Go Back  R/C Tech Forums > General Forums > Electric Off-Road
Car won't turn under acceleration >

Car won't turn under acceleration

Like Tree1Likes

Car won't turn under acceleration

Reply

Old 08-09-2018, 12:14 PM
  #1  
Tech Rookie
Thread Starter
 
Join Date: Aug 2018
Posts: 6
Default Car won't turn under acceleration

Hello, so i just bought my first "real" rc car after re-finding my old tamiya TA02 wich i wanted to entirely rebuild to modern standards but that turned out to costly for me to be my main project. So i instead went and bought a used bx10 from hobby wing, which is a French company and seems to have really good quality for their price.

So yeah first off the engine broke after 5 minutes, it was already making a wierd grinding noise when i bought it but i thought that was just the worn down spur gear or the motors original sound since it is pretty old.
Unlucky.. but anyhow he will give a 30 euro refund so im quite happy, came with lots of parts and so on.

Any how, to the point. The original servo for the 5 minutes i drove it seemed to steer fine even though it was much weaker.
But now that i've had a chance to drive some more since i reglued the rotor to the magnet in the motor(learnt alot about alot of glue types with all the damn tries i did),
the car will steer fine when going under a sertain speed, but when i pass a sertain speed on the emitter, it wont steer at all, it goes dead straight, whats up with that?

I was going to try the og. reciever emitter i got with the car again but the motor loosened again.. so can't test that out right now. Soon i will have a new motor!
But for the feew secs i could drive it seemed to have kindof the same problem but much less but it could altso just have been over steering

Anyhow, my reciver/emitter combo is a Spektrum Radio DX2E Active + SR310 SPM2335 reciever, was on sale for 50 euros so good enough, but if i dont remind wrongly, i think i read somewhere that either the reciver or emitter sent the steering info and throtthe info att same rate so he had to slow down to turn, can that be something?

So as you might notice ima complete noob, but i love projects and manifacturing parts and fiddeling with stuff,, which is why i went into RC the first place lol, so thanks in advance for any help.
xplodedchicken is offline  
Reply With Quote
Old 08-09-2018, 03:43 PM
  #2  
Suspended
iTrader: (1)
 
Join Date: Oct 2017
Posts: 786
Trader Rating: 1 (100%+)
Default

Does the car do the same thing if the car is on a stand? Under hard acceleration the BEC from the speed control might not provide enough current to the receiver, which could cause a lot of issues like you describe. You can try adding a glitch buster capacitor to an open channel on the receiver.


Or you can add a stand alone BEC like this or get a new esc with a stronger BEC.
​​​​​
urnotevenwrg2 is offline  
Reply With Quote
Old 08-10-2018, 12:16 AM
  #3  
Tech Rookie
Thread Starter
 
Join Date: Aug 2018
Posts: 6
Default

I am running my servo directly from the battery pack, in parrallel from the power leeds to the ESC, so i dont think that is the problem.
And the reciever emitter wasnt the problem either, but i put the steering linkage oone hole lower on the servo horn(i think the name is, the servo arm) and tightened the servo saver a bit more but right now its really tight.
I do have a feeling the servo was in a big mechanical disadvantage before because it was so easy to accidentally move the servo kogging when the servo was turned off.
Will try later today when i refix the motor.

But it's really weird because under hard acceleration the wheels didnt move AT ALL but now when the rotor is loose it will steer even when i rev the engine...

And yes BTW i do have a 2 cap pack in the esc

Last edited by xplodedchicken; 08-10-2018 at 12:29 AM.
xplodedchicken is offline  
Reply With Quote
Old 08-10-2018, 04:05 AM
  #4  
Tech Addict
iTrader: (11)
 
Join Date: Dec 2009
Location: Schaumburg, IL
Posts: 645
Trader Rating: 11 (100%+)
Default

I had this EXACT same problem on my old short course truck when wiring the high voltage servo directly to the battery. I'd turn in circles on my driveway, and as soon as I tried to apply more throttle, it would just straighten out. I would definitely try it with the power coming from the receiver, mine worked fine that way and I was running a hobbywing justock and old spektrum DSM1 receiver.
anthonyscardina is offline  
Reply With Quote
Old 08-10-2018, 04:48 AM
  #5  
Tech Rookie
Thread Starter
 
Join Date: Aug 2018
Posts: 6
Default

Okay, thanks for your answer, im just really scared to overdraw my reciever since i blew my old one(verry old 27mhz) one with this servo, it draws up to 4 amps in locking.
xplodedchicken is offline  
Reply With Quote
Old 08-10-2018, 05:38 AM
  #6  
Tech Elite
iTrader: (31)
 
Join Date: Mar 2011
Location: Austin,TX
Posts: 2,879
Trader Rating: 31 (97%+)
Default

You'll want to double check your wiring of the servo such that only the +8.4 positive lead is the only wire coming from your LiPo into the servo... you want the signal lead and true negative to come from the ESC like this:



I sell these wiring harnesses for $5 each + $3 shipping for folks who don't want to mess with soldering.

