Introduction: HPD F1 Evo 1 Ball Differential Axle

This is the description on how to make a carbon rear axle to your HPD F1.

The design is very reliable and durable and gives you the advantage of changing diff/slip settings without disassembly.

This version is compatible with with F1 1.0 -> F1 evo.

Not for HPD Evo 2 and newer.


Step 1: Tools

  • 1.5mm hex driver
  • 7mm socket wrench (
  • Hobby knife

Step 2: Hardware to Buy

  • 8mm outer and 6mm inner diameter carbon tube.
  • 6mm outer and 4mm inner diameter carbon tube.
  • 2pcs M3x8 mm grub screws.
  • M4 threaded rod.
  • 2pcs M3 nuts.
  • 2pcs M4 nyloc nuts.
  • 69T 48pitch spur gear (Kimbrough part no #160)
  • G20 gasket 2mm thick. (Gelia part no 3008024202)
  • ⌀25mm ~0.8mm thick diff washer (x-ray part no 375080)
  • 1pc 4x9mm axial bearing
  • 2psc 8x12x3.5mm bearings

Step 3: Print Parts

Gear seat

Material: PETG or something other heat resistant material.

Print settings: It is intended to be printed with a 0.4mm nozzle in vase mode.

The gear seat can experience friction heat if you have a loose differential setting.

Other components

Material: Of your choice.

Print settings: Of your choice.

Step 4: Manufacture Parts

Cut the threaded rod to 164 mm. (it can be shorter and still work but try to be close to this)
Tips for how to cut a threaded rod is found on the internet, this is how I do it:

Cut the carbon tubes to 135 mm.

Use the jig to confirm the correct lengths.

Step 5: Assembly of Axle

Glue axle

Use epoxy to glue the 6mm tube(s) inside the 8mm.
Use the jig to correctly place and glue the threaded rod

Observe that that it is not symmetrical. The end on the gear side sticks out longer.

Check that the resulting axle is still fitting inside the jig.

Glue indrive and gear seat

Use the jig to determine where to glue the in-drive.
Clean and grind the surface to make the epoxy stick optimally.

Put epoxy glue on the axle and inside the in-drive then mount it.Rotate the axle to see that you do not have a wobble.

Clean the excess glue.

Step 6: Left Hex Drive

Put the M3 nuts into the cutouts.

Screw in the M3 grub screws.

Step 7: Outdrive (right Wheel Hex)

Insert the 8x12mm ball bearings in both ends.

Add bearing_washer.stl on top of the outer side bearing. Mount a wheel directly so you will not lose the part.

Step 8: Differential Assembly (part 1)

Put into the indrive:

  1. The 2mm gasket.
  2. The diff washer.

Add diff grease on the diff washer, then:

Add the spur gear.

Step 9: Outdrive

Take the outdrive mounted on the wheel and put it on the table with the outdrive on the top.

Add in order:

  1. 2mm gasket.
  2. Diff washer

Add diff grease on the diff washer, then:

Mount all on top of the spur-gear.

Step 10: Diff Assembly (part 3)

Add the outdrive with wheel onto the spur gear on the axle.

Add the axial bearing on the axle as shown on picture.

Screw the nyloc M4 screw on place to keep everything together.

Step 11: Final Thoughts

Congratulations! You now have a very durable rear axle for the HPD range of F1 cars.

First a mention of the items printed but not used so far:

shim.stl: Is used to reduce play. Add suitable amount starting on the indrive side.

ball_bearing_adapter.stl: The carbon axle is 8mm instead of the 10mm printed axles on HPD F1 cars prior to version 3.0. Use this adapter if needed.

You will now want to adjust the slip/lock of the differential to adapt to the conditions on the circuit. This is done by changing how much you tighten then M4 lock nut on the differential side of the axle.

Because of the design you will be able to do it in seconds, not minutes.