26.06.2005
Took the crawler bashing and immediately I found areas that needed
work to improve HOOF2. The area where we crawl is very challenging
because it consists of hard dry rocks that are very jagged with
very few flat surfaces. When testing HOOF2, it became apparent
that the truck definitely could use more clearance and that the
power setup was not providing enough torque as the rear axle would
stall at some challenging obstacles.
First
up, to deal with the problem of torque I rigged up some gear reductions.
The initial designs were based off reductions I saw from another
RC crawler enthusiast who goes by the handle of "Rikpal".
Reductions were needed as my original setup was already using
a small 9-tooth pinion and still not providing enough torque.
I
liked this design because the entire reduction fits inside the
gearbox so none of the gears are exposed. It was designed in CAD
then milled out of 6061 aluminum - the result is a reduction from
the original 40:1 (with 9 tooth pinion) to about 60:1 gearing.
I also swapped out the 17x2 motors for a pair of silver cans.
The
first image shows part of the gear reduction unit with the gears
installed. The second pic shows some modifications done on the
gearbox side to accomodate the new setup. And finally in the third
pic you see the gear reduction installed on the gearbox. As you
might expect, the truck now moves very slow but all that speed
is now converted to torque. Another trip to the rocks would show
if the reductions make as big a difference as I had hoped.
However,
I soon hit another snag... after spending 2 nights milling out
the reductions, I installed them and realized that the new position
of the motors (displaced further away from the axles) now caused
problems for the truck's suspension. When articulating from side
to side, the motor can would hit the lower links. After testing
several suspension setups, I finally settled on re-designing one
side of the lower links to increase clearance for the motor. The
next 2 pictures show the unique setup now on my truck.
Next
it was time to find a way to raise the truck's stance - and this
meant hunting for some larger meats. I settled for some tires
which had received good reviews from crawlers and were relatively
cheap to get my hands on locally - MGT tires. These have a larger
diameter than Clod tires (approx 6.5") and are extremely
soft and grippy once the foams are removed.
One
thing I noticed about HOOF2 running Maxx sized rims is that even
with the Thundertech Racing widened adaptors fitted, the track
width of the truck was still quite narrow (at least significantly
narrower than the stock clod). I didn't want a very wide truck
that would expose a lot of the axle to get stuck on obstacles,
but it couldn't be too narrow either making it unstable on slopes.
It just so happened when I was rebuilding HOOF2 that I found a
deal for a second-hand set of Maximizer beadlocks. These had a
wider offset than stock Maxx rims and when fitted, they brought
the width of my truck back to stock clod specs.
An
interesting thing about the rims though, is that they grip to
the beads of the tires so tightly that the tires effectively become
airtight like real tires! They still seem pretty soft, so I'll
test them to see if the tires eventually need to be vented. I
could see some advantages of air filled tires though - they wouldn't
be so soft and collapse easily.
One
more mod... and it looks like this...
The clod design makes the rear axle steer more aggressively than
the front. When running locked diffs and 4WS, this can be a problem
for crawlers because the huge amount of force placed on the steering
can be too much for a standard servo saver. The result is that
the rear wheels don't go where you want them to go because the
servo saver gives way.
I
read about a simple solution to this and decided to give it a
try. The solution was to fashion a simple metal "extention"
to move the mounting point of the link on the servo saver closer
to it's axis of rotation. This effectively reduced the servo movement,
but it also meant that greater force would be required to overcome
the servo saver spring. The above pic shows the setup that seems
to be working well. Plus, it just looks trick too. lol!
The
second pic shows a close-up of the skidplate assembly. Also designed
in CAD, the skid was designed to keep it as close to the gearbox
as possible so as to minimize any loss of clearance at the axle.
HOOF2
has a very low CG even with a relatively high ground clearance.
Check out this pic of it resting on it's wheels sideways.
Articulation
shot...
And
finally some pics of the truck with the new setups installed...
Tune
in for results of the next bash test!
