The hub of
my red Logitech Momo Force that I’ve owned since 2003 broke last week. A replacement part is not available. I came up with a repair method that can also
reinforce unbroken hubs.
I have not
tested the repaired hub yet, because while I was measuring it to design a 3D
model for my friend’s 3D printer, I found a completed 3D printable hub model by user StoraBrollan on thingiverse.com. I forwarded his model to
my friend to look at and continued working on my own 3D model, because I wanted to
include my reinforcement. Then my friend
texts me that he went ahead and printed StoraBrollan’s hub. Link to StromBrollan's replacement hub
With a
little work to correct ABS shrinkage on my friend's printer, StromBrollan's hub design is installed and working. I designed another 3D printable part to add
my reinforcement to his 3D printed hub. My part also keeps the steering angle limiter aligned if the hub breaks in
the same place again, to protect the wheel angle sensor from over rotation. Link to spacer
Repair/Reinforce Method
The force
feedback gear is held onto the hub with 3 internal m3x20mm screws that thread into an
external metal ring. The hub breaks just past the
screw heads because that center section has to transfer all of the gear torque to the
steering wheel. My hub had a crack
almost all of the way around. It didn’t
crack all the way because I finally checked it after
hearing a loud crack and realizing the wheel could tilt.
The large
opening of the hub has inner ledges. I drilled
and carved a metal washer with a rotary tool and metal files until it would sit on
the ledges. Three notches have to be
made to fit around the pockets that prongs on the steering wheel mounting ring
fit into from below. These pockets and notches help because they
prevent the washer from turning. Now
longer m3x45mm screws can replace the 20mm screws holding on the force feedback gear,
and clamp the hub back together.
I made a
spacer to hold the m3x45mm screws
straight, by sanding a piece of 3/4" PVC pipe to fit inside a 1” PVC pipe, gluing them together with PVC cement, and cutting slots. This will hopefully allow the
screws to transfer some torque between each other to the notches of the washer, instead of all of the torque
going through the hub center section and cracking it again.
The spacer needs a gap under the notched washer so that the washer can provide a
clamping load on the hub, my spacer thickness was about 18mm. A spacer could
also be made with no sanding or gluing from a 1”x1/2" PVC bushing, I just
didn’t want to go to the hardware store. Or the spacer could be 3D printed.
I also glued
the crack with ABS pipe cement, and used my repair method to clamp it while the cement
set. The small end of the hub was also
cracking where the wheel angle sensor fits, so that also got ABS cement and
metal foil tape.
 |
| Additional repair materials |
If the cracked section of hub broke into pieces instead of forming a crack, it might
be possible to cut it out completely,
make a new center section, and bolt it all together with my repair method. In that case I might want to run the screws in the other direction so I could fasten them with 3mm hex nuts. I also might drill everything out to use fatter m4x45mm screws and nuts.
3D
Printed Replacement Hub
My friend
printed the hub in ABS, which can have more shrinkage than the PLA that StromBrollan
used. This may have caused the tiny
<1mm loose fit at the bearing and gear contact areas. To see if the part would work anyway, I used layers of metal tape to build up these
contact areas. The gear keyways had to be shaved a
little wider, and the edges of the cone holes had to be shaved for the gear
mounting ring to lie flat. PLA has less
shrinkage and better layer adhesion than ABS, but ABS can be tougher, less
brittle, and can be carved after printing. I currently have no preference.
My notched metal
washer fits in the 3D printed part too, but longer m3x50mm screws are now needed to
reach the gear mounting ring, because a ramp of material to aid 3D printing covers the shapes the notches used to mate with. My local Ace Hardware store had both 45mm and 50mm m3 metric screws. Those shapes only protruded because the injection mold designer removed as much plastic from the hub as possible to save money, which we're not concerned about anymore. My own preliminary hub design on thingiverse is nearly solid and needs some hollowing out and 3D printing overhang ramps, and is actually more suitable for machining than printing. The washer might be able to turn now, so the
3D printed spacer I designed might not transfer as much torque through the 50mm screws to the washer/hub interface,
but it will still keep the steering angle limiter on the steering wheel mounting ring
aligned if the hub breaks in the same area as before, to protect the wheel
angle sensor from over-rotation.
Link to 3D printable spacer
 |
| Test fit |
 |
| Test fit |
Big thanks to StromBrollan and my friend with the 3D printer.
Thank you for sharing. My beloved Momo Red wheel, bought 3 years ago from the original owner, recently made the dreaded crack sound and became a bit too mobile. I managed to find another on eBay for peanuts and this lasted for a month before its plastic hub also fractured. I have followed your approach using ABS cement, plastic spacers, longer hex bolts and have fabricated grooved washers from 2mm aluminium sheet. What a labour of love! Both wheels have also had Loctite applied to the motor screws, so they should hopefully outlast me. Thanks again for helping me to preserve these excellent FFB wheels.
ReplyDelete