Basack

I have an hpi rs4 3 evo that will not drive straight. It drives straight according to settings, but then randomly, i will hit let or a right turn at high speeds, and the car will hold the turn even after i let go of the wheel. It seems to hold the turn a lot of times during use. Everything is symetrical. I applied new silicon lube to the front and rear differentials but no luck. I brought the car into the hoby shop where i purchased, but the kid just seems to be "to busy" to help me out. He said by the looks of it, everything is in tact and you just need to lube your differnetials. I did this, and no luck. Everything works fine, just loose steering control at high speeds/random times. Any ideas what i can check/replace to see if it helps? going on 3 days now cant figure this out. Thanks!!!!!! new to this forum but looks awesome:_)

SyCo_VeNoM

steering servo good?
sounds like its getting stuck (which could possibly be happening cause on RS4 MT2 I have I've seen the knuckle get caught under the diff)
or the servo can't turn it back

Basack

Nah steering isnt getting stuck. Car steering moves perfectly during testing. Also drives straight until i give it some gas... then it seems to shoot off to the left. If i try and correct the problem by messing with the trim, the cars wheels  wobble and it still loses control. Any help or ideas? 

Ttam Says Blarg

Sounds like there is some binding somewhere or a bad servo.. Have you tried a different servo?

378

My Feedback: (4)

Sounds like steering play is allowing it to torque steer. Try taking the front center driveshaft out and going again. If you can keep it from just spinning the back tires it should track relatively straight on or off power. Caster will want to keep the wheels pointed straight when it's in 2WD mode. If it continues to pull then I'd suspect a servo that's on it's way out.

My NTC3 does this to an extent, I trimmed in a slight right merge to counter it. On power it goes straight.

Basack

The servo is operating fine on the ground the wheels turn perfectly left to right. At slow speeds they also turn but sometimes the turn will "hold" its self and will keep turning in one direction. I will remove the front drive shaft and try giving it a drive but i dont think the differentials are the problem. I completely took them apart, relubed them, and reassembled asnd the problem still persists. Any recommendations to check/rebuild if problem persists without front drive shaft? That means its a wheel problem correct? super confused and can make a video if nessecary. Most of my nitro rc problems hbave been an easy fix but THIS one.... is not.  Considering i cant figure out what to fix!!!

378

My Feedback: (4)

Servos can be bad in more than one way. The engine produces a TON of vibrations, which can make a servo that bench tests flawlessly act stupid. A loose wire inside the servo would be a likely culprit here.

If my hunch is correct you shouldn't get any more "Pull to the left on accel" when you've rendered it RWD. It may still pull somewhat, but it will be in seemingly random directions based on the bumps and angle of the road it's on, not whether or not you're accelerating. If that's the case then you'd simply have to rebuild the steering linkage and/or replace the servo gears(They're cheap, 7-10 bucks at the most), as those parts would be worn and allowing some slop in the front end. It could also be a gritty wheel bearing that's not spinning as freely as it could, but again those are cheap and easy to replace.

Ttam Says Blarg

I had a traxxas servo do something similar to me. Sometimes it would hold the turn. I found later that I had stripped the gears in the servo.

Just wondering. Is it a stock servo? Stock servo's always get bad rep and ideally you want to replace them right away.

Imho it sounds like the servo is dying. Just slowly.

Basack

Brand new Metal stearing servo " HI TECH hs-625mg hih torque servo"..... I know the fix should be cheap but just cannot figure it out... Car is fairly new also... Wheels seem to spin seamlessly. I can hold car up and give it some gas a turn. Cant find a thing. Really sucks that not even my local hobby shop can figure this out! Nor will they even take the time!! Any other ideas? Will try driving without the front shaft to see if its the differentials but considering i just checked them all out and lubed them up with silicon lube i think they are ok. Some one help ME!!!!!

378

My Feedback: (4)

What taking out the front shaft will do is tell us if it's just a little steering slop causing torque steer. It's not diagnosing the diffs at all. Torque steer is a natural effect of powering steered wheels, cars tend to want to turn to the left when you nail it. Full scale cars do it too.


If it's torque steer than the best you can do is replace any worn steering parts and throw in about 2 or 3 degrees of toe-in.

SyCo_VeNoM

You are probably better off, a good chunk of hobby shop employees I find are completely clueless, and will sell you the most expensive "fix" (which usually don't fix anything) to you.

Just for the record almost every RTR steering servo sucks ass(sa almost cause I heard one model had a decent one, its name escapes me). Its how things go in the hobby .

Only other thing I can think of is the servo getting enough power. I'm guessing you are using AA's did you try replacing them(if you are)?

Basack

Yes replaced all the batteries! ANd yes i noticed the RTR stuff was kinda bunk. The HPI rs4 3 evo is an awesome car but all the RTR/Stock stuff was **** IE radio, servos, receiver and some stock parts. I replaced the steering servo like i  said. How do i adjust the wheels to make them aim in? cant find anything on the steering linkage that looks adjustable in that sense....  usually i can solve stuff myself but this one just MIND BOGGLES me. Thanks rc universe. Keep the ideas coming

Ttam Says Blarg

Did the car work fine before? Like with the stock servo?
Might seem like a weird question but is the servo centered?

Basack

It worked fine with both servos all setups. No crash either... Just woke up tuesday. Fired her up and she went right off into a spin when i got up to speed! almost crashed it! now everytime i try to drive it it goes off into the dirt or soemthing and im sitting there for 2 hours with "Nitro Force®" cleaning my entire car. Really sucks!

Ttam Says Blarg

I wouldnt worry too much someone will figure it out

Basack

Well. Its sitting right infront of me and im very confused. Im about to just pull the entire front assembly of the car apart and reassemble it. Could the problem Lie elsewhere?

378

My Feedback: (4)

Patience, my friend. Getting pissed and ripping deep into the car won't help.

Ttam Says Blarg

Especially not in the middle of the night

Basack

What to do then? Hpi support cant help. Hobby shop cant help. Forums dont have the answer. Im lost

378

My Feedback: (4)

Pop it on your desk and let it sit until tomorrow afternoon. Maybe you could make a tiny cardboard jackstand to put under one of the front wheels.

Foxy

Could be a diff too, but I'd say it's something in the steering setup. A bellcrank bearing or a servo that doesn't want to center WHEN UNDER LOAD.

Basack

AhHH!!! The bearing!!! Ok... Took apart the little cuffs around tghe wheels. The left bearing doesnt spin NEARLY as well as the right side setup does. Im guessing this is the problem... Ordered a new set.... Gonna suck waiting (

Foxy

I doubt that is the whole problem, but it will be a start. Personally, in your position, I would disassemble the entire car completely and rebuild it from scratch, effectively renewing all threadlocks, bearings, rebuilding the diffs (you should definitely open the diffs and check them), and making sure eerything is straight and not bent, etc. It's the only way to be sure, and of course your car will run like new after.

Basack

Like i said I opened all of the differentials cleaned them and filled them with HPI DIFF silicon lube.  They are fine. I dont want to remove my engine and i dont want to removemy eletronics lol. My front and rear assembly were taken apart along with the differentials and  everything is CHECK besidesthat bearing.... any ideas?

Foxy

If you still have a problem after doing all that, it's 100% the servo not liking centering under load. How a servo behaves when stood still is often not related to how it behaves when load is applied. But as you said, that will be the last option, as the servo is pretty new if I understood correctly. You could always try swapping throttle and steering servos and see if it makes any difference before actually spending money. See hwat happens when you reassemble the front end, probably be fine.