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Author Topic: Brushless repacement for MFA 850 Torpedo  (Read 451 times)

Hotglove

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Brushless repacement for MFA 850 Torpedo
« on: May 14, 2018, 12:20:25 PM »

I have a Dumas Chris Craft 1930 Runabout with 850 Torpedo. the size of the motor means that it cannot line up accurately with the prop shaft. a significantly smaller diameter motor would help.
I am probably asking too much but I would like to find a smaller motor with a noticeable increase in power, fairly quiet and cool-running (I don't want to pierce the hull for water cooling)
I would prefer an adjustable mounting, the MFA mount seems a bit crude. Would not expect the solution to be cheap.
Any suggestions?
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canabus

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #1 on: May 14, 2018, 02:07:06 PM »

Hi Hotglove
I pickup a started Dumas Chris Craft 1949 Runabout (28 and 1/2").
Replacing all the running gear with a 4mm stainless drive shaft with a 32mm 2 blade CNC prop.
Brushless motor(28mm) from Hobbyking( Turnigy X2845 1980kv 792 Watts) and a car ESC 45 Amp(HK-45A)(you require a ESC program card(HK PROG-Card).
Twin Turnigy 1500mah 3S 25C Lipo batteries or a single Turnigy 2650mah 3S 30C.
I can the weight a bit more forward with the twin setup.
I have similar setup in a Sea Hornet (24 and 1/2") and it's a little pocket rocket.
With using the 28mm motor I made an alloy angle bracket and epoxy glue it to the keel.
Added a few pics from my Sea Hornet build from the model boat mag forum site.

Canabus
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Hotglove

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #2 on: May 15, 2018, 07:39:07 AM »

Thanks for the input, my boat is 36 quite heavily built, has two PVC crew figures and runs on 2 5000 Lipos.
I am hoping to find a motor with significantly smaller diameter than the 850 (to allow better line-up with propshaft) but that has sufficient power headroom to run unstressed and, hopefully, avoid hot running.
Are there motors that have a well-established reputation for running quieter and cooler than average?
Thanks in advance.
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jarvo

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #3 on: May 15, 2018, 08:10:27 AM »

Have a look on the Airtec site. They have a massive selection of motors and esc's, they also give the size and spec's of the motor's. You mention 2x5000 lipo's but not the voltage, how much space have you for the motor to fit into? that part is critical to make sure that the outrunner casing doesnt foul the keel.


Would it be possible to cut away a small part of the keel under the motor then reinforce the hull bottom with extra ply on both sides of the cut area??


Mark
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canabus

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #4 on: May 15, 2018, 08:33:05 AM »

Hi Hotglove

As the 850 motor is 52m diameter, dropping to a 35mm brushless like I am using in my 34" Huntsman will give you far more power.
I am using a Hobbyking 3648-1450kv 1600Watts with a car ESC 100Amp(HK-100A) on a CNC 2 blade 40mm 1.4 pitch prop.
Single 3S 5800mah Lipo battery with a run time of a good 1/2 to 3/4 hour.
Very good turn of speed, over scale of course!!!!
I tested 3 blade 37mm prop, it gave better pick up at slow speed, but, prop the top end speed and increase the power on the watt meter.I have pictured my install with the water cool mount, but, it is not used.

Canabus
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Hotglove

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #5 on: May 15, 2018, 11:36:28 AM »

Thanks for replies, my Lipos are 3S, and a recent purchase. I had not thought of using the water cooled mount without connecting, so that is a definite possibility, the type of motor suggested would also give the option of moving the motor back, which would give the freedom to choose a wide range of couplings.
A plan is beginning to form, keep the ideas coming please.
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jaymac

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #6 on: May 16, 2018, 05:40:20 AM »

I replaced 3 x 850's with One Turnigy 3648 1450kv outrunner operating on a 3s lipo. on a 1/24 S-boot great
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canabus

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #7 on: May 16, 2018, 11:43:20 AM »

Hi Jaymac
You must have drop a kilo in weight and added about 6000 rpm with far more power !!!
What prop are ewe running ???
Hold onto your cotton tail if you try it on 4S !!!!
I try it an offshore racer and it was a total hand full !!!
Canabus
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jaymac

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #8 on: May 16, 2018, 01:00:47 PM »

Hi Canabus yes I got it on advice of gra2 who is  down your way  in fact he got the motor for me from hobbyking and posted as no could get it here in blighty. I ran her with the other two props freewheelin (dragging ?)  same props as used with the 850's a X45 mm raboesch 3 blade prop'  The 850 weight and consumption negates its power I think when i tried it on just 2 of the motors running  it was not much different to 3 I think possibly  removing the 3rd motor it might have been  faster
Jay


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canabus

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #9 on: May 16, 2018, 02:33:26 PM »

Hi Jaymac
If you run it without the two free wheeling props and drop to a 40 mm prop.
The speed will increase and you will drop your power rate.
I have tested the 1450kv on a 2 blade 40mm prop and changing to a 3 blade 37mm prop increase the power rate but increase to slow performance.
I swap PDF plans with other forum members both to save them and to swap.
I do not sell them.
So the S is one on my radar !!!
Canabus
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jaymac

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #10 on: May 16, 2018, 07:21:24 PM »

Hi Canabus will bear that in mind thanks not used it for ages hopefully  at it again this year
Jay
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Hotglove

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #11 on: May 17, 2018, 04:05:57 PM »

Hi Canabus, how does your 3648 setup run as far as temperature goes? I have seen several car ESCs that claim to be waterproof, which sounds a good idea. My current installation (no pun intended) includes an esc with cooling fan, which seems to work fine wth the MFA.
As I stated earlier, would prefer to avoid punching holes in the hull.
Also, as a novice to model boats, is there a simple way of setting up that allows the speed control to be restricted?
Thank you.
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canabus

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #12 on: May 18, 2018, 03:19:30 AM »

Hi Hotglove
The 3648 only runs warm on 3S with a 2 blade 40mm prop, but, if you go to 4S cooling is required.
I use the Hobbyking car ESC's (hk45 to 100) as they have the electric fan on top and also small.
The boat ESC do not have an on/off switch like the car ones.
My mate is running the 3648 on 4S in his Spearfish,  but, I install a small computer fan over the motor with air scoops on the aft deck.
Works very well and goes like a bat out of hell !!!

Canabus
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Hotglove

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #13 on: May 20, 2018, 01:58:04 PM »

First steps taken, I have ordered the Turnigy 3648 from Hobbyking, will be interesting to see how long it takes to arrive :-)
Not so sure about the ESC, I quite like the look of one from Hobbywing, it is waterproof and has reverse but rather expensive. Local hobby shops seem to have a good range of car ESCs so will probably buy from one of them.
Also bought a Great Planes motor mount which offers a lot of adjustment and will allow easy and precise motor swaps in future (it also looks like a proper piece of kit as opposed to the MFA piece of bent tin. The new setup should allow room for a free choice of coupling and much better alignment.
Hopefully, when all is up and running, the boat will have an engine room that lives up to the rest of her.
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jaymac

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #14 on: May 20, 2018, 02:38:02 PM »

I use Hawk 50A without water cooling
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Hotglove

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Re: Brushless repacement for MFA 850 Torpedo
« Reply #15 on: May 20, 2018, 06:57:14 PM »

Thank you, will check them out.
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