Right/Left turn circle issues

[macman809]

I noticed that the turning radius on my SCX10ii was not equal, having tested the hypothesis I removed all the front links and servo horn, re-centered my servo, and adjusted each link ensuring symmetrical alignment. when everything was set and re-aligned I retested the rig, but again I am not getting equal turning circles on each full turn. When I turn hard right I am getting a turning radius of 19", when I turn hard left I get a larger radius of 23.5" so I am getting a 7" difference on a full 180˚ turn with a right turning circle being the shorter and the left turn being the larger. does anyone else have this issue or know how to correct the issue.
When I have the vehicle on its roof and turn the steering right to left on full lock, I get what appears to be a good symeytrical turn with both tires being equally spaced from the front trailing arms, before turning my front tires align perfectly with the rear so on the face of things my steering appears to be perfectly symmetrical and yet when driving I get a very different result. I am at a loss, do I realign everything with a bias to compensate or should a technically symmetrical alignment give a symeterical turning circle or am I missing something here?

 

[TheLetterJ]

I think what you're seeing is axle steer. As the chassis rolls to one side while accelerating (torque twist) your suspension geometry lets the drooped wheels move towards the center of the chassis, and the compressed wheels move towards the bumpers. Even with the knuckles perfectly square to the front axle housing, it will still cause the car to turn, imagine how a skateboard turns (but in the case of a linked crawler it will be exactly opposite) and you'll smell what I'm cookin'.

Or I could be full of crap. Your call.

 

[dirtman71]

I think the Letterj has it. But watch your tires and foams and see if they are rolling over to much and pushing. Some of my foam set ups have done that to me. You are probably fine. I think you would have noticed it. But you never know

 

[macman809]

When testing the turning circle I am just crawling on a flat surface trying to eliminate bump and torque twist throwing me off my line and giving me good consistent results. I did try rotating my tires and the results are still the same. what do other scx10ii owners find are you all getting an even measurement on your turning circles I would be interested to know.

 

[dirtman71]

I will go out tomorrow and take some measurements

 

[macman809]

"thumbsup"

 

[dirtman71]

Ok did some testing. And the results surprised me
Scx10.2 with universals one piece axles
Just put the servo on axle with 4 link
10% overdrive gears in the front
Steering goes lock to locks
Hydrax xl tires

44.5” turning to the right
32.5” turning to the left

Much larger than yours and opposite of yours. Looks like I got to do some research and see what is going on. My first thoughts are the overdrive gears causing an overall larger radius. Maybe the one piece axle and stock knuckles are limited. The Hydrax xl tires are pretty wide. And putting the servo on axle it is a real stretch to reach full lock going to the right. Might try to flip servo and connect steering link to the left side rather than the right

Thanks macman didn’t know I had an issue...but I did just put the servo on axle yesterday. Now back to the garage and see what is can fix

 

[dirtman71]

Ok back from the garage. Took a close look at everything and thought I was getting lock to lock but no. The stock draglink from the builders kit which is thicker than the rtr is rubbing this diff cover and both sides are stopping short of full lock

Now remember I just went to 4 link and servo on axle(because panhard bar was rubbing the upper link mount limiting my travel). So I flipped my servo over so steering would connect to the left side of axle and added a longer servo arm, it just clears the steering drag link. Reset all the trims and end points

Steering to the left before 32.5”
Now 32.5”

Steering to the right before 44.5”
Now 34.0”

1.5” difference now. I can live with that. I think the longer arm just 1 hole longer made the difference. As I thought I had plenty of servo throw to the right but the arm would start lifting instead of pushing. I guess you would say I was mechanically out of room. The longer servo horn fixed it

So now I need to either buy a new bent steering link or make one to get my turning radius shorter

 

[macman809]

Glad you ended up with a good result, I appreciate you taking the time out check the issue. Reading through your remarks I realized I should say the front end on this SCX10ii is the stock Axial AR44 axle with upgraded Vanquish Universals and Vanquish Knuckles, the wheels are 1.9 1” wide alloy bead locks fitted with CI foams and Pit Bull XL Rockbeast tires. I realize that not being stock could alter measurements in comparison. I am also using a stock TTX 300 radio. I keeping thinking back to comments from “theletterJ” re the axle steer, I would have thought that given the set up is symmetrical apart from the steering and Panhard links that the axle steer would be roughly the same either direction. I am getting very little deviation in my measurements so I am thinking that it is something either in my set up or it is something that happens even if stock?