Here's an example of what happens if you use both the negative and positive lead from the LiPo to servo:

Here's a closeup of the wiring which is wrong, do not use this method:

billdelong is offline  
Reply With Quote
Old 08-10-2018, 06:12 AM
  #7  
Tech Addict
iTrader: (11)
 
Join Date: Dec 2009
Location: Schaumburg, IL
Posts: 645
Trader Rating: 11 (100%+)
Default

Interesting that you only use positive from the battery, I will have to try that so I can get my HV servo up to full potential. I had wired positive and negative straight to the speed control to keep the wiring neater at the time, do you think that would be okay to do instead of wiring to the battery?
anthonyscardina is offline  
Reply With Quote
Old 08-10-2018, 06:27 AM
  #8  
Tech Elite
iTrader: (31)
 
Join Date: Mar 2011
Location: Austin,TX
Posts: 2,879
Trader Rating: 31 (97%+)
Default

Originally Posted by anthonyscardina View Post
Interesting that you only use positive from the battery, I will have to try that so I can get my HV servo up to full potential. I had wired positive and negative straight to the speed control to keep the wiring neater at the time, do you think that would be okay to do instead of wiring to the battery?
Yes.. if you run your wiring like this, then you shouldn't have any glitching at all... the issue is that you need true ground from the ESC, something about the ground coming from the battery to servo tends to make the signal dirty, I don't know exactly why this is the case but it is what it is
billdelong is offline  
Reply With Quote
Old 08-10-2018, 07:22 AM
  #9  
Suspended
iTrader: (1)
 
Join Date: Oct 2017
Posts: 786
Trader Rating: 1 (100%+)
Default

Originally Posted by billdelong View Post
Yes.. if you run your wiring like this, then you shouldn't have any glitching at all... the issue is that you need true ground from the ESC, something about the ground coming from the battery to servo tends to make the signal dirty, I don't know exactly why this is the case but it is what it is
I think it has to do with the way the pulse width modulation signal on the white wire references to the ground in the receiver. If you hook the servo directly to the battery ground, it refers through the esc BEC to get back to the receiver.
billdelong likes this.
urnotevenwrg2 is offline  
Reply With Quote
Old 08-10-2018, 07:40 AM
  #10  
Tech Elite
iTrader: (31)
 
Join Date: Mar 2011
Location: Austin,TX
Posts: 2,879
Trader Rating: 31 (97%+)
Default

The OP on this thread also posted the same question over here and he confirmed his wiring was using both positive and negative leads from the battery to the servo:
https://www.rcgroups.com/forums/show...r-acceleration

He also raised a good question about trying to understand the relationship between the voltage across the negative lead between battery vs ESC to servo. He also tried running negative from both sources and that didn't work either.
billdelong is offline  
Reply With Quote
Old 08-10-2018, 07:56 AM
  #11  
Tech Rookie
Thread Starter
 
Join Date: Aug 2018
Posts: 6
Default

Thanks guys for the help, im gonna quote myself from another forum.

Knowing electronics, the electrons are actually comming from negative, so the charge has to go through the esc and reciever. And yes, you can run as many negative leads as you want to the negative side of a component.
That being said it didnt help doing as shown on that thread..

I now have two things i think might be it, either the servo is to weak because i can see the servo arm going back straight up or there is to much slop in the steering when i pull hard i can get the wheels almost straight even when steering.

But its so wierd because its only under throttle it won't work, if i go high speed and let go of the trigger and turn it turns...
maybe its some form of centifugal force created by the CVD? What do i know haha.

