grosbeak

It appears that I have fried a couple of throttle servos - the one that came with the plane when I bought it, and a spare I used for testing. Here's the background:
[*]When I first connected the receiver (Futaba 6000HS) and transmitter (Futaba 8FG), all of the servos were performing properly[*]Over the last couple of days I've done some work with the wiring - rerouting, shortening leads and labeling [*]Today after putting everything back together, the rudder and elevator servos responded but throttle servo (Futabe S3152) did not.[*]I noticed as I advanced the throttle past the halfway point the ignition LED goes out. It comes back on again as the throttle is lowered[*]I plugged the throttle servo into another channel on the receiver but it still did not respond - this is when I suspected it was fried[*]I plugged another servo into the throttle channel (3) to test the receiver and the servo responded. This also leads me to believe the problem is with the throttle servo[*]I plugged a spare servo (JR DS821) into the throttle channel (3) to test it and it worked (at first) [*]A second test of the spare throttle servo saw the servo not responding to transmitter input. However, when the receiver is turned on the throttle servo rotates 1/8 turn counter-clockwise and emits a low-volume, high pitched hum - and it gets hot fast. Thus I suspect this servo is now also fried.[*]The wiring of the ignition cutoff (42 percent products Opto Gas Engine Kill Switch) has been verified as correct[*]The wiring of the voltage regulator (Smart Fly 2S Lithium, 5.2V output) has been verified as correct

Here's the wiring diagram:



The lead between the ignition cutoff and the voltage regulator is especially long. While I was cleaning up the wiring I folded the wire back on itself several times and secured it with a zip tie, like so:



I have no idea if this could be the source of the problem but I have since removed the zip tie and unfolded the wire again.

I bought a new throttle servo but I'm reluctant to try it before I can figure out what the problem is. Help would be much appreciated!

TFF

I would plug an old servo into the throttle channel and disconnect the ignition kill and see if the receiver is causing the problem. If you think all is well with the receiver, plug the cutoff back in and see if it burns it up again. Then it would be the kill switch. If it is burning the servo up with the throttle pushrod disconnected you might see if you take it out of HS what happens. I assume the pushrod is free to move with no binding.

KW_Counter

You mentioned you were shortening leads.
Does this mean cutting wires and putting new ends on?
Did you cause a short somewhere?

Good Luck,
KW_Counter

jester_s1

Here are a couple of troubleshooting steps I'd do:

Have you plugged in a meter to your receiver to see if you're getting the right voltage all the time? It sounds odd that your ignition light goes off as you advance the throttle, but I've never used one so maybe that's normal. If you're getting a constant voltage reading, then you know your regulator is good.

Have you spoken to the manufacturer of your kill switch and your ignition to see if it's normal for the LED to go out when you advance the throttle?

As mentioned above, have you tried bypassing the ignition stuff and running your receiver straight off the regulator? That will show you if the receiver or servo is the problem.

grosbeak

Here is an updated diagram showing the Rx power.



Note that there is no voltage regulator between the Rx battery and the Rx.

Here are the wiring changes I made:

ELEVATOR
- shortened both servo leads
- replaced connecter between Y-harness and extension with a solder joint

RUDDER
- Shortened servo lead: wires cut and new connector installed

IGNITION
- shortened ignition LED lead: wires cut and new connector installed

Note that no changes were made to the throttle wiring (except to disconnect it from the receiver, re-route and reconnect). When the original servo stopped working I checked and noticed that its connector into the receiver was reversed. However, with the power connection in the centre of the plug it's my understanding that this can't cause any damage. Could this have damaged the servo or receiver?

When I tried the spare servo in the Rx, it was connected neither to linkages nor extension - I held it in my hand and plugged it directly into channel 3 on the Rx.

Lnewqban

Very nice diagrams !

