SuperCUB with Floats - Motor Stopping....

[bdg]

I've been flying with the SC for several months and decided that tonight would be the time to finally try the floats. I have had ACT removed since my first flight - many many flights ago - and mounted the new 10x8 prop and floats on the SC.

All was great. I put her in the water and she took off just perfectly. No issues. Really not unlike my standard grass or asphalt take offs. Immediately cut back the throttle as I've heard that the stock ESC will not work well with the larger prop under WOT.

Flew around for maybe 4 minutes and decided to bring her in. A nice landing without incident. Decided to take off again but the motor kept "stalling". LVC was my thought - although I can normally run for 8+ minutes and still have my 1300mAhr battery still reading just over 3.7V per cell. "Must be the extra floats and larger prop". Another possibility was that some water might have splashed causing problems?

I let her sit for a while and tried again. She was airborne momentarily and then the motor quit again. A little rough on the landing but ok. The very gentle wind was blowing towards me so I let the wind bring her back.

I did try one more time (getting too impatient?) and the motor stopped again when I was maybe 10' in the air. Another emergency landing but at least it was closer.

I was finally able to retrieve the SC. Voltage was 3.84V/cell.... pretty much where it should have been.

Brought it home and held the tail. Same results with the 3.84V battery. Okay... tried a fresh battery (4.18V) - same result. Under 100% throttle the motor stopped after maybe 3 seconds. Took off the 10x8 prop and ran without a prop for 10 seconds. No problem. Put the former 9x8 (?) stock prop back on and ran to 100% - no problem.

The issue definitely seems to be with the larger 10x8 prop. The stock components just can't seem to push it.

So - now I am in a decision time for water. Options:
(1) Try the 9x8 with the floats. Reduced lift on take off but maybe acceptable?
(2) Replace the stock ESC and motor. I do have a 30A ESC coming from HK (a spare for my toolbox) but do not have a brushless motor on order and would need to come-up with a suitable motor and motor mount for this configuration. I could always pick one up from my LHS.

Thanks in advance for any suggestions / comments.

[cubfanatic]

I would defiantly try with the standard prop first. As you said there would not be as much lift on take off, however the cub is designed to fly at low speeds so stalling would probably not be a major issue, you would just need longer for take off.

[bdg]

Thanks for your thoughts! This will certainly be my first step. I've heard that the SC is a little sluggish with the standard prop with floats - but that is okay as long as it can take flight. I also tried another 25C 1300mAhr battery with similar results - motor cutout. I am not sure why the ESC allowed the flight in the first take-off. Either I wasn't wide open, the ESC was cold and therefore not ready to protect itself, or maybe something happened during this first event to the ESC unit...

I see that many true seaplanes actually use a balloon to cover the ESC and Rx -- is there a similar strategy by SC owners for the stock equipment?

[gagallagher04401]

If everything is stock, and you are using lipos. get some GWS 1060 (10x6) props Best thing for the cub. Works with and without floats.

[flydiver]

The stock ESC is not up to the task of handling the 10x8 float prop long, maybe 15-30sec bursts. Excess throttle can burn it out.

If it gets wet, and it WILL get wet, it can short out.
DO NOT USE IF WET! You can burn out the electronics permanently.
It's likely you've either burned out some of the FETS in the ESC or they got wet.
Let it dry out for a couple DAYS and see it that helps. If not it's replacement time-one way or another.

A smaller prop creates less load on the electronics but at the expense of less thrust.

There is a water repellant called Corrosion-X you can safely dip electronics in. There was a discussion on this a few weeks ago. Search it out.

[bdg]

All great information! The take-away for me is that water and the large prop are the "enemy". I guess that is why the Parkzone Icon A5 has a seal along the hatch and provides a balloon to contain the Rx and ESC - in an effort to keep them dry!

