Jump to content
Ryz82

XV-01 Front Locking

Recommended Posts

Hey All,

First time post, hoping someone might have some insight on an annoying and recurring issue with my XV-01.

Background, had an Asteron (XV-01T) kit laying around for years, and recently got around to building it, with semi conversion to rally. All stock components, no hop-ups or mods at this stage, simply switched out the truck bull-bar for foam bumper, and stuck Tamiya rally block tyres on (if memory serves, as have long since thrown out the package) the Tamiya white rally wheels with +2 offset.

Anyways, when turning (right or left) the front wheels lock out, and the steering fails to respond. I can see the servo (Futaba S3003) attempting to shift, but the lock is persistent. Applying throttle typically unlocks and the steering returns to neutral and you can continue to drive fine without issue, and then randomly turning will trigger the locking to occur again - rarely do i get a run without incident.

I cant see or hear any friction on the steering linkage (again standard plastic ones, though ball raced), and looking as close as i can when the lock occurs, it doesn't appear that the inner rim is catching/rubbing on the front arms - though its pretty dam close, 1mm or less by my poor eye sight.

Has anyone had a similar issue ? Does this sound like steering linkage or arms ? perhaps the ****ty dog bones ? or maybe the front diff itself ?

Should note, that i have also tried adjusting steering trim on the radio and unless its almost completely non existent, the locking occurs.

Share this post


Link to post
Share on other sites

I had something similar which came from using longer eyelets on the dampers and a high torque servo saver. I ended up having to put the steering rods on the other side and use some low profile ball studs.

Something was catching and i could only seem to set it up to avoid catching but at the expense of having some horrendous bump steer but the low profile balls helped.

Share this post


Link to post
Share on other sites

By "lock out" and "steering fails to respond" do you mean the steering doesn't turn away from straight and to the angle you expect, or the wheels turn to the angle you expect but don't return to centre again afterwards?  If the former problem, it's hard to imagine what that is unless something isn't seated properly and intermittently jams.

If the latter, then it's possible the track rod joint is inverting.  I've had this before with a different car (I can't remember which one, I think one of my old race chassis, maybe TA05?).  In some cases the inside hub would turn so far that the track rod went forward of the steering arm balljoint, and when the servo tried to straighten out (and push the track rod into the steering arm) it would actually try to turn that hub even tighter.  Annoyingly the only solution was to pick the car up and flip the arm out by hand.  It's definitely worth checking this.  Adjusting your trim may not solve the issue if the hubs are being turned by steering forces from the ground, especially if you have a weak servo saver or servo.

You say applying throttle fixes it, so it also sounds like it might be that the dogbones are partially popping out and locking up the steering.  Again, reducing your trim might not be sufficient if the steering forces are doing it instead of servo input.  To fix this, you might put another rubber o-ring into the inner drive cup to push the dogbone out further and hopefully stop it popping out of the outer cup.

Share this post


Link to post
Share on other sites
4 minutes ago, Superluminal said:

Something was catching 

Aah - this has reminded me - my M03 had this problem when using a non-standard servo saver.  It moved the track rods closer to the bottom of the chassis and the hard end of the rod end would catch on the chassis on full shock extension and stop it from steering.  I solved it by filing away part of the corner of the plastic rod end and part of the chassis.  Check the inner rod ends on the track rods aren't catching anything.

Share this post


Link to post
Share on other sites

By "lockout" the steering remains at the angle of the turn - typically it happens as full lock (left or right), though has happened at less angle. At which point the steering becomes fixed, the servo for all its worth has no power to unlock. Yet as soon as i apply throttle it unlocks itself and returns fine.

Picture is from the last time it locked up, at this position, attempting to steer (with or without weight on the front end) the servo fails to budge the steering rod.

xv-01-lock.jpg

Share this post


Link to post
Share on other sites

You are using dogbones, no CVD? Do you have the steering angle limiter screws (the BB2 screws going into parts D1/D2 in step 14 of the XV-01T manual) installed? If not, I guess the dogbones might be starting to fall out of the cups and locking the steering. If you apply throttle, I guess the spinning axle might make them slide back into the cup.

