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Old 10-03-2009, 10:41 PM   #1
jskirwin
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Default Hobbyzone Mini Super Cub LiPo Battery Problem

We've been flying our new mini super cub daily for almost two weeks now. After last night's flight my son put the battery on the charger. Today he took it off and installed it in the plane - and the plane was dead. I repeated the install a few times and confirmed this.

I've plugged the battery into the charger. The LED flashes three times then doesn't blink again. I've started checking the battery with a voltmeter and it registers over 7v.

Is this LiPo dead? It sure looks like it to me. Anything I can do to resurrect it?

Thanks!
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Old 10-04-2009, 12:23 AM   #2
Park Flying Fun
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Dead as in the motor will not work but the servos still do? Or no response at all?
On your last flight, did anything stop the propeller while it was under power?
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Old 10-04-2009, 02:48 AM   #3
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No response from the servos. Usually we get a twitchy sound from interference, but this sucker is DOA. Nothing. The last flight was a smooth glide into the grass if memory serves - but there were a few nose dives before that. The mini's circuit board is glued sideways into the plane, so I can't get to it easily to check for loose connections.

But since the battery won't charge, I'm thinking it's the battery. Those 3 flashing lights must mean something.

EDIT: I just rechecked the voltage. The battery is returning 2v dc.
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Old 10-04-2009, 03:42 AM   #4
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Default

Yes, it sounds like one of the cells may have shorted internally, it would then draw down the other cell. Probably a manufacturing error.
Lipo's are fairly robust and can hold an incredible amount of current for their size and weight. But, they are very sensitive to overcharge and over-discharge, they also at times can fail just from being dropped hard enough to crease an edge or corner (seldom).

Actually replacing the battery is an inexpensive fix.

We rework 20-30 Mini Cubs a week here at Park Flying Fun and the usual problem and common to almost all electric planes is one I do not think is addressed well enough for new flyers.

Quickly, go to idle if you crash!

There is a power mosfet and diode on the receiver/ESC that controls the throttle. If the prop is stopped suddenly (from a crash or bumping into something while getting ready to fly) while the flyer is giving it throttle the current meant for the motor will feedback into and through the diode burning out the mosfet and diode.
Caution here, usually just the motor will not run, but sometimes when the mosfet fails, it fails "ON" - so the throttle goes to max every time you plug in the battery, regardless where the TX throttle is set.
Then it is time for a new receiver, or a soldering iron.

Good luck

Robert
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Old 06-26-2010, 04:04 AM   #5
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Default Same Here

Originally Posted by jskirwin View Post
We've been flying our new mini super cub daily for almost two weeks now. After last night's flight my son put the battery on the charger. Today he took it off and installed it in the plane - and the plane was dead. I repeated the install a few times and confirmed this.

I've plugged the battery into the charger. The LED flashes three times then doesn't blink again. I've started checking the battery with a voltmeter and it registers over 7v.

Is this LiPo dead? It sure looks like it to me. Anything I can do to resurrect it?

Thanks!
I've flown my plane twice. The second time, it seemed like it died mid-air. I landed it in a grass field. It started acting like it was going thru a sequence....beeping, etc. The next time I tried to take it out, it won't respond. The charger flashes 3 times, but no light afterwards, and no response from the plane. I don't know if it's the battery, charger, receiver, etc.
Any suggestions??
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Old 08-11-2010, 11:08 PM   #6
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Default

I also have a mini super cub and I am having a problem where when I plug the battery in without doing anything else the propeller spins automatically at full speed. I cannot control it at all. any suggestions?
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Old 08-11-2010, 11:59 PM   #7
Park Flying Fun
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Default Another Mosfet

Hello bearswin8584,

The power Mosfet/transistor and blocking diode on your receiver/ESC are bad, see my earlier post.
Usually this happens when the prop is stopped while under power, current meant for the motor will feedback through the diode damaging them both.

This is very common in brushed motors setups, rarely in brushless motors.
Always return to idle before a crash or if anything is blocking the prop.

The Mini Cub uses a TOSHIBA Field Effect Transistor (2SK2844) for power and the diode is usually marked M1, the diode is the surface mount version of a common thru hole 1N4001 diode.

If you are confident with a soldering iron you can replace these two parts, other wise it's time for a new receiver/ESC.

Good luck

Robert
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Old 08-12-2010, 12:51 AM   #8
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Default

Robert, this may sound silly, but could a replaceable small amp fuse be wired in to prevent the diode and transistor from blowing?

Thinking that soldering these kinds of items into the board is going to be a little beyond the skills of those who buy these birds. A blown fuse would be a lot easier to replace.

