Physics of Stationary and Dynamic Ergometers

By: Nathaniel BrownTim BeauregardAndrew DiOrioBryan Taylor

Ergometer Background

• Exercise machine that measures work done pulling a chain.

• Used to simulate the motion of rowing a boat on water.

• Different types of ergs = different feel and performance.

Static Ergometer

Static: Concept2 Ergometer Diagram of Static Ergometer

• The standard for testing a rower’s power output.• Does not mimic the feeling of a boat well.

Dynamic Ergometer

Dynamic: Oartec Slider Ergometer Diagram of Oartec Slider

• Better mimics the motion of a boat.• Times are generally faster than stationary.• Higher stroke rates are easier.

Problem Statement

• Develop an explanation for differences in measured performance for different ergometers.

• Create a “rule-of-thumb” formula for adjusting

scores on different ergometers.

Approach to Problem Solving

• Measure locations of selected points on rower and erg using video and image tracking.

• Find accelerations based on data.

• Use the accelerations and masses to find work and power.

Assumptions

• Forces only act in x-direction.

• Static center of masses based on three points at the ankle, hip, and neck.

• Frictionless environment.

Expectations

• Static ergometer will waste more energy accelerating masses than the dynamic ergometer.

• The dynamic ergometer will simulate motion

on water better than the static ergometer.

Equipment

• 1 Ortec Slider Ergometer• 1 Stationary 2 Concept Ergometer• Video Camera• Image Tracking Software (Tracker)• Matlab

Tracker

• Open source

• Tracks motion of points using image recognition algorithms

• Exported Data into csv files

Dynamic Erg with Tracker

Procedure

• Four, one minute pieces on each type of erg

• Two pieces at 20 spm, two at 30 spm

• Approximately even splits for each stroke rate (1:52 for 20 spm, 1:37 for 30 spm)

Results

Results (Cont.)

Results (Cont.)

• Rule of thumb: Static wastes 5 more watts for every beat above 16 spm.

Conclusion

• The dynamic erg is more efficient than the static erg.

• The efficiency gap increases with an increase in stroke rating.

• The efficiency gap has a significant effect on performance.