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>> Home > Forum > Electrical Related > 46" Firefloat What Motor/Battery
46" Firefloat What Motor/Battery
(1408 views)
Author Message
moormedic
(Petty Officer)





Forum Posts: 4
18th Nov 2017 19:09  
>> Permalink
mdlbt.com/35950

Hello chaps.
I'm very new to this but have just finished scratch building a 46" Vosper Firefloat in the old Aerokits fashion (ie all wood) to the point where I've primered it, fitted a radio and couple of motors (Graupner 600 chosen at random cos they looked adequate!) and a Lead Acid 6v 12Ahr battery.
Tried it on the local canal today and two problems.
1: its underpowered...nearly gets on the plane with a fresh battery but not quite.
2: The battery only lasts about five minutes.
I'm an old git and don't understand "Lipids" or the benefits of "Brushless Motors" etc and would appreciate any help or advice any of you experienced guys could offer me please on motor/battery choices to get the thing planing and running for more than five minutes.
Many thanks in anticipation
Cheers
John


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canabus
(Fleet Admiral!)





Forum Posts: 123
19th Nov 2017 08:17  
>> Permalink
mdlbt.com/35963

Hi
What type of props are you using(size and number of blades).
I see your basic problem is under powered motors and a very heavy battery.
I made the big switch over three years ago from brush to brushless motors and to Lipo batteries.
With the help on the forum and club members it was a learning curve, but, I would not go back.
A 5800mah Lipo battery is in the weight of 450 to 570 grams and would give you a good 1/2 hour run time.
A good balance charger and safety bag are the main requirements, also maximum charging for the 5800mah battery is 5.8 Amps(same as the old Nicads).
Also a low voltage battery alarm.
Your 600 motors can draw up to12Amps !!!
Replacement same size motors for your mounts would be 35mm brushless motors, but, you will require two ESCs with a Y connector to run on the same throttle channel.
Replacement brushless motors are far more powerful e.g. a Hobbyking 3639-1100kv with a 60Amp ESC on a 4S 5800mah Lipo Battery is 800watts and with two in your boat is 1600 watts!!!
Your old motor would in the 100 watt each mark !!
I have the same size crash tender, but, with a single brushless motor.
I have all the order numbers for the motors etc. and a setup the ESCs if your require.
Canabus


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moormedic
(Petty Officer)





Forum Posts: 4
19th Nov 2017 11:30  
>> Permalink
mdlbt.com/35966

Hiya

Many thanks for taking the time to reply sir...very much appreciated.
All useful stuff.....current battery weighs 2kg!!
My props are three bladed 40mm dia contra rotating. Purchased with advice from "Prop-shop"
Cheers 👍
J.J

jarvo
(Fleet Admiral!)





Forum Posts: 550
19th Nov 2017 12:35  
>> Permalink
mdlbt.com/35967

HI JJ. Your question about a safety bag, Damaged / overcharged lipo's can catch fire, think of the Boeing scandal that grounded the fleet last year. Charging in a safety bag is advised the bag is fire retardant material, which will contain any problem.
Your remarks about the boat not coming onto the plane is down to the weight of the battery, my fireboat started with 7.2v NimH packs 1 for each motor, Graupner 700bb's, good cruise but not quick, but short run time, 10mins. I have re-wired to allow 3s lipo's, but not had chance to test it yet, but should go like stink.
With a fast hull, weight is important, 4 x lipo packs, 1kg, half the weight and possibly 6 times the power delivery.
In your first post you mention 600 motors on 6volts, they are probably rated at 8.4volts, same as my 700's hence the lack of performance, also the battery, at 12ah it should last about 30mins, was it fully charged??? and is it showing at least 6volts, ie not got a duff cell???
Canabus, in his post described an ideal set up with brushless motors, 1600 watts is just over 2 hp, 750 per horsepower so you can see the difference in performance with different motors and battery set up's


Etherow Model Boat Club
moormedic
(Petty Officer)





Forum Posts: 4
19th Nov 2017 17:04  
>> Permalink
mdlbt.com/35973

Thanks Jarvo for the additional info...I did Google the safety bag afterwards actually.
But...given what you've both advised.......as a stepwise approach, rather than discard x2motors plus ESCs plus batteries all at once, do you think perhaps upgrade the batteries first (more power less weight) and re-assess ? Then , if still not satisfactory, change the motors and Escs ?
J

jarvo
(Fleet Admiral!)





