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[Tug]

Change of subject here chaps,

The graupner 600 bb sp 7.2 Volts and running on 8.4 volts in the 3 foot torpedo boat, just aint' enough to get it up.

 I expected about 25% more power.


The 50 Amp speedy. Gets rather as warm the motor almost too hot, though I can water-cool that.

She?s carrying a 40mm 2 blade prop, tried 40X not an improvement, lost the brass Prop Shop one, [crash stop]

[Shipmate60]

I used a stock 550 motor on 8.4 volts and a 40mm fast scale prop from propshop, good speed and duration and no heavy current speed controller required.
Got a pic of her if you want to se4e the performance in a Deans 70ft gunboat.

Bob

[malcolmfrary]

Hi Tug
You don't say what size (capacity) of battery you are using.  Some several years back a friend did a Stepke lifeboat, and fitted it with his accustomed gel cell arrangement.  The thing was sluugish and only ever had a short run time.  When he replaced the gel cell battery with a 6-cell race pack, not only did it go fast enough to plane, but it ran about twice as long.  Adding some lightness usually increases perfomance amazingly.

[HS93 (RIP)]

  Have you got a rooster tail behind your boat?? I have a firetender 34" with two 700 bb on 12 volt n/cads tried all sorts of props, It had a sixfoot rooster tail and it did not mater how much power,  it would not plane ,tried moving things about it was just to heavy   Peter

[Fast Electricals]

That is quite a large boat and a big propeller. The motor is likely to be overloaded and not working at its most efficient rpm. In my experience it is best to load the motor so that it spins at about 80% of its no load speed for maximum output power and efficiency. I have done some calculations for your boat and have worked out that if the set up was installed in a small light fast electic hull you should achieve about 18mph. Your hull is neither light or small and so a realistic scale speed would be about 9mph. The easiest way to achieve this speed is to try a 2:1 reduction gearbox. This will lighten the load on all the drive components and keep the motor reving within its power band. The weight of the boat is also important and should be kept to a minimum. What would you estimate the current on water speed to be?

Neil

[johno 52-11]

Hi Tug

If your MTB is 3ft then I'm assuming its 1/24 scale so the first thing you need is its scale speed. MTB's had a top speed of 40+ Knots
So 40/squreroot of 24(4.899) = 8.1 Knots or 4.16 Meters per second. I do think a combination of the prop Shimate60 put forward and the 2:1 gearbox from Fast Electricals would get you somewhere near. This is based on the propshop prop having a pitch of 1.4 times the diameter which is 56mm this running at 5500 rpm with a prop efficiency of 70% would give the right speed. This can be worked out as 56*5500 = mm that a prop should move at 100% efficiency in a minute 308000 divide 1000 = meters per minute divided 60 for meters per second = 5.13 if you then multiply this by .7 for 70% you get 3.59 m which is close to what you need about 35knots scaled. The 5500 rpm is the about 80% of half the free running speed of your 600 bb motor. What you might find is that as you get the boat going faster the efficiency of the prop will increase and you will get more speed this happened when we increased the volts from 12 to 18 on the Severn for a 50% increase in rpm we got a 65% increase in speed.

Hope this helps

John

[Shipmate60]

Deans 70 ft gunboat.

[Shipmate60]

Powered as above.

Bob

[Tug]

Hey, thanks guys.

I am using nickel metal hyd.. thingies at 3000mA

Lost that prop! fantastic brakes though? only once..

Tried an X40 about the same performance as the lost prop shop item [Think twas 12X15]
Now got a 40 standard to try, and some bigger battery packs.

Actual speed appears to be 6 mph, no room for the gps this time.

I wanted to keep this quiet but the two side shafts 385's 32 mm X4 blade contra rotating props. (prop shop)
 are fed by an 8.4 2000 mA seperate pack and controller.
 The theory was to use the side motors to cruise and the main one for 'escape' situations,
a rooster tail would be good...  you have just got to try it once.

