RC CAR differential #2

RC Car V2:

Updated 08/02/23

This is the differential I use in my RC car V2 design. 

It's a major modification of this design

https://www.printables.com/model/246505-updated-rc-car-differential-gearbox

Key things to know:

I am now using 3 types of ball bearings.  Bringing in two new sizes (MR117 and 6700zz) has allowed me to strengthen the sun gear axle that seemed to be the weak point of my previous design. I also wanted to reduce the width of the differential as much as possible. I managed to eliminate the use of 608zz however I still use MR115-2RS for spider gears. 

So, you need 9 BB total

• 2 MR115-2RS (11x5x4) for the spider gears
• Bearing holders 
  • 2 MR117-2RS (11x7x3) 
  • 2 6700zz (15x10x3) 
• 2 MR117-2RS (crown gear, diff cup)
• 1 MR117-2RS (Diff pinion)

I've simplified the crown gear and diff cup axles which are now one same part (2 instances) named “main axle”. They are to be glued to the crown gear and to the diff cup. 

Remove the sacrificial support layer after you have glued the parts (easier). You can use the sun gear axles to do that.

Only two 30 mm M3 screws + nuts are needed to assemble the crown gear to the diff cup. The diff casing now prints without supports but you need to use casing mounts which are to be glued and assembled with a short M3 screw to the casing (the screw can be removed once the glue has cured) . There are M3 holes in these parts that allow to close the differential assembly. They will also be used to mount the differential to the chassis. 

Finally, I will be using the sun gear axle directly to assemble with the drive shafts…

Overall, the width of the differential has been reduced from 92 mm to 54 mm.

I kept the gears (the teeth part), so the reduction is still by a factor of 2.

I retain my naming convention for parts:

XXXnn-kk-name

XXX = sub assembly

nn part number within this assembly

kk number of instances needed in one single instance of the sub assembly

I've added pictures to help with assembly; spider gears should rotate freely; do not over tighten the 30 mm screw that holds spider gears + axles onto the support.

Due to some tolerances, and depending on you printer the BB holders may be able to rotate. I do not think it's a problem but anyway, the differential support that will allow to mount the differential to the chassis blocks this rotation.

Printing:

I printed everything in PLA at 0.2 with 4 perimeters.

It takes about 10 hours to print everything.