I have thought about adding inexpensive and lightweight bicycle disc brakes to my Minimax for a long time. The main stumbling block is fitting the rotor to the AZUSA Tri-star 6″ wheels. On http://www.lonesomebuzzards.com Walkabout posted a brilliant, cheap way to mount the rotor. More about that later. With the most difficult part resolved it was time to get started.
Finding inexpensive rotors that did not look like something out of the movie Saw was a little difficult but since there is a nearly infinite selection I did finally find a set I liked. I settled on the Gymforward YD-ZXC-SCP001 160mm rotors.
I could have bought two of nearly any bicycle caliper but I wanted something a little unique. If I used the same caliper on the right and left one side would require a longer cable, look odd and possibly cause uneven braking. Finding a set of right/left calipers was difficult until I searched for scooter calipers. Ordered these calipers for $20 from a Chinese seller and it only took about a week for them to arrive. I’ve seen these sold on other sites but this model is the only right/left set of calipers I’ve found.
The mounting bolts on bicycle calipers are spaced 51mm apart. These scooter calipers use a 50.5mm spacing. To figure out all the measurements I used a free on-line CAD application OnShape. After finding a drawing for bicycle caliper mounting bolt measurements I designed the caliper mount in OnShape altering the measurements just enough to account for the 0.5mm difference. The mount is fabricated from 2″ x 2″ x 0.125″ aluminum angle.
Also used OnShape to design the rotor adapters. I knew with the proper bolt spacing the rotor would be perfectly centered. Using OnShape assembly I was able to verify the design before drilling a single hole.
I used 1.25″ x 1.25″ x 0.125″ aluminum square tubing. Each wheel needs three adapters and each adapter requires two cuts and three holes. Very simple to make.
One of the main reasons I am doing this is to have a parking brake. With that in mind I started looking for a brake lever that has a locking mechanism. Found the perfect lever that allows me to set the lock with my pinky finger. Simple, elegant solution.
The final result looks great, I hope they perform just as good!
If you want to build these parts yourself you can download the plans: Caliper-mount-drawing.pdf