MBS Matrix iii (3) discussion

[Dinnye]

I know this thread is mainly for matrix iii stuff, but the rockstar ii pro xl hubs were also discussed here, so I thought I’ll share this here too and it might be useful for someone. I made a 3D printed widener for them:

@Dinnye

If anyone wants to print wideners for the MBS rockstar II pro XL hubs / rims here are the files, I just realised I still haven’t shared them yet:

The step file for 20mm if you want to make your own version
mbs_wide_20.step (75.4 KB)
The STLs from 10mm up to 40mm in 5mm increments
mbs_wide_10.stl (143.3 KB)
mbs_wide_15.stl (171.6 KB)
mbs_wide_20.stl (178.1 KB)
mbs_wide_25.stl (200.4 KB)
mbs_wide_30.stl (206.8 KB)
mbs_wide_35.stl (224.9 KB)
mbs_wide_40.stl (231.3 KB)

The minimum length this design supports is 10mm. Less is not possible, because the lip needs the extra material I added, otherwise it’s going to fail. However, that extra material needs to be chamfered, otherwise it’s going to cause wear on the inner tube. With this version I have personally not experienced extra wear on the tube. Different tire / tube / operating pressure combos might cause a different experience.

They are meant to be printed without supports in this orientation:

• If you suffer bed adhesion problems a brim is recommended.
• The design is meant to be a snug but not too tight press fit into both sides of the hub. This press fit makes sure that the hub’s interlocking feature still works, and helps prevent bent bolts by distributing the load. To achieve this fit, you will need to tweak for the filament’s shrinkage factor. In cura there’s a setting for that, but you can also just scale the whole thing up or down. You WILL need 2-3 tries to get this just right.
• Depending on the accuracy of your printer the holes for the bolts to pass through probably need to be drilled out with a 4mm drill bit. The design has specifies exactly 4mm, no tolerance.
• You need to source your M4 screws. The screws that come with the hub are M4x50 DIN912. To get the correct screw length for the front wheel, just add the width of the widener to this number. For the rear, on BN-AT drives you need to add an extra 10mm. Maybe 5mm extra is also enough, I haven’t tested that yet. So for example, I use the 20mm wideners, on the front I have 70mm screws, on the rear with the BN gear drive I have 80mm screws. Note: you don’t want these screws to bend under any circumstance. Always get the highest grade available, the wider you go the truer this gets. Stainless probably isn’t going to cut it, but you are welcome to test.
• Crappy PLA survived me and I ride pretty hard. PETG is probably the better choice though. Print on the higher end of the filament’s temperature spectrum.

Only the 20mm version is tested at this point. They are very robust if printed well.
This was the “failure” mode for me:

@Dinnye

This happened during a pretty serious crash, which messed up the bearing seat in the hub and deformed the lip too. So I think if you print them well they can take more beating than the hub itself.

Important note:
The hubs have sideset bearings by standard. Meaning, that the load on the bearings is not centered! This normally isn’t in issue if you use the hub as intended, however if you widen it even more, this might lead to increased wear on the bearings and increased load on the bearing seat. Check your bearings regularly! The wider you go, the faster bearings will wear out. I am going to try 3001 double row angular bearings in the hubs soon, those should take the extra load much better. I’ll keep you all updated how that goes. Those however take up more axle space.

Legal stuff:
Use this at your own risk. I do not take any responsibility for it.