OPTO ESCs - RCCanada - Canada Radio Controlled Hobby Forum
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Old 08-16-2016, 05:48 PM   #1
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I have ordered some parts for my first quad build. I have 12A OPTO ESCs coming. I read something about UBECs required on ESCs without an on board BEC. The diagrams show the OPTO ESCs wired directly into the battery. I will be using a 3s 11.1v Lipo and a PDB. Is a UBEC something I need to use?

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Old 08-18-2016, 11:39 AM   #2
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The difference between OPTO and normal ESC's is that the OPTO ones do not supply 5 volts on the signal wire. This 5 volt supply is normally used to power servos and the receiver in fixed wing aircraft. Some use that 5 volt supply to power the receiver and flight controller in a quad but most often they use a separate power supply.

Most PDB's will include a voltage regulator that powers the flight controller and receiver.
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Old 08-18-2016, 03:40 PM   #3
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the OPTO ones do not supply 5 volts on the signal wire
Do you not mean the red POS wire?

tmpearson, no direct experience with your type craft other than I read your ESC's are programmed to react to throttle changes much quicker than other apps require. That makes sense.

However, other than that most of the information should be universal:

OPTO generally means the linkage between the signal input for each phase is not electrically connected but uses an optical source/reader pair. This prevents or reduces the chance for electrical noise to be sent to the radio system and one that becomes even more critical with higher currents. A much more sophisticated method and one that usually is more expensive.

As for the BEC's, it is up to the manufacturer if they want or need to have it onboard. There are a few important factors that come into play. First is that ESC and BEC ratings are in a minimum 5 MPH cooling airflow. If in stagnant or insufficient air those can be significantly reduced. Also, ESC's create most of their heat at mid throttle and if excessive that can bleed over to force the BEC into thermal shutdown.

Finally, most onboard BEC's I have seen are current limited to approx 3A. Not sure why, but with heavy draw, (high number and/or digital servos or other systems such as servoless retracts) there will not be enough capacity.

Add all those together and you could run into problems.

As for your app this is what I suspect. To keep things light and simple they have eliminated the BEC from your ESC's which means you need to provide power for the receiver and control systems another way. I would think the maker of your machine may already have some suggestions or parts there to provide that function.

Otherwise you could power those through a separate BEC, even tied to the same battery. I have done this to all my helis up to 450 class to eliminate the chance of ESC heating shutting it down, (buried in a canopy shows the same issues) but mainly it is that I can now provide a higher current source with less chance of electrical noise.

Separate BEC's can vary widely in output with some providing up to 20A. Depending on factors such as weight and current requirements your options are a lot better this way.

NOTE: Regardless of setup you want to tie all the black NEG together to provide a common reference point and as a place to dump RF. Even if you source your system from a separate battery you would likely find the ESC ground reference via the receiver plug.

ps. On larger helis, especially with main motor currents above 60A you would often find no onboard BEC due to switching noise alone. Also, due to higher current demands the flight system is fed by a separate battery pack.
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