CUSTOM BICYCLE DROPOUTS
Beautiful, Custom, and Functional
Objectives:
Provide a connection point to weld seatstays and chainstays of current/future Bike Builders of Berkeley (BBB) bicycles.
Attain a unique yet functional look.
Adhere to Flat Mount disc brake standard.
Adhere to SRAM Universal Derailleur Hanger (UDH) standards.
Manufacturer specifications
Flat Mount Spec.
Must attain correct spacing to ensure the brake caliper can mount to the dropout.
Flat Mount Spec. cont'd
Must attain correct spacing from axle to fit disc brake rotor.
UDH Spec.
Must create a design to ensure functionality of UDH. UDH will hold the derailleur which shifts gears, so its functionality is essential.
UDH Spec. cont'd
Initial ideation - cad sketching
Dropout Assembly CAD with UDH and Axle Models
Drive side Dropout with UDH Spec.
Non-drive side Dropout with Flat Mount Brake Spec.
Updated Dropout Assembly Render with All Relevant Models
Includes: dropouts, hub, brake rotor, brake caliper, axle
REDESIGN: Brake Mount Issues
MTB Rear Triangle CAD
After finalizing the design, I realized that the current brake caliper mounting would not be compatible with the rear triangle design (designed by another team in BBB). There would not be enough clearance in the rear triangle to mount the caliper.
Redesigned Dropouts
To solve the problem, my teammate and I designed new dropouts with the brake caliper mount rotated up to the seat stay. Since the brake rotor is circular, any point of mounting with the same radius (distance from the axle) will be viable.
Redesigned Dropouts in MTB Rear Triangle CAD
Angle of dropouts matches construction of seatstay and chainstay. Clearance for brake calipers to mount on top of dropout.
Updated Dropout Assembly Render with Modified Brake Mounts
Note the rotated brake mounts on the far side that still provide adequate mounting for the caliper.
Drive Side UDH Spec. Dropout
Non-Drive Side Flat Mount Spec. Dropout
Prototyping
Prototype Dropouts
Printed with PLA for fast prototyping.
Intended to validate design and test fit before machining begins.
Intended to catch any errors in need of redesign.
Prototype Dropouts with All Components Test Fit
Test fit with:
- Universal Derailleur Hanger
- 12mm Thru Axle
- Flat Mount to Post Mount Adaptor
- 160mm Rotor to 180mm Rotor Adaptor
- GX AXS Rear Derailleur
- SRAM Guide RSC Caliper
Verdict: They all fit!! No perceivable redesigns needed.
Machining!
Initial Waterjet of Drive Side Dropout
More machining will be needed to create features for UDH interface.
Fixtures must be machined to hold down work while milling the other features.
Machining of Fixtures
Custom Fixtures in Place
Custom Fixtures in Place
Drive side dropout is secure and ready for milling.
Machining UDH features
Custom Fixtures in Place
After fixturing the dropout, my friend Connor used a mill to machine out the recess and pin features necessary for the UDH to function.
Completed Drive Side Dropout
Completed Drive Side Dropout
UDH fits into the assembly as intended.
All features designed in CAD were transferred into the real-life product!
One dropout down, one to go.
Custom Fixtures
Fixtures with Waterjet Piece
More custom fixtures for constraining motion while machining the other dropout.
Fixtures with Waterjet Piece
Fixtures with Waterjet Piece
Fixtures machined within 0.001" tolerance.
Brake Mount Machining
Mounting tabs for disc brake caliper in progress.
Finished NDS Dropout!
All features transferred from CAD to real life part. Brake mounts to the holes, fits flat mount brake specifications as intended.
Brake Mount Machining
Brake Mount Machining
Alternate view.
Machined Dropouts Test Fit
Machined Dropouts with Components Test Fit
All components mount identically to the prototype 3D printed dropouts!
Includes: UDH, Thru-Axle, Brake Mounting Hardware.
All clearance fits are smooth without any interference.
Dropouts are ready for welding.
Alternate View
Test Fit of UDH Derailleur Hanger and Derailleur
Test Fit of Brake Caliper and Adaptor
WELDED REAR TRIANGLE!
Rear Triangle Welded with Dropouts
All turned out very similar to the CAD
Complete with a "dummy axle" I machined to prevent warping.
Close Up of Welded Dropouts
The FINISHED BIKE
Presenting: The BBB Carbon MTB
After a year's worth of work, the bike was finally finished.
The dropouts work seamlessly and function as intended!