This page now limits the calculation to a declared steady Prony-brake measurement: perpendicular reaction force times arm length gives torque, and torque times angular speed gives shaft power. It does not predict friction, temperature, cooling, uncertainty, capacity, durability or safe operation.
Prony-Brake Measurement Explorer
Enter declared shaft speed, perpendicular reaction force and torque-arm length. The connected animation keeps the friction shoe and reaction arm stationary while the drum rotates; the worksheet reports only measured torque, angular speed and ideal steady power.
Equation Used
- Shaft speed N, reaction force F and perpendicular arm length L are declared simultaneous steady measurements.
- The force line is perpendicular to the arm, so the moment magnitude is exactly FL.
- Ideal steady shaft power is torque times angular speed; horsepower is only a unit conversion.
- The rotating drum and stationary brake/arm animation is connected but not a contact, friction or thermal simulation.
- Scale zero, arm self-weight, alignment, bearing drag, speed and force variation, sensor calibration, uncertainty, friction coefficient, heat transfer, cooling, wear, vibration, structural strength, rated capacity, guards, controls and safe operation are excluded.
Preserves exact declared Prony-brake torque and power identities while removing unsupported performance, thermal, deployment and operating claims.
A stationary reaction arm measures rotating-shaft torque
A Prony brake absorbs shaft motion through friction at a drum. Friction tries to carry the brake assembly with the drum, while a stationary reaction arm transfers that moment to a force balance or load sensor.
The connected animation keeps the shoe and rigid reaction arm stationary while the drum turns. It does not solve contact force, friction or temperature.
Use this page only to audit a declared steady measurement
The worksheet converts declared rpm to angular speed, multiplies a perpendicular reaction-force reading by arm length for torque, and multiplies torque by angular speed for ideal steady shaft power.
It cannot design, rate, cool, calibrate or authorize operation of a brake or dynamometer.
Measure force and speed at the same steady condition
If the force is not perpendicular, the moment requires the perpendicular distance or vector cross product. This page assumes perpendicularity explicitly.
A transparent declared-measurement example
For N=1800 rpm, F=100 N perpendicular to L=0.50 m, angular speed is 188.496 rad/s, measured torque is 50.00 N·m, and ideal steady shaft power is 9.425 kW or 12.64 hp.
No temperature, cooling duty, uncertainty or safe rating follows.
Power arithmetic is not a complete dynamometer result
Real measurement requires verified arm geometry, force and speed calibration, simultaneous steady readings, zero and tare treatment, alignment, bearing-drag treatment and an uncertainty analysis. A physical absorber additionally requires machine-specific thermal, structural, guarding and operating controls.
The former universal accuracy, operating windows, cooling predictions, named deployments, cost claims, service intervals and troubleshooting rules are removed because the sources do not establish them for one documented rig.
Prony-brake ledger questions
Does shaft power equal FL omega?
Yes for the declared simultaneous steady measurements and perpendicular force assumption.
Is that also a cooling-system rating?
No.
Does the animation calculate friction?
No.
Can this size or authorize a real test rig?
No.
Prony-brake measurement references
- IIT Madras NPTEL, Mechanical Measurements, Example 17: spring-balance Prony-brake schematic, torque arm and power relationship.
- Penn State ME 345, Mechanical Measurement Lab: measured arm length, force, rpm, angular speed, torque and power workflow.
- University of Florida ABE 4171, Prony Brake Dynamometer: absorption topology and P=2 pi N F L/60000 in kW.
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