Stock motor/prop/thread - Lets get it straight

[flydiver]

There is a lot of ongoing confusion over the power train in the STOCK Cub. Let's try to straighten some of it out.

1. The ORIGINAL (red) Cub used a brushed motor, 7-cell NiMh battery (9.6v fully charged), and a 10x8 SLOW FLY (fat) prop. No one KNOWS for sure what the speed control (ESC) will handle but estimates hover around 13A. PZ will not divulge the specs.
With that system power draw:

HZ Supercub 10x8 Prop
Stock 7-cell NiMh
50% throttle = 4.37A and 39.9W
100% throttle = 10.07A and 83.4W

PZ 8-cell NiMh
50% throttle = 6.05A and 59.7W
100% throttle = 10.94A and 95.1W

Notice there isn't a lot of improvement at full throttle but is at half throttle.

Then the 'blue + 3S lipo' Cub came out. Prop was reduced to a 9x6 slow fly. There is a jumper you can pull that changes LVC to ~ 8.8-8.9v (which I consider inadequate and too low). Other than that there WERE NO CHANGES OR IMPROVEMENTS TO THE POWER TRAIN.

Power draw using a Master Airscrew 10x6 prop (pretty similar to the new stock 9x6 in terms of amp draw...I think)

3s Lipo (1500mAh, Zippy 20-30C)
50% throttle = 5A and 55W
100% throttle = 12.5A and 131W

Notice the bump to 12.5A on 3S lipo with a smaller prop. This is why the 3S lipo is preferred primarily. Lipo is also lighter and supports it's voltage under load better so the over all performance is noticeably improved.

But, the float prop suggest is the old NiMh-based 10x8.
Power draw for that is:

3s Lipo (1500mAh, Zippy 20-30C)
50% throttle = 6.82A and 83.2W
100% throttle = 18.37A and 212.7W

Note - the 1500mA Zippy lipo probably performs better than the stock PZ 1300mA lipo. IMO the stock lipo is poor performing and over priced.

Notice the Amp draw is around 18A with the 10x8. You can pretty much be sure the ESC will not take that on a continuous basis, nor will the stock battery for that matter. Most ESC are rated on a Continuous/Max usage rating. Usually the Max is for no more than 30 seconds. So, with the larger prop you can get away with bursts of full power for short periods, not continuous running. If you try it you will shorten your stock battery life if by some odd chance the ESC lives long enough to permit that. The motor also will not have a long life. These components were just not designed for that load. You can be pretty sure PZ fully knows that the stock components will be kept long enough to get through the learning phase and then the plane will be sold or seriously upgraded.

Short story - a power train is balancing act between the motor+prop+ESC+battery. You cannot just arbitrarily throw whatever you want together. You need to know the specs and performance of each component and balance them to the plane and performance you are looking for.


Motor/gearbox weighs 142gm.

[bdg]

Excellent compilation! Thank you for pulling together this information for the group!

[shandley]

Awesome! Thanks! What are the ratings for the stock ESC and Motor (specifically the blue + 3S lipo version)?

[flydiver]

No one knows. PZ does not release that info.
You want a sticky but the answer to your question is in the posting above. Just goes to show you how much good stickies often are.

Read the whole thing again, several times until it makes sense. There is a lot of data in there.

[thorvald]

I just did a couple of flights stock with my Super Cub LB and some of my Eagle Tree telemetry toys installed (just for fun).

With the stock prop and stock battery I found the following max, measured from the eLogger V4 was 12.86 Amps and a max speed (gps measured) of 47.8 Mph.

So your measurement of the stock setup was bang on.

I'll try to do a flight later today with the "float prop" and no floats to see what the max is on the stock setup.

Cheers
Tim

[flydiver]

Stock battery?
The stock battery is 'lame' and is kind of a safety limitation on this setup. A GOOD battery will allow even more power to be fed through the system further endangering the ESC.

[robbie8800]

Is engine temperature an issue that should be monitored with the stock blue cub?

[flydiver]

Jul 15, 2013 2:51:42 GMT 1 robbie8800 said:

Is engine temperature an issue that should be monitored with the stock blue cub?

ALL electronics (except the RX) need their temps monitored when you first start flying them. Over stressing any of them can cause overheating which can lead to failure. The usual rule of thumb is 'if it's too hot to hold, it's too hot'. This can kill a lipo fast, cook a motor, or fry an ESC. A nice tool is one of those IR thermometers.

