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Jun 25, 2019, 10:53 AM
Flying again - 4th time
FOGeologist's Avatar
Thread OP
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How do you separate a speed controller from a receiver?


I will be attempting another giant-scale J3 Cub and desperately want to avoid the disaster I had with the last one, where I bought a Hobby King speed controller which burned out on me in flight, leaving me with a Coke machine 90 feet over my head.

So I would use a separate battery to power my flight controls if my motor or speed control pooped the bed... How does that ESC get the signal from the receiver to control the throttle?
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Jun 25, 2019, 11:09 AM
Flying again - 4th time
FOGeologist's Avatar
Thread OP
Let me clarify.

The ESC on my original Cub exploded into flames and pieces. The wires from the ESC to the battery burned off, and I was left without power to the receiver. Instant Coke machine!

Is there a way to completely isolate the power circuit from the receiver? To prevent any back EMF or surges from roasting it as well?

Obviously, I won't be buying trash from Big Evil any more, and my intention is to go with a Castle Creations 100 amp job... so maybe my concern is too pronounced. But with Giant Scale stuff, redundancy and awareness of the Rules of Murphy's Laws are just far safer than thinking of the plane as an 1100 mm foamy warbird.
Jun 25, 2019, 12:49 PM
Registered User
Any "opto" ESC should have an isolated input which will definitely protect you from any power surge because of the optocoupler.
It won't protect from fire and explosion, though.

You can check if servo ground and battery ground are connected, if not it's an "opto" ESC.
Jun 25, 2019, 01:56 PM
AndyKunz's Avatar
Quote:
Originally Posted by FOGeologist
Is there a way to completely isolate the power circuit from the receiver? To prevent any back EMF or surges from roasting it as well?
I don't think you need to go "opto" here.

I would simply disconnect the red wire on the ESC where it plugs into the receiver. This is very easy to pop out with a #11 blade tip. Use the tip to slightly bend the plastic retainer back, then pull the wire out. Put heat shrink or tape over it to prevent it from shorting.

You now need a battery to power the receiver. The flight pack will power the ESC/Motor, and nothing else. The receiver battery will power the receiver and servos, but not the ESC.

This gives you the isolation you need.

It has the added advantage that, if you are using a telemetry system like we sell (Spektrum) then you can monitor both batteries indepedently.

Andy
Jun 25, 2019, 02:11 PM
Registered User
The only way to completely isolate the receiver and ESC would be to have two batteries. If you wanted to use one battery you could take something like this https://hobbyking.com/en_us/kingkong-5v-3a-ubec.html. They make different voltages and currents so you would need to match to your receiver and servos. Run power from the one battery to the UBEC and the output from the UBEC to the receiver and servos. Then run power from the battery to the ESC. If ESC burned like before you would still have power to the receiver and servos.
Jun 25, 2019, 04:00 PM
Registered User
I would not rely on a HK BEC that states 3A and is good for maybe 2.
Also, it may be possible the ESC is shorting the battery when it burns, rendering the whole setup useless as before.

Just connecting the ground and using a non-opto ESC will protect against ESC burnout but maybe while burning the ESC will connect battery plus to servo signal, which may kill the Rx.
It's not very probable, but possible.

An optocoupler on the other hand has easily hundreds of volt of isolation and whatever happens on the ESC side will not interfere with anything on the Rx side, in fact the Rx wouldn't even know.
At least if the layout is responsible or the opto is an external circuit plugged in between ESC and Rx.

It would still be possible to use telemetry by reconnecting GNDs...
Jun 25, 2019, 05:09 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by FOGeologist
... where I bought a Hobby King speed controller which burned out on me in flight ...
Which make/type controller?
What were the calculated and measured current at WOT?

Make sure you get the correct ground for your receiver, no ground loops.
And use a switching SBEC as a BEC, not a linear LBEC, or use dedicated battery for controls.

Vriendelijke groeten Ron
Last edited by Ron van Sommeren; Jun 26, 2019 at 01:31 PM.
Jun 26, 2019, 10:00 AM
Dave the Rave
dmccormick001's Avatar
There are several possible solutions already offered here, but one thing I think the OP might not realize.

