P70 Data Cable Testing

We have experienced several unexplained shutdowns of Jetcat engines recently. In several instances the data cables were suspected of contributing to problems. As a result we decided to perform some tests to identify what symptoms are realized when the cables fail.

A cable assembly was fabricated that ran through a box with an array of momentary switches that are normally closed. This assembly allows a momentary interruption of signal to any one of the conductors in the cable.


For this test, the following are the locations and numbers of conductors.








6 5 4 3 2 1
Looking at the receptacle in the engine/ecu









1 2 3 4 5 6
Looking at the end of the cable

This cable assembly was tested in 3 different configurations on a P70 engine and the results recorded.


The first test was with the data cable assembly connected from the ECU to the engine. The engine was powered up but not started. Each of the conductors was interrupted (open connection) with the following results displayed on the GSU:

Conductor and Resulting display on the GSU

1 No change to the display
2 EGT went from ambient temperature to flashing alternately between "xxx" and "E", RPM went to Zero when spinning the engine with air.
3 EGT went from ambient temperature to flashing alternately between "xxx" and "E", RPM remained active when spinning the engine with air.
4 EGT went from ambient temperature to flashing alternately between "xxx" and "E", RPM remained active when spinning the engine with air.
5 EGT went from ambient temperature to flashing alternately between "xxx" and "E", RPM went to Zero when spinning the engine with air.
6 EGT flashed alternately between "E" and temperatures around 950


The second test was also with the cable assembly connected from the ECU to the engine, but was conducted with the engine running. Each of the conductors was interrupted (open connection) with the following results displayed on the GSU:

Conductor and Resulting display on the GSU

1 No change to the display
2 EGT went from normal operating temperature to flashing alternately between "xxx" and "E", Engine shutdown with off condition of "Low RPM". Upon repowering, off condition indicated "Powerfail".
3 EGT went from normal operating temperature to flashing alternately between "xxx" and "E", Engine remained at same RPM and throttle became non responsive.
4 EGT went from normal operating temperature to flashing alternately between "xxx" and "E", Engine remained running and throttle was still active.
5 Display went to Jibberish, engine shutdown. When powered back up, off condition indicated "Powerfail"
6 EGT flashed alternately between "E" and temperatures around 950. No effect on throttle. All else OK.

The third test was with the cable assembly connected to the ECU and LED board. The engine was running during this test. Each of the conductors was interrupted (open connection) with the following results displayed on the GSU:

Conductor and Resulting display on the GSU

1 No change to the display, All items appear active.
2 Display went blank, engine slowly went to idle, then slowly back up to set RPM.
3 Display froze and retained last numbers for everything.
4 Display froze and retained last numbers for everything.
5 Display went blank, engine ran fine and responded to throttle.
6 No change to the display, All items appear active.

Similar tests will be performed on a P120 engine and results compared.

Not being an engineer type person myself, so please dont' think I'm being a smart ass, but I didn't understand one thing you said in your post. I guess the question I have, was the cable bad?

Dude,

You wouldn't last very long in Vegas on the Crap Table !!!! ... Talk about making your point the hard way !!!!!! Did it occur to you to just replace the cable in question[sm=idea.gif] and see what happens before building a Trident Missile launch control box.???? Good grief !!![sm=spinnyeyes.gif] Dude, I conclude 1 of 2 things.... 1- You are the smartest person I've ever heard of and know a hell of alot more that the rest of us, OR.. 2- You shouldn't even be playing with matches !!!! Good luck on your endevour !!!..

Danno

P.S. I too want to know if the cable was bad or not ?????

Well,
I think it is good info (and a very precise way of testing the different faults) !
Up until now, the only explanation I have gotten for the famous "Power Fail" was that the power from the receiver (throttle servo connector) was bad, or the turbine battery was somehow disconnected shortly during flight. But this test suggests that a simple bad connection of the datacable to the turbine might do the same !
I have seen that a couple of times, the temp sensor reading going bad because of the cable (a simple cleaning of the connector resolved that)

That was excellent!

I have experienced several "Low RPM" and "Power Fail" conditions with my P70. The next time it happens, the data cable connections will be the first thing I look at.

Thanks for the effort and sharing your results.

Bob

Thanks a lot for this truly informative post ! Gives good insight in what is actually happening without having to blindly replace stuff and hope that was what is causing the flameouts.

I am glad I was not the only one who did not understand this. I wonder if this has happened with the 160sx? So what really happened and how do you tell if it will happen before it happens?

Very usefull diagnostic info. Thanks for your efforts.

Sorry about the confusion of this post. It was intended for informational purposes. I am usually not good with words. Following is reasoning behind the testing.

We fly lots of models routinely, all powered by Jetcat engines. We run P70's, P120's and a P200. They have all been very reliable and we have had very little problems with them. Some of our models carry expensive research equipment so we do everything we can to reduce risks of losing a model. Whenever we suspect problems with a data cable, we replace it. When an engine has any problem we cannot identify, we send it to Jetcat for servicing.

The data cables are often blamed for problems. Jetcat is currently undergoing some design changes that will eliminate the current type of data cable with something more robust.

With that in mind, this study was to determine what kinds of symptoms you get when you have a faulty cable. Since the cable has 6 conductors and any one or more could fail, the symptoms are not always the same when a cable is faulty. Also cable issues are often intermittent and only occur when the cable is moved or under strain. The results show that depending on how a cable fails, symptoms vary significantly.

Also, just because you get some of the symptoms noted in the results, doesn't always mean the data cable is bad.

The testing was not because of one data cable in question. It was due to several problems we have had on numerous models recently. Discussions with Mr. Matt and Bob Wilcox have been inconclusive, but the most likely cause of our problems is due to static discharge. We have not been using anti static solution in our fuel in the past, but will begin using it from this point forward.

Thanks for the explanation on the purpose of your testing. I still don't understand much of it but at least I feel better about it.

Me too !!!! If Bobo feels better, I feel better !!!!!

Danno

Boy, I'm most interested in this one, "5 Display went to Jibberish, engine shutdown. When powered back up, off condition indicated "Powerfail"
"...