opto esc

[David Holland 2]

Good afternoon, gents. I have recently let all the magic smoke out from a 60 amp opto esc. Totally my fault and hopefully a lesson learned and i shan't do it again (yeah, right). When the esc fried it shorted out the pos, neg and signal wires from the rx which shut down the radio link and resulted in a small J3 Cub shaped depression in the flying field. I have almost completed the repairs to the airframe but before re-installing the electronics I wondered if I could reduce the risk of a future failure. Can I disconnect the red, pos cable to the esc, does the esc only need a signal and neg to function or does it need all three? My thinking is that if the power supply to the receiver is not compromised then I would at least have some control over where the crash happened. Thanks in advance for your thoughts.

David

[MattyB]

EDIT - Re-read your OP, looks like you are fitting an opto ESC anyway. In that case pull the pin and test on the ground and see what happens; based on the posts below, I suspect the ESC will do nothing.

Matt

Edited By MattyB on 02/02/2017 14:42:17

[Alan Gorham_]

David

Because your ESC is opto-isolated, there is no electrical connection between the motor battery and the "logic" side of the ESC. That means that the ESC derives it's logic supply via the receiver and down the signal leads, so you will not get away with your proposed solution.

 

It would be interesting to know exactly what the cause of your original problem was, perhaps a better solution can then be suggested...

Edited By Alan Gorham_ on 02/02/2017 14:37:34

[Denis Watkins]

Am afraid an opto isolator needs both feeds to function David, and even if there is another way, you know heat in small spaces can always be catastrophic with wiring. The boys will have an answer

[David Holland 2]

Thanks for the responses, chaps. Alan, the original problem was purely carelessness. The 5s batteries that I had been using were losing capacity, this aircraft is quite a few years old, and I thought that using the 6s packs I already had would not be a problem. I failed to go down a size on propellor or check with a wattmeter and about 5 minutes into the first flight a smoke trail appeared and then control was lost. MattyB, the original esc was opto as is the replacement and I can see it will need a power supply from the rx to function.

David

[Alan Gorham_]

David

So the failure was caused by user error. Even if you had been able to prevent the ESC to Rx signal leads from shorting out you would still have fried the ESC and had an in-flight fire.

As you admit it was your error in overloading the power system in the first place. Very hard to design that failure mode out...!

Interesting stuff.

[Dickw]

When using an opto ESC I have frequently put a small value resistor - something in the 5 to 10 ohms range - in the red wire between Rx and ESC at the Rx end.

In the event of a fire like yours it will limit short circuit current to less than 1A so the Rx should keep working, but there will still be enough power to run the opto circuit in normal operation. No need to worry about the signal wire as shorting that won't cause a problem.

Dick

[John Emms 1]

I think you have the answers, and it is very unfortunate that the destroyed controller also took out the radio link...

1) NEVER pull the pin out of a plug, as you can never be sure of a good link if you need to re-fit it.

2) An OPTO ESC has complete optical isolation between the radio side, and the power (FET) side of the ESC, so it needs all three leads for the positive, negative, and signal to be provided by the receiver - in effect, an OPTO controller is just like a servo, but with an electrical output, rather than a mechanical output.

3) If you have a BEC controller, and want to use a Rx battery rather than the BEC circuit for radio power, then use a servo extension lead with the red lead cut between the Rx and ESC (I have one somewhere in my tool box). You still would not have an OPTO controller, but you would be able to use the controller with BEC in future - which is the reason why anyone would have bought a BEC controller in the first place.

I hope that is of some help,

John

[MattyB]

Posted by John Emms - Puffin Models on 02/02/2017 16:24:32:

...1) NEVER pull the pin out of a plug, as you can never be sure of a good link if you need to re-fit it.

Sorry, but I can't agree with that. I tend to make up my own leads to the right length for tight installs - are none of to be trusted because they were made up at home? I have pulled out and refitted hundreds of pins across my modelling career and never had an issue; 99.9% of the time the pin is entirely undamaged by the process, and it is always very obvious when you pull it out if the crimp is not good enough. Similarly it is equally obvious if the pin does not seat back fully in the shroud simply by looking at it.

[David Holland 2]

Alan, you are completely correct. Too polite to allude to the nut that holds the steering wheel being the problem!! Hindsight is a wonderful thing and thinking now that the original cells were ancient very low C rated 1S3P packs in series that probably were not capable of delivering sufficient amps to trouble the esc and I tend to fly the Cub at very low throttle doing circuits and touch and goes. The 6S pack are much more capable and, fully charged, were trying to turn a 14 X 8 prop at 18500rpm at WOT! I hope that I am old enough and daft enough to not take things for granted in future but, having been flying exclusively electric for a lot of years now I suppose a bit of complacency had set in. Interesting idea, Dickw, might give that a try. Thanks everyone for the input, all taken on board.

David

[John Emms 1]

Posted by MattyB on 02/02/2017 16:32:09:

Posted by John Emms - Puffin Models on 02/02/2017 16:24:32:

...1) NEVER pull the pin out of a plug, as you can never be sure of a good link if you need to re-fit it.

Sorry, but I can't agree with that. I tend to make up my own leads to the right length for tight installs - are none of to be trusted because they were made up at home? I have pulled out and refitted hundreds of pins across my modelling career and never had an issue; 99.9% of the time the pin is entirely undamaged by the process, and it is always very obvious when you pull it out if the crimp is not good enough. Similarly it is equally obvious if the pin does not seat back fully in the shroud simply by looking at it.

Hmmm, of course, anyone is free to pull the pin out, and push it back in again. My recommendation comes from seeing far too many controllers (even one is far too many) that have been sent back to me simply because a pin that has been previously removed is not making good contact, and when that is the red pin on a BEC controller the ultimate problem is very likely to be the reason for this thread in the first place.

Of course all pins and sockets have to be crimped to the cable, whether commercial or home made (and I have used both with never an issue - with the exception for a model I bought that I later found had one of the servo plugs removed and re-fitted). My previous post is PURELY about using pins that have previously been removed, and says nothing at all about not making up leads using new pins and the correct crimping tool. The issue is that the pins have clips on that are not intended to be removed, so I guess the answer is to fit a new pin if the old one is removed from that plug - but IMHO the real answer is to use an extension lead with the red lead cut out of it - and it doesn't matter if that is home made or a modified commercial lead.

Matty, May I humbly suggest that rather than simply looking at a re-fitted pin, that you give the affected lead a really good pull to ensure that the pin is actually securely home?

Kind regards,

John

[MattyB]

Posted by John Emms - Puffin Models on 03/02/2017 14:03:04:

Matty, May I humbly suggest that rather than simply looking at a re-fitted pin, that you give the affected lead a really good pull to ensure that the pin is actually securely home?

Of course, I do that every time. I also always double heatshrink any red wire pins removed to disable an onboard BEC; so far the rate of failures is exactly zero.

My point about visually checking was that a pin that has not seated into position correctly will not be retained in the plug by plastic "tongue" in the housing, so that will be sticking up. There will also be a tiny bit of metal from the crimps visible where the wire enters the housing. I have never seen a plug where the pin seats fully into the casing with the tongue in the correct location that subsequently fails the "give it a tug" test, but I will continue to do it just to be sure.