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n00b In need of help - loss of power

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Old 08-10-2013, 03:36 PM
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Gabe84
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Default n00b In need of help - loss of power

First up, I hope this is an appropriate place for this kind of post. Sorry if not, I'm very new to the Air section here...

So I'm reasonably experienced in RC, having had a boat (electric, brushed) for many years, and owned a couple of nitro trucks for the last 6-7 years. But this is the first time I've owned a plane, and the first time I've dealt with brushless.

I bought my 2013 model Skyartec Cessna 182 probably just over a week ago. It's a 7ch model with gyro. Before buying the plane I'd already had a go at some simulators using my PC keyboard, and since buying the plane I've had a couple of flights with it and done a fair bit of practise on the simulator using the radio - a bit different to keyboard. So my success rate for the flights has been so-so.

At my most recent attempt to fly and not crash, I went out with a fully charged battery and everything looking good. But when I pushed the throttle, the prop simply cut in and out in quick bursts. I cut the throttle and tried bringing it up again gradually, which seemed to work fine, and at 100% throttle it started down the runway. The problem is, it wasn't enough power to take off.
I tried reconnecting the lipo pack, turning the tx on and off, raising the throttle trim to +100, but nothing got the prop to spin any faster. It was spinning consistently and enough to move, but not fast enough for take off. I tried both accelerating slowly and pegging the throttle, but results were the same.

The thing is, in my last failed flight I bumped the nose and snapped one of the prop blades. I wasn't too concerned because it wasn't a high-speed impact, and mechanically everything seemed of (including the motor) so I just went home and replaced the prop for next time.

So basically, I wanted to know if a bump in the face can cause the motor to behave the way it is, and if there's a way to potentially fix it or if it needs to be replaced, or if there are other things I should check as well before spending any money. I just really don't know how a system like this normally behaves and what kind of anomalies can happen, because I've never dealt with the electronics of either a plane or a BL system.
Hope you guys can help. Thanks!
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Old 08-10-2013, 06:31 PM
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Welcome to the addiction!

Okay guessing the motor was spinning when you had your incident. What can happen is the motor jambs and there is a huge amp spike. It can do some rather ugly things.
Like short the esc, or even the windings on the motor. The "cogging" you had happening is one or more of the sets of windings, or leads from the esc are open/shorted.

First thing, don't try running it until you have the problem corrected. You can do additional damage.

Alright then, lets do some checking. Another cause of this can be a poor connection, between the esc and motor. You need to physically check the solder points/connections at the point where the esc and motor connect on the three leads. If you have a cold solder joint on a connection or one of the connectors it causes an open circuit on one of the leads. This ends up basically causing one of the 3 phases of the motor to do nothing. So you a motor that acts like an engine with a really bad miss in it.

Also check the three motor leads where they go into the motor itself. See if a bare wire is touching the case, or one has come loose. You can also check the three leads with an ohm meter. Check each one against the others to make sure you are not getting a ground indicator between them. Also check each against the bell for a short to ground.

While you are in there poking around, look at the esc. If you see melted heat shrink or any signs of overheating, more then likely it's been damaged.


If you pass all the above, it's time to play elimination. Start swapping out parts. Remove the prop from the plane, and try another esc and/or motor. See if one or the other corrects the problem.

Best of luck!
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Old 08-11-2013, 03:55 AM
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Thanks for the reply!
I had a look at everything and checked the circuits wherever I could get access to, and it seems to be ok. What I did find though is that the lipo pack is only putting out 7.7v instead of 11.1, and it should be close to full charge. Is it worth it/safe to try and discharge and recharge the pack? Maybe there's a dead cell in there...?
And I thought going back to electric would be easy...
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Old 08-13-2013, 08:55 AM
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If the pack reads 7.7 on a 3 cell pack, its dead. One thing about lipos if you run them down past 3.2 volts per pack they will die. You need to replace the pack. The cutting in and out it the safety on the ESC shutting it down.
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Old 08-15-2013, 09:23 AM
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Quote:
Originally Posted by Gabe84 View Post
Thanks for the reply!
I had a look at everything and checked the circuits wherever I could get access to, and it seems to be ok. What I did find though is that the lipo pack is only putting out 7.7v instead of 11.1, and it should be close to full charge. Is it worth it/safe to try and discharge and recharge the pack? Maybe there's a dead cell in there...?
And I thought going back to electric would be easy...
Sounds like, in your crash, you broke a wire in the lipo pack, 7.7V would be a partially discharded 2 cell pack. A 3 cell pack should not be discharged below 9V.

The pulsing you were getting from the motor was probably the LVC, the low voltage cut-off which is there to preserve power for the receiver and to help prevent you from over discharging your lipo.

You will find all this explained in the e-book at this link.
EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT
http://www.rcuniverse.com/forum/m_7100376/tm.htm
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Old 08-15-2013, 04:10 PM
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Haha, 2 days after I did my previous post I found that my life battery is done, I discharged and one cell went down to 1.98 v the other was 3.2 its toast.
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Old 10-25-2013, 05:28 PM
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Quote:
Originally Posted by Hawk131 View Post
Haha, 2 days after I did my previous post I found that my life battery is done, I discharged and one cell went down to 1.98 v the other was 3.2 its toast.
Don't give up on the pack yet, sometimes you can bring them back to life with a super slow trickle charge...
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Old 10-25-2013, 05:39 PM
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I have also put a bad pack on my park zone 12v car charger it doesn't have a low voltage safety unlike my Hyperion charger. It will some times bring them back as long as its not completely dead. As for a life battery I have used the charger " lipo" by the way to bring back a life battery. I charged them only to get it up above the minimum voltage. Most guys will disagree with me on this because of it being a life battery charging on a lipo charge.
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