Register and gain access to Discussions, Reviews, Tech Tips, How to Articles, and much more - on the largest Large Scale RC community for RC enthusiasts that covers all aspects of the Large Scale RC!

Register Today It's free! This box will disappear once registered!

Wide open throttle won't drive straight

Discussion in 'Losi Desert Buggy XL' started by modex20, May 17, 2017.

  1. modex20

    modex20 Member

    Joined:
    May 15, 2017
    Messages:
    10
    Likes Received:
    0
    My DBXL with stock motor and Bartolone tuned pipe pulls to the left off the line. It straightens out, then pulls to the right at the peak of the power band before going straight again at max speed. It will roll straight.

    I have
    • replaced all four suspension arms
    • replaced every wheel hub and outdrive bearing on the truck
    • replaced the steering drag link
    • refilled the shocks with 5000cst fluid
    • refilled the diffs with Front/Center/Rear weights of 50k / 100k / 30k
    • replaced all hinge pins, hinge pin braces, and hinge pin brace inserts
    • replaced the tires and wheels with losi 5t wheels and proline trencher tires (original dbxl foams)
    I'm well on my way to building a new truck here. I cannot figure out what is going on. The wheels spin straight if I prop it up on a bucket and blip the throttle. I don't believe the servo arm is glitching.

    Here is some video footage of it pulling to the left on throttle. Sorry for the camera work. I was trying to record and drive at the same time.



    Here is the truck propped up on a bucket.



    I am losing my mind with this truck.

    Does stiffer fluid in the front diff make sense? Are the weights of different brands all about the same at these values? I know under 1000cst the weights are not interchangeable. Would more front toe out help stabilize it on power?
     
    #1 modex20, May 17, 2017
    Last edited: May 17, 2017
  2. Whoduh

    Whoduh Well-Known Member

    Joined:
    Mar 25, 2014
    Messages:
    151
    Likes Received:
    27
    Location:
    Fairfax, VA
    Is the servo saver tight?
     
  3. modex20

    modex20 Member

    Joined:
    May 15, 2017
    Messages:
    10
    Likes Received:
    0
    Servo saver nut is screwed in all the way. My take is that it shouldn't be fighting the steering that much.
     
  4. Whoduh

    Whoduh Well-Known Member

    Joined:
    Mar 25, 2014
    Messages:
    151
    Likes Received:
    27
    Location:
    Fairfax, VA
    My dbxl pulls to one side....don't remember which side though. Going to look into it when I get home.
     
  5. Bajhaha

    Bajhaha Member

    Joined:
    Mar 7, 2013
    Messages:
    18
    Likes Received:
    0
    i can actual see the front tire turn in the video. maybe its a rod end. my stock servo starting doing weird things before it quit. if u have another servo maybe try it out.
     
  6. Phill2

    Phill2 Well-Known Member

    Joined:
    Apr 29, 2015
    Messages:
    84
    Likes Received:
    5
    Location:
    Yeppoon QLD Aus
    It's behaving like a 2WD
    How's the front diff oil?
     
  7. modex20

    modex20 Member

    Joined:
    May 15, 2017
    Messages:
    10
    Likes Received:
    0
    Refilled the diffs front/center/rear to 50k/100k/30k
     
  8. Phill2

    Phill2 Well-Known Member

    Joined:
    Apr 29, 2015
    Messages:
    84
    Likes Received:
    5
    Location:
    Yeppoon QLD Aus
    Got me then
     
  9. modex20

    modex20 Member

    Joined:
    May 15, 2017
    Messages:
    10
    Likes Received:
    0
    I got a pair of new diffs for the front and rear from dollar hobbyz. They are filled with the stock oil. I will give those a shot next.
     
  10. djvrs

    djvrs Well-Known Member

    Joined:
    Jan 31, 2016
    Messages:
    81
    Likes Received:
    19
    Looks servo related.... I have a small RC that when the battery voltages drops, it does exactly the same thing but far worse... Almost like the servo isn't strong enough or being fed enough volts to keep it pointing forward.

