XRAY - Model racing cars

Hi guys
For the first time ever I am really stuck and do not know what to do; so help please!
I have completed the build of my new 012 and there is something wrong with the rolling chassis.

Scenario 1
Put the car down (on asphalt); turn the wheels fully to the right and accelerate. The car just breaks into immediate 360s.

Scenario 2
Put the car down (on asphalt); turn the wheels fully to the left and accelerate. The car starts to turn; then for the briefest of moments it goes straight ahead(wheels are still fully turned to the left) then it bites and starts turning left again.
So the problem is not symmetrical.

The car is built to kit spec except
2.8 springs on the front.
Alu shocks (from the my 009)
Ball diff fitted, brand new. I then took the diff out and put in the ball diff from the 009 – no change
Ride height 6.0 rear and 5.75 front with downstops changed to compensate for the increase over kit ride height

The car is fine on the Hudy setup station.

I have visually checked everything (famous last words!) but can see nothing wrong. Everything looks symmetrical left to right and I cannot detect anything sticking in the drive train, wheels etc. I am now going to pull the hubs apart and check the wheel bearings but they are brand new out of the box
The car has done one lap and a variety of circles on the straight and in the lane outside my house.
Full steering lock on both wheels is the same, 25-26 degrees.

I have used 2 sets of wheels.
The tyres have no heat or additive – but as I am not getting 360s turning left I am assuming this is inconsequential.

Oh yes when I built the car I fitted new spool steel outdrives (with 3.5mm caps on the drive shafts) but I have swapped these for the kit composite outdrives(with no caps on the drive shafts), with no affect.

One last point. The servo horn is not absolutely vertical – the positioning of the ridges on the servo stub relating to the grooves in the servo horn do not enable fully vertical. Now I have never ever done it this way before but should I be using the steering trim on the transmitter to get the horn fully vertical before setting up the steering? This is the first time I have had this type of steering system. I have always done this before with zero trim and and getting the angle between the servo horn and the servo link as close to 90 degrees as possible.

I kind of feel this last point is a red herring, but may it is not?

oh and.. The manual says to tighten the two screws that attach the dual servo saver to the steering plate and then back off 1 third of a turn. Well in the lane just now one of the screws came out - which I was always very dubious about; so they are now both tight. But again, tight or backed-off has made no difference to the problem.

I would personally use trim to make the servo horn vertical then try to get everything else to line up, but that won't be your problem.

Have you limited your end points for steering?
If the steering knuckles go too far and touch the C-hubs you may find it then starts to twist the chassis as there is no movement available in the steering.

I would also remove the shocks at the wishbones and check that they all move freely etc.

Make sure that the C-hubs are both 4deg and that one is left and one is right.
Check that the wishbone pivot pin holders are the same on both side of the chassis.
Check that the spring retainer at the bottom of the shocks is seated properly on each shock.

Skiddins

Hi,
Check the pins in the drive shafts.

It might also be the 52mm driveshafts in the rear.
They are a little too long.
If you remove the shocks in the rear. Push the rear arms up while turning the rear wheels, you will feel resistance if the driveshafts rub against the diff. It might only be one, if the alu shims are wrong.

Else take the car apart and check all moving parts.
When you put it together, add one part, check movement, add one part, check movement ......

Let me know if it works
BBN

Thanks guys I am going to start pulling the car apart tomorrow morning so I will report back on your points tomorrow night. Some I am sure I can tick but I will recheck nonetheless.

Interested on your point on the 52mm shafts BBN. I recall a thread on this maybe some 6 months ago but I cannot recall the context. Is this a T3 thing? I have running 52mm shafts into a ball diff on my 009, 008 and T2, ie for years without a problem - I will check though.

Oh, I missed that you are using a ball diff.
It is a 52mm and gear diff thing.

Hi guys, well I have checked everything suggested so far but all to no avail.

The steering blocks are very close to the C_hubs so I backed the steering angle right off; my thinking being that whilst on the bench the steering arms were not touching the C-hubs, maybe under the dynamics something was causing one of them to touch. But no change.

I also reset the steering angles, this time using the steering trim to get the servo horn absolutely vertical before doing so. The left turning circle and the right turning circle are the same.

But the asymmetrical symptoms remain. I have to say the symptoms are so extreme I just don’t get it – no doubt it will turn out to be something blindingly obvious! I checked the manul 3 or 4 time to make sure I did not have the c-hubs on the wrong side!

So more suggestions please!

