OpenZ: 1/28 scale RWD mini RC car

A highly modified version of the OpenZ frames currently shared by Guaro3d (https://www.guaro3d.com/openz) as well as Rockracer (https://www.thingiverse.com/thing:4360727).

I printed both the deisgns above but wanted to tighten up the steering and other issues. One thing led to another and by the end I had changed every single part.

Note that parts are mostly NOT INTERCHANGEABLE with the above 2 designs.

I made changes mostly to fit my own needs/capabilities of my printers/availability of specific items. This might not work for everyone, especially the ball hubs and ball links, not sure if an FDM printer can print this in the tolerances needed.

Changes made include:

Front End:
Front plate modified to just use M2 screws for everything
Front suspension using rubber band (see photos)
Front arms and wheel hubs printed with ball connectors
Front steering using printed ball links

Main Chassis:
Main chassis widened to accommodate my specific lipo (might have issues fitting shells)
Top brace split into front and main to accommodate taller servo horn

Rear Suspension:
Spring based suspension using spring from a pen and an M3 screw

Rear End:
Beefed up the trailing arm with M3 instead of M2 screws
Modified motor housing to account for gear mesh with 12T pinion
Modified motor housing to fit brushless motor (Atomic 5500kv used here, others might not fit)

Wheels:
Tires and rims all redesigned, tires printed by FDM in PLA+, rims were printed by SLA
Tire remover STLs included (don't work super well but better than nothing)
Rear wheels are made of 2 pieces, hub and rim to allow for installation of M2 screw to axle
RH rear hub is screwed directly to a 40T spur gear

Body Shells:
I have included 2, one generic just to let people know where to place the magnet posts and another based on Guardo's Dodge Challenger (https://www.thingiverse.com/thing:2861048) which was scaled and edited to include the posts for magnets. His design also was nicely split into easily printable sections.

Outstanding issues:

Still not happy with the front steering

• Can't get any more extreme steering angles
  (EDIT: with the latest dual servo horns and some other changes this seems ENOUGH, not as extreme as off the shelf solutions but enough)
• Steering affected by suspension
  (EDIT: this has mainly been resolved by the point below, also using the Front Plate with Arm Stop helps to prevent the arms from over extending downwards and allows for a stronger rubber band to be used for the front suspension)
• Steering pumps at maximum travel
  (EDIT: this has been reduced by using the dual servo arm and offset top arms and arm holder, also swapping the left and right hubs (3mm with 2mm caster) so that the push rods are flatter)
• printed servo ball links not ideal, recommend buying proper M2 ones
  (EDIT: I bought M2 ball links but they are the same size if not BIGGER than my printed ones!)

Low speed control

• No idea if this is an ESC problem, a drive train problem, a tire problem or just me being new at drifting, I can't get the car to operate at a smooth low speed for smooth drifts
  (EDIT: This has been partially resolved for me in part by moving from 12T/40T to 9T/43T as well as swapping out the flat profile back tires with the rounded profile ones)

Rear axle issues

• Currently either friction of glue to adapt the axle to the rear hubs, sometimes slips
• My current axle DOES NOT FIT the MR63ZZ bearings! They are a hair too thick, reverted to using FDM printed bushings

Build Videos & More Tips:
https://youtu.be/RWnS4nuS2_8 - Main chassis build
https://youtu.be/zcyxhbhvejE - Electronics
https://youtu.be/pXL0igheFt8 - Shell

List of STLs used in the video:

Main Body

• MainChassis98mm.stl
• TopBrace98mm.stl

Front Assembly

• FrontPlate_WithArmStop.stl
• FrontBrace_MagnetHolder.stl
• Arm_Top_Offset_LH.stl
• Arm_Top_Offset_RH.stl
• Arm_Bottom.stl x 2
• ArmHolder_Offset.stl
• FrontRim.stl x 2
• FrontTire_Thicker.stl
• BallStudHub_3mm_LH_Caster2mm_Thicker_Orlander.stl
• BallStudHub_3mm_RH_Caster2mm_Thicker_Orlander.stl
• DualServoHorn_SmallServoGear_Orlandoo.stl

Rear Assembly

• MotorHousing_Brushed.stl (will fit Rocket 3500kv bushless)
• TrailingArm.stl
• MotorHoldDown.stl
• RearRim.stl x 2
• RearTire_RoundedProfile_Thicker.stl x 2
• RearHub_LH.stl
• RearHub_RH.stl
• Rear_43T_Gear.stl
• SuspensionHolder.stl
• SpringSuspension_Pivot.stl
• SpringSuspension_Stop.stl

Shell

• MagnetHolder_Porsche_Front.stl
• MagnetHolder_Porsche_Rear.stl

If you do not have the Orlandoo ball links and want to print your own, replace the Ball Stud Hub & Dual Servo Horn above with the following:

• BallStudHub_3mm_LH_Caster2mm_Thicker.stl
• BallStudHub_3mm_RH_Caster2mm_Thicker.stl
• BallLink_Combined.stl
• Servo_FixedLink_Small.stl
• DualServoHorn_SmallServoGear.stl

List of non-printed parts:

Hardware
M2 screws - https://www.aliexpress.com/item/10000...
M2 Wheel Nut - https://www.aliexpress.com/item/32988...
Orlandoo Ball Heads - https://banggood.app.link/KGEnreRIp8
Orlandoo Pull Rods - https://banggood.app.link/IAHq0oNIp8
Orlandoo Pull Rod Head - https://banggood.app.link/CF9osESIp8
3mm shaft - https://www.aliexpress.com/item/40003...
Gear Pack - https://banggood.app.link/JteiJCUIp8
Only 9 tooth gear - https://www.aliexpress.com/item/40001...
Bearings (MR63ZZ & MR62ZZ) - https://www.aliexpress.com/item/32833...
Magnets - https://www.aliexpress.com/item/32711... (look for 5x2mm and 5x5mm ones)

Electronics
Rocket Mini 3500kv Brushless Motor - https://www.aliexpress.com/item/33027...
XT30 connectors - https://www.aliexpress.com/item/32888...
Emax 300mah 2S lipo - https://banggood.app.link/IV532e4Ip8
Sinohobby Servo - https://banggood.app.link/WwnRZOWIp8
Flysky GT5 Transmitter - https://banggood.app.link/Qir2lpZIp8
Flysky BS6 Receiver - https://banggood.app.link/KQ7oFx1Ip8
ESC (You need to know how to reprogram this!) - https://banggood.app.link/Zl9MKnBJp8
5V BEC (the exact one I used I can not find it anymore) - https://banggood.app.link/xQsrtTNJp8

Shell
98mm GT3RS - https://nl.aliexpress.com/item/400038...

NOTE: I do not recommend using my ESC/BEC combo, buy a dedicated brushess (or brushed mini ESC instead as my route requires programming the ESC using an Arduino)