MAN TGX Project
Page 4: Upgrades!
Because I didn't have room for the shift servo and therefore the
3-speed transmission was useless, I used a CVT (Continuously Variable
Transmission) here. Not one to just buy something assembled and
start using it, I began by disassembling the CVT as much as I was
able. You can see the parts carefully arranged here on the
table. There are no instructions for this unit so it was important
I remember how everything was assembled.
I could not disassemble this rear part of the transmission because it
uses tiny hex bolts and although I have a tool which fits them, there
was no clearance around the head to actually use the tool. The
screws were all installed with thread lock so a good grip is needed to
break them loose. The right hand picture shows what I could see of
the internals of this rear gearbox.
Here the main housing has been attached to the rear gearbox. There
is a lot of fake detail on the outside of the housing representing
manifolds, valve covers, and an oil pan. The right hand image
shows the hollow interior. The hole at the top will allow a gear
to pass through and drive the rear gearbox.
I know that most CVTs work by adjusting the relative position of a belt
between an input and output cone, thus changing the ratio. But I
wasn't sure what mechanism actually caused the belt to make the
adjustment. From what I can surmise from the parts above, the 6
steel balls move radially outward from centrifugal forces as a function
of shaft speed. As they roll out, the mating bell housing is
pushed away from the plate, thus squeezing the lower cone and forcing
the belt up the ramp. That's my theory anyway.
Here is the completed cone and belt assembly. The lower pulley is
driven by the motor and the upper pulley is the output. There's a
compression spring that pushes the top right cone to the left. The
lower cone is shown fully engaged (maximum clamp) which would pull the
belt down and open the upper cone against the spring. As you slow
down the ball assembly on the lower left would shift to the left,
opening the lower pulleys. The upper pulleys would squeeze shut to
match, powered by the spring. The right hand picture shows the
whole thing assembled with a Holmes Hobbies brushed motor.
The CVT is intended to bolt right into a Tamiya tractor truck chassis,
but it is not completely compatible with the crane I added. In
particular, the rear transmission mounting brackets interfered with the
crane support rails. In the photo on the right you can see the
notch I had to cut in the aluminum rails to allow room for the CVT
bracket to fit beneath.
The next interference was with one of the outrigger tubes. The
outer tube interfered with the rear of the engine housing. I was
able to notch the outer tube as shown to clear the transmission housing
while still leaving room for the inner telescoping outrigger tubes to
slide freely.
The CVT is longer than the original 3-speed transmission which means the
original drive shaft no longer fits. I looked through my bin but
didn't have a dogbone style shaft of the right length. instead, I
was able to cut down a universal shaft from a CC-01 to the right length
and I squeezed it in as shown. The drive shaft runs very close to
the hydraulic hoses so I have some concern about wearing holes in them.
Every Tamiya tractor trucks needs lights, but I needed a new plan since I
didn't have room for an MFC. I used a combination of the TLU-01
LED light unit and the TLU-02 to control it. This accepts a
maximum of 16 lights on 8 channels, but I was able to extend that to 20
by wiring a couple of them in parallel. I used all 12 light
buckets on the front grille and 8 of the 10 available tail lights.
On the front this means that on each side I have two headlights, one
fog light, one turn signal, one amber marker light and one white marker
light. On the rear on each side I have two brake lights, one turn
signal, and one reverse light. There aren't any marker lights on
the side and the lights in the sun shade above the windshield are not
functional.
The picture on the left shows the extensions I had to patch into all the
wires for the tail lights. This was a lot of solder joints and it
took some time to hide all the wires. I did what I could to make
the wires neat under the cabin as shown on the right. There are
two ESCs, two receivers, and two light controllers here with all their
wiring and the interior still needs to fit above. Not shown is the
Y-harness I needed to make so both ESCs could share the same battery.
The tail lights are almost completely hidden by the rear outriggers but there is a bit of light visible around the edges.
Voila! All the lights are installed, the wiring is done, the CVA
is working (kind of), and the crane is functional. I think that's
enough work for this model.
©2019 Eric Albrecht
