MB-01 veers left and right on power

[PotatoRally]

A few days ago I took my MB-01 for a spin after a few weeks of sitting on the shelf, only to find out it no longer drives straight. To keep it short, any amount of power causes the car to steer left/right slightly depending where the wheels pointed to last time. If I take the car up to speed and let it freewheel, it goes absolutely dead straight every time. Car runs a hobbywing 1080, injora 14kg touring low profile servo.

List of things I have done and checked:

steering mechanism rebuilt, steering moves freely

arms shimmed up with no binding

no suspension binding

no drivetrain binding

diff rebuilt

replaced worn tires with brand new, this helps a little

 

There's the usual MB-01 play but with all the things I've done to it it's no worse than my M-06 which runs perfect. What I find funny is that out of the 10 or so RC cars I own, half of them have developed this or similar steering issues over time as I ran them. It is not the worst thing to ever happen, as it can be easily mitigated with gyro, but I like my cars running as well as possible even with no aids.

[nowinaminute]

My GF01 dump truck was like this. Checked all bearings, diffs etc. Made sure tyres weren't slipping etc. It definitely did it more if you hit the throttle hard.

Several false positives such as ball joint on one of the steering links being a bit tight from grit but took it back out and exact same thing.

Different servo: same.

Swapping arms around incase one was tweaked: same 

In the end I gave up. Then a year later I converted it to TL-01B long arms and driveshafts. Everything else the same....straight as an arrow! Still don't know exactly what the issue was.

I do know a little slop is fine and even necessary in some ways. A car like the MB01 should inherently want to track straight and a little play in the steering will give it the freedom to do this even if the servo centers fractionally different each time etc.

Sometimes I've had rigs where the servo saver or some other part is a bit stiff/catches and has robbed the car of that slight freedom to settle on a straight line and will stick slightly to one side when the servo returns to centre. 

Have you taken the wheels off to check if any fluff or hair etc has gotten caught up?

[El Gecko]

25 minutes ago, PotatoRally said:

steering mechanism rebuilt, steering moves freely

Not sure how much of the steering you've rebuilt, but it sounds like a servo saver issue to me. Most likely it's binding up because the bolt is too tight, so it takes extra time to return to center. If the wheels are already straight, it stays put.

[PotatoRally]

Well of course, as soon as I post the thread I magically find the exact solution to the problem. I decided to check on the rear tie rods to see if my higher than suggested amount of toe in, for stability sake, is causing problems. Because I noticed the rear wheels toe in quite excessively on throttle from the play in the arms. As soon as I took the tie rods out I was surprised to see the tie rod mount (or steering bridge at the front) is completely hanging off loose on one side. The screws I used were too short and one of them decided to eat the thread in the plastic over time. So I put a longer screw in and as soon as I did the car goes more straight than it ever did. Guess that serves as a lesson to quadruple check that no part of a car is loosely hanging off.
 

1 hour ago, El Gecko said:

Not sure how much of the steering you've rebuilt, but it sounds like a servo saver issue to me. Most likely it's binding up because the bolt is too tight, so it takes extra time to return to center. If the wheels are already straight, it stays put.

I avoid servo savers like the plague for this very reason, until one day when I kill a servo of course.

[Rinskie]

Do you have a spare servo to test? I battled with my M08 the entire time I had it. The poor thing just refused to steer consistently. I ended up pulling the electronics and selling it which freed up the low profile servo I had it it. I decided to try that servo in my TT02 only to have the M08 gremlins carry over. I decided the testing was over, bought a new servo for the TT and threw away the gremlin of a low profile servo in the trash where it could be of better service. I hope you sort it out. My MB is so much fun to drive.