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THE BUILD -
Part 6 |
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the Steering |
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| This is definitely
one of the areas where you have to pay most of your attention.
Steering and suspension are what makes the crawler either chew
up the terrain, or be chewed by it. With the Red Bull
RockHer II, we wanted a crawler that had a super tight turn, and
had a suspension that could handle the bumps, jumps, and huge
climbs, yet be stable enough for the big vertical drops and
twisty technical sections. Because of the
WE Rock competition
rules for the Pro Modified class, we had to use a mechanical
steering box to turn the wheels left and right. Though we
are allowed to use a hydraulic ram to "assist" the steering, the
mechanical box must be able to steer the crawler if the ram is
unhooked. That means you have a steering "draglink" that
goes between the steering box's "pitman arm" and the steering
knuckle or steering "tie rod". Note: we could try to
design a rack and pinion setup or put the steering box on the
axle, but the hassle and expense is just not worth it. The
photo below will help you understand if you are new to the terms
I used above. This is not the new crawler we are building,
it is just a reference photo. |
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| Having a draglink
makes it more difficult to design a front suspension as you have
to worry about the axle moving side to side compared to the
steering box which is in a fixed position on the chassis.
If you cycle many suspension designs, the axle position changes
left to right...in other words, the distance from the steering
box to the lower connection point of the draglink changes.
When that happens, your wheels will turn left or right without
you even turning the steering wheel. That is called
"bump-steer". To understand this, imagine the vehicle has
bump-steer and your steering is fully cranked to one
direction...as the suspension cycles the wheels will turn
either: Less than maximum which we do not want...OR...more than
maximum, which will stress and/or break the steering components.
To counter bump steer, Bender chose to build the most common
type of front suspension which is a three link with panhard bar
(also known as a trackbar). This suspension, if set up
properly, causes the axle to follow the same cycle motion as the
draglink follows and eliminates bumpsteer. The draglink
(on the steering), and the panhard bar (on the suspension) are
built to be the same length and run parallel at the same angle,
therefore they end up following the same path (in layman's
terms).
After choosing the type of suspension, the next job was to
lay it all out. The first step was mounting the steering
box that was built by
Matt at West Texas OffRoad. It is a custom "high
mount" box with forward facing gearing, which means the pitman
arm points forward, not backward as on most vehicles. It
has been tapped for a hydraulic ram assist which we'll get into
later.
For mounting, Bender made a template of how he would mount
the box on the tube frame and Matt designed a plate to hold the
box in place. Any place where the bolts would run through
the plate and through the tube, Bender drilled a large hole
straight through and placed a small "insert" in the hole and
welded it in place. This supports the tube from crushing when
you have to tighten the steering box mounting bolts so tightly.
The extra holes on the steering box mounting plate get "plug
welded" to add more strength to the mount. |
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| Bender then built
the panhard mount (the chassis end) right next to the steering
box and used the one mount to support the other, and vice-versa. |
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| Because of the
design of the mount and the location and maximum possible length
of the panhard, the Blue
Torch Fabworks crew figured out that they had a problem.
There was no pitman arm available that would turn left to right
in the proper path, yet allow the draglink to be the correct
length and at the proper distance (front to back) from the
centerline (side to side) of the axle. With the steering wheel
cranked "full right", the point where the pitman arm needed to
connect to the draglink was about 4" forward AND 4" to the
passenger side of the vertical centerline of the sector shaft.
The sector shaft is the male splined part of the steering box
pictured above. The problem was that the line from the
sector shaft to the connection point was interrupted by the
steering box mount and panhard mounts. Sound confusing???
Wait'll you see the answer! Bender figured if he could have a
custom pitman arm milled out of a big chunk of 3/4" thick steel,
he could make exactly what he needed. That would be
difficult, expensive, and time consuming. Dan came to the
rescue with an idea to use the plasma cutter they have in their
shop. Using three pieces of 1/4" steel, they could cut out
the shape they needed on the plasma and TIG weld them together.
They did exactly that, but look at how trick the whole process
turned out...BTF again shows just how creative and kickass their
work really is!
First they cut out the flat plate and welded it together into
the "boomerang" shape...then they welded in the proper section
of female tapered steering spline. The left hole in the
following picture shows the spline I am talking about. |
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| They cut that part
off making a "ring" of spline, then inserted that ring into the
new fabricated pitman arm that had a hole with the same "inside
diameter" to match the "outside diameter" of the spline ring.
It was welded in place and the unfinished pitman arm was
installed to be sure it would fulfill their needs. |
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| Then, some bracing
and a double-shear tab was built and Dan TIG welded it all in
place. On the left of the first pick, you can see the
spline section welded in place. |
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| HANDS DOWN the most
bling pitman arm I have ever seen! Here's a shot showing you
how the pitman must curve around the steering box and panhard
mounts at full-right turn. |
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For the steering, the draglink crosses from
the pitman to the right
Dedenbear knuckle in front of the axle and then the double
ended high steer arm on that side allows us to mount the tie rod
(that connects the left and right steering knuckles together)
BEHIND the axle. The bar you see in the middle that runs
parallel to the draglink is the panhard bar. |
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| Here is a photo of the wheel turned
to 45 degrees...you DO NOT want to have this tight of steering
unless you have super strong knuckles, axles, and u-joints.
As the u-joints are binding heavily at 45 degrees, the axle
deflection places VERY HIGH stress loads on everything. |
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Jumping backward but I did not get this until
now, here is the SolidWorks movie of the pitman arm Matt drew
up. You will see an arcing slice in the top and bottom
plate that looks out of place. That was an actual cut made
on purpose so when the plates were welded together, they could
weld the middle of the arc fully as well, making the unit far
stronger. After they filled the arc in with weld, they
sanded it clean so you cannot tell it was ever there.
These BTF guys don't miss anything! |
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| Then, here is the
custom steering arm they built for the passenger side.
This Blue Torch Fab high steer arm takes advantage of the 5-stud
design of the burly Dedenbear knuckles. The last bolt is simply
redundant strength for the cap. The actual arm are being
CNC milled exactly to our specs and again, without Ackerman. |
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| I will continue this
section with more, including the ram assist that will mount
behind the axle on the tierod, at a later time. |
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Back to "the GROWING BULL" menu |
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Forward to the next story - "THE BUILD part 7 (the interior)" |
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Blue Torch FabWorks, Inc
Red Bull
RockCrawling Team
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