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Author Topic: Torpedo 850's  (Read 4087 times)

2772e

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Torpedo 850's
« on: June 18, 2006, 06:41:07 PM »

After my 3rd sea trials today with my new 850's. I thought i would have a good turn of speed. Perhaps not! 50mm 4 blade brass props and i still need more speed to get her on the plane properly.

I had 800's originally and thought at 9700 rpm the 850's woul be better.

Can you get bigger motors?

Any advise would be appreciated please.
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johno 52-11

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Re: Torpedo 850's
« Reply #1 on: June 18, 2006, 08:48:39 PM »

Hi 2772e

Can you give us some more information about your boat what is it what size is it what voltage are you running on do the motors get hot.

You can get motors bigger than an 850 my friend Robert runs is 1/12 Severn on just to motors and gets scale speed you can see it on our website http://www.lifeboatmodels.co.uk
I know speedline are using 4 850's in the same size boat to get a good performance.

If the motors are not getting hot you could look at increasing the voltage, which would give you more RPM.

It took us a number of years of trial and testing to get the Severn right.

Regards

John
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2772e

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Re: Torpedo 850's
« Reply #2 on: June 18, 2006, 10:03:48 PM »

Hi John,

Shes a 68 inch, 1/12th Vosper Rttl running with twin 12 volt lead acid, i need to play around with the battery location as well. Someone suggested changing to three bladed plastic 50mm.

The motors do get very hot, i have set up cooling rings but these were not in use today?

Any suggestions are welcome.

Thanks

Simon
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Stavros

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Re: Torpedo 850's
« Reply #3 on: June 19, 2006, 06:21:57 PM »

Right then shipmate the answer is quite simple had teh same problem myself with a Sea queen change your prop size to a 55mm 2 blade prop supplied by MFA with the case of the motors running hot obviously you have cooling coils fitted,add a MFA water/fuel pimp these are available cheaper than MFA from pandan models these only draw 400ma amps connect the motor wires to the + and - of the boat motors and this little beauty will pump at a speed in relation to your throttle as it will be controlled from your ESC I hope this will help Stavros
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ukengineman

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Re: Torpedo 850's
« Reply #4 on: June 19, 2006, 11:24:37 PM »

I agree about the two blade props. Another thought is to save weight in the battery area. You could consider replacing the two 12V lead acid accumulators with a ten cell pack of the new GP 4300mAh NiMh batteries. Model Power amongst others will be selling them. Correct charging procedure is of course required.
Alan
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2772e

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Re: Torpedo 850's
« Reply #5 on: June 20, 2006, 08:58:47 AM »

Thanks for the advice.

Where can I find MFA? Two new props ready to order.

So how long would I get on these new cells?

What if I run a single 12volt and put the weight further back? It is easy to take a spare pack or two to the lake.

Regards
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dougal99

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Re: Torpedo 850's
« Reply #6 on: June 20, 2006, 10:01:49 AM »

MFA
Worth
Deal
Kent

Tel: 01304 612132
Fax: 01304 614696

www.modelflightaccessories.com

HTH

Cheers

Doug
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Tug

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Re: Torpedo 850's
« Reply #7 on: June 20, 2006, 01:10:43 PM »

2772a,
What if I run a single 12volt and put the weight further back? It is easy to take a spare pack or two to the lake.

 MFA 850 draws up to 12 Amps each, me-thinks you will melt the single battery in very short order,

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Shipmate60

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Re: Torpedo 850's
« Reply #8 on: June 24, 2006, 01:10:24 AM »

Have you considered Car Fan motors, cant remember which , but some do run to decent speeds and will not draw too much current and onlt ?5-10 from scrapyard.

Bob
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ukengineman

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Re: Torpedo 850's
« Reply #9 on: June 24, 2006, 03:27:03 PM »

My experience of car fan motors is that you will get plenty of duration but not much speed. Bearing in mind that 2772e was looking for speed, I think he has the correct motors. There is another direction which 2772e could go and that is to use brushless motors. Higher efficiency means more power from less weight and lower input power for a given shaft power. Costs will be higher. Robotbirds, who sell to the aircraft market have some reasonably priced motors in the 300W to 400W region.
Alan
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2772e

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Re: Torpedo 850's
« Reply #10 on: June 24, 2006, 06:29:35 PM »

Alan,

Would i be right in thinking that brushless motors do not have a reverse facility?  Would i also have to change speed controllers?

