To UBEC or not to UBEC

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To UBEC or not to UBEC

Postby cynr100 » Wed Jan 25, 2012 10:54 am

A short story first.
Some months ago I purchased a clone 450 V2 and destroyed it 10 minutes after the first battery charge :oops: . I was attempting a blade track when the verandah furniture jumped all over my heli at full throttle due to a brain fade. I was left with a main frame, motor, ESC, UBEC (or is that an SBEC), battery, 1 servo and some velcro tape.
I have spent many hours hunting down and reading info, plus chasing bits to rebuild. Rather than buying a new one I now have a heli that I know inside out and back to front (mechanically) and it spins up smoothly.
I am now following Radds School of Rotary Flight (no more mucking around).
I am only running one 11.1v 2200mah 20C which I allow to cool before and after each charge (2 new ones on the way from HK to satisfy my hunger and keep Radd off my back(hahaha)).
On the 3rd charge following a series of 7-8 minutes at 50% throttle with 5 degree pitch I suddenly only get 3-4minutes at the same settings, if I have zero throttle from 10-60secs I can get what appears to be another minute at 50%. The ESC and SBEC(??) are hot to touch and battery cables are warm. I should mention here the motor is KV3680.
Back to the internet for more info (I drown when it comes to electronics).
The original ESC has no markings at all so I went searching for a replacement thinking mine was dodgy and this is where to start, however looking at the variety available I have become totally lost.
Now back to the subject title.
I would appreciate a steer in the right direction, should the ESC be 30, 40, or 60amps?? will a plug and play suffice or do I get one with a programming card, should it have a 2,3,4,5amp BEC or should it be a stand alone.
Any info greatly appreciated.
This unit was orignally purchased as a prelude to bigger and better things however once I have mastered a hover and a simple circuit I will hang it up, buy an AXN and move to Tokoroa those guys know how to have fun. :mrgreen:
Not enough time in the day for all my crazy ideas, I'm not slow, I'm just pacing myself
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Re: To UBEC or not to UBEC

Postby kaptain_zero » Wed Jan 25, 2012 10:02 pm

I do not fly helicopters.... keep that in mind.

I also could not find the recommended size of motor for a 450 so I don't know for sure how large an ESC you need, but I'm going to say probably 40amps or larger. There is no harm, other than weight, in going larger (more amps) on an ESC and the larger they are, the more current they can handle before getting to hot. KV3680 only tell how many revs per volt, not how much power the motor puts out. As for programming cards... they are handy, but you can program using your transmitter on most ESC's I think, but it can be a pain.

A separate BEC can be used, but I'm not sure if it would be of much help to an inexperienced pilot. If your ESC shuts down due to a low battery, it also shuts down the built in BEC.... having that separate would keep your receiver and servos working, even if the motor has shut down.... A separate BEC will also have some minor weight. If the heli has an ESC and a BEC, I would keep it that way. Again, I'm not the one to tell you what size of BEC you need... I don't fly heli! :twisted:

Now as to your initial problem.... sudden reduction in flight times after only 3 cycles..... it could be several things, so I shall list them here but you will have to do the detective work.

1. Mechanical issues.... has the drive train developed additional drag/friction? If it has, it may be the cause of both reduced run time as well as extra heat coming from the ESC. A watt meter would be helpful in displaying how many amps are being drawn. Once you have the numbers, simple math will clarify what's going on. If you are drawing too many amps, they are being wasted somewhere. If you are not drawing that many amps or the voltage is dropping seriously, it could be a bad connection somewhere, bad wire, bad ESC, bad motor, bad battery.

2. Battery issues..... Is the battery balanced? Is your charger working correctly? Again, that watt meter would have been handy as some of them can read the voltages on each cell of your 3 cell pack and some can even do the balancing work for you. Perhaps your battery is failing and no longer able to keep up with the demand. You mentioned being able to get another minute of flying time if you let the heli sit for a while... this is simply the battery chemistry catching up to the demand during a period of no load but it does not tell us why.

3. Connection faults.... Bullet connectors, cold solder joints, bad connections inside your battery, a failing or faulty ESC.... all are suspect if everything looks OK otherwise. I've seen bullet connectors where it's burnt inside but still showing a connection.... just not a very good one. Badly soldered battery connectors with too much resistance to carry the current. Check to see if the connector is hot after flying.

