Seaview

[MFR1964]

That's a good point Mark, good ventilation is a must, normally you can use the rule, the diameter of your propellor may not be bigger than the diameter of your motor, don't know if you can apply this when using a gearbox, but using direct drive it's a marker.
I would suspect that you can go a little bigger when using a gearbox, this way i run my type VII, it has gearboxes ratio 3:1, no problems sofar.

Manfred.

[greenman407]

The search goes on. Thanks Manfred.

[greenman407]

Im going to call Mr. C and see if he has a source for more motors.

[Subculture]

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.

If you halve the voltage you halve the current (ohms law), unless you alter the windings and stator of the motor, as the resistance remains a constant. A 12 volt motor running on 6 volts will draw roughly half the current. I say roughly because many factors affect voltage scaling on a brushed motor, brushless motors scale more accurately- no brush drag.

So the motors will only produce about a quarter of the power if you halve the voltage, which will affect both the torque and RPM of the motor.

12*5= 60 watts
6*2.5= 15 watts

Flipping that around if you take a motor wound for 6 volts and run it on 12, you are now putting four times the power through those windings. Not surprisingly, it's going to get a little warm unless you do something about it, either by increasing the resistance to the windings or chopping the current.

So in a nutshell I agree that running a motor at or near it's nominal voltage is required if you want the best performance from it, but bear in mind that current will not double in a motor when you halve the voltage.

[greenman407]

Way over my head. OK so I took some new 12 volt motors that I got from Caswells and decided to try to break them in a little better. I took two D cells , glued them together and soldered them up in series. Next I took a can of water and dropped the motor in it. Within 2 minutes the water had turned black. I let it run for at least 45 minutes and then blew it out with compressed air. I let it run too long because when I checked the brushes.......they were all gone.
Ok, so lets not let them run so long. The next two I did the same way except I only let them run for three minutes. That did the trick. Now the brushes appear to fully conform to the commutator. Should see an improvement. If you look in at the brushes you can see light shining thru between the brushes and the commutator. Not Good. After the break in procedure, that went away.

[greenman407]

Also, the aftermarket modified motors, for the most part are not useable in this situation because the shaft is too short and its got a flat running all the way up it so that a shaft seal wont work on it.

[greenman407]

However, if you use this style 3.5" bulkhead with internal gearing then you can use the aftermarket motors because you dont have to worry about a shaft seal on the motors.

[greenman407]

Heres a picture from inside of the motor mounting locations that I cut in with hole saw and Forestner bits. Note the spring loaded teflon shaft seal.

[Subculture]

You said way over your head in response to my last post. A lot of modellers get confused with electrickery, but it's really very easy to get your head around.

If the talk of volts, current, resistance drives you nuts, then think of it like plumbing. Imagine your motor is a bucket that needs to be filled with water. The bucket may vary in size, a small motor will equate to a little bucket, and a larger motor equals a big bucket.

You use a pipe to fill the bucket and the diameter of that pipe is equal to the resistance of the motor, smaller pipe equals higher resistance and and a larger pipe equals lower resistance.

To get the water to the pipe will require a certain amount of pressure, this is our voltage, low pressure equals low voltage, high pressure high voltage.

How much water we flow through the pipe is equal to current or amperage.

Overall amount of water in the bucket equals our wattage.

Now if we wish to fill out bucket as quickly as possible, there are two ways of doing this- we can increase the flow (current) or we can increase the pressure (voltage).

Increasing the flow will work up to the limit of the pipe diameter, after that the pipe restricts the flow (resistance). We either need a bigger pipe (lower resistance) or a higher pressure (higher voltage). If we can't have a bigger pipe then we can raise the pressure (volts), but there's a limit to this, increase pressure too far and the pipe will burst (you burn out your motor).

On the flipside if we have a large bucket (big motor) and a large pipe (low resistance), but low pressure (low voltage) then the bucket will take a long time to fill (low wattage). This because the water requires a degree of pressure to overcome the resistance of the pipe

Not sure if that helps or confuses you even more!

[Kazzer]

You said way over your head in response to my last post. A lot of modellers get confused with electrickery, but it's really very easy to get your head around.

If the talk of volts, current, resistance drives you nuts, then think of it like plumbing. Imagine your motor is a bucket that needs to be filled with water. The bucket may vary in size, a small motor will equate to a little bucket, and a larger motor equals a big bucket............................................ .......................

Not sure if that helps or confuses you even more!

Perfect! I had that explained to me years ago, and had forgotten it.

[He Who Shall Not Be Named]

I once read in a short-story (Killdozer) how to apply the electricity analogy to hydraulics -- had something to do with fuel-injectors.

Good stuff, Andy -- as usual, you make the hard easier to understand.

David

[greenman407]

By the way, after you break in your motors using this water method, make sure after you blow it out with compressed air, you run and lubricate it . DUH.................

[greenman407]

Looks like we will be able to test this on Monday.

[greenman407]

OK Dave, what kind of problem is this going to create? By adding a thrust bearing between the impeller and nozzle, it moves the impeller blades forward, partially out of the nozzle. I can cut down the hub but it will only move the impeller back 3/32", not all the way. Is this any big deal?

[He Who Shall Not Be Named]

Good enough. Get to it!

M