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Thread: Longer Steering Drag Link vs. Shorter Drag Link?

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Old 05-08-2008, 04:27 AM   #1
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Default Longer Steering Drag Link vs. Shorter Drag Link?

So I'm going to be a big noob here and ask, is there any difference and how so?

I've seen some comments in builds that say that having a longer drag link helps steering. Not sure I understand the how/why?

I have read the excellent tech article on our main page btw. But no mention of this specifically.

Thanks in advance for the answer/help. Curious to hear...
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Old 05-08-2008, 04:47 AM   #2
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If you're building a scaler, with a chassis-mounted servo, a longer DL will keep bumpsteer to a minimum. Mount the servo to one of your chassis rails and run the DL to the opposite wheel. If the DL's pivot point is on the same plane as the links' pivot points you can eliminate bumpsteer altogether. A Hi-Lift steering bellcrank will help; their profile is a lot lower than a servo's, so the pivot point tucks into the frame nicely.

Using an axle-mounted servo, the DL should be long enough to let the servo horn sit vertical at center.
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Old 05-08-2008, 05:40 AM   #3
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Basically, you want the steering to be pushed sideways, not up and down. ;) Any force up and down is wasted, and harder on parts.
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Old 05-08-2008, 12:59 PM   #4
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Thanks. That all makes sense.

So I'll even be specific. AX10 Axle, with offset servo plate. The servo mounts off-center to the driver's side left.

The stock kit, provides a very short drag link 1" - 1.5" to the driver's side left knuckle. It sits level and parallel to the tie rod, it's just short.

So there would be no advantage to using a longer drag link 3.5" inches to the right side instead?

I just see alot of guys doing this. Especially with TLT axles too. The Drag link to the knuckle is always to the longer side.

Thanks again.

-Mike
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Old 05-08-2008, 02:17 PM   #5
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Going with the longer link is more efficent, and generally works better. There probably isn't a huge performance advantage, but when its so easy to do, why not?
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Old 05-08-2008, 02:44 PM   #6
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Arrow This is why a longer draglink is prefered.

I hope I can explain this clearly.

It’s called radians. This the distance along the outside of a circle that something travels. For example, the tip of an arm of an analog watch travels a further distance then the inner part of the arm. In this analogy the outside of the arm has more torque acting against the clocks drive than the inner part of the arm.

A servo works the same way, only there is an extension/draglink to the outside of the servo horn that is also moving along the circumference of that same circle. This draglink acts oppositely to the servo horn. As your servo rotates, the draglink end moves along the outside of the servo horn’s rotation. While this occurs, the force shifts from a horizontal motion to a vertical motion. The shorter your draglink the faster the motion shifts from horizontal to vertical.

To help you visualize, make a stick that is 6 inches long, and make one that is 3 inches long. If you raise one end of both sticks the same distance you’ll see that the shorter stick has a steeper angle. See picture:







That steeper angle caused while using a shorter draglink, reduces your turning power by focusing more of its power in the vertical motion. The longer draglink having a lower angle maintains more of its power in the horizontal motion, resulting in stronger steering.

So yup… there is a reason why the engineers of r/c vehicles utilize the longer draglink.

I hope this helps you.
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Old 05-08-2008, 04:13 PM   #7
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Great explanation crazy_kanaka!

That makes a ton of sense. I appreciate that and the pic too!

-Mike
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Old 05-08-2008, 04:14 PM   #8
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No problem
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