MRC24 - 3d Printed Micro RC Rock Crawler

MRC24 is a micro RC Rock Crawler in approx. 1/24 scale using small hub motors to directly drive all wheels. It's a fun toy to climb slowly rocks and terrain.

All main parts are 3d printed: chassis, front and rear axle. However, you will need additional electronics and hardware to complete the crawler. Basic 3d printing and RC knowledge is recommended before starting this build. Feel free to mod parts and share them by using the hashtag #mrc24.

.stl files

• Thingiverse or Printables

Filament

• Esun PLA+

Electronics

• RC - e.g. Radiomaster MT12
• 8mm Servo - e.g PTK 7308 (with standard horizontal ears)
• brushed ESC - e.g. simple or dual channel
• 4x N20 motors (I used 200rpm/6v for 2s)

Wheels

• 1" wheel tires - e.g. Injora Comp Pins

Hardware

• Linkset - Links - Balljoints M2
• 4x Shocks
• M3 Screws/nuts: 2x M3 16mm + 2x nuts to mount knuckle on front axle
• M2 Screws from 4 to 16mm
• 4x Mr63zz 3x6x2.5mm Bearings
• M2 heat inserts (OD3.5mm L5mm) 
• XT30 connector
• 2s lipo
• Velcro Tie (battery)
• optional: Tungsten Weights (I used 1/4ounze; 9mm dia)

There are 7 files, overall 10 parts (print wheels 4x). Prints sliced by SuperSlicer are tested on a Vz235 using Esun PLA+ with 99% infill. PETG and ABS will work too and probably last longer, but are more difficult to print.

• Print with full infill (99%)
• Print rearaxle and knuckles vertically to ensure sufficient strength for holding N20 motors
• Use supports on buildplate
• 0.2mm resolution is ok

1. Simply insert the wheels into the tires. Ensure, that a foam sits inside the tire.
2. Apply glue between the tire beads and the wheel. Use glue on both sides!

1. Use a soldering iron to install heat inserts on top (1x) and front (2x) of the rearaxle
2. Insert N20 motors into motor mounts. You might need to smooth the inside to press fit the motors.
3. Solder silicone wires (24AWG) to motors. You need 2 wires per motor.
4. Optional: snap Tungsten weights into weight holders.

1. Use a solder iron to install heat inserts: 2x in the front, 4x at the bottom, 2x in the back

1. Insert N20 motors in frontknuckles. You might need to smoothen the inside to press fit the motors.
2. Insert 8mm servo into front axle. The servo faces to the front indicated by the MRC24 logo. Mount with 2x M2x4 screws.
3. Install bearings in frontknuckles (2x) and frontaxle (2x).
4. Apply heat inserts in frontknuckles (2x) and frontaxle (4x) and steering rod (2x)
5. Cut 4 wires. Thread trough the small holes on the frontknuckles. Then solder wires to motors.
6. Put knuckles on front axle so that the bearings are touching. Use M3x16 screws and nut to connect securely.
7. Connect the knuckles with the steering rod using M2 screws.
8. Use a short double ball link to connect servo arm and one knuckle.
9. Optional: Insert Tungsten weights

1. Connect axles to chassis using 4x ball links and 2x shocks. The pictures show my setup, it is for sure not perfect and provides room for improvement.

1. Switch the power plug to XT30.
2. Solder motor wires to the ESC. Front motor wires go to CH1 output, rear motors to CH2. Before soldering check polarity so that both motors on the axle turn in the same direction.
3. Connect ESC to the Receiver. The main cable with 3 wires go to CH1, the single wire to CH2. Connect the servo to CH3.

• For programming the radio, please watch the video, it is rather complex.
• You may just use a single ESC controlling all motors, which allows for a simple 2CH radio system. However, you won't be apple to use crawling features like variable power distribution between the axles.

1. Press fit the wheels on the motors. Take care of the D-shape. You may apply a bit of heat to make the press fitting easier.

• The crawler can be used indoor and outdoor. Objects like rocks or furniture are best to try crawling.
• Stay safe and take care of your environment!