Forum Posts: 550
19th Nov 2017 17:16  
>> Permalink
mdlbt.com/35974

Hi J. Your motors are nominal voltage 7.2v. Try a single 7.2v 3300 NimH pack, quality from Component Shop. It will be short running time, powering 2 motors but will give you an idea of performance, then you could buy a second, 1 for each motor, if this did not work out or you want more performance then go for brushless motors, still with the 2 battery packs.
I would try the single pack first, suck it and see, develop it from there without breaking the bank!!!!
Cant see any ESC, have you got 1 or 2? if 1 use a 'Y' lead to connect the second battery.
Mark


Etherow Model Boat Club
moormedic
(Petty Officer)





Forum Posts: 4
20th Nov 2017 10:30  
>> Permalink
mdlbt.com/36000

Thanks again
Will give that a try first and then perhaps see if Santa brings me some brushless motors 😁
Cheers
J.J
PS
At the moment using a single ESC( 20A Mtronics) but would probably go for two if I move to brushless.

jarvo
(Fleet Admiral!)





Forum Posts: 550
20th Nov 2017 20:53  
>> Permalink
mdlbt.com/36030

Hi JJ. Just a word of warning, your Mtronics esc will not work with brushless motors, also 20amps is close to its limit with twin motors and fairly large props, performance wise, brushless is the way to go, but will need 2 esc's, wont run with one, if your dropping hints to the elves, spec your motors at about 700 watts and 600-700kva great torque with good revs at 7.2v even better at 12v

Mark


Etherow Model Boat Club
Schmango
(Apprentice)





Forum Posts: 1
21st Jan 2018 03:12  
>> Permalink
mdlbt.com/37657

Hi gents
I too have the same boat and have the same question . I only have shafts and rudders so I am looking for the whole package. I know little about brushless too but I think a boat like this needs them. From the research I have done I can see 880kv twins with 2 60 Amp water cooled esc will
Work. I would
Like to know what brand motors I need and what prop sizes to and esc brand to get. I’d like 20 min run time too.

canabus
(Fleet Admiral!)





Forum Posts: 123
21st Jan 2018 10:09  
>> Permalink
mdlbt.com/37662

Hi Jarvo
I also have a 46" Fire boat, but, it's only single shaft as I am the second owner.
I am using a L5055-700kv, 4S 5800mah 40C Lipo, 60Amp esc and a 2 blade 52mm prop.
In a twin setup a pair of Hobbyking 3639-1100kv on 3S or 4S batteries with 60Amp ESC's and 3 blade 37mm props and if you wish more speed a straight change over to the sister motors the 3648-1450kv but you may have to drop the props back to 2 blade 40mm.
Canabus

pmdevlin
(Fleet Admiral!)





Forum Posts: 364
21st Jan 2018 21:40  
>> Permalink
mdlbt.com/37720

Hi John,

you might now be scratching your head, and wishing you have not asked the original question! This seems to be a common issue, as the boating community is light years behind the other disciplines, rc cars, planes helis and so on, its probably due to the facts general boating doesnt really need the later generation technology, the average boater age is probably higher than the other disciplines so budgeting might be an issue, and there is less younger blood in the clubs to explain the lipo/brushless etc.

We see posts with a load of numbers, specs, warnings etc, its enough to put people off.

Im a big fan of brushless/lipo/ 2.4 etc, been doing it for years, its cheaper and more efficient (once you have the basics) but for the average guy, who just wants to spend an easy afternoon at the local lake gently cruising around, brushed motors, nimhs batteries, even lead acid, will do the job👍

Your 4 foot ply boat, once painted, with fittings, will be heavy, I know, I own one. Those 600 motors are not big enough, they are better suited to the smaller 3 foot boat, then, pushing them with a 6v lead acid, just cant do it. The battery will be screaming HELP!! I started 15 years back exactly the same, 600 motor, 6v battery, massive 50mm prop, I knew no better and took advise from people who didnt know what they were talking about😡, remember those gold hi tech speed controllers!! I had one, it melted, literally melted on the first use😭

Get 700 size motors, they will need to be water cooled, as mentioned by jarvo, the nominal voltage or below isnt good enough, power them at the max voltage. Brushed means you can use one apropriate esc, look out for electronize (are they still in existance?) or mtroniks, preferably use nimhs batteries over lead acid with a high mah.

If after all this you want to venture into lipos and brushless motors, go to a club, spot a boat that is similar in size to yours, if you like the performance talk to the owner and gain experience and knowledge that way, it will save money, lost time and a lot of disappointment, I have been there so feel your pain.

I say I would never go back to brushed motors and none lipo batteries, but I always want silly speed, not runtime, after 15 minutes Ive had enough and am bored. Rambling over!

My 4 foot boat is twin brushless and uses 4 lipo 5000mah cells per motor, it will do 25mph for 15 mins, then I go home😁

Message is, you can get a "reasonable" performance from brushed motors, with the correct batteries, right props, but weight is the enemy. Looks lie you are at Biddulph, get onto Dave M a moderator on here, and arrange to go over to see the crewe and district boys on one of their sailing days, take your boat with you, they will help👍


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