Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[Nordlys]

Does anyone have any idea as to what might be the equivelant electric motor size
for a 10cc petrol engine?
It is for a 41" pleasure cruiser type boat which I have just started to
work on known as a Sirius Star. 11" draft.
Thanks.....
Nordlys.

[essex2visuvesi]

If you want brushless then something like this one:-
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14405

Advertised as a direct replacement for .60 (10cc) glow engines

As for brushed motors I really dont know

[Nordlys]

Thanks - It would be a brushed motor though. I haven't ventured into the brushless zone
as yet.
I was guessing at fitting a 700BB Graupner Speed @ 8.4v which revs at
something like 14000. The boat is quite heavy so its hard to judge whether it needs power or
whether it can handle reasonably high revs.

Nordlys.

[nick_75au]

It will be more expensive to get a brushed motor and ESC with equivalent power than a brush less with ESC.

RPM alone is not enough to determine the suitability of a motor for an application.

The brushless motor linked is 1000 watts, a 700 for normal use is about 150 watts, you can extract 3-400 watts out of one with extensive cooling and high voltage (P.S. watts is a direct  equivalent of Hp, 745 watts equals 1 H.P)

Certain Plettenbergs, and Astro cobalt motors are close in power but go for big dollars, adding to that a high amp ESC.

You need to determine what size prop you are going to use and what sort of performance you are looking for.

Ps brushless is no more complicated/ than brushed

Nick

[Tug Fanatic]

An 11" draught for a 41" model is a lot.

Any chance of a picture?

[Nordlys]

[IMG]http://i1182.photobucket.com/albums/x460/SeaScout1/SiriusStar12-1-12001.jpg[/IMG]
Hi,
I think I should have stated the size 11" as WIDTH and not draft.

I'm not into brushless yet as it requires investment in batteries and chargers
and I have only just got kitted out with conventional equip.

Nordlys...

[Nordlys]

2nd picture did not upload
This should work......?

[roycv]

Hi, you are starting from the premise that the 10 cc engine is needed.  I would suggest that 250 watts will be more than enough to get the boat planing and give a satisfactory performance.
good luck with the project,
Roy

[HS93 (RIP)]

the power output of a 10cc engine that may have been in the boat when built is a lot less than a modern 10cc so as Roy says you may not need such a big engine, also as long as you don't want the boat to accelerate like a F1 car you can use gell cell batteries in a big boat without a problem just don't wack the throttle open and expect a rocket ship but it will plane fine and you can get higher amp batteries cheaper

Peter

[richald]

Nordlys

You can go brushless without investing in new Lipo batteries and chargers -
thats what I have done - brushless speed controllers seem to work fine with 7.2v NiMh battery packs...

Richard

[Tug Fanatic]

Nordlys

You can go brushless without investing in new Lipo batteries and chargers -
thats what I have done - brushless speed controllers seem to work fine with 7.2v NiMh battery packs...

Richard

Yes or lead/acid or anything else. The motor just knows that there is electricity there - not where it comes from as long as your power source will cope with the discharge rate required by your motor and is of a voltage that your controller & motor can live with.

[Nordlys]

Hi Roy,
Yes, I am starting from the prmise that a 10cc would be fitted on an original build
This size engine was stated in a Model Maker article from 1994. That is my starting point,
but only as a rough guide.
I am trying to determine, before buying, whether an 8.4v motor running on Nimh batteries would
be capable -if anyone might know - of moving the boat at reasonable speed
I may be asking an impossible question of course, for anyone to really know whats suitable,

I am not that au fait with electrical power ratings so what does 250 watts equate to in motor type
ie. Graupner sizes?
Many thanks .....

Nordyls.

[roycv]

Hi Nordlys, well 250 watts is 1/3rd. HP.
Practically if you multiply the current in amps by the applied voltage you get Watts.

  So 12 volts at 10 amps = 120 watts.

If I were restoring the boat I would look to that as a maximum combination, just 120 watts.

There are many motors to give you this amount of power.
NiMh cells should be fine but the time on the water will be limited to the amp hour capacity of the battery.  There is a small gain to be made by going for a higher voltage if you have the choice.

I suspect that the boat will look very nice on the water at a very modest power input, just 40 or 50 watts.  (8.4 volts at 6 amps), you can adjust prop size to suit required speed.

good luck Roy

[Circlip]

Yes, I am starting from the prmise that a 10cc would be fitted on an original build
This size engine was stated in a Model Maker article from 1994

  As you stated, the 10cc engine quoted was from the original of 1954 and was Max's flagship powered by a Petrol engine, not one of the bandsaw glows. Speed quoted from original artical was 3 1/2 (?) to 11mph by controlling the spark advance and retard and even with a comparitvely slow revving sparkie, it planed superbly at maximum speed.