 

[Voodoobrew]

Is the weight symmetrical or do you a giant battery on the passenger side? If the passenger tires have the best traction how would that effect the turn radius?

When you flip the vehicle upside down and you have a bent tierod to avoid the pumpkin, does clear the pumpkin better because gravity is now pulling it up and away.

Try to keep the speeds the same going both direction. This is probably obvious.

Sent from my SM-N950U using Tapatalk

 

[Daycrawler]

Is the weight symmetrical or do you a giant battery on the passenger side? If the passenger tires have the best traction how would that effect the turn radius?

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I agree check the weight distribution. Also did you ever have a bad wreck? If so check that something isn't bent, including the frame.

 

[zane!]

I don't think I've ever measured my truck's turning circles...

But I have used the radio's EPAs to limit the steering angle to keep the wheels turning because there's enough steering throw to stuff the 4.5" Pitbull tires firmly into the lower links. My truck has a Vanquish link set which has a bent tie rod which no longer hits the diff cover, as well as some other bits to improve steering angle.

So instead of matching left/right turning circles, I prefer to maximize steering angle as much as possible. I drive it slow and technical on steep rocks so I'll take as much angle as I can get.

 

[macman809]

Thank you Voodoobrew, Daycrawler and Zane! for those follow up comments, I will look into all of your points and Zane! I take you comment on the steering and I agree.
Re battery position, my rig layout is still the stock SCX10ii and I use a 3S 138 x 47 x 24mm battery which weighs 289 grams, and the battery is offset from center so i will move the battery and see if it changes the results, just to know.

 

[macman809]

OK this is embarrassing ;-) but also a lesson point or learning moment. I checked my alignment and re measured the turning circles and I still got the same difference. So I raised the truck off the ground and double checked my steering angles, and hey presto 32 degrees vs 45 degrees of rotation , this could be the reason :idea:, so I set up the truck with a jig and reset my endpoints on the receiver and then tried again and yes I now have two equal turning circles. I had set my endpoints but maybe I did not close out the sequence properly or they didn't take for some reason, either way everything looks good. Lesson learnt re check all points before posting and never assume everything is right at the start. I did recheck all the mechanical points but completely blanked on re-checking the radio. Thanks for the support sorry for the slip up.

 

[Voodoobrew]

Is this a spektrum radio? I have seen an issue where changing one setting resets another setting. Can't rember what settings were affected, wasn't these as far as i remember. But it maybe what happened.

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[macman809]

No it is a Tactic TTX 300 radio, nothing fancy I went over setting the end points and cannot see how I got it wrong, once you have the radio in program mode you make the adjustments shut everything down as usual car first, radio 2nd and then on restart everything should take. I will double check my radio tomorrow morning and re test again to make sure my settings are still good. Fingers crossed.

 

[wblteen]

Is this a spektrum radio? I have seen an issue where changing one setting resets another setting. Can't rember what settings were affected, wasn't these as far as i remember. But it maybe what happened.

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I think it was the Dx4c your talking about. The aux channels would reset. Had that problem with mine. I had to set all my models starting at model 20 and work my way down. Everything has been fine for years now

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[TacocatIsAPalindrome]

Stock Servo?

 

[wilgarn]

I have a similar issue with my RBK but I don’t have a setup stand or any tool to measure angle. When I turn full right the back of my left tire hits the suspension links but when full left turn it’s about 3/4” to 1” away from hitting on left side. I moved my servo horn 1 tooth to the left and now the left side hits links but right doesn’t. I want it to hit in both directions so I can set my endpoints where the tires are just like 1/16” from hitting. Longer servo horn??

 

[wilgarn]

Forgot to mention I’m using a Samix front bumper/front servo relocation mount and Samix servo horn.