Motor Sizes

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Motor Sizes

Postby thunderchild on Sat Jan 21, 2012 5:35 am

Good Day All

I don't know if this has been posted in the right section.

I'm after some information on motor sizes. My next build's are going to be the HMAS Arunta (36.5 knots), WWII Australian Tribal Class (Hull length 1.580mm (62"), Beam 150mm (6") and weight allowed 7.4kg (16lb 5oz) and HMAS Moresby (19 knots), Survey Vessel (Hull length 1.430mm (56"), Beam 180mm (7") and weight allowed 6kg (13lb 8oz), both are 1/72 scale, both have twin shafts.

If someone can help me with the motor sizes for these models in would be much appriciated. I'm after scale speed.

I brought the semi kits through Allan Pew quite some time ago, and was going to work on each after the Fremantle had been completed, but have been thinking about it lately and have decided to fit the engines and shafts into them at the same time.

Richard
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Re: Motor Sizes

Postby AdmiralOgle on Sat Jan 21, 2012 11:29 am

I used Fleetscales 777's on a 1/72 type 22 frigate (see Chatham somewhere on here -at National Warship Weekend in Vidoes) weighting in very heavy... :o She was ran on 6v -12v dependant on what i required at the time of sailing. Using 6 x 6v 4mAh batteries she would plod round for about 6 hrs. On 12v the temptation to race was too much and I'd get about 40 minutes max; she'd be doing bursts way over scale speed at times....:oops:

On the 1/64 type 42 weighing in around same as yours, (again Edinburgh video here somewhere) I use 777's again, but on a single 12v 20 mAh battery on the water. Scale speed sailing has allowed enough to run most of day if other systems aren't draining her (radars etc), and still with big bursts for emergency when required. They both had/have twin shafts. I found Graupner motors power hungry.

The 777's are very popular here in the UK and recommended by the Glasgow lads who are very knowledgable when it coes to anything 1/72

Anything smaller I use 555's. Only thing I've learnt is the speed of revs of the prop double when voltage is doubled -so a motor giving 5,000 revs at 6v goes to 10,000 at 12v. Scale speed sailing doen't require that many revs, probably only 100 to 400 (guess) for most purposes depending on prop fitted, once moving she can plod on reduced revs using her own inertia, so your power isn't eaten up quickly. I'm sure Big Bri can/will give you better and fuller advice.
regards Bry

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Re: Motor Sizes

Postby brianc on Sat Jan 21, 2012 6:11 pm

I think you`ve covered it well Bry, I`ve used both these type of motors and they cover my needs admirably. The 777s are the very popular up here for 48 and 72nd scale ships.
For smaller ships, Model Motors Direct do something called a Mecca Motor, I`ve installed these in My River class Minesweeper and they are brilliant little motors, I`ll certainly be buying more of them.
Graupner do a fantastic range of motors too, the speed 500, 600 and 700 motors would suit most warships dependant on size.
I would challange you about double the voltage double the revs though mate, you can easily burn out a motor by overpowering it, it always pays to check the designed voltage for the motor you intend to use ;)
You must remember though, scale speed is controlled by the digits on your hand, the farther forward you push that stick, the faster the model goes, it really is that simple..... I must admit though, it`s sometime hard NOT to rush about the pond like a boy racer :roll: :D
If you use a computerised R/C set, you can alway programme it for each of your models, most modern speed controllers are very easilly programmed also ;)
Last edited by brianc on Sat Jan 21, 2012 6:17 pm, edited 1 time in total.
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Re: Motor Sizes

Postby thunderchild on Sun Jan 22, 2012 4:12 am

Thank you Bry and Brian

I've had a quick look on the fleetscale website, the 555 are listed, but couldn't find anything on the 777's. Cornwall models, list the others.

Are the 777 rated as a 700 size motor.

Regards
Richard
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Re: Motor Sizes

Postby Admhawk on Sun Jan 22, 2012 2:16 pm

Brian, many DC motors have a voltage range listed for operation, usually 6-12 but can be 1.5 to 6 or 12 to 24, depending on how they are made. When a range is given, the RPM normally doubles with voltage.

Notice my use of the words 'many' and 'normally'. There are so many different models that you need to check the specs for each motor before assuming anything. And always test before installing.

And for Richard, my experience is that you want to have more than scale speed available. Especially when you are not alone on the water. You need to have the ability to stop quickly or get away from others to avoid collisions.

I don't stick to standard motor sizes. I like to hunt through surplus places and find motors that have been removed from commercial equipment. You can often find relatively cheap 12VDC motors that have a very good torque and low current draw. RPM varies all over the place from a couple of hundred to over 15,000.

I recently found a nice big 12VDC motor about 3" in diameter that draws 1.2A at 3300rpm that will push my next big model along nicely. No clue about what it came out of, but for $20, I think it's a good find!

One other thing I try to do, match the motor diameter to the prop diameter. It helps to ensure enough torque for the motor to push the prop through the water without straining itself and overheating from excessive current draw.
Last edited by Admhawk on Sun Jan 22, 2012 2:21 pm, edited 3 times in total.
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Re: Motor Sizes

Postby AdmiralOgle on Sun Jan 22, 2012 5:17 pm

I should have made it clear that the motors; re; double rpm to voltage, was on motors with ranges from 6v - 12v. not all motors work on a range of voltages.
regards Bry

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Re: Motor Sizes

Postby paulswainson on Mon Feb 24, 2014 12:14 pm

The talk of motor size is very interesting but what if you are building a 8ft long 1 foot wide Model that will way in at some 15 Kg plus and the scale is 1/96, how would you work out the size of motor to use then? There are three props, center one is 14 inches long the other two are 21.5 inches long 4mm thick with 45-50mm propellars. Is there any formulars to help get a sence of the motor size.
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