squirrely steering servo

Joshnewb

Joshnewb

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maybe i'll get a response in the electronics forum


i tried installing a hitec 7985 in my brushless ruckus (with AVC) few weeks ago
it worked, but it seemed to not center, would "stick" left or right, which ever way i had just turned, or whichever way a bump directed it, but i know the servo was just fine
(currently running 7 cell NiMH)
pretty sure just was not getting the constant power it needed? it's current draw at stall is 3A
would simply upgrading to a LiPo help my issue?
or would i need a LiPo And/or an external bec?

running stock setup esc rated 6V/3A
 
The battery won't have anything, directly, to do with it. It's the ESC that supplies the power to the receiver and any attached devices. Check the specs for the ESC. How much power does it supply?

How do you know the servo is okay? Have you tried the servo in another car (if possible)?
 
i sent it back, got another one, both did the same thing, very much doubt i got two faulty servos


the specs on tazer brushless sensorless 45A ESC say
constant/peak 45A/290A
bec output 6V/3A


the specs on the servo say
operating current 4.8 - 6.0V
current draw at idle 9mA
no load operating current 240mA
stall current draw 3000mA
dead band width 1
 
The stall current references the current draw at the servo when it can no longer turn: the load has exceeded the servo's torque strength. The BEC in the Tazer ESC should be plenty for the servo: to stall the servo you'd have to get the truck wedged in between some rocks and be going crazy with the steering wheel.

I see that the Hitec 7985 is programmable. I don't know what its default parameters are. I can't believe that you'd need to first have to program the servo to use it properly.

Do you still have the stock servo? Does it behave properly?
 
sent back the 7985 and got a refund til i figure things out
have the stock back in and all is good
 
someone else suggested that my nimh battery simply cant provide enough constant juice for the "higher end" servo
and that maybe it would perform better with a lipo...
 
Interesting. A LiPo certainly does outperform a NiMH battery in that respect. But the ESC's BEC is supposed to be providing 6V/3A. And you also had a capacitor installed.

I ran a Ti-geared, high-torque (13kg/cm), high speed servo in a Boost with the stock ESC for a while and experienced no issues. But I was also running a LiPo battery. When I upgraded to a brushless system with a Hobbywing ESC that output 6V/2A the steering servo really woke up. But even at 2A current max output I never experience any issues. I have the same servo and ESC combination in two ECX cars.

I still suspect the ESC.

I'd recommend you look into the Savox 1258TG servo. It's a fast, powerful servo that costs less than the Hitec 7985. The Hobbyking Turnigy 1258TG is almost exactly the same in terms of spec and according to at least one tester is MORE EFFICIENT than the Savox servo and it costs about half! (I have a Savox 1257 and two of the Turnigy 1258s and they have been performing well.)
 
well i'm still running stock spektrum 4201 receiver
if i get the Savox it's got a 5000maH current draw at stall, and in general more power hungry
then i would need a BEC instead of capacitor
what's a good BEC to run?
only problem is i don't wanna mess up the install, i'm new to this, i don't think it's just plug and play for a BEC.
 
You also have a Spektrum DX2E transmitter? The SR4201 is AVC compatible. I wonder if the AVC was interacting weirdly with the Hitec servo?

Anyway, which Savox servo are you looking at? The stall current draw is if you ever completely immobilize the servo or apply a torque that exceeds the servo's own torque. This is, in a practical sense, the EXTREME limit of the servo's current draw. In reality, you're going to be somewhere in-between idle and stall which is typically indicated as "running current." "Running current" is the amount of current the servo will draw at a given voltage when it is rotating back and forth- like your car is just sitting on the ground and you're rotating the steering wheel back and forth. As you're driving, the servo will work a little harder as it holds its angle against bumps and tire traction. Running current is typically in the neighborhood of 100mA (milli Amps) to 150mA. If your ESC's BEC supplies 3 Amps (3000mA) then you can see you've got a lot of "headroom" with regards to current load.

I'd recommend that you hold off on buying a separate/stand-alone BEC (like those available from Castle) until you are sure you need it.

I think with a quality ESC you'll not have any issues.
 
yes on the DX2E
ok, that all makes sense
thanks for the easy to understand explanation
looking at the 1258, i was before i got the hitec, but savox and amain both warned of possible needs for bec with savox and spektrum combo
and i turned the avc off before installing and centering the hitec servo
but i now wonder if i should upgrade esc before servo, maybe even go motor/esc combo
 
I only have one car with a Savox servo (paired with Spektrum radio) and have not had any issues. And this is in racing with lots of other radios on at the same time. But yes, I have also read the dire warnings about Savox/Spektrum and haven't yet found any solid info. Spektrum DOES make a little "glitch buster" capacitor that you plug into a free port on the Rx to prevent any interference. Less than US$10.

Yeah, upgrading your ESC would be a good first step since it's what provides power to all other on-board electrical components.

I can't speak to combined components (like motor/ESC, or ESC/Rx) but my feeling is that unless they solve a problem (like a lack of space in a cramped chassis) then they might not be worth it: if one or the other part dies, then BOTH components are useless. Personally I prefer separate components for ease of replacement.
 
didn't mean motor and esc in one, meant combo deal on motor and esc
not sure i'd want a motor and esc in one unit
 
Sorry to revive an old thread, but I was curious about the resolution with this issue. I also have a brushless Ruckus 2wd, 3014 model, and installed a new metal gear servo, the Jx Pdi6221mg, and it will not quite return to center. My truck came with the DX2E radio as well. Slightly left after a left turn, slightly right after a right turn usually. I noticed it also would turn a bit under hard braking.

Is there a way to fully disable the AVC (if that is the issue), not just dial it down?
Maybe this is a servo issue and I should try one of the others...?
Any best practice or setup for a new servo?

Thanks all!
 

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