Simulation
Praxis Hinged Transmission Simulation
Dynamic simulation of the Praxis 4-speed hinged chained gearbox, computing drivetrain loads and power losses through all four gear ratios as the transmission shifts under load.
A New Drivetrain Architecture
Praxis recently unveiled a 4-speed chained gearbox under the name "Hinged Transmission" — a reference to the mechanism by which the larger sprockets are inserted into the chain's load path. Each gear change physically alters which sprocket in the gear set carries the chain tension, as opposed to a derailleur system where the chain moves laterally between fixed sprockets.
The architecture raises engineering questions that differ from those of conventional derailleur or hub-based systems: how do loads distribute across the chain contact zone during a shift, what are the power losses in each gear ratio, and how does the transmission ratio sequence affect the cadence distribution across a realistic power profile?
Model and Assumptions
The author's own in-house drivetrain simulation tools were applied here, testing their versatility on a novel drivetrain topology. The model computes drivetrain loads and mechanical power losses as the transmission cycles through its four gear ratios under representative cycling loads.
The simulation resolves the gear mesh forces in each stage, chain tension distribution, bearing loads, and the efficiency contribution of each component. Power losses are computed at each gear ratio as functions of load and speed.
What the Simulation Demonstrates
This is a topology and dynamics demonstration rather than a published efficiency verdict: the specific gear-ratio steps, loss figures and validation remain tied to ongoing product development. The animation shows the Hinged Transmission shifting through all four gears while the model tracks instantaneous drivetrain loads and cumulative power losses through each transition. Its value is in the modelling itself — an established in-house drivetrain model adapts to an unconventional, hinged-chain load path with minimal reconfiguration, resolving gear-mesh forces, chain-tension distribution and bearing loads as the active sprocket changes mid-shift. That adaptability is the point, at a time when genuinely new drivetrain architectures are reaching the market with increasing frequency.
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