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[dougal99]

I have built a 1:48 Us Customs 87ft cutter and powered it with two Rocket 400 motors. It is far too fast, even at low throttle and I'm looking to replace the motors with something less powerful. Would the MFA 380 be Ok or is it the same beast as the Rocket 400?

[Tug Fanatic]

Speaking to the knowledgeable but have you considered that you could just run it with lower voltage?


If you are saying that even at very low revs the boat is too fast then changing the motor will not help - or are you saying that your controller/motor combination will not give you very low revs?


Does running with just one motor give you the speed that you are seeking?

[John W E]

hi there

Been doing some reading of an out of date MFA Como Drills Catalogue No.12 - ancient it be - my friend - just to see if I could the specs for the 400 Rocket Motor and I see that it is actually designed to be used as a 'free flight' motor and in the text it says for full specs and dimensions compare it to RE380 - so now - go to that page -  see its operating voltage is between 3 and 7.2 and at constant 7.2 voltage she is revving at 26000 rpm.   I think that is a bit too fast for what you want.   Personally, I would go for a 380/1 (3 Pole) and run that on 6 volt and that should give you in the region of 11500 rpm or you could go to the 385 (5 Pole) and run it on 12 volt which would give you 12600 rpm.

Or

have a look on Ebay - there is a guy selling this type of motor for a couple of squid from China.
http://www.ebay.co.uk/itm/For-Mabuchi-RS-365SH-DC6V-20V-12V-18V-19400RPM-High-Speed-Carbon-Brush-Motor-DIY/252839734005?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

John

[Tug Fanatic]

I think that the motor was sold with a Olympus 3:1 (or so) reduction gearbox for model aero use. Might make it more suitable for model boat use as well.

[Mike Fry]

Hello Tug Fanatic.
Try 385 motor, low revs, low drain and high...ish torque. I have one in a Matchbox Corvette and a 1 /60th scale Island class Royal Navy vessel 38'' long, with a 40mm dia three blade propeller. The motor on 7.2volts does not get hot and goes for at least two hours, the motor is a MFA 385 noise attenuated 12volt and is happy on 6volts. You have two so it should be good, have a look at the motor specs.

[Tug Fanatic]

Hello Tug Fanatic.
Try 385 motor, low revs, low drain and high...ish torque. I have one in a Matchbox Corvette and a 1 /60th scale Island class Royal Navy vessel 38'' long, with a 40mm dia three blade propeller. The motor on 7.2volts does not get hot and goes for at least two hours, the motor is a MFA 385 noise attenuated 12volt and is happy on 6volts. You have two so it should be good, have a look at the motor specs.

It's not me but rather dougal99.

[Mike Fry]

Hello Tug Fanatic.


Sorry.

[dougal99]

Thanks everybody. I knew the motors were designed for aircraft as when I was given them they had aircraft props fitted, but I was unprepared for the speed even on a moderate 6 volts. Thanks Bluebird for the data. I will look at motors running at about 10k.

[malcolmfrary]

A pair of 385 motors (15 volt type, run on about half voltage) should be fine in a 2 foot ong displacement hull, as well as being a virtual drop-in change.

[Tug Fanatic]

craft

Thanks everybody. I knew the motors were designed for aircraft as when I was given them they had aircraft props fitted, but I was unprepared for the speed even on a moderate 6 volts. Thanks Bluebird for the data. I will look at motors running at about 10k.

These are very high revving motors for direct drive model aircraft. They must have been for a specialist use. What props were they fitted with - I am guessing 6 x 3?

[dougal99]

Just found the props ( I was given the motors and props several years ago) in one of my spares boxes. Tug Fanatic you are spot on (almost) the props are marked 5.7 x 3. I'm not a flyer (not for over 50 years anyway) so if any body wants these for the cost of postage give me a PM.


That is props and motors, 

[dougal99]

Props and motors gone to a new home.

[John W E]

hi ya there, pity they have gone to a new home did you ever hear the story of someone fitting 2 of them into the MGB that you could build from a free plan in the model boats magazine - just to see how fast it would go and I bet you have never seen a gun boat become airborne and flip over

I was using an old transmitter 9volt power pack to power them and by gum it couldn't half shift

happy days

John

[dougal99]

The speed on 6v at most 1/3 throttle was way too fast for me and the stern was almost awash. Turning she nearly flipped over. Not a viable combination.