My next two courses of action at the moment are
1. Swap out the servo; I fitted a new Savox servo, I am going to fit the KO servo off the 009; maybe the Savox is defective.
2. Take 100% everything apart and just methodically start over again

Well I finally got the 012 lapping around the track this morning. The problem has not absolutely gone away but you wouldn’t know it to see the car go round.

It is without doubt the best XRAY I have had, stable as a gyroscope; a bit of tuning to the steering on the transmitter got it turning in beautifully and it sure looks fast; traction out of some of the difficult tight corners was awesome.

It sure is a whole lot easier to drive than the 009.


We were running kit setup except for ball diff and 2.8 springs on the front – and dodgy shock piston settings . For the final run we put the kit 3.0 springs on the front and gob-smackingly it was even better.

So when I collected the car I just had to give it a great big gobsmacking kiss, it was so good.

So what was the problem solution? Still not sure. I swapped the front drive shafts to opposite sides and it did improve, albeit turning right was still likely to do 360s more so than turning left. I had already swapped out the spool outdrives so I am not convinced that swapping over the drive shafts stopped something sticking. So I am still scratching my head.

If we can get down the track on Saturday I am going to fit the 009 front axle and c-hubs and try and track down the problem by process of elimination, but it sure is good enough to race with.

Could it be that you inadvertent changed something on the radio that makes the servo(s) operating different left to right? Is your car left to right balanced? And is the rear suspension moving freely (mainly inside)? How about the rear hub bearings? Those could look like new and nevertheless they could have an 'O-ring' from felt inside when running on carpet.

Thanks for the suggestions Greenwing

Re the transmitter; you know my brain has been turning that one over day after day, I do not think so but if I have I just cannot see it. I have set the steering up physically twice from scratch in the past week, using the Hudy setup station, and have the steering EPAs set to give me the same steering angle at full turn, as measured on the setup station.
I have also double checked every steering setting on my KO Esprit 3 and cannot see anything that might be catching me out. Personally I am convinced this area is where it is and have now decided to swap out the servo as the next step rather than swap out the front axle.

Balance; when I put the car together and tried to run it the first time, no it was not balanced. I got caught out by the narrower chassis moving the motor side equipment further in board and, as the LIPO hangs over the edge, I assume its positioning is similar to the 009 where the Lipo does not hang outboard. I have a strip of weights along the outside edge of the battery(s) so I just turned the battery 180 degrees to put the weight strip along the centre line and that gave me L/R balance using the Hudy balancing points, but this had no positive impact on the problem - it no doubt would have improved the handling of the car had I actually been able to run it at that moment in time!

Rear suspension: I would have to say yes. The suspension arms swing freely on the pivot bars. With the shocks and roll bar fitted, lifting one wheel raises the other wheel and this movement when lifting either side seems to visually provide the same movement and timing on the other wheel - if that makes sense, I am sure you know what I mean! Lifting both wheels together feels clean and equal. Exactly the same on the front.
I have the tool which measures the consistency and equality of the L&R shocks under compression and decompression and they all passed that test when I built them.

Rear hub bearings - I don't do carpet; cannot be naffed with felt getting everywhere Good suggestion but I did in fact pull the rear axle apart yesterday and checked the bearings even though they are brand new out of the box.

This is why I am tearing my hair out; on the bench I just cannot determine anything. I am convinced now that it is something happening under load hence my approach now to start swapping elements over from the 009 to try and isolate it. The good thing is the car is driveable now and I just have to be a bit conservative when planting the power on a right turn exit.

You see, having just said that reminds me that I do not understand why swapping the drive shafts over to the opposite sides improved the situation, as I could not see anything wrong with them, so the issue may reside in the axle somewhere. As I can do it in advance I will swap the servo and setup the steering again and if that makes no difference I have the axle components off the 009 and ready to be fitted. I will let you know how it goes!

Your car might show up balanced left and right despite having one corner being heavier than the other. Check corner weights.

Check if the bodyshell is fouling with the carpet (tell-tale black lines on the shell edges) or with the tyres on full lock.

[You can check for this statically on the setup board as well by pushing the bodyshell down on each side and checking at full lock.]

I had the bodyshell fouling once, and drove me crazy trying ever more weird setups, but what was happening on turn in, the front edge of the shell would catch the carpet and spin the car out....

It is also possible (but less likely) for the chassis to foul with the carpet if you run quite a soft setup/low roll-centres

Once again thanks for your support on this one guys and to Mikey and Charles for your posts yesterday. I am happy to say it is now 100% sorted - it was indeed all due to a duff servo. No idea why, it all seemed OK on the bench but as I alluded to the other day I was sure it was something happening under load. Servo in the trash can and now focussing on the new season with huge anticipation