Seaview

[Subculture]

The motor you linked to will run hotter than hades on 12v, too fast, plus it's blooming expensive.


500 size.Will give you 5000RPM unloaded shaft speed geared 3:1.

http://www.ebay.co.uk/itm/3750-15000RPM-3-12V-High-Torque-Cylinder-Magnetic-Electric-Mini-DC-Motor-/121152634485?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item1c35427e75

Bit slower-

http://www.ebay.co.uk/itm/DC-12V-13500RPM-3A-1900g-cm-Magnetic-Micro-Motor-DIY-Toys-/290913157070?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item43bbc67fce

[greenman407]

Thanks Andy. I was going to reduce the voltage on those motors to 2 cell LIPO (7.4)since they are rated for 7.2 volts as most cars are. The good thing about the first link you showed was that the shaft is 20mm long. Much better.

[greenman407]

Those people wont ship to the U.S. Ill look over here at our Ebay.

[Subculture]

Those people wont ship to the U.S. Ill look over here at our Ebay.

Ahh, okay sorry about that, didn't spot the U.S as an exclusion. I've ordered from them and found the products good.

If you want to go for a car motor, then you should be looking at either a 45t or 55t motor.

[greenman407]

Our Ebay has nothing like that, that I can find. The links that you posted give some useful info about the motors, so that you can make a informed choice about what you are buying.

[greenman407]

Thanks. If youll notice this link, it shows the relative speeds of brushed motors.A 55 turn is 7700 RPM. If you run a 3 to 1 gear ratio thats only 2567 RPM and thats no load. It would drop under load. According to the chart, their 28 turn would turn 14,500 no load. At 3 to 1 that would be 4833 RPM no load. Perhaps that would be better.http://www.ansmann-racing.de/cms/eng...ic-motors.html

[greenman407]

At another site, their 35 turn turns 1450 RPM per volt. So thats 10,150 divided by three gives us 3383 RPM, perhaps a little slow. I dont know.

[Subculture]

I thought you were running a 12 volt system- that's what I was basing my figures on.

[greenman407]

Well, I was, but it wont hurt anything, if need be to take out a 3s batt and put in a 2s and retrim. If need be. As it is , it looks like I wont have any choice. I like those EBAY/UK motors that you posted a link to but I cant buy them.

[Subculture]

Very easy to work out a ballpark figure for what you're looking for too.

Simple bit of mathmatics- multiply the pitch of the prop in inches by the RPM, then divide by 1408. This gives you a mph figure equal to 25% prop slip.

So for instance lets say your props are about 1:1 pitch to diameter ratio (many model props are but pitch can vary from about 0.8-1.6 times diameter)

1.56*5000/1408= 5.53mph

This is very simplistic, as lots of other factors like the drag of the hull and prop blade area alter the balance, but it gives you a good basis to select motors. Generally for direct drive, the motor can should be 75% or greater the diameter of the prop for it to spin it easily. Again there are other factors that can alter that, especially if using brushless motors, but for the type of motors being used here it works fairly well.

[greenman407]

I just have a hard time understanding why those 12 volt motors have such a hardtime turning those little empellors, especially at 3 to 1. I took one of the motors apart and looked at the brushes. You can see where the brushes were only touching the comm. in two small places. That has to effect motor operation. Maybe I just need to break in the new Caswell 12 volt motors and install them and note the improvement.

[MFR1964]

That is looking familiar, happened to me with my balance device inside the type VII, was trying to run a12v motor on 6 volts, it did work for some time, only eating away the brushes.
It has to do with the current, power is voltage times current, for example, your motor has 60 watt of power, the current at 12 volt will be 5A, at 6 volt this will be 10A, this high current will eat away your brushes.
Always try to get the voltage of your battery as near as possible to the pecs of your motor, 7.2 volts will kill your motor on the short term, unless you use a 6v motor.
Replaced my 12v for a 6v motor and it is still running great, done this 5 years ago.

Manfred.

[trout]

I got the math!
Power = voltage X current
60w = 12v X 5amp.
60w = 6v X 10amp.
60w = 7.2v X 8.3amp
does running a 6v motor at 7.2v cause a problem?

[MFR1964]

Yes, that can be done, but not for long periods on full throttle, most of the time we don't drive on full throttle, so in general your 6v motor will last for a longer period.

Manfred.

[greenman407]

Another thing that we are dealing with is lack of ventilation. Our motors are all sealed up inside the Subdriver. It has been said that for good health an RC motor should not go above 130 degrees F. Motors in your RC car get good ventalation going down the track. So it would seem that you need a motor that can handle your prop with power to spare so that you dont get too much heat buildup.