Many/most ESCs are actually a combination of two devices, the Electronics Speed Controller, and a Battery Eliminator Circuit, or BEC. The BEC is designed to do exactly the opposite of what you want to do, it eliminates the need for a separate battery to power the receiver and servos, they are instead powered from the motor's battery. If you lose the ESC due to over-current to the motor, you may or may not lose the power to the receiver, but you probably will. There are a lot of very good ESC's available that do not include a BEC, and these give you the option of either using a separate BEC (which is wired straight to the battery and does not depend on the ESC for anything), or using a separate Ni-MH, Li-Ion, or LiFE pack to power the receiver.

As Andy said, if you have an ESC that does include a BEC with it, you can effectively disable the BEC by removing or snipping the red wire on the ESC's receiver cable. it will still read the throttle signal and work as a speed controller, but will allow you the other two options. If you decide on a separate BEC, make sure it has a maximum amperage rating sufficient to handle your servos.

Two other pieces of advice. Buy a larger ESC than the motor says you need, the ESC doesn't "push" current to the motor, the motor "draws" what it needs, so there's no danger of a bigger ESC doing any damage. And don't run your batteries for too long before you land and recharge. Not only is it hard on the battery, but as the battery's voltage drops the motor tries to make up for it by drawing more current, which can over-tax the ESC and cause the problem you had.

OK, three. make sure the ESC has plenty of air circulation to cool it. I cut the heatshrink of most of mine. I don't know why they make them that way.
Jun 26, 2019, 01:36 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Better not cut the red wire, you may need it again in another plane.





Jun 26, 2019, 01:42 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by learningarduino
Any "opto" ESC should have an isolated input which will definitely protect you from any power surge because of the optocoupler. ...
And make sure it's a real optocoupled ESC, not the Chinese scam, where opto means no BEC. (I call a car with no brakes a coconut car.)

Vriendelijke groeten Ron
Jun 26, 2019, 01:44 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
It is a good practice to have some headroom built in.
About derating motors, controllers, batteries, electronics in general:
Vriendelijke groeten Ron
Jun 26, 2019, 01:48 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
(UBEC is a propriatery brand name, no info,I prefer LBEC (linear) and switching SBEC (switching), gives more info.)

The higher the power-pack voltage, the fewer servos a non-switching = linear BEC can handle. Switching BEC's hardly have this restriction.

The higher the battery voltage, the hotter a linear BEC will get, for a given current/load/servos.
Or, in other words ...
The higher the battery voltage, the lower the current a linear BEC can supply.

In depth:
All about BECs for RC model planes (24 min 58 sec)
Jun 27, 2019, 12:02 AM
Registered User
vollrathd's Avatar
Quote:
Originally Posted by FOGeologist
Let me clarify.

The ESC on my original Cub exploded into flames and pieces. The wires from the ESC to the battery burned off, and I was left without power to the receiver. Instant Coke machine!

Is there a way to completely isolate the power circuit from the receiver? To prevent any back EMF or surges from roasting it as well?

Obviously, I won't be buying trash from Big Evil any more, and my intention is to go with a Castle Creations 100 amp job... so maybe my concern is too pronounced. But with Giant Scale stuff, redundancy and awareness of the Rules of Murphy's Laws are just far safer than thinking of the plane as an 1100 mm foamy warbird.
I have the Castle Creations 100 Amp ESC that is installed in a model with two aileron servos, two flap servos, two rudder servos, and throttle. All servos are the Hitec 645MG units. My "VoltSagger"project (Measures receiver voltage 5000 times per second, and shows lowest voltage measured) set off an indication that the CC BEC voltage had dropped below 4 Volts DC, 2.5 Volts DC less than the programmed 6.5 VDC.

Arduino Nano Voltsagger
https://www.rcgroups.com/forums/show...t#post40495307


So, consider going to the CC Talon 90 Amp unit that has a real high powered BEC. Or use their 100 Amp unit with a separate CC 10 Amp BEC, which is what I did.

For larger $$$$ models, it is wise to provide a backup receiver power source for your receiver/servos that can save your model if the ESC blows up.
Last edited by vollrathd; Jun 27, 2019 at 12:10 AM.


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