I am building tadpoles trike with "dual crossed drag link" type steering, and having been using the spreadsheets below to get the Ackermann compensation right. I am however not really sure how to get best results. If anybody uses these, or had a more up to date/simpler resource to point me to, do let me know!


I am also familliar with the much simpler "point your control arms at the rear wheel", but I am not sure how to apply it to a tadpole trike with drag link steering.


Edit: Here's a picture of the Dual Crossed Drag Link configuration.

From (http://forum.atomiczombie.com/showthread.php/5192-Crossed-Dual-Drag-Steering)enter image description here

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    all im seeing for drag link steering is this wiki page, but im having trouble imagining what your trike will look like, could you post a picture of what youre building or trying to build? – Patrick Zissou Feb 22 '18 at 22:38
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    as you are building it couldnt you do a mock-up where the steerer arms have multiple holes for the linkage so that you could test it real life? – Patrick Zissou Feb 22 '18 at 22:49
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    @TrassVasston this question is now over a year old - how did you get on? What have you tried and how did it work? Feel free to post and accept your own answer, that's permitted and encouraged by SE. – Criggie Mar 7 '19 at 8:39
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    I would cheat by making a full-sized mockup out of flat and tube cardboard , swivel pins, duct tape, and the steering arm brackets that you already have and intend to use. Lego might work but its not cheap stuff. – Criggie Mar 7 '19 at 18:50
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    @Criggie I made 1/10th model out of foam core and long pushpins - it was good for establishing the validity of some other concepts but not accurate at that scale. 1:1? perhaps! – Trass Vasston Mar 10 '19 at 16:29

The story about pointing to the center of the rear axle is valid but sometimes you have to set the ackermann a bit of in the positive or negative direction. In my setup the full ackermann works fine.

You might be able to solve your problem by making an animation of the setup so you can see the angle that the wheels are making when you turn the handlebar. I tried but I did not succeed in it.

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  • Welcome to the site! Unlike others you might be used to, we're not a discussion forum and the format of the site into questions and answers means that back and forth "How did it go?" type questions don't work at all well here. I edited that part out of your post, leaving the part that answers the posted question. I hope that's OK. There's more information about how the site works in our short tour and in the help center. – David Richerby Mar 7 '19 at 12:35
  • An animation? How do you mean? I will soon post my solution(s) as an answer, as they are in plain sight. – Trass Vasston Mar 10 '19 at 16:39

Ok, I sort of figured it out. I will unstar my answer for a better one, should it arise!

The diagram in my original post is the answer, I just did not understand it.

1) first set your arms with 0 Ackermann - the the drive and slave* arms will be parallel (shown by the dotted lines)

2) Calculate your Ackerman the same way you would with rack and pinion - it is the angle from the center of your rear axle to a front wheel.

3) Now subtract your Ackermann amount. This will open the angle of the drive arms (shown with the solid lines)

4) Wow that worked!

However this only provides ONE correct solution, out of an infinite number.

  • The arm's "straight" setting can be swung forward and backward, so long as they are parallel.

  • the radius of the arms can be different on the drive and slave*. This can be used limit the steer sensitivity, but affects the correct compensation.

So in the end I say: use the method I describe, along with the image in the OP, then use the spreadsheets to experiment with other solutions. I also found a program called "Solve Space" which I have not dug into yet, but is free and can simulate linkages.

*If there is better terminology, do let me know.

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