Servo 'Jitter' and modifications

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Servo 'Jitter' and modifications

Postby tgdavies » Thu Apr 19, 2012 1:53 am

I have the following setup to go into a smalll model boat:

- Two channel HK 2.4 GHz tx/rx
- 5 x NiMH AAA rx pack
- A small (8g) VS-5 servo (steering)
- A standard VS-2A servo which has been converted for continuous rotation by removing the mechanical linkage between its position and its position sensing potentiometer. (throttle)

I have two questions:

- I can adjust the pot so that the VS-2A doesn't rotate at the centre point of its channel -- but this needs constant fiddling, and after running the servo forwards or backwards the setting seems to get lost. Should I remove the pot and replace it with a couple of resistors?
- When the pot isn't quite right, the VS-2A sits there 'chattering' -- making tiny motions back and forth, or intermittent motions in the same direction. While it does this the VS-5 also chatters, but when the VS-2A is running smoothly (because I've given it some throttle) the VS-5 is still. Why does this happen and is there anything I can do about it?

Thanks,
Tom
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Re: Servo 'Jitter' and modifications

Postby RCModelReviews » Thu Apr 19, 2012 3:17 am

The deadband (the amount of movement the pot will accept before it triggers movement of the servomotor) is too low to accomplish what you want.

Fitting a resistive divider would help only insomuch as it would probably be less susceptible to changes due to temperature or vibration. Also note that your transmitter pulses may be drifting a little. Can you reduce the EPA settings on the transmitter for the channel you're using to drive the servo? If so, that will probably help somewhat.
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Re: Servo 'Jitter' and modifications

Postby tgdavies » Thu Apr 19, 2012 6:48 am

Thanks for the suggestion Bruce.

I don't think my cheap TX http://www.hobbyking.com/hobbyking/store/%5F%5F16252%5F%5FHobby%5FKing%5FGT%5F2%5F2%5F4Ghz%5F2Ch%5FTx%5FRx%5FAUS%5FWarehouse%5F.html has that capability, at least not on the throttle channel.

It's just an annoyance really.

Do you know why the jitter in the 'throttle' servo makes the rudder servo stutter too?
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Re: Servo 'Jitter' and modifications

Postby RCModelReviews » Thu Apr 19, 2012 7:35 am

How are you powering your receiver/servos?

It could be a weak battery or BEC.
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Re: Servo 'Jitter' and modifications

Postby tgdavies » Thu Apr 19, 2012 11:44 am

5 *elderly* AAA NiMH -- I will be using a 2S LiFePO4 once Hobby King gets stock of something small enough -- in the meantime I'll steal the good NiMHs from the TV remote and try them :-)
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