double drag link steering

[shemesh]

hi
i've got an AX10 RTR. the one with all plastic - i am a newbie.
i am having lots of fun with it!
lately i'm getting disturbed by its clumsy steering, i've already got rid of that servo saver and using a normal servo horn (still plastic).

what i'e noticed now is that the plastic tie-rod is very flexi and sometimes it makes my wheel face each other like so: / --- \

so i've started looking at some rigid steering setup and noticed that everybody is using the drag-link + tie-rod combination...
got me wandering...

why?
why not use two drag-links and eliminate the tie-rod?

get some round servo horn and attach 2 drag-link to both wheels! this will eliminate the "middle man" = the tie-rod.

am i missing something?
why not?

[ax10]

Your not missing anything. I have aluminum steering links. Short one goes from servo to steering knuckle. Long one connects both knuckles together

[TSK]

Originally Posted by ax10

Your not missing anything. I have aluminum steering links. Short one goes from servo to steering knuckle. Long one connects both knuckles together

Your setup is what he is not describing. He want's two drag links, one to each wheel as opposed to one drag link to one wheel and a tierod between the two.

And to anser the OP, no real reason not to run it like you mention, but unless the servo hron is centered in the axle, the wheels will not turn in equal amounts and the side with the shorter drag link will move less than the side with the longer drag link.

[C*H*U*D]

I ran a setup like that for awhile, but didn't care for it much. Using a tie-rod keeps both wheels turning the same no matter what. When you have a drag link going to each knuckle, the amount each tire turns changes as the horn rotates because it moves in an arc.

It's hard to explain, but if you try it, you'll see what I'm saying.

[Super Fabrication]

One of the people who runs a bully (can't remember his name) ran a setup like that and it worked out ok. If you scroll through the bully steering thread, you'll see it.

[opek]

Originally Posted by C*H*U*D

I ran a setup like that for awhile, but didn't care for it much. Using a tie-rod keeps both wheels turning the same no matter what. When you have a drag link going to each knuckle, the amount each tire turns changes as the horn rotates because it moves in an arc.

It's hard to explain, but if you try it, you'll see what I'm saying.

It depends on a million different things, but with near true ackerman knuckles oriented forward it works out not much different than a tie rod. It lets you get rid of some of the reverse ackerman while keeping the toe out down.

[JeremyH]

Originally Posted by opek

It depends on a million different things, but with near true ackerman knuckles oriented forward it works out not much different than a tie rod. It lets you get rid of some of the reverse ackerman while keeping the toe out down.

That's assuming that you can mount the tie rods to the servo horn in the exact same spot....which you cant physically do.

[sourdojack]

It's possible, it would just look goofy and be harder to Fab than a tierod setup...

[opek]

Originally Posted by JeremyH

That's assuming that you can mount the tie rods to the servo horn in the exact same spot....which you cant physically do.

One in front and one in back, one screw and one nut! If you offset them then the ackerman gets super duper tunable.

See here: another ax10 build, it's a 2.2 esse

[opek]

Originally Posted by sourdojack

It's possible, it would just look goofy and be harder to Fab than a tierod setup...

I think it's considerably easier to make, though setup requires a bit more thinking.

[JeremyH]

Originally Posted by opek

One in front and one in back, one screw and one nut! If you offset them then the ackerman gets super duper tunable.

I thought the same, until I tried it. No good. Even with zero ack knuckles, the steering moves at different arcs.

[C*H*U*D]

I didn't say it couldn't be done, just that I didn't like it. I think there is a reason tie-rods are pretty much the standard over dual drag-links.

[opek]

Originally Posted by JeremyH

I thought the same, until I tried it. No good. Even with zero ack knuckles, the steering moves at different arcs.

Did you try it with near true ackerman knuckles?

[C*H*U*D]

Originally Posted by opek

Did you try it with near true ackerman knuckles?

I think the issue is the way the servo horn rotates (on a normal comp rig). It doesn't matter what knuckles are used, the servo horn moves each knuckle a different distance as it travels through it's arc.

I have no doubt that a dual drag-link can work, but I don't believe it can ever duplicate the benefit of having both wheels locked together with a tie-rod.

I've tried it, Jeremy says he has tried it, and I'm sure there are many others who can say the same. That's why I said there is a reason that almost everyone runs a tie-rod.

Out of curiosity, do you run a tie-rod or dual drag-links?

[opek]

Originally Posted by C*H*U*D

I think the issue is the way the servo horn rotates (on a normal comp rig). It doesn't matter what knuckles are used, the servo horn moves each knuckle a different distance as it travels through it's arc.

I have no doubt that a dual drag-link can work, but I don't believe it can ever duplicate the benefit of having both wheels locked together with a tie-rod.

I've tried it, Jeremy says he has tried it, and I'm sure there are many others who can say the same. That's why I said there is a reason that almost everyone runs a tie-rod.

Out of curiosity, do you run a tie-rod or dual drag-links?

If you check my post above you'll see a link to my build thread, specifically a post where you can see the dual link setup I ran for awhile. I used it to take some reverse ackerman out of my rig. Dual link setups are discussed on lots of other RC forums as means to control Ackerman. I ran both and opted for the tie rod eventually because of packaging when I still had the servo mounted like normal. The change hurt steering performance significantly.

[C*H*U*D]

So you had better performance with dual drag-links?

[opek]

I had less reverse ackerman at lock while having less toe out at rest. This is with near true ackerman knuckles. Having the 'right' amount of reverse ackerman to fit my caster and shock placement gave me more turning.

[JeremyH]

Originally Posted by opek

Did you try it with near true ackerman knuckles?

Define "near true ackermann knuckles".

[JeremyH]

Originally Posted by C*H*U*D

I think the issue is the way the servo horn rotates (on a normal comp rig). It doesn't matter what knuckles are used, the servo horn moves each knuckle a different distance as it travels through it's arc.

Bingo.

[C*H*U*D]

I'd be willing to try it again if I had the time, but from what I remember it wasn't for me. I'd be curious to see what would happen if the horn rotated with the knuckles instead of on a different plane.

Right now though I have too many other projects on my plate.