When I die, I want to go like my Grandfather did, in his sleep...... Not screaming like the passengers in his plane.
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Old 08-12-2010, 08:44 PM   #9
Park Flying Fun
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Default Fuse

Although some seem to have success with a fuse, they may have just been more careful, I am not sure that a regular fuse will work.

While there is a spike in amps, it's the reversed flow of current back into the components that causes the damage.
The diode (M1) is a blocking diode and is designed to block current reversal. It is just not able to withstand the amount of current forced back into it when the prop is stopped while under power. A fuse would still allow the current to pass in reverse until it reached enough Amps to take out the fuse.

E-Flite had the same issue with the E-Flite Blade CX & the early models of the CX2; it was very common to have to replace the 4n1 or 3n1 (expensive).

Fortunately the Raychem Company came out with the "PolySwitch PPTC Resettable Device" basically a resettable fuse, it is quickly tripped by a change in temperature not amps, but once it is powered off the fuse resets itself with nothing to replace. - In most cases it does a better job of protecting the electronics.

E-Flite started installing these in the second generation of the Blade CX2's and in the current CX3's and they seem to work well.

I had intended to go over the "Polyswitch" specs to see which one to use in the Mini Cub. But I am afraid that other things keep taking up my time. I'll try to review them sometime in the next few days at the office and then post it here.

Robert
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Old 08-15-2010, 03:33 PM   #10
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Default Update

Just an update, I've placed an order for several different versions of "Polyswitchs" and will test them first before posting here.
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Old 10-25-2010, 02:00 AM   #11
Park Flying Fun
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Default Finally got it done!

I've finally managed to test a number of resettable fuses on the stand for the Mini Cub. Here are some of the observations.

The Mini Cub pulls between 3.15amps to 3.75amps
at full throttle on the test stand with a stock Mini Cub 2S 7.4v battery - producing 5.1ozs to 6oz of thrust.

A higher "C" rated battery and/or changing props will bump it up quite a bit. So how much is too much? Hmmm

As a note, the Mini Cub circuit board & components are almost identical to the HobbyZone Firebird Phantom's PCB, you have to look really, really close to see any differences. The few differences are some of the trace's and of course the firmware programmed for the V-tail on the Phantom.

The Phantom and the Mini Cub both use the same power mosfet to drive the same size motor. The difference is that the Cub uses a gear-reduction so it can swing a larger prop, while using fewer amps.

A Phantom with the same motor and an 8.4v nimh, but with a direct drive pulls as much as 5.65amps at full throttle. (I've also tried a Phantom with a 9.6v nimh battery pulling 6.2amps. It produced +6.7ozs of thrust and flew like a rocket for a few seconds . . . until the wings folded . . .)

Test were done with various sizes of Poly brand & PTC Resettable Fuses, while they may or may not be the best choice, I settled on either of the following for my Mini Cub, and prefer the RGEF600 - these trip faster than the RHEF series with the same hold current and are used in the same applications and are specifically for DC motor protection!

RGEF600 16V PTC Resettable Fuse; 6.0A Holding Current 10.2ATripping Current (preferred)
RHEF600 16V PTC Resettable Fuse; 6.0A Holding Current 10.8ATripping Current

The key points to consider is:
**Operating Voltage: the lowest I've found for the amps is 16V
Holding Current: above 4amps
Tripping Current: below 12amps,
I blew a mosfet when one peaked at 12.3amps

These are available at many places like DigiKey or Mouser here in the US and element14 in the UK!

I soldered the fuse inline on the positive lead just before the motor under the cowling, they are not polarized so it is an easy connection with some solder and heat shrink tubing.

**A note from the spec sheets cautioned that using a fuse with a higher voltage rating (30V+)

"... may withstand higher interrupt current at lower voltages. Each application will need to be individually evaluated."

I can verify this, a 30V fuse on 7.4v didn't trip until almost 14amps and I lost a diode and mosfet with that one!

I may place a few of the fuses in my eBay store and/or the Park Flying Fun web site. All I need is the time.

Below is the data sheet. Hope this helps, I'll try and get some pics up soon.


Robert


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Old 01-26-2011, 03:12 AM   #12
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Default Same Rx issue, can I fix it!

Hi, I have the same issue on two of the esc/rx's. Thanks for the info Robert. So let's say I'm willing to try and replace to two items; Mosfet/transistor and blocking diode, but I can't seem to identify what is what. Do you have a picture of what I should be looking for.
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Old 08-04-2014, 12:52 AM   #13
The R.C. Guy
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Default well

i have the same problem with my Super cub DSM and i dont know what to do.
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