This is my first attempt at building a custom Clod Buster.
My goal was to build a rock crawling truck. I wanted it
to be reasonably light with high approach and departure
angles, and have a flexy suspension with good travel and
lots of articulation. I think I have achieved my goals
fairly well. Below are the truck specs and how I built it.
SPECS:
Front axle vertical travel: 3.25"
Front axle articulation: +/- 31 deg
Rear axle vertical travel: 3.5"
Rear axle articulation: +/- 31 deg
Axle clearance: 1.75"
Chassis clearance: 4.5"
Wheelbase: 13.25"
Track Width: 16.5"
Weight (w/battery): ~8 lbs.
I used stock Clod gearboxes with the stock motors wired
in parallel. Each motor also uses a Traxxas clip-on heat
sink. I used 2-part epoxy on both axles to glue
the diff gears together and lock the diffs. When I first
built the truck I locked the rear in this manner, but
not the front. Up front, I used a trick someone mentioned
on RCMT.
I added two rubber o-rings to the main gear shaft.
When the gearbox was bolted together this applied greater
friction to the diff gears and formed a limited slip action.
However, it only worked slightly and started wearing out
over a short period of time. I decided to lock the front
diff as I had the rear. Steering was affected a bit but
not too greatly. Climbing ability was greatly increased.
Climbing vertical faces such as this is easy now.
I wanted the steering system to be simple, strong, and
mounted as high as possible for clearance reasons. I
fabricated servo mounts to attach the servos vertically
on the side of each gearbox. To each mount I added a
FMA Direct 355M metal gear servo and Kimbrough large gas
(#124) servo saver.
Draglinks and tie rods are made from pieces of
6-32 rod sleeved with aluminum tube and attached to
the axle using Traxxas rod ends. For added clearance,
the tie rods were moved to the top of the knuckle arms.
To decrease turning radius, the plastic steering stops
were trimmed from the axles. An aluminum skidplate was
also added to the front axle to protect the steering rods.
I had originally decided to build a chassis using cantilevers
to get the travel and articulation I wanted. However,
I saw a Tim Powers truck at a local track and decided
to work on a simpler design along those lines. I made
the main chassis from 0
.60" sheet aluminum and ¼"
aluminum rod. This structure houses the battery and
electronics, and serves as attachments for all the
suspension rods. This yields a lightweight, rigid,
and compact chassis.
The four-link at each end mounts high with two near-parallel
links connecting to the axles where the upper braces
normally go. The other two links, forming a vee, converge at an
attachment point on top of each servo mount. This setup
provides lots of articulation and high clearance as well.
All links are at reasonable angles to horizontal so that
geometry does not vary widely as the axle moves up and down.
Upper links are aluminum sleeved 6-32 threaded rod.
Lower links are aluminum sleeved 3/16" steel brake
line tubing with additional steel rod inserted
inside the brake line. All rod ends are Traxxas parts attached
using 3mm screws. Front shocks are Traxxas XL shocks
and rears are Losi 0.93" aluminum bodied shocks.
Each shock mounts between the upper part of the chassis
and a point on a lower suspension link. I use nylon cable
clamps for lower shock mounts.
The shocks are mounted so they can
swivel as the links travel up and down. Through changes
of springs, oil weight, and lower shock mount location
the ride height, suspension rate and dampening are
adjustable. One big advantage I've found in this system
is that it is very simple and does not have the tire
clearance problems often found when using cantilevers.
Electrics include a Super Rooster ESC and Futaba Magnum
Jr. radio system. Wiring is Dean's Wet Noodle. The stick
pack batttery rides low in the chassis and is held in
place with a custom quick-release
retainer. Four wheel
steering is used and the rear servo
is operated through an adjustable servo reverser.
Rear steering rate is setup to be slightly less than
that of the front by using a shorter servo saver radius.
Stock wheels and tire are used, but the
tires have been cut to make them more flexible and provide
greater voiding areas for better tractions on rocks. To
increase track and prevent the tires from rubbing on the
lower links I fabricated a set of 0.4" aluminum spacers, one
for each wheel. This increases track just enough to allow
the tires to clear the links without adding unnecessary
strain or tire scrub.
The body I used is a 1/8th scale Mugen Toyota Xtra Cab truck
body. This was my first time painting lexan, so I kept the
paint scheme fairly simple. I made a quick relaese body mount
for it that leaves
no mounting posts or hardware behind on the chassis once the
body is removed.
Copyright (c) 2000 by Jay Kopycinski, All Rights Reserved.