The LiPo battery had been splashed a little on the underside but the ESC (above the battery, as we know in the stock configuration) seemed to be dry. The ESC works great with the stock prop but is definitely cutting out with the larger prop. The 10x6 as suggested sounds like a good compromise overall. Wouldn't a blown FET be obvious with performance of the standard prop - likely characterized by uneven / rough rotations? The FET should fail open or closed... closed would be an obvious problem so the only other option would be for it to be opened and thus the potentially uneven performance.

I like the idea of the Corrosion X suggestion. I am really thinking that a new name brand Rx and ESC are in my future.... but that also means a change of the motor to a brushless version as well.

Definitely lots to think about with this configuration. I really like the idea of the floats on the SC - just need to make it robust enough!!!

Thanks for the suggestions / feedback.

[flydiver]

You will get no where near the same flight times once you put floats on. The extra drag taking off and flying plus the larger prop will eat your battery.

From an earlier post:
[still have my 1300mAhr battery still reading just over 3.7V per cell. ]

That is a DEAD battery. Unless you like buying lipos never fly your lipos lower than 3.5-3.7v resting. As soon as you put power to a cell that low it'll drop below 3v in nothing flat. Of course it LVC.

If you've been flying to LVC on a routine basis that is slow early death to your lipos. The LVC on the stock is poor and set too low. It cannot be reset.
To top it off the stock lipo is in keeping with the rest of the electronics....barely passable.

[bdg]

flydiver - Thanks for your comment. Reduced flying time would certainly be a normal expectation with the floats due to the extra drag, but I would think (maybe incorrectly) that we should be able to reduce throttle with the larger prop and therefore the additional load on the battery would not be incredibly different... but I could be wrong!

I normally run the Lipos to 3.75V or so. I have never had the batteries in the cub below this level and I have never seen LVC on the cub. My understanding is that 3.7V under no-load is the lower threshold, for sure.

My comment above was that I thought that LVC was being reached - but again each cell was at 3.84V (no load) and therefore there really should have been ample capacity in reserve for another pass or two.

As mentioned previously - I tried this same set-up with a 25C 1300mAhr freshly charged LiPo (12.6V) and the same cut-off takes place with the larger 10x8 prop... no issues with the stock 9x6 prop.

[flydiver]

There is an optimal efficient prop for all electric motors. Too smallyou lose thrust and efficiency. Larger you gain some thrust but also lose efficiency. All power not converted to movement in a motor becomes heat. Essentially their watt rating is their ability to dissipate heat. Push a motor too hard and the excess heat burns it out. You are trading efficiency for thrust with the 10x8. I'm going to make a guess that the most efficient prop for the stock motor would be a GWS 9x5. You wouldn't like the way it flies (puny) but it would fly a longer time.

If your motor is cutting out it is likely the battery sagging or something wrong with the ESC. Only sure way to tell is replace the ESC or get a wattmeter so you can see what it going on. I'm merely speculating from a position of more experience but I really don't KNOW. To do that you need data or known good parts to swap up. This of course makes the proprietary electrics even more of a problem.

[bdg]

First of all, I'd like to thank the SC community for consideration through this post. What a great forum for like-minded people!

IF brushless motors are similar to those which I work with on a regular basis in industry - there are some inconsistencies with your comments and industry norms.

(1) Wattage is a measure of shaft horsepower (in this case fractional horsepower!) and not the amount of heat that the motor can dissipate. Horsepower (1hp=746W) is measured at the shaft as Torque * rotational speed in rad/sec. There are definitely losses between the electrical energy provided and the mechanical energy delivered. These losses include I2R losses (heat, as you describe), windage losses, noise, etc. In this scenario, a 250W motor would provide 250/746 which is approximately 1/3hp. The electrical energy required to deliver this 250W would typically be in the order of maybe 350W (more or less) depending upon the efficiency of the motor. The case that you describe is that the motor needs to dissipate the heat as Watts and that this is the measurement on the motor.... this would certainly be the case for a standard resistor (think toaster) but not for a motor.

(2) The power required to drive a fan is a parabolic relationship between torque and speed. Low speed requires very little torque (almost no shaft power) BUT the torque demand grows very quickly as speed increases (and shaft power increases accordingly).

