Erratic Hitec Throttle Servo

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cpercival

RC Newbie
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Location
Sturbridge, MA
RC Driving Style
  1. Bashing
  2. Racing
I recently installed a brand new Hitec HS-965MG servo to control my throttle/braking. The servo immediately started acting erratically though. It randomly would start twitching and stuttering or if I pulled the throttle trigger and held it, the servo might begin to turn as it should, but then slow way down as it approached its endpoint. It's action was not very smooth either; it seemed to vibrate excessively as it moved. Additionally, it would sometimes randomly blip. The servo would turn quickly an 1/8 turn or so and come right back to zero. It would do this on its own. It also would not center itself very well. This kind of action would obviously not be good for a throttle servo.
I tried plugging the servo into the steering channel and it did not improve. I also tried plugging it into an entirely different car with a different transmitter and receiver. Same thing. All batteries were brand new or fully charged and no other servos I have were showing these symptoms. The symptoms seemed to resemble interference, but both test vehicles are 2.4 GHz, which I thought was supposed to be less susceptible to interference.
Figuring it was a bad servo, I sent it back to Hitec. They checked it out and could find nothing wrong with it. They did send a replacement though. However, the replacement is experiencing the exact same symptoms. I am including hyperlinks to 2 videos I took of the servo. I wasn't able to catch the blip, but the twitching is pretty obvious as is the issue with the servo not being able to center itself quickly.

I know a lot of people use this servo, and I haven't heard of this yet. I am getting pretty frustrated and would really appreciate some help. I'm not ready to give up yet, but I'm getting close.

Videos:

[ame="http://www.youtube.com/watch?v=PzBz2QjXNTU"]YouTube - Servo Twitching[/ame]

[ame="http://www.youtube.com/watch?v=auPwrVlGtaQ&feature=mfu_in_order&list=UL"]YouTube - Servo Twitching 2[/ame]

I'm running a Revo 3.3 2.4GHz with a Picco .26 Red Dot
 
Is the servo horn shown in the video the same one that you used on the first and second servo? Is it the stock one for the revo? If so the horn or the insert that goes into the horn may be stripped. I can't remember if the Hitec servo splines are 24t or 25t, or if the stock Traxxas horns are compatible with them. Maybe someone else does. I had a similar issue and my fix was there. Hope that helps.
 
There was nothing in either video that would make me think a servo horn is stripped. It's not connected to anything, so there's no way to tell that.

I'd say you have a bad servo, contact the company you bought it from. The horn has nothing to do with how it operated in the videos, with no resistance on the servo it should operate just fine.

Are you positive they sent a replacement, or could it be the same one you sent them?
 
May have an answer for this one. This from Tony at Hitec:

"The problem you are having is an incompatibility of the Traxxas Link 2.4ghz system and analog servos. With that Traxxas system, you must use digital servos because of the fast refresh rate. Analog servos cannot keep up with the fast refresh and will either jitter or sometimes burn up...It appears to be only the Traxxas TQ Link that does not work with analog servos. The Older Traxxas TQ worked fine."

It's strange that I have not heard this before. This servo seems to be the most popular throttle servo upgrade. I guess it's hard to tell who's running these on the Traxxas TQ Link and who's running them on the Traxxas TQ. Anyway, I'm going to exhange the HS-965MG for its digital brother and we'll see what happens. I will let you all know how it goes. We may want to spread the word on this one though, so others don't pull their hair out trying to solve this puzzle.
 
This makes sense. I've read something about this situation before. The new servo should solve your problem and be silky smooth.
 
The analog uses a pulse signal the 2.4 is a digitized signal. apples/oranges
 
May have an answer for this one. This from Tony at Hitec:

"The problem you are having is an incompatibility of the Traxxas Link 2.4ghz system and analog servos. With that Traxxas system, you must use digital servos because of the fast refresh rate. Analog servos cannot keep up with the fast refresh and will either jitter or sometimes burn up...It appears to be only the Traxxas TQ Link that does not work with analog servos. The Older Traxxas TQ worked fine."

Thanks for that info. I'm pretty sure it's new info for all of us.
We appreciate you posting it here.
 
Same thing happens with the Futaba FASST setups when running in HRS mode.

It happened to me once way back when I first got my 3PKS with FASST. I now only use digi servos in order to never have the problem. Most computer transmitters allow you to change modes in order to use non-digi servos.
 
Good post as I was looking to upgrade my serovo's here in the next few weeks!
 

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