Help a noob with servo twitch!

[ianc]

Hi guys,

I'm pretty much a noob at this, but I've spent a few hours reading over the forums and still have some questions please.

Ever since new, my GT3 has had a twitchy front end. With car and transmitter powered up, the front end will twitch slightly. My friend has a CLK that I've driven, and it is very stable compared to mine.

Yesterday I broke the front servo gear and so had to disassemble the servo to replace it. While I'm in there, I'd like to have a whack at seeing if I can fix this twitch that's plaguing me. I get no twitch from the throttle at all.

With the servo apart and car and transmitter powered on (yes, I'm being careful), even in the neutral trim position, I can adjust the small pot on the ESC all I like, but can't get the servo motor to completely stop twitching. Is this normal?

When I reassemble everything back into the servo case and then test with the lid off, I find that the servo motor doesn't want to return easily to the center position; it kinda moves almost all the way, then twitches back. Could this be because there's too much friction in the servo gears? If I try turning the gears manually, there seems to be quite a bit of resistance there. I tried oiling their contact surfaces with a light oil, but it didn't seem to help.

I've also read some disussion about motion of the front pot causing problems as well. I made a tiny shim to fit behind the pot for a tight fit, but it didn't seem to affect matters at all. I'll also try cleaning it, although since it has displayed this symptom since new, it's probably not dirty...

What exactly is the function of the pot in the servo?

Any information would be very helpful and I know there are some very experienced and knowledgeable fellows, so I'm hoping for some insight. Thanks for reading!

ianc

[Mondo]

ianc ,

Sorry to hear about your woes.
As far as the pot in the servo housing is concerned, that's to centre the steering. It's provides an axis position to the RX steering FET.

As for the twitching try the following:

Put your TX crystal in your freind's radio and see if it continues.
If that remedies it, check the batteries in the TX/transmitter.
Make sure the antenna wire isn't frayed and that the antenna is secure
The same applies to the motor wires
Check the motor capacitors.
If the problem persists I suggest you return it to the supplier.
If you can't, perhaps change from 104-106 ceramic capacitors

I reckon our tinkerking Draconous can help.

[Draconious]

This wont totaly solve it but it will help partialy.. shim the potentiometer and the motor inside the servo so it can not rock back and forth...

A layer of scotch tape, trimed so there is no over hang, around the block round area of the potentiometer will snug it up, a piece of paper between the white piece that holds the pot straight and the pot itself (it will snap together) will help.

The motor can use 2 or 3 pieces of paper under it, and on mymotor I used a slightly bent, so it would have some spring in it piece of thin aluminum for the top to provide down force, the 3 pieces of paper under maintain the gear mesh like the drive motor spacers.

The servo will be a bit harder to turn the wheels by hand, more risk of breaking a gear if you do so, so just dont do it by hand. My servo is twitching half as much as usualy now.
Just dont over shim it, or you can overstress the plastic... if when attacking the top and bottom of the servo case, there is a gap between them check the wires etc, any gap will cause more twitching cuz more room for the motor to rock side to side with gears etc, etc...

[ianc]

Hi guys,

Thanks very much for the tips. I shimmed the pot so that it's quite tight and I don't really think there's a possibility of it moving. although I must admit that I have no idea what this means: ;-)

It's provides an axis position to the RX steering FET.

At any rate, I don't think shimming the motor is going to help me because the motor is vibrating when it's not even mounted in the servo case, and it's this vibrating action that's causing the twitch.

Are you fellows able to adjust your servos so that the motor returns to the center position and sits there nicely without moving? I can't seem to do this, and I'm wondering if it may just be a fault in the wiring or the ESC?

Thanks again for your help!

[Mondo]

ianc,

I reckon take it back to whoever you bought it from
There is a varicap on the PCB for centering the servo.
But if its happening all the time, you have a problem