Ackerman angle and steering questions

Jonesn · Mar 29, 2016

I'm messing around with building automotive style steering for a radio flyer wagon. Read up on Ackerman angle some and tried to incorporate it into my design. I'm still having issues of the inside knuckle wanting to go over center at full lock. I've messed with the offset distance from the kingpin and it didn't seem to make much difference.

I know this steering won't make much difference if it is off some, but I mainly want to learn how to fix it if I had to when scaled up.

1tonyj · Mar 29, 2016

Paging patoyee!

TBItoy · Mar 29, 2016

what degree steering angle is that?

Looks like way too much.

joho75287 · Mar 29, 2016

Maybe I'm being overly simplistic, but wouldn't steering stops on the "inside" wheel so you are limited how far that wheel will turn, solve your problem? I know I have them on my KP 60...

muddinmetal · Mar 29, 2016

It's a ****in' little red wagon... they all do it. the only way to avoid it would be a major redesign, but at some point it is still going to happen. Any time two parallel tires are tied together by a straight rod it will always happen to some degree

gottagofast · Mar 29, 2016

Simple as can be.... You NEED steering stops

mr.mindless · Mar 29, 2016

for the sake of argument, what happens if you increase the legth of the steering arms by say 30%?

Beerj · Mar 29, 2016

I think you need to move the steering linkages closer to the wheels

1993toy · Mar 29, 2016

Try the locations in the pic.

TBItoy · Mar 29, 2016

Re: Re: Ackerman angle and steering questions

1993toy said:
If you look at most, if not all vehicle steering; the tie rod points are offset outside of the pivot points.

Try the locations in the pic.

Most vehicles have the tie rod on the front....

You're missing the point of Ackerman

1993toy · Mar 29, 2016

Re: Re: Ackerman angle and steering questions

TBItoy said:
Most vehicles have the tie rod on the front....

You're missing the point of Ackerman

Nope, I'm not...just trying to help him "improve" on his current setup.

TBItoy · Mar 29, 2016

Re: Re: Re: Ackerman angle and steering questions

1993toy said:
Nope, I'm not...just trying to help him "improve" on his current setup.

Putting the tie rod connections out where you drew them would make it have negative Ackerman and would make the tires scrub real bad when turning instead of tracking properly.

1993toy · Mar 29, 2016

Re: Re: Re: Ackerman angle and steering questions

TBItoy said:
Putting the tie rod connections out where you drew them would make it have negative Ackerman and would make the tires scrub real bad when turning instead of tracking properly.

I agree, my suggestion will change the Ackerman angle. By the way, my suggestion is slightly exaggerated to how far they should move.

Changing the tie rod points will not affect the scrub, his steering axis is straight up, not angled.

TBItoy · Mar 29, 2016

Re: Re: Re: Re: Ackerman angle and steering questions

1993toy said:
I agree, my suggestion will change the Ackerman angle. By the way, my suggestion is slightly exaggerated to how far they should move.

Changing the tie rod points will not affect the scrub, his steering axis is straight up, not angled.

Not scrub radius...

The whole point of Ackerman is that the left and right tires follow different arcs when turning. With positive (correct) Ackerman the tires will naturally turn/track better than no Ackerman or negative Ackerman.

If your outside tire turns tighter than your inside tire (negative Ackerman) then they are fighting each other and will scrub around the turn, rather than rolling smoothly

Beerj · Mar 29, 2016

He's definitely got positive Ackerman, maybe just too much. I do think moving the tie rod ends a little further outboard would help. Still has a way to go before hitting negative or even neutral.

TBItoy · Mar 29, 2016

Re:

I don't understand what what he's saying about the knuckle going over center at full lock.

Even in the pics where the inside tire is turned to the frame, the steering isn't over center.

Beerj · Mar 29, 2016

I'm not sure what he means about that either. :dunno:

gottagofast · Mar 29, 2016

His Ackerman angle is perfect in his drawing... Changing it at all would be a mistake... His entire problem is that his wheels are allowed to turn too far.... Hence steering stops.

mac5005 · Mar 30, 2016

Re: Re: Ackerman angle and steering questions

gottagofast said:
His Ackerman angle is perfect in his drawing... Changing it at all would be a mistake... His entire problem is that his wheels are allowed to turn too far.... Hence steering stops.

This x2

tallnate · Mar 30, 2016

The geometry doesn't line up so it's definitely not perfect. The turn center should match a constant point throughout the turn. I think he needs to shorten his steering arms by roughly 20% and then lengthen his tie rod to match the new arm mounting position. Currently, it looks like his steering arms are close to 25% of the tie rod length. They need to be more around 18% of the tie rod length. Hypothetically if his tie rod is 25 inches, his steering arms should be 4.5 inches.