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Author Topic: Graupner Speed 400 7.2v - Brushless equivalent ?  (Read 3052 times)

Martin [Admin]

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Graupner Speed 400 7.2v - Brushless equivalent ?
« on: June 28, 2017, 06:07:31 PM »

 
Hi all!

Any guesses on a Brushless equivalent  or close match for a  Graupner  Speed 400 7.2v please?

Operating voltage range 2.4 to 7.2V
No-load rpm 18000 min.
Current drain when stalled 25amp
Length of case excl. shaft 37.8mm
Diameter 27.7mm
Free shaft length 13.8mm
Shaft diameter 2.3mm
Weight 73g

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canabus

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Re: Graupner Speed 400 7.2v - Brushless equivalent ?
« Reply #2 on: June 29, 2017, 07:43:09 AM »

Or something like this!!
https://hobbyking.com/en_us/turnigy-aerodrive-sk3-2836-2500kv-brushless-outrunner-motor.html

You would require a 2S (7.2 volt Lipo battery).
On 3S=18000rpm
Shaft=3.175mm
Dia=28mm
Weight=80 grams
Total length=54mm
Power=405 watts, but that is on 3S battery, so it is less.
Amps= 35 but I would use a 45A(like the car ESC HK-45A and program card (very easy to setup).
I can give you our club setup for this ESC if you require.
Canabus
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Tug Fanatic

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Re: Graupner Speed 400 7.2v - Brushless equivalent ?
« Reply #3 on: June 29, 2017, 08:52:12 AM »


Martin


What do you mean by equivalent?
Power?
Size?
Mounting points?
Revs?


Both motors suggested are far more powerful than a 400 motor. One is the same diameter and the other is smaller.
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Martin [Admin]

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Re: Graupner Speed 400 7.2v - Brushless equivalent ?
« Reply #4 on: June 29, 2017, 09:55:46 AM »


Mainly Power & Revs as it's going to be for a out-of-the-box conversion of a Baby Severn, so size not critical. 
   :-))
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Netleyned

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Re: Graupner Speed 400 7.2v - Brushless equivalent ?
« Reply #5 on: June 29, 2017, 10:32:06 AM »



You would require a 2S (7.2 volt Lipo battery).




Who supplies these?  ;D ;D


Ned
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Tug Fanatic

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Re: Graupner Speed 400 7.2v - Brushless equivalent ?
« Reply #6 on: June 29, 2017, 11:06:24 AM »




OK


The first thing is that the figures you give are, I think for the 6v Speed 400 and not the 7.2v.


The 7.2v has 16400rpm at nominal voltage and a stall current of 21A but importantly has a current draw of 3.3A at a maximum efficiency of 72%. This low efficiency at a low ampage explains why Speed 400 motors get so hot if you put a real load on them when the efficiency dips well below the 72% and all the rest is heat.


A Speed 400 7.2v thus has a kv of around 2300 but this does not directly translate to a brushless motor. A brushed motor when placed under load has a much greater tendency to drop revs than a brushless motor. For equivalent performance we are thus looking for a brushless motor of around 2000-2200kv which will happily cope with loads of 5amps without getting overly warm. The bigger & heavier the motor the cooler it will be. I confess that I like larger motors than strictly necessary for the lack of heat issues. If weight were critical for performance I could go smaller.


Your suggested motor would do the job perfectly well as long as you chose the 2200kv option.


I also like this motor at 52gms (Speed 400 73gms) and 28mm diameter (same as Speed400) which will give you enormous headroom when asked to do what a Speed 400 did. I have used, & abused, this motor in model aircraft with very good results. 
https://hobbyking.com/en_us/d2826-6-2200kv-outrunner-motor.html


Link corrected 11:25 but appears to be out of stock in UK at the present time.


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Martin [Admin]

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Re: Graupner Speed 400 7.2v - Brushless equivalent ?
« Reply #7 on: June 29, 2017, 11:51:02 AM »


The first thing is that the figures you give are, I think for the 6v Speed 400 and not the 7.2v.


OK thanks TugF, I grabbed those numbers from an ebay sale,  maybe I should have  checked them a bit better....

This enquiry has come about because of my build - http://tinyurl.com/y86u6gk9

Having run my boat, I thought the Graupner Speed 400 6v was a bit to quick and a milder motor and maybe the Speed 400 7.2v would be a better match .... and going Brushless, well, 'it's the future!'


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Tug Fanatic

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Re: Graupner Speed 400 7.2v - Brushless equivalent ?
« Reply #8 on: June 29, 2017, 12:16:44 PM »




You most certainly are not going to be underpowered with any of the motors suggested. If the model will take the weight then the prop & your thumb will determine the speed. Either of our 50gm motors will easily beat a 73gm Speed 400 6v or 7.2v!










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Norman H

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Re: Graupner Speed 400 7.2v - Brushless equivalent ?
« Reply #9 on: June 29, 2017, 06:53:52 PM »

Firstly may I say thanks to Martin for posting this question, he's effectively doing this on my behalf as I had asked him via pm about motor choice as I am about to convert a baby severn and he brought it to the forum as it would appear that brushless is now the way to go. Also thanks for the replies thus far. I am leaning towards this motor  https://hobbyking.com/en_us/d2826-6-2200kv-outrunner-motor.html as it's highly recommended by tug fanatic who appears to have virtually tested it to destruction, I just need to find the right ESC and ideally a suitable battery pack to go with it preferably from hobbyking so I can order everything in one go , I'm sorry for all the questions but I'm new to this and the more I've looked the more confused I've become, so hopefully you can help me get the propulsion side of things sorted,
Regards Norm


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Tug Fanatic

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Re: Graupner Speed 400 7.2v - Brushless equivalent ?
« Reply #10 on: June 29, 2017, 07:46:38 PM »



The Turnigy motor is a badged generic Chinese motor that is sold with lots of labels & is a good motor. There are obviously better that cost more.


The motor suggested by Martin is, I think, a Suppo and again Suppo has a good reputation at the price point.


I have searched the RNLI Severn model & I do question, if it around 11.5in long, whether you need a motor anything like this powerful. I have no experience of models this small. A good number of these have, I gather, been motorised so what have others used? Remember weight is the enemy of good performance in a planning or semi displacement hull.

Might I suggest that you read this thread which puts an equivalent motor in a 25in model.
http://www.modelboatmayhem.co.uk/forum/index.php?topic=53348.0
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Norman H

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Re: Graupner Speed 400 7.2v - Brushless equivalent ?
« Reply #11 on: June 30, 2017, 07:07:16 PM »

Many thanks, I'm sorted Now.
regards Norm.
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