Once you have a power system 'balanced out' you can mostly ignore it. On an RTF that 'theoretically' this balancing has been done by the manufacturer you mostly don't have to be as concerned about it...mostly. Some cheap RTF's are assembled so poorly the components are not well matched.
If you mess with any parts of the Cub power system (new prop, bigger battery, etc.) then it's a new game needing overview.

Note-I'm not at all shy about my opinion that the ESC in the CUB is the weakest link in the entire package and is stressed to it's limit in it's current incarnation. Pushing it very hard often results in failure. As we have often seen, some fail out of the box.

A common mistake is propping for the plane, as in 'it's a Cub so it needs a 9x6 prop no matter what motor I use' ....no no no.
You prop for the motor. You pick a motor for the plane. You pick an ESC for the motor+prop combo. You pick a battery for the whole package. It's a calculated art+science that needs to be learned. Once you start messing with power systems a wattmeter is an important tool. Without it you are messing in the dark unless you copy a successful system exactly.

This is worth it's weight in unfried electronics.
RC Electronics Watt's Up Meter - a Quick Look
www.rcgroups.com/forums/showthread.php?t=311574

[flydiver]

I think this thread needs a bump again. Lots of new people on the forum. Stuff gets buried.

[hghost]

I asked about Prop-Motor-ESC-BEC-UBEC-SBEC on another thread somewhere in Cub Club World (http://supercubclub.proboards.com/thread/5408/esc-bec-ubec ) and you gave me some great information in a link www.wattflyer.com/forums/showthread.php?t=31368


That may help some others with questions.

I still struggle with figuring electronics out.

I worry battery drops to low, how will LED's affect the voltage drop ?,what is it suppose to be ?, but how when flying do you figure it out?
Setting TX to 5 minute flights and than checking the battery and seeing if the ESC is getting hot seeing a number and than trying to figure out how much longer can i fly with the battery, 6 minutes ,8 minutes - 10 perhaps ? In the field it is hard to figure ( my head does not work that well )

I try just to stick with the electronics that come with the plane, but not even sure if they are sufficient as they claim in some of them .

I also have a couple Brushed planes, i would like to change to brushless at some point, will need to know the Correct KV Motor and ESC and Prop combination for the different size planes ( a future investment )

I been reading off and on, but retaining allot of that in my head is a chore.

I figure there are allot of new people to the hobby that never consider any of it at all....and some may read what others might say and just assume what they read is correct, with out researching to find out. A site recommends X Prop for Z Motor and Y Esc....but they are out to sell, and if you fail they sell more products to you, they do not care if it works or not, or if it wrecks or burns up, they sell parts that is their business.

Why i always come here and ask my never ending daunting questions and sometimes more than once.It takes allot to make me understand now days.

Funny how i can remember things that happened years ago,and can point out land markers, roads that are no longer there, Homes, farms, that once there and yet now gone for example ,memories of by gone days even , but can not remember what i was told or what i have been reading in the past month ?

Why i come here for information, I need all the help I can get.

[sham]

I'm very new to this sport but the electronics side is a universal with any other field that uses them. The way I always work with electronics and electrics is a simple rule. Load and not supply is what governs what happens.

The battery will supply what the load demands (if it is capable of doing so) and a load of extra milliamps will just let it do so for longer - of course, you need to make sure it is the right voltage and can supply the wattage.

The load is set by the motor and the prop combination on a plane. Too big or too aggressive on the prop will overload the motor and make it draw more power than its meant to, get too hot and fail. Get it right and the motor stays cool and works well, great. Then the ESC comes into play, is it rated for the amount of current the motor/prop combo is now flowing?
If so, and the battery can produce that much power... Then you're golden.

If you want to be a bit techie about it - grab a multi meter and measure the draw at the motor at full throttle with the prop spinning, then you can work out how long the battery will last when you know its capacity. If the motor manufacturer gives specs and you have a load of props to try then you can prop the plane using a multimeter to check loading.

It all gets very silly, but if you're changing stuff you need to get the motor/prop combo (load) right first and then spec the rest out to cope with the load.
As I start with this hobby, I've been reading loads and it seems people struggle most when they start with the battery and spec the plane that way.. You need to know the load first.

I'm keeping mine stock though, and will use my budget to replace any failed parts... Long days flying achieved by simply having a couple of spare batteries. That's even simpler