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Author Topic: Johnson 888 motor  (Read 4095 times)

Stour-boy

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Johnson 888 motor
« on: November 28, 2015, 03:42:40 pm »

Hi Guys,
   Does any one know about Johnson 888 motors, i.e. min max voltage ? and Vintage. I have a Lesro or Keil Kraft Launch based on the 34" fire tender that this motor pushes I am in the throws of restoring said boat and would like to know a bit more about it.


Steve.
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knoby

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Re: Johnson 888 motor
« Reply #1 on: November 28, 2015, 04:29:14 pm »

They were the go to motor for fast electrics back in the day ( that day being 40 years ago).  Rated at 6-12 volt, around 10000 rpm on 12v if memory serves me correctly. prone to running hot if worked anything other than lightly & were quite noisy ( electrically speaking), but pretty built proof.  Ripmax also marketed them as Orbit 805 & they came in a very fancy red box.  Personally, I would use it as it is right for the era of the boat & with decent suppression & modern battery technology you should get a reasonable performance.
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Stour-boy

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Re: Johnson 888 motor
« Reply #2 on: November 28, 2015, 04:42:32 pm »

Thanks for that Knoby just what I needed it will be full steam ahead now for next year.  :-)
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inertia

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Re: Johnson 888 motor
« Reply #3 on: November 28, 2015, 05:20:03 pm »

Steve
Caution says that you should take the motor out of the model and test it with a radio, speed controller and the proposed battery pack as the next job. That way if it doesn't come up to the mark then you've time to find and fit another type of motor before the restoration gets too far along.
If you intend to use a 2G4 radio then a good ceramic disc capacitor of 0.1-0.22uF soldered across the motor terminals should be adequate suppression.
DM
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Stour-boy

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Re: Johnson 888 motor
« Reply #4 on: November 28, 2015, 06:04:29 pm »

Hi Inertia,
 Thanks for the caution, I have just put 12v. across the motor and it runs up fine, I had understood that capacitors from each terminal to the motor body will suppress interference but thinking about it the body is not connected to either pole which would mean both capacitors would be in series with one another , so putting one across the poles would be the same ,yes?


Steve.
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malcolmfrary

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Re: Johnson 888 motor
« Reply #5 on: November 29, 2015, 09:59:03 am »

Hi Inertia,
 Thanks for the caution, I have just put 12v. across the motor and it runs up fine, I had understood that capacitors from each terminal to the motor body will suppress interference but thinking about it the body is not connected to either pole which would mean both capacitors would be in series with one another , so putting one across the poles would be the same ,yes?


Steve.
Yes.  Probably better, since using fewer components usually increases reliability.  As far as I could ever see, the case capacitors only ever did anything worthwhile if the motor casing was grounded to the battery negative rail.  And doing that was another potential fault in waiting.
Using 2.4, the need for suppression is much reduced for your boat, but is is good practice to consider other users - if a boat (on 2.4) radiating lots of local interference sails near to one running a more traditional setup, it could mess up that boats operation.
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chas

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Re: Johnson 888 motor
« Reply #6 on: November 29, 2015, 11:32:20 pm »

For more info on the motor, google graupner johnson 888. I am asuming it's the same motor. You'll get results in German, but the figures are easy to follow.
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inertia

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Re: Johnson 888 motor
« Reply #7 on: November 30, 2015, 09:06:00 am »

Hold everything! It says quite clearly that the 888 motor is rated at 6v only. It will go like hell on 12v but the bearings and windings probably won't last very long. Go for the Speed 700 12v motor instead  http://www.gliders.uk.com/SPEED-700-BB-Turbo-12-V/productinfo/G6317/  the faster of the two 775's from Component Shop http://www.componentshop.co.uk/775-dc-motor-12000rpm-with-mounting-bracket.html - or go brushless for best performance.
DM
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