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servo glitch /onboard glow??

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Old 07-17-2007, 11:18 PM
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mvallyman
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Default servo glitch /onboard glow??

I have a homemade onboard glow system on a plane using 72Mhz Futaba. The onboard glow is activated by a microswitch at low throttle and Im noticing that when the switch clicks either on or off the servo's glitch. The antenna is on the other side of the fuse of the glow wires, I have separated the glow wires from any other wires and it still creates the glitch. This wasnt a problem when I first installed the system a couple months ago. Could it be a worn switch?? Is there something I can install to stop this problem?
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Old 07-18-2007, 08:24 AM
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tomlee
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Default RE: servo glitch /onboard glow??

A lot of people are not aware of the amount of current that a glo-plug can draw. When the switch either opens or closes it can create an arc and wearing out the points of your micro switch.

The micro switch probably has a set of points which is too small for the load created by the glo. If you replace the switch, please make sure to buy one which has a larger current rating.

Also check the glo-plug to see if for some reason it has changed.
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Old 07-18-2007, 11:27 AM
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Rodney
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Default RE: servo glitch /onboard glow??

As tomlee says, it is the spark that causes the glitch. This interferance will be wide band and effect all radios including those on 2.4 GHZ. Unfortunately, if you have any loose connections in that on-board glow, you can get continious glitches when the engine is operating due to vibration recreating this spark many times a second. So, you not only need a healthy switch, you must make sure to have very good tight connections at all junctions.
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Old 07-18-2007, 07:39 PM
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mvallyman
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Default RE: servo glitch /onboard glow??

Thanks for your replies. I can understand how the spark could effect the reciever signal and all connections are all soldered and still tight.
Last night I fully charged the glow battery and now the servo's wont glitch when the glow micro switch is opened and closed. Can anyone explain how the difference in battery charge can change things?
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Old 07-19-2007, 11:48 AM
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Default RE: servo glitch /onboard glow??

no i can't explain that !

I had a set-up that did the small glitching you describe. It was a very small glitch, since I had it set to only come on at idle I just flew with it as it was. When in actual use, i never detected anything funny with the planes performance, flying/taxing/taking off/landing.
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Old 07-24-2007, 04:27 PM
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Default RE: servo glitch /onboard glow??

Homemade glow drivers, bad bad news... I had one one my plane, got a lose connection on the glow plug or? setting on the runway, then straight up about 75 ft a snap roll and planted it. with out touching a stick. There fun to play with but it might cost you[X(][X(][X(]
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Old 07-25-2007, 12:03 AM
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Default RE: servo glitch /onboard glow??

Thanks for the info, thats good to know. I'll keep an eye on those connections.
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Old 07-25-2007, 10:41 AM
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Don J
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Default RE: servo glitch /onboard glow??

mvallyman,

Try putting a diode (purchase at Radio Shack)across the neg and positive side before the switch.
This needs to hook up so that the cathode (side with the band) is hooked to the positive side
and the anode (side without the band) is hooked to the negative side.
Hooked up backwards, bad things will happen.
What could possibly be happening is that when the switch releases, a voltage spike is being sent down the
negative side right into the receiver. The diode will "bleed" the spike off the neg side before it gets to
the receiver.
Not sure on your electronic expertise, but if you need help, feel free to pm me.

Don J
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Old 07-25-2007, 11:14 AM
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Default RE: servo glitch /onboard glow??


ORIGINAL: Don J

mvallyman,

Try putting a diode (purchase at Radio Shack)across the neg and positive side before the switch.
This needs to hook up so that the cathode (side with the band) is hooked to the positive side
and the anode (side without the band) is hooked to the negative side.
Hooked up backwards, bad things will happen.
What could possibly be happening is that when the switch releases, a voltage spike is being sent down the
negative side right into the receiver. The diode will "bleed" the spike off the neg side before it gets to
the receiver.
Not sure on your electronic expertise, but if you need help, feel free to pm me.

Don J
A diode is used to dissapate stored energy. Since a glow plug element is pure resistance there is no stored energy. A diode will be of no help.
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Old 07-25-2007, 11:20 AM
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Default RE: servo glitch /onboard glow??

I'm not sure about the diode. Could please let me know how that would help in a non-inductive load such as a glow plug. I would think putting a .1 uF cap across the switch would help in getting rid of any ark but that should be minimal with a resistive load of a glow plug. By the way, the last time I measured the current draw from a plug I seem to remember that it was around 1.5 amp. I wonder how much of the problem is contact bounce?

Pete
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Old 07-25-2007, 12:50 PM
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Default RE: servo glitch /onboard glow??

Diodes are ment to direct current not to dissipate it. Hence their symbol of an arrow and bar.

http://en.wikipedia.org/wiki/Diode
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Old 07-25-2007, 03:44 PM
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mvallyman
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Default RE: servo glitch /onboard glow??

Don, could you explain to me how the current gets to the negative side of the reciever?
This onboard glow is a separate system than the reciever circuit. This problem only occurs when my glow battery is low, since I'v kept it charged it hasnt given me a problem but it would be good to have some kind of safety device on it as you've described. Could I solder it right to the switch at the Neg. and Pos. terminals?
Greg
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Old 07-25-2007, 04:00 PM
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Default RE: servo glitch /onboard glow??

actually, at high enough frequencies, the coiled up wire in the glow plug would be inductive..
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Old 07-25-2007, 04:05 PM
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Don J
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Default RE: servo glitch /onboard glow??

mvallyman

I wasn't aware it was on a separate system.
My impression was that it was hooked to the same battery.

Here is a little reading on setting up relays and switches.
http://www.kpsec.freeuk.com/components/relay.htm

Unless somewhere in your system you have a shared ground, I would then say your problem is at the contacts
of the switch.
When your contacts disconnect, they are causing an arc which in turn is being picked
up by your receiver.
In my shop when I turn on the fluorescents, the servos in my planes will twitch.
This is not due to the lights, but the switch in the wall.

I would first try the diode across hookup points on the switch. (diodes are cheap)
I would imagine you just have the positive wire going through the micro switch.
Put the banded end (cathode) towards the battery and the other end (anode) towards the glowplug.
Another option would be to acquire a better micro switch. As stated earlier, make sure it is large enough to handle
the current of the glow plug.

Keep us posted,
Don J
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Old 07-25-2007, 04:24 PM
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Don J
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Default RE: servo glitch /onboard glow??

mvallyman,

As far as the "glitch". I wouldn't let it bother me unless you have
the glowdriver hooked up to your throttle servo,
ie; lower third of throttle engages glow driver.

But I assume you just have it hooked to a channel that you can cycle on and off.
The arc is only momentary and I imagine your plane will still be in the pits when this happens.

Side note:
fizzwater2... THANK YOU !

Lets see... coiled wire(In the glow plug)... Inductor... It's fuzzy, but I think I see a connection.
Sorry, had to do that. [X(]

Don J
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