Oscillating Throttle/Brake Servo
 

After a 'Work-out' around the track yesterday with the JQ WE, I came across this rather strange behaviour with my Throttle/Brake servo.
The breed of the Throttle/Brake servo is a Hitec HS-7945TH Multi-purpose* and the receiver is a Sanwa RX-451R 2.4GHz FHSS-3 Super Response.
Power is supplied from a Dynamite 7.4V 2000Ah Lipo pack that still had a 90% charge at the time of observing this strange behaviour.

What's happening:- The servo is oscillating steadily and quite slowly, windscreen wiper speed, approximately 5'-10' either side of its neutral position.
Even if I turn the transmitter OFF (BTW, the engine has been shut down) this steady oscillation of the servo continues.
Once I apply the full throttle or brake command, the behaviour stops, but when I release the trigger for it to return to neutral,
that strange oscillating behaviour starts immediately.

Any clues to the cause of problem would be much appreciated.

I'm no expert, but it looks like the pot in the servo might have an issue. It seems like it's trying to center and never actually achieves it.

Martin Paradis

sounds like a bad pot in the servo
or maybe a broken tooth on a gear

Many thanks Martin and you ffejrxx.

All the gears check out okay, but I suspect the 'pot' may be the cause of this issue. I forgot to mention that these servos were not new when I purchased them from a mate, who assured me that they had hardly been used. :sneaky: He uses servos without their mounting grommets!! I'm pretty sure that the 'pot' brush/wiper would not like that, as the engine vibrations would cause bounce or hammering of the brush tips on the carbon track.
Getting a replacement 'pot' will be costly, so I will take this servo out and use it for spares. I see that in RCTech, many favour the Savox servos, so maybe that's the way to go for reliability.

Thanks for your tips guys.


.

the pot in the servo should be fairly cheap (under $1 from mouser/mcm ect..)
just gotta take it apart and get the model from it

http://2.bp.blogspot.com/-50KtwAX6Fv..._Breakdown.jpg

use a meter to measure the resistance across the 2 far poles
most are 5-50k ohm

and mark which wires go to which spots on it when replacing