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Author Topic: Advise needed re brushless.  (Read 2012 times)

Watchleader

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Advise needed re brushless.
« on: October 07, 2010, 11:49:39 AM »

Hi all.

I am sure this must have been covered before somewhere, but I cant find it!    {:-{ {:-{
I am running a 37" Perkasa, I had a 555 running with a single 40mm prop and I was happy with the performance   
Planed nicely, didn't wave hop.   O0 O0
I was running it a little high for the ESC and popped it eventually.(on 13.2 NiMh cells)    <:(
The 555 now has corroded somewhat and so I think I'll redo it and fit brushless motor and esc.   O0

Currently installed an MFA 800 and 12v 2.4Ah SLA. Hardly gets out of bed!!   :(( :((

I'll get there in a minute, honest! :} :}

What I would like is some recommendations of a suitable brushless motor and esc setup. Please!! :-)) :-))

Just want it back and looking good on the water.
 

John
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andrewh

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Re: Advise needed re brushless.
« Reply #1 on: October 07, 2010, 07:36:27 PM »

John

There is a dreadful inevitability about answers like this:

I don't know, we havn't got any information to go on.

How long did you get the acceptable performance with the 555 on what battery? 
What was the current draw?
What was the ESC rated at before the smoke came out?
what is the KV of a 555.  What 555? (it just means a long armature 540 with 5 poles)  Did it have a brand name?

Any of those would give us an estimate of the power that gives the kind of performance you like - then selecting a suitable BL is a little more scientific :}
OR
Find a boat of similar size, mass and performance and copy a successful installation slavishly

What do you intend to do for batteries? - generally gelcells do not appreciate the current draws that BL motors impose (but there are several honourable exceptions)

If you can help with some of these answers I and some people who know will attempt to help
andrew
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nick_75au

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Re: Advise needed re brushless.
« Reply #2 on: October 08, 2010, 04:17:56 AM »

If you use the 40 mm prop, a 1000 Kv to 1200 Kv motor in a 36-42 or similar size and 3 cell Lipo, If you stick with the Nimh at 13.2 volts then go with the  lower end of the Kv range. you could drop down to a 800 Kv and that would give you very close to the 555 performance I would think.

http://www.hobbyking.com/hobbyking/store/brushless_motor_rc_data.asp?diameter=2

link gives a range of motors, most of these are very similar to the Giant Cod range if you prefer a U.K. supplier

Nick
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HS93 (RIP)

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Re: Advise needed re brushless.
« Reply #3 on: October 08, 2010, 04:26:25 AM »

http://www.overlander.co.uk/motors-propellers-edfs.html?kv=108

this is also a good starter the thumper motores have a good reputation, or for a bit more speed try. you will have to experiment with props but go for a nice 3 bladder with a big pitch and work up from about 45mm get some cheap plastic till you get a nice balance between heat speed and run time.

http://www.overlander.co.uk/motors-propellers-edfs/tornado-thumper-v2-4240-890kv.html

Peter
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Watchleader

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Re: Advise needed re brushless.
« Reply #4 on: October 08, 2010, 11:20:56 AM »

Hi Guys.
Many thanks for the prompt and helpful replies.

Andrewh. 
Of course you are completely right about insufficient info at the start.
John

How long did you get the acceptable performance with the 555 on what battery? 
What was the current draw?
What was the ESC rated at before the smoke came out?
what is the KV of a 555.  What 555? (it just means a long armature 540 with 5 poles)  Did it have a brand name?


What do you intend to do for batteries? - generally gelcells do not appreciate the current draws that BL motors impose (but there are several honourable exceptions)

andrew

5-7 mins on NiMh 13.2V (2000 mAh) 11 cell AA pack.
Never measured current under load,
Mtronicks Viper 20A. With 10A fuse (car type)  Didn't smoke just stopped (probably over volt, rated at 12V)
555 From model motor direct. Unloaded gives 9400 RPM at 12V

Have 12V 2.4Ah SLA's available. OR Could go back to 13.2V NiMh OR may invest in Lipo if appropriate.

I hope that will help you give me some good advise. :-)) :-)

I will follow all the links provided and try to understand this world of BL a litle more.
Again thanks to all

John

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boatmadman

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Re: Advise needed re brushless.
« Reply #5 on: October 08, 2010, 11:34:56 AM »

Thinking about the power consumption of the 555 with 40mm prop. You had a 10a fuse at 13.2v, so power is 132w not counting losses.

Look for a brushless outrunner that will give you the loaded revs you had with the 555, the kv value is revs per volt, so divide your revs by 13.2 and look for a motor with a slightly higher value, then get a suitable esc to match the motor with a little to spare, plus appropriate fuse

This should work, but just in case it doesnt, I am off away for a few days so you can knock me off my pedestal with impunity   %)
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if at first you dont succeed.....have a beer.....

nick_75au

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Re: Advise needed re brushless.
« Reply #6 on: October 08, 2010, 11:53:29 AM »

You gave enough information for me  :-), Prop size and type of boat (eg displacement or planing with an idea of performance required) and Voltage

800 Kv motor on 13.2 volts give unloaded rpm of 10500 RPM. Almost spot on to your figures ;)

Dump the AA's and the SLA's, neither are designed for high discharge that planing hulls require. you could go for a 7.2-9.6v sub-C Nimh stick pack as used in the buggy's with the higher Kv motor if li-po doesn't suit.

The performance of Li-po is superior to anything else at the expense of being fussy in their requirements (read lots before going that way)

The M-tronics I'm fairly sure didn't like the over voltage, their 12 volts is a maximum rating,a fully charged 11 cell Nimh pack could be up to 16 volts.

Brushless ESC's I would go for 30-40 amp model, gives a good safety margin.

Regards
Nick
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nick_75au

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Re: Advise needed re brushless.
« Reply #7 on: October 08, 2010, 12:04:34 PM »

Here is a quick Video of a 32" Ski boat I'm building, 36-42 1250 Kv Turnigy motor and 40 mm prop on an 11.1 volt Li-po, unfortunately the battery reached the Low Voltage Cutout  so full speed is only for a few seconds.

http://www.youtube.com/watch?v=lYJtODg_hQk

Nick
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