My Truck

draft version, 11 October 2006

  Introduction
"My Truck" is neither a ZipZap SE nor an MT, yet it combines parts of both.  With a lot of sheet styrene, some brass rod, a couple of Lego parts, and other stuff, my intention is to produce a working truck.  Building in modular fashion, piece by piece, I will strive for the following objectives:
  • six-wheel drive
    • custom solid axles
    • ZZMT wheels and tires
    • ZZSE steering servo power for each axle
  • dual articulation
    • free twisting articulation
    • motor-driven turning articulation
  • ZZMT electronics
  • multi-celled batteries in parallel configuration
  • plug-in, stand-alone battery charger
  • joystick-modified dual-frequency ZZMT controller
  Drive Modules
Three drive modules are required for the truck.  All three modules are built the same and are designed to be mounted either horizontally or vertically.  The axles are 3/32-in. dia. brass rod with a helical gear from a ZZMT drivetrain. A ZZSE steering servo with motor provides the power to the axle.  The servo shaft has been shorted and a matching, shimmed helical gear has been afixed to the shaft.  These components have been placed in a fabricated sheet-styrene box.  Axle adapters of 3/32-in. id. styrene tubing press-fit over the brass axle.  The adapters have a 6-32 nut threaded on one end to capture the ZZMT wheels.  At the nut end the tubing has been threaded for a 4-40 thread.  Short 4-40 machine screws and washers secure the wheels and tires.
 
The following describes the design and fabrication of a drive module:
 

prototype version
    
prototype version
 
Materials:
  • 0.060-in. sheet styrene
  • 3/32-in. id. styrene tubing
  • 3/32-in. dia. brass rod (K&S Engineering, stock no. 163)
  • 6-32 hex nuts (6 required)
  • 4-40 x 1/4-in. socket head cap screws, black (6 required; Du-Bro, cat. no. 569)
  • no. 2 plastic washers, black (6 required; Ace Hardware no. )
  • modified ZipZap SE steering servo and motor (3 required)
  • ZipZap MT helical drivetrain gears (6 required)
  • ZipZap MT wheel and tire sets (6 required)
Materials may be substituted to suit individual design requirements or availability of materials.
Fabricating the Motor Housing
Materials for the Motor Housings:
 
note:  All styrene pieces are cut from a styrene sheet, then sanded and trued with 220-grit sandpaper to the dimensions indicated, using a machinist's square and a digital caliper.
  • housing base -- 1.00-in. x 1.00-in. x 0.060-in. styrene, 1 required for each housing
  • interior sides -- 1.00-in. x 0.33-in. x 0.060-in. styrene, 2 required for each housing
  • exterior sides -- 1.00-in. x 0.45-in. x 0.060-in. styrene, 2 required for each housing
  • top spacer -- 1.00-in. x 0.300-in. x 0.060-in. styrene, 1 required for each housing
  • plastic bonding solvent (Plastruct Weldene, or equivalent)
motor housing materials, exploded view
Assembly:
 
note:  Precision of assembly is somewhat necessary.  I discovered the motor housing needs to be "square" to operate properly.
   1.  Add the sides by first cementing the side of an exterior side to the edge of the housing base.  Use a square to hold the pieces perpendicular and let it set.  Repeat with the other exterior side.  click on the pictures for larger images
 
my note:  I disassembled my machinist's square and used a part of it to hold the exterior side perpendicular, and like much of my life, it shows I'm off about a quarter of a bubble.
   2.  Complete the sides by secondly cementing the side and edge of an interior side to inside of the joint formed by the exterior side and the housing base.  Gently clamp the interior and exterior sides together.  Repeat with the other interior side and let them set.
 
my notes:  Spring clothes pins worked well as inexpensive clamps.
   3.  Add the top spacer by cementing it between the exterior sides and atop the interior sides.  Make sure the assembly is square, then clamp it with a rubber band and let it set.
4.  Create the axle shaft holes location by scribing marks 0.225 inches from the top and end of each exterior side.  With a pin vise and very small drill, hand drill pilot holes perpendicular through the sides at the intersection of the scribed marks.  Again with a pin vise and 3/32-in. drill, slowly drill through each side.
 
my notes:  I began with a no. 69 (0.029-in. dia.) drill, and progressed to larger sizes, and finally drilled through both sides with a 3/32-in. dia. drill, as shown.  The final drilling made sure the axle holes were aligned so as to accept the axle.
5.  If the drive module is to be mounted vertically on the truck chassis, then cement the mounting flanges to the top of the top spacer and bottom of the housing base.  Clamp with a rubber band and allow it to set.
6.  If desired, paint the assembled motor housing and set it aside to dry.
 
my notes:  I painted the housing primer gray.
7.  Ever so slightly, enlarge the axle holes to permit the axle to turn freely.  Do not make the holes overly large.
 
my notes:  I again used a 3/32 drill, this time as a reamer, to enlarge the axle holes.
Rebuilding the Motor
Materials for the Motor Assembly:
  • motor -- ZipZap SE steering servo and motor, 1 required
  • output shaft shim -- small piece of electrical wire insulation, 1 required
  • helix gear -- ZipZap MT gear, 1 required
  • mounting screws -- small screws, 2 required
 image:  motor assembly materials, exploded view
Assembly:
Fabricating the Axle and Wheel Adapters
Materials for the Axle and Wheel Adapters:
  • axle -- 1.75-in. x 3/32-in. dia. brass rod, 1 required for each axle
  • helix gear -- ZZMT gear, 1 required for each axle
  • wheel adapters -- 0.75-in. x 3.32-in. id. styrene tube, 2 required for each axle
  • hex nuts -- 6-32 hex nuts, brass, 2 required for each axle
  • washers -- no. 2 flat washers, 2 required for each axle
  • cap screws -- 4-40 x 0.25-in. socket head cap screws, black, 2 required for each axle
 image:  axle and wheel adapter materials, exploded view
Assembly:
Assembling the Drive Module
The basic issue in assembling the drive module is the alignment of the helical gears.  It seems best to be able to power the servo while making minute adjustments to the location of the motor assembly.
  Articulated Steering Module