By reversing the connector, you may have damaged the electronics that are supposed to feel pulses rather than 6.6 volts.

http://www.incedo.org/~sjoholmp/heli...os/servos.html

jester_s1

So you have tried it without the ignition stuff even plugged in to the receiver using just the LiFe to power the receiver and have gotten a glitch with a different known good servo that works properly on other channels? In that case, you've isolated the problem to the receiver or transmitter.

grosbeak

I found evidence that channels 3 and 7 are linked in the transmitter:

http://www.youtube.com/watch?v=ZJkG0R9P7MU

I can't for the life of me figure out why. I've checked and there are no mixes in place. I created a brand new model in the transmitter and it has channels 3 and 8 linked!

grosbeak

Okay, it's quarter after two in the morning and I found it.



I Googled 8FG delete entire memory and found an old thread where a guy was having the same problem with channels 3 and 7 linked. Turns out that the Function menu within the Linkage menu is where you assign functions to channels. Channel 7 had a VPP (I'm assuming variable pitch propeller) function linked to J3 - the throttle stick. When I removed the VPP function and went back to the servo menu, hey presto! Now channel 3 is no longer linked to channel 7!

Of course, now I have to prove to my satisfaction that the linking of throttle and ignition kill in the radio were responsible for burning out the throttle servos (which doesn't make sense to me)... or find another cause.

grosbeak

Here are the results of some voltage tests I did on the receiver.



A few notes...

• At no time did turning on the ignition change the voltage in the receiver
• Tests 1 through 6 were performed on channel 3, which I had assigned to an undefined auxiliary function shortly before. Channel 5 was assigned to the throttle at that time
• Tests 9-10 and 17-18 showed the voltage creep up with repeated cycles of the throttle from no throttle to full and back again
• Tests 15-22 were conducted with the throttle function returned to channel 3, and the undefined auxiliary function assigned to channel 5.
• Tests 15-18 showed unusually high voltage and I'm puzzled as to what might be the cause.

grosbeak

In any case I think we have a cause for the servo failures.

The receiver, a Futaba R6008HS, was in HS mode the whole time. None of the other servos were bothered by that, but the original Futaba throttle servo and the spare test JR DS821 could not play nice with HS mode and offed themselves out of spite.

I have just changed the receiver to normal mode. This is an IMAC place and normal mode will be fine.

However...

Given the chart in the previous post the question still niggling at me is, why is channel 3 putting out such high voltages in tests 15 to 18?

grosbeak

I ran a few more tests this morning and we are definitely into the weirdness. These tests were of the voltage at channels 3 and 5, and of the Rx battery itself.



Throttle position had no effect on these tests; nor did the state of the ignition (on or off). However, the voltage started high and just kept going higher - even when the receiver pack was tested directly!

The only thing I can think of is that the meter is defective.

jester_s1

6.7v is low for a fully charged LiFe, but 7.4 is dead on. Did the lower voltage test have any substantial load on the pack? I would expect a voltage difference if you are comparing loaded vs. unloaded. I might also suspect your battery connector given that you saw the same phenomenon by testing just the battery by itself. Of course, you could also be right that it's a bad meter.

grosbeak

I've been told the following by a member in another forum:

[quote]If you see voltage rising with a multi meter you're usually seeing a capacitor charge. So your meter is probably just charging a cap in an unloaded circuit. It's not valid data.[/url]

If that's the case things may be functioning properly after all.

grosbeak

With fresh batteries in the meter I went downstairs to ponder the situation when a light came on. Load... why not plug my throttle servo into channel 3 and advance the transmitter throttle stick all the way to create a load... then plug my test lead and multi meter (with its fresh batteries) into the unused channel 5, and see if there are any voltage changes? Like so:



Heyo! 6.52V, constant for 30 seconds.

At this point I don't see the need for further testing. I agree with the conclusion that the receiver's HS mode caused the death of the two throttle servos; the receiver is now in normal mode.

grosbeak

I really appreciate all of your input and help.

Thank you!

jester_s1

I've never heard of the capacitor charge issue, but I'm wondering even if that is possible where the cap is that you could have been charging in the situation before? Either way I'm glad you figured out where your little demon was in the system so hopefully you'll have smooth sailing from here on out getting the plane in the air.