(3) A standard drive - which I believe is very similar to an ESC - will vary the firing of the transistors on the DC bus to the motor. The resultant 3-ph waveform is a pulse-width modulated signal. In this case, the RMS voltage to the motor varies with the firing of the transistors. Power is also Current * Voltage, so we effectively can reduce the power also required to the motor through the ESC.

I don't want to "harp" anymore.... this analogy is entirely based upon industrial drives and motors but (I think) is directly transferable to the hobby world through the ESC.

I completely agree with your comment that the prop is a compromise. I also agree that if you push a motor too hard it will generate excess heat (through I2R losses) as the torque (current) demand will be too high. This will indeed cause the motor to fail.

Thanks again for the comments. Absolutely great information, for sure. I do have a spare brushless ESC but do not have a brushless motor to try it with for testing (at least not yet!). I also concur that the ESC is stopping the motor to protect itself from excess current draw. The only problem that I have is with the larger 10x8 prop --- no issues whatsoever with the standard 9x6.

Note that I did try the 9x6 with the floats. She definitely took off but I required pretty much full throttle for several seconds to get her off the water. Not unexpected. After that, I reduced the throttle and the plane performed a little more sluggish than normal but not too badly overall.

[flydiver]

Good enough. Your sophistication in motor theory exceeds mine. I try to keep it simple. In this forum I generally don't try to exceed the assumed understanding level of the person asking questions. I missed your level, but you didn't offer. I do rewind and test brushless motors. I've done a LOT of reading on ESC since the 'black box' nature of the units puzzled and annoyed me. That's my level of expertise.

In keeping it simple.
The electrics suck. That alone makes diagnostics difficult.
The 10x8 is WAY too big for the ESC. Horizon does NOT release specs but it's generally assumed to be around 13A.
The stock battery is lame.
Fly with floats and your electrics WILL get wet.
Fire up wet electrics and you WILL fry them.

I stand by my recommendations. Swap out the ESC (unfortunately...or fortunately since that means the RX too) or get a wattmeter to see what is happening.
The Cub ESC is has no sophisticated protective mechanisms like overheat throttle back, unless they changed something recently. It just burns up, or historically has. The way yours is acting it is either defective or has some electronic changes. It could also just be lame batteries. The motor is not in the clear but is the least likely problem.

[bdg]

Thanks for your suggestions! I agree fully with your conclusions.

I replaced the motor yesterday with a new unit from my LHS. The bearing in the other motor allowed for some sideways play which I did not like. As expected, a little noisy too. No difference.

Not sure if I want to stick with stock or modify for brushless. I do have a spare Rx and ESC - just need the motor to make it fly!!!

[flydiver]

In the long haul, and likely even the short one a new motor and complete electronic replacement is both a better and less frustrating option. Lots of motor suggestions in that section of the forum.

[bdg]

Some new electronics in my SC.... removed the stock ESC/Rx and replaced with a separate 30A ESC (w/BEC), dedicated receiver, and new brushless motor (from my LHS). The motor seems a bit oversized at 200W (http://www.bphobbies.com/view.asp?id=A1400125&pid=B2632605) and especially so with a new 10x7E prop. I am flying quite comfortably between 1/3 and 1/2 throttle, compared to previously at maybe 1/2-2/3 with the stock equipment. I am contemplating a change back to a 9x6 to help increase the motor rpm a little.

The added benefit of these new components is that I was able to open-up my battery compartment to allow for easier vertical placement of my Lipos. The stock compartment was just too small for the dimensions of some of my non-Parkzone batteries.

Flew off a local lake earlier this week which resulted in some erratic flight characteristics. Flew from the grass this evening with the floats on to get a better feel for the new flight characteristics... definitely wants to level out faster (as expected). Had to hand launch (no problem) and the floats stopped the plane very quickly in the grass without incident.

I'll be trying the water again soon.

[cubfanatic]

200w seems about right really, so what is the maximum size battery you can fit in vertically? I would be interested in doing this mod as the stock battery is too small and expensive for its size, and it would be nice to have some longer flight times.