Servo keeps "locking out" left turns.
 

I've got this posted over at RCShortCourse, but figured the more minds, the better!

Here's the set up: Exo, stock gearing, running a Castle 3900Kv 4 pole SCT system, Axial tx/rx, and Axial AS-3 servo with top bearing mod (per Axial's blog).

Originally, the rig ran like normal, no difference between L & R steering actions. No significant crashes/impacts...a few tumbles & roll overs, but nothing that has damaged the steering, linkage(s), or servo mount. Now, fresh battery in, tx on, buggy on, it will run normally, but after a few minutes the ability to go left gradually goes away. It seems as though it starts to clock to the right, to the point where I have to turn the tx wheel full lock left in order to go straight. There is no mechanical binding, debris in the steering, etc.

Initially, I pulled the servo horn off, reset everything to 0, reinstalled the horn, and it works normally again... Until a few minutes into the next run, and it's back to wonky. On second inspection, I pulled the servo out, reset all limits to 0/neutral point, installed a plain horn (for visual reference), and started my adjustments. It seems now, that when the dual rate is being adjusted, that the steering will now move biased more to one direction than the other, similar to adjusting the L/R trim. Not sure if I'm just misunderstanding the adjustment, or if it's truly wonked? My understanding is that L/R trim will bias the direction of the wheels one way or the other, and that the DR adjustment will be more of a servo internal adjustment, limiting the end points of the rotational throw. If I'm correct in my thinking, the DR shouldn't cause the servo to move independent of the L/R trim?

Everything's back together, and a Castle BEC has been wired in. Fresh pack in, everything calibrated & powered on correctly, and actions are normal. I haven't had the opportunity to really run it since (raining), so I'm still leaning towards the issue not being corrected...won't know until I can get out for a bit.

Has anyone run across this before?

Re: Servo keeps "locking out" left turns.
 

Servo horn possibly striped or skipping teeth?

Re: Servo keeps "locking out" left turns.
 

I would try a new servo horn and then open the servo to look for stripped gears. The servo saver in the Exo doesn't provide a lot of protection for the servo and the AS-3 is pretty easy to break with the Exo.

If it is your servo, you should replace it with a high speed servo such as a Savox SC-1258TG. Crawler servos don't have the speed that you need to steer the Exo at high speeds.

Re: Servo keeps "locking out" left turns.
 

D/R is not same as endpoint.If your using D/R to adjust endpoint this could be your problem.

Re: Servo keeps "locking out" left turns.
 

Could the servo have gotten water in it? When my servo fails its waterproofing, the servo locks up. It may be yours has some water in it somewhere. Pull it apart, look for water droplets. DRY, Reassemble. Waterproof.
Just One scenario...

Re: Servo keeps "locking out" left turns.
 

Thanks for the input! (It's crickets over on RCS!) I should've mentioned, servo horn is good - no stripped teeth. I did have the servo opened to check gears, and everything is good. As for the DR/end point issue, I may have misunderstood/misadjusted. There's only the 2 adjustments on the tx, ST-Trim & ST-DR.
Also, while doing my initial investigation, with everything powered on, and resetting my horn position, there would be a random audible beep from the system. It was the same beep as you would hear on power up, from the motor. In conjunction with the beep, the servo would twitch/reposition itself. This would lead me to think that there was a voltage drop/draw, and that may be the cause of the servo issue? All the electrics are new & unmodified, and have less than a dozen runs on them. Like I said, I've since wired in a CC BEC, but have not had a chance to really give it a go.

Re: Servo keeps "locking out" left turns.
 

I didnt see a BEC on your list of
I missed that last post see you got one

"thumbsup"

Re: Servo keeps "locking out" left turns.
 

Update: With the servo horn removed, and the system powered up, if left alone the servo will buzz & twitch. Sometimes not much, but then it will jump left & right. I've also installed a Castle BEC, but it didn't seem to make a difference. I swapped with a brand new, straight from the package Savox unit, and it was the same thing. I'm thinking that maybe it's a tx/rx problem. Anyone run across something like this before? RX & TX are standard Axial 2.4ghz units.

Re: Servo keeps "locking out" left turns.
 

I know this is prob against the forum rules but I haven't been on here long enough to post a question. I have a similar problem w my new crawler, redcat rs 10 xt. When I turn the steering to the right the crawler wants to move backwards very slowly... it makes the same sound as if I were giving it throttle and the motors twitch slightly. Turning left no prob, and everything else works great, it's prob a bad receiver or transmitter? All batteries charged, but still using the scrappy wall charger, no apparent loose wires.... any help would be much appreciated, I'm no rc electrical guru, I know one of you out there is.. thanks again...

Re: Servo keeps "locking out" left turns.
 

Afew years back in my nitro gas oval racin [sprint car] I ran into the same problem your having ,,Popped the reciver apart ,there was a little rock in there shorten it out ,,dont know if it will help , also try changing out radio batterys ,,,Hope this helps

Re: Servo keeps "locking out" left turns.
 

Possibly a reception issue, with your receiver getting interference? You might double check that your receiver antenna is not touching/facing metal. Had a similar sounding issue before. Good luck.