 600 brushed motor and gearbox
« Reply #2 on: April 07, 2018, 06:21:34 AM »

I am using a similar set up, but at 960Kv on my 37" Brave Swordsman. Very effective. So anything between 900kv and about 1200Kv should suit your needs. You may need to play with the prop set up slightly, shallower pitch but bigger diameter seems to be best on outrunners.
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