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Old 01-17-2011, 03:28 PM   #1
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Default Trottle glitch with FET servo

I'm having a little problem with an old servo I've decided to revert back too recently.

The servo in question is a KO 2123 FET. A little old but very fast and it never let me down before.

Its in my TC with a KO KR-302F receiver and a GM Genius 90 speedo running a GM 10.5 motor.

Basically the issue is that without the servo plugged in the throttle is fine. With it plugged in the throttle is OK for the first 20% or so but then it starts to jitter and glitch all over the place, but only the throttle glitches, the servo is fine at all times. The FET lead is soldered directly on to the positive terminal on the speedo.

The only thing I can think of is that I don't currently have the FET lead resistor (choke) on. If I put one on do you think it would eliminate the issue? Or is it because these sorts of new speedo's aren't designed to be used with FET servo's that require a lead?

Finally, does anyone know the value of one of these resistors that go on the FET lead. I lost mine some time ago so need to buy another.

Cheers in advance everyone.
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Old 01-17-2011, 03:57 PM   #2
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Quote:
Originally Posted by housey View Post
I'm having a little problem with an old servo I've decided to revert back too recently.

The servo in question is a KO 2123 FET. A little old but very fast and it never let me down before.

Its in my TC with a KO KR-302F receiver and a GM Genius 90 speedo running a GM 10.5 motor.

Basically the issue is that without the servo plugged in the throttle is fine. With it plugged in the throttle is OK for the first 20% or so but then it starts to jitter and glitch all over the place, but only the throttle glitches, the servo is fine at all times. The FET lead is soldered directly on to the positive terminal on the speedo.

The only thing I can think of is that I don't currently have the FET lead resistor (choke) on. If I put one on do you think it would eliminate the issue? Or is it because these sorts of new speedo's aren't designed to be used with FET servo's that require a lead?

Finally, does anyone know the value of one of these resistors that go on the FET lead. I lost mine some time ago so need to buy another.

Cheers in advance everyone.
It may well be the choke that is the problem. It's not a resistor!

They should still be find-able, Trickbits do one #TB2036, I have seen one by Mtroniks too, perhaps other brands also. They cost pennies!
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Old 01-17-2011, 04:03 PM   #3
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What is it then? They ('choke') look suspiciously like resistors to me as far as I remember. Thanks for your input, its much appreciated.
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Old 01-17-2011, 04:34 PM   #4
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I'll correct myself, they are inductors aren't they?

I found an old thread on here that says I need one with a value of roughly 10 uH (mirco henry), can anyone confirm that that is about right?
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Old 01-18-2011, 02:46 AM   #5
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Is this what you are after?

http://demonpowerproducts.co.uk/prod...roducts_id=769

hope that helps
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Old 01-18-2011, 04:47 AM   #6
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...Finally, does anyone know the value of one of these resistors that go on the FET lead. I lost mine some time ago so need to buy another
Hey,

I also tried my old FET servo some months ago.

The part is a inductor (called "choke coil" in the KO infos) of 4.7 ÁH, and it needs to have a DC resistancee of less than 0.5 Ohms.

Officials Infos from 20 years ago : "set for use with a high-frequency ESC (from 2 to 10 kHz), in order to prevent servo errors or even damage, due to spike noise in the Ni-Cd (+) lead of the high-frequency ESC."


At that time, I used it with a ESC with special wire for FET servo, but I did not test it to see if it was an output with constant current like for BEC, or if it was only wired to +lead.

Now, I tried the same FET servo on two different brushless ESC, and put the inductore between the "FET wire" and + of ESC.
Actually, it's soldered on the + side of my capacitor.

I am not sure your problem comes from that missing part, but better try and install it.

Hope this helps

EDIT: did not see that DemonProduct shows a capture of KO infos.
At least, it confirms the one I had from my old manuals.

Last edited by FFred; 01-18-2011 at 05:44 AM.
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Old 01-18-2011, 05:18 AM   #7
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sorry, double-post

Last edited by FFred; 01-18-2011 at 05:42 AM.
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