Battery Advice Needed For Middle School Competition

[fechter]

Can we pick the direction of rotation on this motor or is it predetermined?
We are proposing to thread an aluminum tube onto the shaft threads of the motor.
If it turns counterclockwise, it will tend to unscrew our propeller shaft!

Yes, it should be no problem to reverse the motor. This is done by rearranging the hall/phase wire sequence to the controller. It may take some trial-and-error but it is not really hard. There are some threads on how to do this.

Some controllers have a reverse function, but this typically limits the speed to some really slow setting in reverse.

[BlueBell]

Thanks, good to know.
Slow reverse is fine, maybe even good.
It appears from the videos the direction of rotation is correct for a right hand propeller.
This is good as there are way more of those to choose from than left handed propellers.
Unfortunately, it's going to want to unscrew our threaded shaft.
Nothing a bit of Loc-Tite wont fix.
Thanks everyone.

[999zip999]

From what I know a 3-phase motor will run forward or reverse there's 36 wire combinations that can help this there's even a chart where you can map them out when you change the wires and you just mark it off the chart so shouldn't be a problem can we see a better picture of your controller from my understanding a motor doesn't know voltage or Direction
A three phase motor does no amperage and Watts as it will melt

[BlueBell]

Okay, the plot thickens.
I'm asking for propeller recommendations on a known boat forum and uncertainty has arisen over shaft RPM at reduced power levels.
In the different heats there is either ~200 watts or ~400 watts available to the motor.
What RPM's could be expected?
I thought at 48 volts the RPM would be the same, ~467 as the spec sheet indicates.
The thread is here for your reference:
https://www.boatdesign.net/threads/what ... ost-818907

[999zip999]

Back to the controller what is the upper limit on the controller is it 42.5 if its 42.5 volt 48v could be out of the question. You can't give us a limit then take it away.

[BlueBell]

999zip999
Sorry, you lost me there...

[DrkAngel]

Okay, the plot thickens.
I'm asking for propeller recommendations on a known boat forum and uncertainty has arisen over shaft RPM at reduced power levels.
In the different heats there is either ~200 watts or ~400 watts available to the motor.
What RPM's could be expected?
I thought at 48 volts the RPM would be the same, ~467 as the spec sheet indicates.
The thread is here for your reference:
https://www.youtube.com/watch?v=rx2qG_YMrDs

Unloaded rpm would be the same.
But, under load, rpm will be restricted by a "load" line, propeller should be optimized for rpm at available watts.

I approximated up a graph comparison of 400w available vs 200w available, with comparative rpm (not to be taken as actual or optimal!)

400w vs 200w.jpg (209.19 KiB) Viewed 396 times

Attempt at 200w from motor simulator resulted in a fault-flaw, lines went wonkie, so I drew in a reasonable estimate.

Wind resistance on "load" line should be somewhat similar to water resistance, for like comparison purpose ... or at least a starting point for physical trial.

[BlueBell]

Ohhhhh, that's what those graphs were all about, sorry, I completely missed the connection.
Is this motor selection far too big then?
Probably not or you wouldn't have recommended it.
Thanks for all your patience.

[DrkAngel]

Larger than needed for 200w solar, close to perfect for 400w+ battery input.
Spare capability for ... ?

Larger than needed is much preferable ... than smaller than needed.

[999zip999]

So what are the limits we are working with ? This seems so abstract.

[DrkAngel]

Another, perhaps overlooked, factor is that the motors bearings are not designed for axial stress.
The bearings are for stress perpendicular to the motor shaft.
The propeller shaft will press directly into the shaft.
Solution is the use of a thrust bearing supporting the shaft.

A spherical roller thrust bearing recommended for axial and lateral support.

[BlueBell]

DrkAngel,
Not overlooked, but thanks for your concern.
That issue has been addressed.
Don't forget, this set up only has to last about 30 minutes at peak performance.
As you know, the loads aren't terribly high.
We are, however, looking at copper tube, water cooling on the motor if need be.
Thoughts? Will it get hot at 400w over 25 minutes on an 80 degree fahrenheit, calm, sunny day?

[DrkAngel]

I can't believe overheat to be an issue ... even at 400w input continuous.
Just don't restrict airflow unduly.
Monitor during testing?
Water cooling = spray bottle?

[BlueBell]

DrkAngel,
And the lipo, would it heat up during discharge like that?
Not likely or you would have mentioned it.
A spray bottle is not an option as the pilot is not in a position to operate it and too busy with other tasks anyway.
The copper tubing would have been the ticket.

[DrkAngel]

Lipo designed for 15C 60A continuous, discharging at ~2.5C ~10A should only get mildly warm, no heat issues.

[BlueBell]

Cool, thanks DrkAngel!

We heard back from the prop guru and he thinks a 2-bladed, 13" x 20" pitch would work well for all the heats.
Even up to 22" perhaps.
Good luck trying to find one of those in the R/C airplane department...