Front Shift Stand with Controlled Load
Authors
Evelyn Kucera – SRAM
Cherry Durfee – Solubit
Sarah Morales – Solubit
The Challenge
SRAM needed a system to mimic a front shift while applying a controlled load. This system must realistically simulate the load on the front shifter while a rider is pedaling. The biggest challenges to overcome with this simulation are the significant gear ratios common in front gears, along with irregular event timing. The shift event occurs randomly, thus controlling torque and speed during this event requires a sophisticated system.
The Solution
A system that drives a bicycle drivetrain forward while applying a load to the system. There are two main use cases for this system: Evaluating the capability of a front shifting system and replicating the Front Derailleur Endurance Machine.
The system requires a custom operator UI design for low user input with a set of test sequences to pull. The system is also capable of running experimental tests. In these use cases, configurable user inputs are leveraged to create custom test methods and test outputs.
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About SRAM
SRAM’s founding was based on one man’s dream to create a more fun, efficient, and faster experience on a bicycle. Today, SRAM is a global team of people delivering that same passion for improving the experience as well as expanding the potential of cycling.
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SRAM RED eTap AXS offers a wider range and closer progression, so you’re always in the right gear. A quiet, secure, and smooth ride, whatever the terrain. A system that does exactly what you want, when you want. And it’s still wireless.
RED eTAP AXS Front Derailleur is the most responsive, quick, and precise front shifting to date.
Simulating Human Riding
DAQ data was collected over several “Front Shift Ride Tests” during which trained test riders attempt to perform front shifting under various loads in all cogs. This test data has been used to define the system load and speed requirements.
This data was collected by SRAM and instrumental in Solubit’s development of the test system. Given the specific requirements of a “complete shift sequence” and the variations of the rider’s load on the unit under test throughout the sequence, a simulation under control was developed.
PID Control
The biggest success of this solution is the PID control because the test operator is able to maintain the applied torque at a high reaction rate. This capability was accomplished utilizing the LabVIEW PID toolkit and PID Autotuning VIs.
Autotuning VIs are instrumental in the continuous fine-tuning of the PID control as the system may change over time. The PID Advanced Autotuning VI was required for this system because the control is handled within the RT code.
When autotuning, the amplitude was set to mimic a reasonable change in torque when a front shift occurs; this allowed us to find proper gain values for a front shift occurrence.