[johno 52-11]

? Have you got a rooster tail behind your boat?? I have a firetender 34" with two 700 bb on 12 volt n/cads tried all sorts of props, It had a sixfoot rooster tail and it did not mater how much power,? it would not plane ,tried moving things about it was just to heavy? ?Peter

Hi Peter

I have read your post a couple of times and I'm puzzled by it acording to the Graupner web site the spec on the 700 is

"
Specification
Nominal voltage 12 V
Operating voltage range 7,2 ... 19,2 V
No-load rpm 11600 min?1
No-load current drain 2 A
Current drain at max. efficiency 12,5 A
Current drain when stalled 43 A
Max. efficiency without gearbox 75 %
Length of case, excl. shaft 67 mm
Diameter 44 mm
Free shaft length 14 mm
Shaft diameter 5 mm
Weight 350 g
"
so thats 12V x 12.5A x 75% means that your output per motor is 112.5 watts at max effciency and you have 2 thats over 200 watts in a 34" boat
We only use a little over 350 watts to push a 58" 1/12 Severn class Lifeboat at a scale speed of 7Knots.



Is your firetender a scale model of a real boat. If so what scale is it how heavy is it and do you have the spec on the real thing and what was its top speed.

The only thing I can think of is that its a displacement hull and not a planning hull and no matter how much power you through at it it will never plane.

[johno 52-11]

Hey, thanks guys.

I am using nickel metal hyd.. thingies at 3000mA

Lost that prop! fantastic brakes though? only once..

Tried an X40 about the same performance as the lost prop shop item [Think twas 12X15]
Now got a 40 standard to try, and some bigger battery packs.

Actual speed appears to be 6 mph, no room for the gps this time.

I wanted to keep this quiet but the two side shafts 385's 32 mm X4 blade contra rotating props. (prop shop)
 are fed by an 8.4 2000 mA seperate pack and controller.
 The theory was to use the side motors to cruise and the main one for 'escape' situations,
a rooster tail would be good...? you have just got to try it once.

Hi Tug

Do you Know what size the props where on the real thing scaleing them down is a good place to start also you will probably find that they used all 3 motors to get there top speed so you will probably have to do the same. You could increse your power capasity without incresing your weight by looking at the 4300mA power packs I've just got one to put in my Atlantic.

John

[HS93 (RIP)]

  Johno   The boat is all timber and very heavy ,mine is a 25 year old nor-star firetender kit. It was built over many years and finnished abt 5 years ago .At the time n/cads where still a bit limited abt 1700mh so 4 ah "d" type cells where used to give some run time the b/heads where of 1/4 ply and the rest all very heavy two watercooled speed cnt, mixer small rx battery pack etc .the kits when they came out where in the main ic so where prob a bit lighter  the fulsize boat "pic " did plane as it was a come back boat after a long lay off it was put on the shelf and new ver built .very light weight kingston f/g hull lite ply and abs and gearboxes and two brushless motors and 4300 nicads all up less than a third of the weight of the old boat but with a lot of detail..thanks for interest . Peter

[Too Large - attachment deleted by admin]

[CalicoJack]

Johno   The boat is all timber and very heavy ,mine is a 25 year old nor-star firetender kit. It was built over many years and finnished abt 5 years ago .At the time n/cads where still a bit limited abt 1700mh so 4 ah "d" type cells where used to give some run time the b/heads where of 1/4 ply and the rest all very heavy two watercooled speed cnt, mixer small rx battery pack etc .the kits when they came out where in the main ic so where prob a bit lighter  the fulsize boat "pic " did plane as it was a come back boat after a long lay off it was put on the shelf and new ver built .very light weight kingston f/g hull lite ply and abs and gearboxes and two brushless motors and 4300 nicads all up less than a third of the weight of the old boat but with a lot of detail..thanks for interest . Peter

It seems to me that this topic has turned from "how to get more power" to "look at my boat". I have seen many models, not just boats, that run on brushless motors. Heavy wooden models work fine weather they are on brushless motors or brushed. It's ok saying that you have brushless motors BUT WHAT TYPES AND SIZES?

The model aircraft and cars use brushless systems quite a lot with huge success and it would be my recommendation to use brushless motors if you're after higher speeds. Brushed motors burn up quite a lot of energy in the commutators and the coil is on the inside of the motor, this means they tend to get hotter since there is nowhere for the heat to dissipate.