As when you rebuilt your heli, you need to methodically check each system to track these problems down. Something like this HK watt meter or Turnigy watt meter would be very helpful in tracking things down. The Turnigy has a memory so if you hook it up and spool up the heli for a few seconds and shut it down, it will still display the peak amp draw. The HK one does not have a memory but it can balance a battery pack for you.

Hope this is of some help until someone with heli experience can step in.

Regards

Christian
"I'd like to live as a poor man with lots of money."
-- Pablo Picasso
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Re: To UBEC or not to UBEC

Postby cynr100 » Wed Jan 25, 2012 11:18 pm

Thank for you reply Kaptain_Zero.

When I did the rebuild I was very carefull with the mechanical side to ensure everything was straight and balanced, I did not pay any attention to electrical connections.
I have purchased a muli-meter and soldering iron, I am also going to source a new balanced charger/checker (currently a Titan B3 :roll: )and watt meter.
This will aid me checking your recommends.

The original unit came with a separate BEC so I will be looking in that direction, on that note my understanding of a separate BEC is one that is wired to the main body of the ESC and not enclosed in the main body??

Again thanks for your response it all helps.
Not enough time in the day for all my crazy ideas, I'm not slow, I'm just pacing myself
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Re: To UBEC or not to UBEC

Postby cynr100 » Thu Jan 26, 2012 12:20 am

Have been playing with my new digital meter and have checked the LiPo battery, each cell has returned 3.96v. The battery has not been recharged since my original power drop problem emerged 2 days ago.
I would like to think that this would indicate that the battery is not the issue, having sustained 50% throttle for 3-4 minutes and now showing very little voltage drop.
In past uses of the battery it has at best only been warm (like a cuddly blanket) then again it has only been sustaining 50% throttle, I still waited for it to be room temp before charging.
Still looking reading and learning, you're never too old!!!
Not enough time in the day for all my crazy ideas, I'm not slow, I'm just pacing myself
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Re: To UBEC or not to UBEC

Postby kaptain_zero » Thu Jan 26, 2012 2:01 am

Well, you are on the right track... systematically checking/measuring things until you find the problem. Battery balance is fine, remember not to store it fully charged but rather around 3.85v/cell, often called a storage charge. Batteries don't like to be cold or hot, a nice normal room temperature gets the most out of them. Around here on a cold day, we just stay home.... Lipo's go dead in -40 weather, much like RC pilots. :evil:

Don't let your "I was very careful with the mechanical side" catch you with your pants down (and don't ask me how I know that). Something *could* have slipped or moved, causing additional friction/drag. Not likely, but it never hurts to give the chassis a quick once over and see if everything feels OK.

I've only seen BEC's and SBEC's in little baggies, all my ESC's have them built in so they don't show. I'm pretty sure if you check closer, you'll see your BEC wired to the battery leads of the ESC.

Regards

Christian
"I'd like to live as a poor man with lots of money."
-- Pablo Picasso
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Re: To UBEC or not to UBEC

Postby cynr100 » Thu Jan 26, 2012 3:15 am

HAHAHAHA!! "don't ask me how....." know exactly what you mean, I have bruises to prove it.
I can't function in anything less than 20C, your -40 just does'nt compute. Thats why I live in Cairns, Australia, the 24hr temp ranges are winter 15-28C, summer 29-34C its just the rain that gets to you 4500mm pa and the odd cyclone (last one Yasi 2011).
I'm in the middle of resoldering all my connections, put everthing back together again and see what happens until my new purchases arrive.
Cheers
Dennis
Not enough time in the day for all my crazy ideas, I'm not slow, I'm just pacing myself
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Re: To UBEC or not to UBEC

Postby cynr100 » Sat Jan 28, 2012 8:41 am

Success!! resoldered the ESC to motor connections and (because I have a new Turnigy3500 on the way) I stripped the motor down and found a small 5mm dia washer parked between two magnets. Put everthing back together and spent the next 10 minutes practising tail control at 50% with no hint of power loss!! and this battery was not recharged.
Soft start and spin are much improved, its like removing a rock from you shoe.
Can't wait to get my watt meter and new charger from HK, find out what is really going on.
Thanks again to Kaptain_zero
Not enough time in the day for all my crazy ideas, I'm not slow, I'm just pacing myself
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