This is a work in progress. It is also unlikely that I will update it. So I am including working files, as messy as they are (fusion 360) for anyone to modify on their own!
I modified a variation of the previous design by pgote. Then adapted it to fit my roller blind specifically. My first prototype showed that my blinds are way to heavy for the little 5v motor. My blinds just free-spooled to drop on the floor. I adapted by printing a larger cog to go onto the blind itself, keeping the same size cog from the original design. Proto 2 still dropped to the floor, so I implemented a clutch system.
This clutch prevents the roller from dropping and allows the little motor to stop and hold at any point. However the motor is still too small to lift the large roller (48"x78"). I will probably publish a new version once I have sufficient power. Currently waiting on a nema 17...
The clutch itself is based on design from the manufacture. In the photos the white plastic is the original, which used a 4mm beaded rope to drive the clutch. I simply kept things similar and modified to print from plastic. The spring is a 8 wind, that fits on the 14mm spindle.
The mechanism of the clutch is when the cog is turned it pushes open the spring, when the collar in the roller blind(gravity) turns the spring tighter. I looked on aliexpress but couldn't source the exact spring. If you are attempting to make a clutch, you will likely need the spring first, then adjust the diameter of your spindle so the spring fits slightly snug on the spindle. Then you can adjust where the collar and cog pieces touch the spring.