Throttle glitch with FET servo

[Swalls]

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.

[captainlip]

you need a power cap, had the same issue

[Swalls]

The GM already has a pretty big cap and I can't really add to it.

[super__dan]

Yes you do need a Fet choke for a 7.2V servo, running it is essential to cut out exactly that kind of issue. I doubt a receiver cap would help as with a 7.2V servo no power is drawn through the receiver hence no voltage dip to guard against.

[Swalls]

This 'choke' is just an inductor right? Is the value I want around 10uH (micro henry)?

Cheers you guys, knew I could rely on a quick answer hear.

[john333]

I have the same servo in my cat, with an LRP speedo.....no problems so far, but would be interested to know what spec is needed so I can fit one just in case

[Swalls]

I went down to Maplin and spent 64p on a 10uH choke. Soldered in place and......

Instant success! Super fast servo and perfect throttle control. Was so worried it wasn't gonna work. Electrics can be so temperamental some times, but for once it worked out brilliantly.

To the race track.........