  • Like 3

Share this post


Link to post
Share on other sites
1 minute ago, FuzzyFlynn said:

You are using dogbones, no CVD? Do you have the steering angle limiter screws (the BB2 screws going into parts D1/D2 in step 14 of the XV-01T manual) installed? If not, I guess the dogbones might be starting to fall out of the cups and locking the steering. If you apply throttle, I guess the spinning axle might make them slide back into the cup.

Yeh no CVD at the moment, fully stock kit, and everything as per manual. I don't remember seeing the dog bones falling out of the cups when i looked. I do plan on upgrading a few components post xmas/new year, so it may eventually sort itself out, but as for now its just an annoyance that i can't visually identify as yet.

Share this post


Link to post
Share on other sites

Alternative guess: If you have the long ball ends mounted on the dampers, the ball ends on the steering rods might be blocked by the chassis. But your description that it gets unlocked by applying throttle does not quite match this theory. Compressing the suspension should be what is required for unlocking then. The vibrations from the spinning wheels might be sufficient though.

  • Like 2

Share this post


Link to post
Share on other sites

I remember trimming the chassis slightly under the steering rack as it bound slightly when the suspension was fully extended. Disconnect the servo and move the steering around while the suspension is fully extended and you should be able to feel what/where is it locking. 

Alternate number 2 - electronics issue? Odd that it springs back when applying throttle.  

  • Like 1

Share this post


Link to post
Share on other sites

Cheers for all the feedback. I will start delving deeper and testing based on the various responses tomorrow, hopefully with some success on, if not a solution, at least identifying the actual cause.

Share this post


Link to post
Share on other sites

Update.

@FuzzyFlynn you may be right with the dog-bones.

I just gave the car another quick run, and the locking persisted, and would appear to be isolated to the inner wheel (in terms of turning circle/direction).

A few times, annoyingly, it unlocked as soon as i picked up the chassis to investigate. However, on a few occasions i managed to get the chassis up and in a position to have a look.

Initially i thought it was the dog-bone/shaft catching on the shock coil due to vibration at higher speed; as it did appear to to rub on it, if not fully catch.

But upon further inspection i believe, based on what i manged to see with minimal light, is that the dog-bone/shaft is decoupling from the wheel axle/cup. I think i managed to capture it in this photo.

Only thing i can think of that might cause this, is that the foam bushings in the axles/cups of the differential have either been compressed beyond belief causing the shaft to slide way too much, or perhaps fell out during initial build without me noticing. So guess its a tear down of the front end tomorrow in new light to see.

 

xv01-dogbone.jpg

  • Like 1

Share this post


Link to post
Share on other sites

UPDATE.

So pulled about the front end, and went over everything, and i cant believe it, but i did miss the 2 screws on the arms that reduce the steering angle :angry: hard to believe that without the 1.5mm, at most, of screw protruding, the dog-bones can slip that much due to the steering angles produced.

I haven't checked other manuals, wondering if this is specific to the "T" variant of the chassis, or common across all XV-01 variants ?

In any case, some quick hard runs, with plenty of full steering lock and power slides, and no sign of the problem. So i think I'm good; though definitely think the universals will be on the shopping list post xmas/new years.

  • Like 1

Share this post


Link to post
Share on other sites
On 12/13/2020 at 3:50 AM, Ryz82 said:

I haven't checked other manuals, wondering if this is specific to the "T" variant of the chassis, or common across all XV-01 variants ?

XV-01, XV-01T, and XV-01 Long Damper come with dog bones and their manuals demand the limiter screws to be mounted. The XV-01 Pro variant comes with CVD out of the box. Accordingly, its manual does not list the limiter screws.

So, when you upgrade to CVD at the front, you can safely remove them and enjoy the increased maximum steering angle. :-)

  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...