Hope this information helps.

[Tug]

I started a topic on the brushless in daze of old, but am still non the wiser,

Prey tell, what brushless combo is a directly comparable to say a 545?

Then which way do the numbers change to ?double? the output?

then I will have some idea planted in to the last remaining brain cell to mull over for the future.

[Martin (Admin)]

T
Too right there tug - you get as many answers about brushless motors as people you ask!
There seem to be no "hard and fast" or even "rule of thumb" rules around anywhere concerning brushless motors.
I had a chat with a guy from OMRA at the wings and wheels show, he seemed to know a lot about them.
Is there anything on the OMRA site about brushless motors in boats? - www.boatracers.freeserve.co.uk/index2.htm

Also, have a look at www.astecmodels.co.uk they have info on brushless motors
http://monster.traxxas.com/showthread.php?threadid=79819

[Model Boats Website]

Lets go right back to the beginning. Tug asked the question how to get more power since his original setup

Graupner 600 bb sp 7.2 Volts and running on 8.4 volts in a 3 foot torpedo boat

was not enough to get the boat to lift.

Torpedo boats have the same shape hull as Fireboats so I hope I can give Tug some helpful info about this subject.

First of all I started of with a standard 540 motor running on a 6v 5Ah Lead Acid battery, this moved ok but was not very fast and definatly no lift on the hull.

Second I tried a Groupner 600 motor also on the 6v battery, this made the boat a little faster but not a huge deal. This motors optimum voltage was 7.2v so I thought it a good idea to purchase a 7.2v NiCad battery for it. It went faster again which would be expected but no great speed.

The third motor I tried was a 777 motor from Model Motors Direct, it looked good on display but this was certainly a down grade of motor which was even slower and heavier than the 540. The one advantage it did have is that it drew less current than the other two but was no good for the speed I was looking for.

I then went back to the Groupner for a while, until the NEC model show last year. The model show exibited all sorts of models, very few boats in comparison but displayed many brushless motors in all sorts of models. This show made me realise just how good these motors were since they consume less current and run much faster than ordinary brushed motors.

I purchased a motor at this show and tried it out, it was powerful enough to get the boat to lift just on the 7.2v NiCad and it still has a capability of going up to 15v which would double the speed again! The speed is now running speed as opposed to walking speed and there is no need to apply a bigger voltage since the boat would probably flip anyhow.

Tug asked the question,

Prey tell, what brushless combo is a directly comparable to say a 545?

Well I searched the internet to try and find the best comparison as possible. A 545 motor runs at 750RPM/v the nearest motor I could find to that was the Kontronic KBM 67-07 brushless motor seen on this page:- http://www.motocalc.com/data/motor.html but to be quite honest that is only a speed comparison and the chances are the brushless motor will run much cooler and weigh less.

Brushless motors are approximatly 3+ times faster than brushed motors and currently holds the fastest model speed boat record (120.7MPH!).

If you need to know more on the difference between brushed and brushless motors try this link :- http://www.modelfireboats.co.nr/ue/motors/types.html or contact me via the website.

Stephen.

[HS93 (RIP)]

  Try ringing radcliffemodels

http://www.radcliffemodels.com/shop.php?category=Motors&subcat=Brushless

I rang them and got lots of info , they race boats with this type of motor  and seem to know what they are talking about,It seems its not as straght forword  to compare motors  (brush/brushless)

Peter

[Fast Electricals]

My first boat was a similar shape and size to the one described. The original motor was a Speed 600 which gave quite disappointing performance and ran extremely hot. Upgrading to a 12 cell setup and using a 9.6v 700BB turbo motor produced loads of power and really transformed the model. I would certainly recommend this motor for fast scale applications as a cheaper alternative to brushless motors.

[Tug]

 Hey well explained Stephen, lots to go on there, which motor did you settle on?

For now thanks to Fast Electricals cheapest option is the 700. so I will go there first.
The hull is not straight enough to warrant the expense of 'proper motors'

But for the next one.......  yes there will be one.