It seems weird to me the way its acting


EDIT: haha that's me btw
xplodedchicken is offline  
Reply With Quote
Old 08-10-2018, 10:58 AM
  #12  
Suspended
iTrader: (1)
 
Join Date: Oct 2017
Posts: 786
Trader Rating: 1 (100%+)
Default

Drive shafts want to run straight. So you need a steering system mechanically strong enough to overcome those forces in order to steer the wheels. The car you have is pretty much what we around here consider a toy. I would not doubt that the steering assembly is deflecting under load. Take the front driveshafts out of your car, run it on the stand, and see if the steering returns to center without the drive shafts wanting to straighten out. Also, the momentum of the car moving forward is going to fight the forces trying to steer the wheels. That means if the steering rack is deflecting, your car will want to go straight.

Here and here are a couple forum posts discussing pwm and ground. The pwm signal is generated by the receiver and has to reference the ground of the receiver.
urnotevenwrg2 is offline  
Reply With Quote
Old 08-10-2018, 12:38 PM
  #13  
Tech Rookie
Thread Starter
 
Join Date: Aug 2018
Posts: 6
Default

Well for being a toy it holds up quite well, my friend just drove it straight into a fucking step/wall, and the only thing that broke was the bumper and the metal part that holds the arms to the diff housing, it fucking bent hard(luckily i got a plastic replacement one from the guy when i bought it), everything else held up.
Honestly it seems to be really well built and the steering is totaly ok, just the plastic wheel "hubs?" the things that hold the wheel bearings and connects the steering that is quite flexible.
It's a hobbytech, for the price they seem to be realy good, but what would i know haha.

Anyhoo, i changed back to the original servo, aparantly they use team asociated servo, although its just a 5kg servo it holds up so im starting to think it's just my servo that's gone bad.

Edit, and i tried to run it with ground to reciver, but that didnt change anything, so its either that i need to run the plug straight to the reciver or the servo gone bad.
But i dont think running a high voltage servo through my reciever is a verry good idea.
xplodedchicken is offline  
Reply With Quote
Old 08-10-2018, 12:59 PM
  #14  
Tech Master
iTrader: (26)
 
Join Date: Dec 2005
Location: Ontario, Canada
Posts: 1,092
Trader Rating: 26 (100%+)
Default

I dont understand why you think you can't run the HV servo through the receiver? its just going to run at whatever voltage your ESC is putting to the receiver which is probably 6v anyway. I do this literally every time I run my cars since I've never seen the need for the boost in specs the extra voltage gives with the servos I'm using. I think you're just adding a lot of complication and potential issues for no reason.
bobf24 is offline  
Reply With Quote
Old 08-10-2018, 01:41 PM
  #15  
Suspended
iTrader: (1)
 
Join Date: Oct 2017
Posts: 786
Trader Rating: 1 (100%+)
Default

Originally Posted by xplodedchicken View Post
Well for being a toy it holds up quite well, my friend just drove it straight into a fucking step/wall, and the only thing that broke was the bumper and the metal part that holds the arms to the diff housing, it fucking bent hard(luckily i got a plastic replacement one from the guy when i bought it), everything else held up.
Honestly it seems to be really well built and the steering is totaly ok, just the plastic wheel "hubs?" the things that hold the wheel bearings and connects the steering that is quite flexible.
It's a hobbytech, for the price they seem to be realy good, but what would i know haha.

Anyhoo, i changed back to the original servo, aparantly they use team asociated servo, although its just a 5kg servo it holds up so im starting to think it's just my servo that's gone bad.

Edit, and i tried to run it with ground to reciver, but that didnt change anything, so its either that i need to run the plug straight to the reciver or the servo gone bad.
But i dont think running a high voltage servo through my reciever is a verry good idea.
See if you hold the left front tire and steer the car if it makes the hub's bend out of the way.

I run an aluminum steering rack and servo horn on my race car because even the very high quality stock plastic stuff on my car flexes more than I like. I also have all the plastic parts on my car replaced with the harder plastic version because when you race you work the car so hard, that less flexible plastic makes the car handle more consistently.

See if they have an aluminum version of the hub available. Keep in mind that they are made of rubbery plastic to prevent them from breaking when you crash. Aluminum hubs will transfer crash forces to other parts, and the hop-up slope is slippery one.

Lastly, the first thing you had to do was fix a defective motor. There have been several other things you have had to fix. That is not what I would call a high quality car. I am not trying to belittle what you have, because this hobby is about having fun doing your thing. Just know that a lot of people on this forum spend a lot of money to build race cars. Cars which are highly adjustable and are driven to the limits of the laws of physics. Again not trying to insult you, I am genuinely trying to help you so you can drive your rc car.
urnotevenwrg2 is offline  
Reply With Quote

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service