First build, Grand Daddy

MTScott

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Linked below is a guy's video explaining Ackermann in the clearest and simplest way I have found, definitely watch it if you want to be able to steer your kart without the front wheels scrubbing and sliding. When you reach the 5:00 minute mark, he explains how you can use those 90-degree spindles just as they are, by bolting the pitman arm ends of the tierods separately instead of on the same bolt. The ends reach an inch or two further, going past themselves to reach their bolt holes. Gives same exact Ackermann for either leading arm or trailing arm setups, without having to change the angle of the spindle arms.
GoKart steering explained,including Ackermann Theory.WATCH BEFORE YOU WELD! - YouTube

That was a good video.... most valuable part to me was to get your angle on the spindle arms to meet at the center point of your rear axle which makes sense to me to get the proper arc on the inner and outer circle of your tires. I think I can accomplish this easy enough by adding brackets to my rear facing spindle arms to connect the hiem joint in the proper spot.

I'm using a steering rack, so..... I think the concept is still the same as a single pin pitman arm. I had originally built a steering box that was 2" wider than the plans called for, in large part because I knew I was going with the 11" rack and I wanted the pivot points of the rack hiems to be similar to the A-arms, and it turned out fairly close. I'm actually intending on cutting off my steering box nose, and redoing it because it ended up a little twisted and off level from the rest of the frame. So I'll have a chance to make the width "exact" to whatever would be appropriate, or, attempt to.

What I can't really wrap my head around - is while in a turn, and hitting bumps, the pivot point of the rack hiem will still be off from the A-arm joint, so, I don't know how you can avoid bump steer in a corner. I think the best I can do is avoid bump steer while driving straight??? Thoughts gents?
 

Functional Artist

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Keep the tie rods as straight as possible
...& (if possible) have steering pivot points "in line" with the A-frames pivot points :thumbsup:

Here is a demonstration video, showing what/how I did it, on my Slingshot kart ;)

 

MTScott

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Keep the tie rods as straight as possible
...& (if possible) have steering pivot points "in line" with the A-frames pivot points :thumbsup:

Here is a demonstration video, showing what/how I did it, on my Slingshot kart ;)

Ah.... I guess if I thought about it enough (sometimes hard), the pivot points at the rack (ideally, in line with the A-arm pivots) will move with the attachment/pivot points at the spindle arm, so... the geometry the should stay relatively the same.
 

MTScott

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Hmmm.... if I add L brackets to move the attachment point of of the spindle arms inward (to obtain ackermann angle), I would think I would need to maintain the over all length of the tie rods relative to the the A-arm, so I'd need the pivot points of the rack connections to be set inward as well.
 

madprofessor

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Attaching an Ackermann discussion from earlier tonight with Functional Artist. It has a good example of brackets to put on the spindles to get Ackermann, and that's the way to go for you since you're using rack and pinion....................

...& then, some shapin'
SAM_4258.JPG

* All done with simple (mostly Harbor Freight) hand tools (tape measure, scribe, a drill & a variety of bits & a grinder (rough & smooth)
...& some imagination:sifone:

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madprofessor

"Loose Cannon Creations"​

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The spindle brackets are a good idea, looks like one bolt hole attaches to 90-degree spindle arm hole, and the other bolt hole attaches to tierods. Maybe the long length is to parallel the spindle arm and weld to it? Or drill another pair of holes to bolt it?
Pitman arm looks like it won't work as is, but you've almost got it. When spreading the tierod bolt holes apart to create Ackermann angle that way, the left tierod end does not go in the left side bolt hole, it reaches across and goes in the right side bolt hole. Vice versa for the other tierod end. Therefore the pitman arm bolt holes have to be shifted North/South enough for the tierods not to hit each other. Like maybe one of them North a 1/2", the other South a 1/2".
 

MTScott

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So, on the topic of bump steer.... given that the A arms are exactly the same length, and spaced the same vertically, there is no imaginary intersection point at which to align steering rods. The tires move up and down perpendicular to the frame.

My small brain then says to eliminate bump steer, the steering rod length (eye to eye) should be the same as the A-arm length (eye to eye, pivot point to pivot.... you get what I'm saying).

As it stands, my 11" steering rack is still wider in the hinge points on my A-arms, even though I widened the nose/steering box by 2" (from 5 to 7).

If I create brackets to move the connection point of my spindle arms inward (to create ackermans angle), the rods will get even shorter.

So, if I use 11" steering rack, it seems I might have to just live with some bumpsteer, or am I missing something?

Side note: I do plan on cutting off this steering box/nose assembly and rebuilding it, as it ended up with more twist than I want to deal with - so, I could make it wider, but the front end is already kinda wide.

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Mvp6905

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Any update on your steering? I just built my control arms. What a pain. I need a bender some round tube A-arms would probably be easier than these multiple pieces welded together. I am no pro, looking at your build to know what to do haha.
 

MTScott

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I am no pro

You're in good company then, I'm just figuring this out as I go :). So... I'm not sure if taking any ideas from my build is wise or not...

Yeah the A-arms are a pain, could have been a much easier process with a different design... now that I've done it once I might try something else.

Steering... well, here are my thoughts. The A-arms move in parallel, exactly the same length - there is no point in space in which their angle of movement will cross which is a common point of conversation when figuring out steering rod length and joint location. My theory with these A-arms, is that if I keep length of the steering rods equal to the length of the A-arms (and straight), they'll move with the A-arms, regardless of joint location. So, I somehow need to do that, and I've got a few ideas but it'll involve some modification to the steering rack.

I think getting ackermanns angle correct is probably more important than avoiding bump steer, what I plan to do for that is run a line from the spindle kingpin on center, to the middle of the rear axle. The steering rod joint needs to be on that line which will require the fab of a small bracket on the spindle steering arms. If the rack pulls the rods straight, this should create the difference in angle in the wheels necessary to steer skid free through a turn.
 
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Denny

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Bump steer is far more important than Ackerman. How would you like to make a turn at high speeds every time you hit a bump. Very hard to control and frustrating to drive. You could live without Ackerman. But while you are building it is the time to take care of all those issues. Unless you would like to have to cut it all back apart to fix it after the kart is finished and painted. Your choice, you can pay the man now. Or pay him later, your choice!
 
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