    # It looks like the stock servo has been replaced.
     
  11. modex20

    modex20 Member

    Joined:
    May 15, 2017
    Messages:
    10
    Likes Received:
    0
    Yeah I have a new Savox steering servo with a 6.6V LiFe battery. It was doing the same thing with the stock servo. I did that upgrade hoping it would improve things. It didn't. But at least I have a nice beefy servo and better battery.
     
  12. MonkeyWrench

    MonkeyWrench New Member

    Joined:
    May 1, 2017
    Messages:
    3
    Likes Received:
    0
    Location:
    Fairfield, CT
    Does it have traction control? Losi calls it AVC. I bet if it does have it, the chip is defective or it is mounted incorrectly. It should be facing straight forward so it knows not to turn the wheels when your punching it. It wouldn't behave the same on the bucket because it isn't experiencing g forces. Check that the receiver is mounted straight. If not, the thing thinks it's being jerked to the side when you punch it straight forward (probably why my Mini WRC came with velcro holding down the receiver). If that's your issue im gonna s&!# myself, cuz I don't know jack. I'm new. Good luck man!

    Sent from my LG-H900 using Tapatalk
     
  13. modex20

    modex20 Member

    Joined:
    May 15, 2017
    Messages:
    10
    Likes Received:
    0
    A good thought but no AVC. Just a regular 3 channel futaba radio.
     
  14. Whoduh

    Whoduh Well-Known Member

    Joined:
    Mar 25, 2014
    Messages:
    151
    Likes Received:
    27
    Location:
    Fairfax, VA
    A few things I noticed after watching your videos again, especially the one with it raised.
    1. It wants to go left if its raised or if its on the ground...except when its raised, there is no load, the wheels have a chance to balance themselves out cause there is no load stopping them from doing so. when you give it gas...the truck starts vibrating LEFT off of the bucket...
    2. The torque of you giving it wot is causing your chassis to flex.The entire front side of the chassis is flexing to the right because of the torque.
    3. The control arm to the left wheel that is moving all over the place where as the right side has some movement but not nearly as much as the left./Slow the video down to .25 speed start and watching at 2secs. and 15secs. you'll see what i'm seeing..
    4. The wheel hub/spindle thing on the left side has ALOT of play. way more than the right(from what i can see watching the video) The play might not be noticable if you just try to move the wheels yourself...but it shows up when the torque shows up. Try shimming your front end it to see if yo can minimize the movement.
    Thats all I got for now....

    what do ya'll think?
     
  15. modex20

    modex20 Member

    Joined:
    May 15, 2017
    Messages:
    10
    Likes Received:
    0
    Which part of the front end do I shim?
     
  16. Bajhaha

    Bajhaha Member

    Joined:
    Mar 7, 2013
    Messages:
    18
    Likes Received:
    0
    My next guess was a AVC receiver but that got checked off the list. Could be bearings.
     
  17. modex20

    modex20 Member

    Joined:
    May 15, 2017
    Messages:
    10
    Likes Received:
    0
    So the steering tweak to the left went away after I preloaded the hell out of the front left and rear right shock springs. Instead, it would start straight then pull right at the peak of the power band then continue straight.

    The weird part is I could not undo the effect, even after backing the springs out. It would continue to start straight the pull right at the peak of the power band.

    I just increased the front toe out and remounted the front and rear bulkheads to make sure each screw is torqued evenly. Now it starts straight and pulls the other way at peak power.

    Something must be warming up and/or shifting.

    I will double check the camber and toe. Not really sure how to get it exact.
     
  18. Whoduh

    Whoduh Well-Known Member

    Joined:
    Mar 25, 2014
    Messages:
    151
    Likes Received:
    27
    Location:
    Fairfax, VA
  19. Whoduh

    Whoduh Well-Known Member

    Joined:
    Mar 25, 2014
    Messages:
    151
    Likes Received:
    27
    Location:
    Fairfax, VA
    Any luck fixing the issue?
     
  20. modex20

    modex20 Member

    Joined:
    May 15, 2017
    Messages:
    10
    Likes Received:
    0
    The tweak off the line seems to have subsided, but I still get some (torque steer?) right at the peak of engine torque. Not really sure how much is an acceptable amount with a tuned pipe. I might try to get some video with a go pro on the car looking at the suspension.
     
Loading...