jonnyjo
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| posted on 15/6/05 at 01:56 PM |
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How to measure Akerman Angle
I know what Akerman angle is, however I don't know how to accurately measure it on a vehicle. Take a look at this image which I created in MS
Paint,
The steering arm changes shape as it moves away from upright towards track rod. You can see there are 2 different angles in that image - which is the
correct one for akerman (or are neither correct!)? The first angle is the angle between the point where track rod connects to steering arm, to the
centre of the steering arm where attached to the upright. The second angle is the angle between the point where track rod connects to steering arm, to
the inside of the steering arm (which obviously makes it a smaller angle than the first angle considered).
I've searched the net and books and found nothing! Any advice is much appreciated!
Thanks
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britishtrident
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| posted on 15/6/05 at 02:31 PM |
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Dosen't work that way with rack & pinion steering. Classical ackerman geometry only works on ancient cars or trucks with a steering box,
and centre track rod.
With rack and pinnion steering effect is really swamped by the effect of fore-aft position of the steering in relation to the outer track rod ends.
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jonnyjo
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| posted on 15/6/05 at 02:50 PM |
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The Track rod is connected to a rack. I realise that the akerman angle is always changing due to turn radius of track corners. What I want to know is
the static akerman angle when the steering wheel/uprights are in their neutral position. As you can see in the image above, the track rod makes an
angle with the steering arm, which I believe is the static akerman angle. The question is where exactly to measure this akerman angle relative to
track rod. I have offered 2 seperate ways to measure this, which would give very different angles; it is therefore important to know how to measure it
properly.
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smart51
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| posted on 15/6/05 at 03:05 PM |
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Ackerman goes through the centre of the contact patch of the tyre on the road. You will need to define a plane that goes through the centre of the
contact patch, the centre of the hole at the end of the uprights steering arm and the centre point of the rear axle. I guess that the angle is
measured between this plane and straight ahead.
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pbura
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| posted on 15/6/05 at 03:13 PM |
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I think neither of your pictures quite gets it. The pertinent link is from the king pin pivot (center of rotation for the upright) to the center of
the steering arm pivot. Zero Ackerman is when these links are parallel.
Good illustrations here:
http://www.rctek.com/handling/ackerman_steering_principle.html
Pete
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britishtrident
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| posted on 15/6/05 at 05:38 PM |
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To answer the question you asked it is measures from the steering axis (ie kin pin or virtual king pin centre lin) at the height of the outer track
rod end ball joint centre. On most modern suspension this will be very small almost zero as it is only there for clearance between the track rod end
and the brake backplate. Ackerman is achevied a by the steering rack location.
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andy d (rizla)
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| posted on 15/6/05 at 05:49 PM |
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could always contact marc at mnr,the vortx has this angle built into the desighn
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jonnyjo
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| posted on 15/6/05 at 07:03 PM |
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Ok- Just to confirm, here is an image i created in MS Paint showing kinpin inclination and ackermann angle.
Just want to check if this is correct?
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