Double drag link no tie rod?

[day215]

I was reworking my caster on my AX10, and I got to thinking, would it be possible to have two draglinks and eliminate the tie rod? Mount the drag links one in front and one behind the servo horn, the other ends bolt to the left and right knuckles. It looks like it would work in theory, but there must be a reason that I haven't seen it done before. This is on a standard front mounted forward facing servo, offset to one side, it would definitely help with gaining some clearance by getting rid of the tie rod.

[dschaetzly]

only thing i can think of as to why guys dont do this is as the servo horn steers left and right it also goes up in the circular motion. with 2 drag links it will go up on both sides possibly loosing usable steering as with the tierod is fixed on both knuckles and thats making it to where you wont lose more or les on each side as the servo turns. so lets say tou turn left and as the horn moves left and up the left knuckle could lose steering while the right pulls all the way and vice versa? idk maybe ive been up too long.. its bedtime haha

[Rook82]

It would also change the toe in/out. As in when the servo is set up normally, the servo horn points basically strait down from the servo. And the servo mounting hole for the link is basically at a level horizontal line. When the servo turns to either side, it swings up. This would turn the strait horizontal line into a v. Decreasing the front toe in when it is turned to either side and increasing this effect the more the servo motion reaches its end point as it is climbing higher as it moves in its circular motion.

One of the side affects that actually has a purpose is having the tie rod (link from one axle to the other) below the drag link (servo to axle knuckle). It makes the tie rod come into contact with things (rocks, etc) before the drag link gets wacked. It helps to an extent to protect the servo. i know the servo takes some stress from the tires getting pushed around and any other hit to the steering or wheels. but the impact from a link that is directly connected to the servo horn would be worse in my opinion. My tie rods are beat and bent and scratched to hell. but the drag links look like new. I haven't killed a servo in a crawler yet so this is just theoretical.

[day215]

Originally Posted by Rook82

It would also change the toe in/out. As in when the servo is set up normally, the servo horn points basically strait down from the servo. And the servo mounting hole for the link is basically at a level horizontal line. When the servo turns to either side, it swings up. This would turn the strait horizontal line into a v. Decreasing the front toe in when it is turned to either side and increasing this effect the more the servo motion reaches its end point as it is climbing higher as it moves in its circular motion.

One of the side affects that actually has a purpose is having the tie rod (link from one axle to the other) below the drag link (servo to axle knuckle). It makes the tie rod come into contact with things (rocks, etc) before the drag link gets wacked. It helps to an extent to protect the servo. i know the servo takes some stress from the tires getting pushed around and any other hit to the steering or wheels. but the impact from a link that is directly connected to the servo horn would be worse in my opinion. My tie rods are beat and bent and scratched to hell. but the drag links look like new. I haven't killed a servo in a crawler yet so this is just theoretical.

This is what I was looking for, before I went to the trouble of fabbing up new drag links only to find out my theory was wrong.

[crawl-o-matic]

kind of sounds like a zero ackerman steering set up.

Originally Posted by day215

I was reworking my caster on my AX10, and I got to thinking, would it be possible to have two draglinks and eliminate the tie rod? Mount the drag links one in front and one behind the servo horn, the other ends bolt to the left and right knuckles. It looks like it would work in theory, but there must be a reason that I haven't seen it done before. This is on a standard front mounted forward facing servo, offset to one side, it would definitely help with gaining some clearance by getting rid of the tie rod.

[Charlie-III]

Originally Posted by crawl-o-matic

kind of sounds like a zero ackerman steering set up.

Ummm.....nope.
"0" ackerman is related to the angle between the axle, the knuckle pivot & the steering link mount.
It wants to be 90* for "0" ackerman.

The described steering setup can have issues because of the arc sweep of the servo arm, the different length links (unless the servo horn is equadistant to each knuckle) and the front/rear centering of the servo arm relative to the knuckle attach point.

Would it work?
Yes.
Would I do it?
Nope.
Would the OP notice some of the issues?
I don't know.

[WAM]

It's actually anti-ackerman because the "V" shape gets more pronounced at either extreme left or right and thus distance between knuckles decreases. IE toe-in. Interestingly, if you mounted the horn upwards, it would now act as positive ackerman. As the horn gets lower at extreme left and right, the distance between knuckles increases. But the drag links would be working at extreme angles -- that couldn't be a good thing for vertical loads on the knuckle arms. And lost servo leverage.

I had previously thought about dual drag links for BTA Gatekeeper geometry, because they say for some reason the current BTA's don't work with that chassis. I didn't get too far with it for the same reasons. I figured out a way, but it was complicated and I didn't want to build it.

[JeremyH]

Originally Posted by WAM

I had previously thought about dual drag links for BTA Gatekeeper geometry, because they say for some reason the current BTA's don't work with that chassis. I didn't get too far with it for the same reasons. I figured out a way, but it was complicated and I didn't want to build it.

Actually, there have been a few guys who ran a bta setup with that chassis. Turbofest showed us a good idea and Rowdy copied it on his GC3A:
http://www.rccrawler.com/forum/showthread.php?t=282652

[WAM]

Yeah, by current BTA I meant production ones. Like you say, I've seen a number of customs. I'll probably have to build one myself if Gatekeeper doesn't put theirs into production by the time I'm ready.

[sumquak]

Originally Posted by day215

I was reworking my caster on my AX10, and I got to thinking, would it be possible to have two draglinks and eliminate the tie rod? Mount the drag links one in front and one behind the servo horn, the other ends bolt to the left and right knuckles. It looks like it would work in theory, but there must be a reason that I haven't seen it done before. This is on a standard front mounted forward facing servo, offset to one side, it would definitely help with gaining some clearance by getting rid of the tie rod.

is this what your looking for. had a friend try this and was happy with the results. i've been running this setup on my ax10 for about a year and put it on my scx. i did not like the results originally on the scx with a hitec 645 mg. i tried it again but with the hitec 7955 tg and am happy with the results.







i'm still running stock dogbones and would like more steering but had an issue with the cvd pins so won't run those

i don't completely understand steering angles and what is proper setup, i just know this is working for me so far

[crawl-o-matic]

looks like you could turn this into an ackerman type setup just by adding the center off-set plate. (I'm calling it "off-set plate" because I have no idea what it's called, just trying to describe what it looks like to me) But, I'm thinking it would need to be centered to work correctly???http://www.rctek.com/technical/handl...principle.html

Originally Posted by sumquak

is this what your looking for. had a friend try this and was happy with the results. i've been running this setup on my ax10 for about a year and put it on my scx. i did not like the results originally on the scx with a hitec 645 mg. i tried it again but with the hitec 7955 tg and am happy with the results.







i'm still running stock dogbones and would like more steering but had an issue with the cvd pins so won't run those

i don't completely understand steering angles and what is proper setup, i just know this is working for me so far