HPD F1 Evo 2 Ball Differential

A differential is essential in competition. This is intended for the HPD F1 Evo 2.

• 3 pcs 8x12x3.5mm Ball bearing
• 1 pcs 4x9mm Axial bearing
• 8 pcs 3.175mm (1/8inch) diff ball.
• 1 pair ~24mm outer diameter diff plates
• 2 pcs 25x3mm ~(3/4 x 1/8 inch) Gasket
• 1 carbon tube with outer 8mm and 6mm inner diameter.
• 1 carbon tube with outer 6mm and 4mm inner diameter.
• 1 M4 threaded rod.
• 2 pcs M4 Nyloc nut
• 2 M3x8 grub screws
• 2 M3 nuts
• Super glue
• Diff grease

Printed parts:

https://www.printables.com/model/245261-hpd-evo-2-ball-differential

1. Cut the carbon tubes into equal length, between 134 and 136mm. (more than 136m make the car illegally wide)
2. Cut the threaded rod to ~165mm length.
3. Glue the thinner tube inside the wider.
4. Glue the threaded rod inside the thinner tube.

1. Put the in-drive into the "Applicator" with the flat side outwards.
2. Push the axle through all the way until it stops. Mark position with tape.
3. Take the in-drive from the axle
4. Apply super glue in the position where the in-drive will be.
5. Repeat step 1 and 2.
6. Wait until glue has set.

1. Put one ball bearing into either side.
2. Put the bearing cap outside the ball bearing on the hex side.

1. Drop the 3mm nuts into the slots on the non hex side.
2. Screw in the grub screws enough that they hold the nuts but not entering into the bog hole.

Insert the diff balls into the small holes in the gear.

1. Put the axle into the applicator with the diff side up.
2. Put one ball bearing on the axle and move it all way down. Ensure that the bearing can move freely up and down on the .
3. Insert gasket into groove.
4. Lay the diff plate on top of the gasket.
5. Apply diff grease on diff plate.
6. Put the Spur gear on place.
7. Apply diff grease to the other diff plate.
8. Put the diff plate with the grease side down on the spur gear.
9. Put a gasket on top of the diff plate.
10. Slide the out-drive down and fiddle the gasket and diff plate into postion.
11. Add a rear wheel.
12. Drop in the axial bearing on the axle.
13. Carefully tighten a M4 nylock. Over tightening is easy, use a light touch.

1. Slide down one bearing seat on the axle. The wider side towards the in-drive. This can later be glued on place but wait with it for the moment.
2. Put the axle into the motor pod from its right side.
3. Slide in a bearing seat on the left side.
4. Slide the hex drive on place.
5. Secure the hex drive by tightening the grub screws, be careful not to over tighten.
6. Add the left wheel, use a M4 nut to secure it.

The base setting is to get the differential to go as smooth as possible without too much slip.

Tightening the M4 nut on the right/differential side is reducing slip in the differential. Some slip is OK and often preferable.

There is two ways it can slip, between ball and plate and between plate and rubber gasket.

If you have slip between balls and plate you will soon get a gritty feeling and you will need to rebuild it with fresh diff grease.