  Regards   Ian.

[Nordlys]

Hi Roy,
Thanks for that useful information.
I know what the voltage will be depending on what battery I buy
The motor has an operating range of 4.8v -12v
The current values of the motor I am looking at are
- No Load drain 2.5a
-Max Efficiency drain  = 15a
Stalled drain =   75a.
So, if I choose to use say a 9.6v supply and use the max effic value of 15a that equates to 144watts?
Am I using the correct value for current here?

Or using an 8.4v supply, power will be 126A
I think I'm getting near to the numbers you quote here.?
Or should I go lower still?
Thanks

Nordlys

[Nordlys]

Hi Ian,
You appear to have, or have read the article ! Yes the speed ranges from 3-11mph.
But that doesn't mean much to me from the bank!
I have computer images of the article sent to me sometime back.
Its a fairly large and heavy boat hence my attempt to determine a suitable motor
to make it sail with grace at my lake!
I have only just started work on it tho' this week.
regards

Nordlys....

[roycv]

Hi Nordlys, you have probably got the right motor.
However you cannot choose what current the motor will run at, it depends on the size of the propeller and how much effort is required to turn it.
It may be an idea to have a few props available.  Putting a big prop on which takes a higher current is not necessarily better than having a smaller prop that spins faster.  I would try a 40mm prop, try the P first and maybe switch to an X.  These are different pitches, the X being coarser.

When working out the best combination of speed versus duration it is best to change only one thing at a time.
Do you have a local model boat club to give you some guidance?  You may possibly see a similar boat and look at the battery / motor/ prop combination.

At the power requirement you are stating 20 minutes running on a battery is about all you can expect.

Apart from anything else, you need to have control of the boat.  At the start most modelers know where there boat is but not necessarily where it is going!
kind regards Roy

[Nordlys]

Hello Roy, What you are saying now makes a lot of sense. The run time I hadn't considered
How did you work out that number?
I do belong to a boat club at Bluewater - they mainly sail Tugs - not a lot of older classic boats there
but I have picked up plenty of good information especially with regards to propeller choice as you have
also pointed out .
I have fiited only P type on my boats and generally 30 - 35 mm dia. As you say size isn't the main criteria!
Even the smallest prop on my SeaScout makes it fly!
I have also spoken to Westbourne models and I think I'm likely to fit the Graupner 700BB race 9.6v
based on what I have now found out.  Battery likely to be Nimh type - the boat doesn't need large amounts of ballast
so lead acid not on cards at this time.
All this is some way down the line yet tho'!

Regards

Nordyls

[Tug Fanatic]

.............the boat doesn't need large amounts of ballast.................

It is a planing hull. It doesn't want any extra weight. Basically the lighter the better.

[Nordlys]

Ahh! Thank you TF - thats verified my thinking about using NiMh batteries -
much better I think.
The hull is quite flat in section apart from the sweep up to the bow.

Regards

Nordyls......

[roycv]

Hi Nordlys, You ask where did the numbers come from?
I made a copy of the old Bassett-lowke Streamlinia about 30+ years ago and this is 40 inches loa and 8 inch beam.  Weighs in at about 8 or 9 pounds.
 This planes nicely on less than 30 watts input. All very carefully calculated as it used to be steam driven and I had made my own tachometer and she would just plane with steam at 2000 rpm, but the boiler could not keep up the 30 lbs pressure required.

 I converted to use a 5 pole 550 type motor (Duplex) on 12 volts and the motor has a 2 :1 gear box so prop runs at half motor speed.(2000 rpm) I use the same  prop 50mm brass 3 bladed as used under steam, and get half an hour's running from 3.5 Ah lead acid battery.  Separately interesting as it gave the steam plant an equivalent output in watts!  The model being a little less in weight under electric power.

I have tried 18 volts as an experiment but it did not go much faster.

I would aim for the lowest acceptable speed, this way you get the best on the water time.

My Streamlinia would, after a while, disturb the water on the lake quite considerably and I would only run the boat when there were no small models around.
regards Roy

[Nordlys]

Hello Roy,
My boat weighs in at 4.3kg  - thats without any elecrics.
Interesting about the steamer- I will look to find out more about the Streamlinia.
I am relatively new to modelling so I am running to catch up on tech detail.

Regards.
Nordyls...

[Stavros]

http://www.ebay.co.uk/itm/300511267976?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

As much power as you will need,run it on 2 x 8 v stick packs that will give you 16v and yes that motor will cope with 16v water cool the motor as anything over 12v you will need to try and fit a prop of around 45mm to 55mm a 2 blader and it will fly,speed controller off ACTion will suffice


Dave