Feigao 2 pole motor - physical timing?

[ReddyWatts]

Do we need to get the power stroke of the 2 pole motor in time with the 2 blade prop, since we are running surface drive?

Has anyone thought about the physical timing of a 2 pole rotor in relation to the prop position as it powers through the water on a 2 blade prop? This would not matter on a 4 or 6 pole motor, but it could make a difference on a 2 pole, since the motor travels 180 degrees on each short power pulse and the blade travels 180 degrees on each water stroke. Instead of only 90 or 60 degrees on a 4 or 6 pole motor. If they were in time would it help in power transfer to the water? Are we wasting power, like when a car engine is out of time?

Am I all wet on this idea? What do you think?

[hammertime]

sounds logical to me

[Fluid]

You are confusing "ignition timing" with phasing the power "pulses" to the load. Internal combustion ignition engines use advanced spark timing to match the maximum cylinder pressure with the power stroke of the piston. BL motors use timing advance to match maximum field "pull" with rotor position. These are all internal engine/motor issues.

You are speaking about matching motor output to external load. I have tried this with a few boats but could not see a difference on any easily measured parameters. Speed for instance was the same at either end of a 90-degree change in prop orientation. I suspect that rpm and rotor momentum are so high that prop position doesn't matter. But a more detailed study could show something different, as could larger diameter props......


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[ReddyWatts]

Actually, I was making a point by comparing the loss of efficency for something being out of time.

Maybe the weight of the prop and drive train act as a flywheel to continue the inertia through the loaded portion of the rotation. Does this mean a wire drive will not work as well on a 2 pole motor as a 4 or 6 pole, since it does not have as much mass? Would the timing be more critical for a 2 pole with wire drive?

What size prop did you test it with?

I was hoping someone had looked into this before. Thanks for sharing with us.

[Rex R]

you might want to look into the 'odd-fire' v6 to see if anybody has published anything on its torque variations (90 & 105degrees). I would think that with a flex drive( and to a lessor extent wire drives) trying to match prop position to torque pulsations could be an exersize in futility :)

[ReddyWatts]

Good point rex. How could you set the prop timing when using "FLEX" drive? (ha!) A good way to truly test it would be with a "SOLID" direct drive.

[Rex R]

supose one could test the theory using a shaft driven boat like the 'hammer'. think you would see a bigger change by (somehow) reducing the rotating mass...hmmm aluminum prop mayhap?

[ReddyWatts]

Oh well, we are using flex and wire drives, so it just got more complicated than I want to mess with.

It is probably more critical for a nitro, since they only have one power stroke every 360 degrees of rotation and a gas that only has one every 720 degrees.

[Rc1racing]

"It is probably more critical for a nitro, since they only have one power stroke every 360 degrees of rotation and a gas that only has one every 720 degrees."

The Zenoahs are two stroke engines. They spark every 360 degrees. Are you talking about a 4stroke 1 cylinder? They have a power stroke every 720 degrees, but are a rare find in an rc boat. The higher rpm and less weight of the 2 stroke make it a better choice.

But you have a good point. You would have to wind the flex shaft tight to find the prop position in reference to the rotor position. This would be a hard thing to do. I guess you could try turning the prop 1/8 a turn or so on the shaft and try it. And keep turning the prop and testing for top speed. But this would not be an easy thing to test.

[ReddyWatts]

Exactly and then how could you relate it to anyone else or boat, since they are using a different length flex cable and power.

[marker]

The rotor is a two pole but the stator is three phase so the coils are energised three times every revolution.
Mark

[Rex R]

that was something I couldn't figure out when I was trying to figure noise freqs for a given rpm, just how many power impulses does a 2 pole motor have per rotation. I mean they have 2poles and what looks like 3 windings.

[ReddyWatts]

Ok, so marker says there is pulses every 120 degrees, then what is it for a 4 and 6 pole motor?

if you manually turn the motor you only feel 2 magnetic poles every 180 degrees? If you turn the kb45 you also only feel 2 poles at 180 degrees? Explain that.

i guess I better do some research on 2, 4 and 6 pole motors. Do they all have 6 pole stators? The more I think about it the more i dont understand it.

[ReddyWatts]

Marker "The rotor is a two pole but the stator is three phase so the coils are energized three times every revolution."

I guess that means for a 4 pole motor the controller will energize the coils 6 times for each revolution.

If true, it means for a 6 pole motor the controller will energize the coils 9 times for each revolution.

The controller uses the pulse from the wire not being used while it is energizing of the stators to automatically sync with the rotors of the different pole motors.

2 pole energizes every 120 degrees
4 pole energizes every 60 degrees.
6 pole energizes every 40 degrees.
8 pole energizes every 30 degrees.
12 pole energizes every 20 degrees.


Therefore "prop physical timing to the rotor" does not matter.

Now that makes me wonder if you need the best quality of controller for the higher pole motors? They are really switching on and off at a higher rate and need to run cooler.

I just learned another interesting fact. The timing in a controller is designed to be in time with the rotor under loaded conditions, so when you run them on the bench with no load, they will get hot quickly because their timing is off.

[ReddyWatts]

Thanks guys for your input and keeping me pointed in the right direction. It really helps to bounce this stuff off you.