The Ship Model Forum

Hey! seaphoto ! Do what I do . I specificially use CANON copier drive motors and 12 volt power.The motors can be found at any flea market or electronics surplus dealer.There are MANY formulas that can be relied on but, I use this formula.If it,s a tug I use a motor at least as big or bigger than the prop.The rest I use the motor that will give me the most run time (two hours so far ! ) and stay cool during operation.I sometimes will use small fans (computers etc. ) mounted in a hollow stack to blow cool air over the motor.If you do this make sure that you build weather baffles in the stack to keep water out of the hull and off the electronics. Make sure you have the radio capacity to carry all you want to run!.

I do a lot of hunting around for surplus motors, which often have little or no specs. I have had good luck with motors using three pieces of information - the voltage, the RPM, and the shaft diameter. For most of our boats, we are running on either 6 volt or 12 volt - this is usually driven by the speed controls, battery choice, or personal preference. RPM for scale boats is usually 4000 - 6000. Much more, and you will need to gear down, which I prefer to avoid. Shaft diameter is a good indication of the torque of the motor, as manufacturers generally size components to the load. For a destroyer, I find a 1/8" shaft diameter motor to work well, for a larger vessel, I look for a motor with at least a 3/16" output. My Gneisenau, in 1/100 scale, utilizes 3 Pittman industrial servo motors with 1/4" shafts, and it has all the power you could ever want.

Kurt

...And there's the old adage - spin a prop with a diameter no bigger than the case of the motor.

I'm not sure how to take that one, though - for displacement vessels we want low (<3000) revs for more torque; and more torque, through gearing down, can mean bigger props.

I need to think more about this.

Andy

yet more info to digest, I just love this forum many thanks guys

Roy

Typically, the number refers to the size of the can of the motor; a 540 is 54mm long, a 360 is 36mm, etc. Sometimes, the larger can size may mean a motor that has more torque, but fewer RPM- depends on the motor. There some other differences that occur- typically 550's come with an integral cooling fan.

If memory serves, this numbering convention was started by Mabuchi- who makes most of the small electric motors of the world.

your calculations are incredibly close Andy as for the weight displacement hadn't worked it out yet but will trust with your expertise thanks.
spoke to an ex R/Cer the other day he said i needed a 545 but if im reading it right the higher the No the more power. The BK 1125's were not designed for speed so a 545 might be to big. I have come to the conclusion also that i will have to make a rudder extension for sailing only.

Roy

roy allen wrote:I intend to build a WWII Soviet bk 1125 river boat in 1/24 scale.
Single prop partially housed in tunnel max dia of tunnel is 24mm so am thinking of 20mm 3 bladed screw

Interesting vessel! If I've got my facts right, this will be just over a metre long, draw less than 3.5cm and displace around 3kg?

My gut reaction would be a '500' - just about any one would do.

Andy

I intend to build a WWII Soviet bk 1125 river boat in 1/24 scale.
Single prop partially housed in tunnel max dia of tunnel is 24mm so am thinking of 20mm 3 bladed screw

Roy

roy allen wrote:After spending some time yesterday looking up suppliers on the net i'm a bit confused with the types and makes. The No's they quote mean nothing to this newbie Heeeeeelp

I feel your pain, Roy.

I see I've written an 800-word essay to ease the calculations regarding motor & prop size to boat size and speed, but it's too verbose, and I'll post something tomorrow after a major edit session.

Andy

Well,

I cant say much about non-german motor suppliers.. I get my motors either from scaleship.de (the propulsion motors, I usually stick to Buehler), and electronics scrapyard - functional motors (radar antennas etc), taken from VCRs, Cassette, CR-ROM drives, etc for free of course.

Generally, you have some criterions when you select:
1) Number in the name, like Graupner 500 or Buehler 490 - it indicates a general size/power of the motor. The larger the number, the more powerful it is.
2) RPMs - how fast the thing spins on different voltages. For a displasement ship, you take a slow-turner, meaning a one with not more then 5000-7000 RPM unloaded. Usually I also use lower voltage for the motor, running a 12V unit only up to 6V or so. I never use geared motors, due to a high noise level.
3) dimensions of motor and shaft - for mechanical stuff
4) Normal or Brushless motor. Brushless is much more expensive, and needs special units to control. But much less electronic noise.

Which ship are you going to motorize? Which size of the screws you plan? Maybe Ill be able to suggest something...

Regards,
Petr

After spending some time yesterday looking up suppliers on the net i'm a bit confused with the types and makes. The No's they quote mean nothing to this newbie Heeeeeelp

Roy