Regards

Simon
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ukengineman

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Re: Torpedo 850's
« Reply #11 on: June 24, 2006, 11:38:14 PM »

Simon,
Brushless motors have three wires going to them (they are AC motors) and to reverse the motor you swap over any two of them. Not the easiest thing to do, could possibly be done with a servo operated heavy duty microswitch. You would need a new speed controller. Each motor has to have its own speed controller.
I was thinking about the power needed to get yout large RTTL to give good planing speed. At 68" long, if glow motor powered you would be thinking of about a 10cc motor - that would give say 1 bhp or about 750 watts. The 850 motors are rated at about 12A at 12V ie 144W or 288W for two of them which is just over a third of that power. This makes me think that you just don't have enough power with the 850s, a possibility is a pair of Graupner speed 900s running at about 18V or a pair of 400W brushless motors as mentioned earlier.
Alan
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johno 52-11

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Re: Torpedo 850's
« Reply #12 on: June 25, 2006, 10:34:47 AM »

Hi Simon

As I said before Roberts Severn is running 2 motors that are doing what other people are using 4 850s for and getting better performance. They are running on 18V from a 12Amp battery set-up and give about 20 Mins good running. The props are 75mm 4 blade, which makes them a lot more efficient than an 850. The down side is the weigh a lot more than an 850. There are some stats on the performance testing page which might helphttp://www.lifeboatmodels.co.uk/severnspeedtesting.htm I know Robert has a few spare motors he might be selling.

John
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2772e

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Re: Torpedo 850's
« Reply #13 on: June 27, 2006, 07:36:42 PM »

Hi John,

Thanks for your advise, love the website and the rib is sick. I noticed from the videos that you have used Falmouth as a backdrop. I have a house in Pendennis and spend as much time as I can down there. I saw a large model of a lifeboat in the RNLI window last year; I assume this is one of yours? Take my hat off to those guys!

Anyway to business, I am loosing the plot. Are we suggesting that I stick with 850's, add the cooling, change the voltage to 18 and swap props?

You seem to have spent quality time on R&D so I appreciate your comments.

The boat is not overweight so I think I could take heavier motors. I am in search of as close to scale speed as I can get. I think the real ones were good for 30-40knots and the experimental over 50!

Can you advise me in your opinion what you think the best set up is? Is yours on a 12v and 5v or three 6v? If so what is the connection figuration. Electronics is not really my thing.

I will try anything to get her going! Any advice would be great.

Regards

Simon
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johno 52-11

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Re: Torpedo 850's
« Reply #14 on: June 28, 2006, 01:33:24 PM »

Hi Simon

Your right about some of the pictures being taken in Falmouth but most of the testing pictures and video was taken at our club pool in Dudley. We take the boats down to Falmouth for Lifeboat Day, which is held in regatta week in August. This year it on Sunday 6th August on Custom house Quay so if your down there come and say hello. The model in the shop window is not one of ours I think its a Solent that was given to the Station.

If the real RTTL's where doing 30 - 40 Knots then a scale speed for your boat would be 8.6 - 11.5 knots or 4.5 - 6 Meters per second
Do you have any way of setting up a measured distance that you can run your boat over we had 30 Meters from the end of the jetty to a transit with a pole that can be seen in the videos.

How much more speed do you think you need A bit more or a lot more??

As you already have the 850's installed it might be worth trying some of the changes that have suggested with them but if there getting hot on 12v they will get even hotter on 18v and draw 50% more amps but it will also increase the RPM by 50% but it may not increase the speed by 50%.

If you think you need bigger motors I will email you Roberts contact details I know he has a couple of sets of motors that we used in the Severn. This would give you the option of running bigger props the ones on the Severn are 3inch by 2.5 inch pitch. Do you know what size the props are on the real thing.

The battery set-up we use on the Severn is a 12v 12amp/hr and a 6v 12amp/hr in series to get 18v we connect the positive of the 6v to the negative of the 12v this way round we get 20mins good running time do it the other way round or use 3 6v and you get about 5mins good running time. What amp/hr batteries have you got.
we have done some testing and on 18v each motor is pulling about 14amps so they seem to be a lot more efficient than the 850's.

One more question do you know what the all up weight of your boat is and how much you have to play with for motors and batteries. The motors and batteries on the Severn total nearly 9Kg.

I will email Roberts contact details to you if your interested in the motors.

Regards

John

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