WLtoys K989 DIY RC Car

Last year, I set myself the challenge of designing a 1/28 scale radio-controlled car, and I’ve finally decided to share my model.

This small RC is fast, it runs well and it's very fun to drive, but first and foremost, it's a truly fun build experience!

If you have any questions, suggestions or requests, please feel free to share them on Facebook

If you like this model, feel free to visit my Store to get the STEP files and support my work! 

What to expect ?!

My design choices

• Fun

  •  I prioritize fun and ease of assembly over performance

• Attractive

  • I wanted the design to be appealing and encourage people to get into the making

• Dirt cheap 

  • To be honest, it’s cheaper to buy the real thing on AliExpress, but if you’re looking for a truly fun building experience, this model is the one for you ;-)

• Whenever possible

  • Easy to print

    • 3D printable as much as possible

    • Printable with a 0.40mm nozzle

    • Printable with no supports

  • Easy to assemble and disassemble

    • Parts should "print-in-place"

    • Parts should "snap" together

    • Assembly should not need heat-set inserts

    • Assembly should not require screws

    • Assembly should not require glue

  • Easy to maintain

    • Differentials and gearbox must have a grease port

• Customizable

  • Choice of body shells

    • From AliExpress or fully printable

  • Choice of Drivetrain System

    • All-Wheel Drive (AWD) or Rear-Wheel Drive (RWD)

    • Open(limited-slip) or Fixe differential 

  • Choice of tires

    • Rally or Drift tires

Alt Build

This model can also be assembled solely as a "Display Model"

Without any of the “Required or Recommended parts”

BOM

Required parts

This model is designed around these parts; they cannot be replaced by similar parts

• WLToys Spare Parts

  • Metal Upgrade Gear Differential Drive Shaft Bearing

  • K989-06 Engine Motor

  • Metal Motor Gear

  • Metal Servo

Recommended parts

These are the parts I had on hand; they can be replaced by parts of equivalent dimensions

• Brushed ESC

  • QUICRUN WP-1625 Brushed ESC

• Radiomaster Receivers

  • R85C Frsky D8 / D16 and Futaba SFHSS compatible receiver

  • ER3C-i 2.4GHz ELRS PWM Receiver

• LiPo Battery

  • Spektrum 7.4V 350mAh 2S 30C LiPo Battery

Body ( Shell )

• AliExpress

  • WLtoys K989 Body Shell Cover

• Printables

  • WLtoys K989 DIY RC Car Boby (Supra Remix)

  • WLtoys K989 DIY RC Car Body (Skyline Remix)

Other parts

• Gyro

  • DASMIKRO Super Nano Drift Gyro V5

  • TPU tires don't offer much grip, so the gyroscope helps enormously

  • I also use dual-rates to limit the top speed because it is surprisingly fast

• Double side tape or VELCRO

  • VELCRO Brand Sleek & Thin Stick On Hem Tape

  • Very useful to attach the electronic components

• Bearing ID 5 x OD 8 x W 2.50 (1x)

  • One extra bearing is needed if you want to build a Rear-Wheel Drive transmission

• M3x8 screws (4x)

  • M3x8 screws are needed if you want to build it as a "Display Model"

Radio Controller ?

New to RC modelling and you don't know which radio controller to buy?

• Maker's dream ;-)

  • Radiomaster MT12 Surface Radio Controller

    • This is the Surface Radio Controller i use.  It might seem expensive, but it offers features equivalent to high-end radios for a much lower price. Some will tell you that EdgeTX has a steep learning curve, it's true, but there are tons of videos on YouTube that make it easier to learn. If you really want to get into RC Car and Boat modelling, this is the radio for you ;-)

• Very Affordable

  • MEUS RACING ME-8B RC Transmitter with 04B Receiver

    • I don't know this radio personally, but I've noticed that several people recommend it on forums and in groups. I imagine it can't be bad, especially considering its very affordable price for a transceiver

Before printing !

• As a precaution, check the dimensions of the drive shaft and wheel hub bearings included in your AliExpress kit. If they do not match the dimensions listed below, leave a message on the Facebook Group, maybe I will be able to produce a suitable frame. The gear differential bearing dimensions are uncommon, but they generally fit

  • Drive Shaft and Wheel Hub bearing dimensions : ID 3 x OD 7 x W 2

  • Gear Differential bearing dimensions : ID 6.30 x OD 9.50 x W 3.15

• I included a test print to verify the part's tolerances as well as your print profiles. I think it would be best to start by printing and assembling the "test_print" before printing the entire set

Recommended PETG Print Settings

• Printer : Original Prusa MK4S MMU3 0.4 nozzle

• Print settings : 0.15 STRUCTURAL

• Filament : Generic PETG

• Infill : 15% (Gyroid)

• Perimeters : 3

• Perimeter generator : Classic

Test_print

• Please refer to the corresponding section

  • frame_bottom_plate

  • frame_top_casing

  • wheel_hub

frame_bottom_plate

• Pay attention to the seam position

  • Paint-on seam

frame_top_casing

• Pay attention to the seam position

  • rear_diff_casing : Paint-on seam + Seam position (Rear)

  • front_diff_casing : Paint-on seam + Seam position (Rear)

  • motor_casing : Paint-on seam 

wheel_hub

• Pay attention to the seam position

  • Seam position (Rear)

steering_and_shock

• Pay attention to the seam position

  • Seam position (Rear)

rail_mount

• Pay attention to the seam position

  • Seam position (Rear)

rim

• Supports : Paint-on supports + For support enforcers only 

alt_wheel *

• Intended only for the assembly of a "Display Model" 

  • M3x8 screws are required for assembly (4x)

• alt_rim : Paint-on supports + For support enforcers only 

• alt_hub : Seam position (Rear)

Recommended FLEX/TPU Print Settings

tire_rally & tire_drift

• Printer : Original Prusa MK4S 0.4 nozzle

• Print settings : 0.20 STRUCTURAL

• Filament : Generic FLEX(TPU 95A)

• Infill : 0%

• Perimeters : 2

• Solid layers : Top=4, Bottom=4

• Seam position : Aligned

• Perimeter generator : Arachne

• Single perimeter on top surface : All top surface

• Only one perimeter on first layer : checked

Assembly

• Lay out the parts

• Orient and position the parts

  • Double check the orientation and position of the parts

• Snap the parts together

Test Print

*Ensure that the front steering arms are positioned downwards

All-Wheel Drive Frame

*Double check the position of the rear and front top differential casings (They are different)

Rear-Wheel Drive Frame

*Use the extra bearing mentioned in the BOM Optional parts (ID 5 x OD 8 x W 2.50)

Brushed Motor

*You can use a small hammer to help you close the motor casing

Servo Motor

*You can use filament or M2x8 screws if your servo did not come with self-tapping screws

All-Wheel Drive Hubs

*Ensure the wheel spins freely (Do not over-tighten)

Rear-Wheel Drive Front Hubs

*Remove the front wheel axle; ensure the wheel spins freely (Do not over-tighten)

Wheels, Suspension and Steering

*Position and snap the parts together (Careful, the steering parts are fragile)

Mounting Rail

*Use Double Side Tape or Stick On Velcro to attach the electronic components   

ESC Switch

*You can use filament, M2x8 screw or self-tapping screw to hold the switch in place   

Body Shell

*Slide the Body Shell Cover on the rail mounting tabs