A mode of obtaining an egg-shaped elliptical movement

Only the input is driven; every other part of this model moves by physics (MuJoCo), and its ratios are measured. Run it live, change its parameters, or switch the friction off to see the output stop.

Modelled as

A crank (4 cm radius, the one driven joint, 20 rpm) carries one end of a 22 cm bar on its pin. The bar slides between the two walls of a swivel block pinned to the frame 18.5 cm away (real contact, 0.02 cm clearance). A ring 5.5 cm along the bar from the crank pin traces the dashed egg, 8.0 x 5.7 cm. No gravity. gen172.py.

Measured

The block follows the crank at +0.177 / +0.122 / -0.272 rad/rad in three windows, the bar on the pin at -1.09 / -1.27 / -1.10 rad/rad (r2 above 0.99); the bar swings from -3.5 to +21.5 degrees. Penetration 0.

Notes

Reading of the figure: the bar is jointed to the crank-pin and slides through a swivel block on the frame, and the ring on the bar is the tracing point. Walls 6 cm long hold the bar to within 0.4 degrees of the block line.

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