Another cyclograph
Another cyclograph. The elastic arched bar is made half the depth at the ends that it is at the middle, and is formed so that its outer edge coincides with a true circular arc when bent to its greatest extent. Three points in the required arc being given, the bar is bent to them by means of the screw, each end being confined to the straight bar by means of a small roller.
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
- Brown's elevation (the instrument lies on the drawing, so no gravity). A straight bar with an upright at each end carrying a small roller, and a screw working in a nut in the bar's middle. The elastic arched bar is 15 short pieces jointed end to end, each joint a spring with the bar's stiffness there; its depth halves from the middle to the ends, and its stiffness grows from the ends to the middle as the bending moment does, so it bends to a true arc. The screw (the one driven joint, 9 rpm) rises in its nut by its threads and pushes up the arch's middle with its head; each end piece is held under its roller. Contact only: threads in the nut, the screw's head under the arch, the ends under the rollers.
- Measured
- The screw rises its pitch (1.6 cm) per turn and carries the arch's middle up with it (both slopes 0.00255 m/rad). The bar bends alike along its length: the joint at its end and the one between bend 1.07 times as fast as the joint near the middle (1.0 for a true arc), and the two halves bend alike (slope -1.0). Penetration stays under 0.4 mm.
- Notes
- The rollers bear on the end pieces' upper edges rather than on separate toes; the joint stiffnesses are set from the rollers' distance so that the arch closes on a circle; Brown's thumb-screw head is drawn as a plain cross-handle.
Film (MP4) · Still (PNG) · Spec (YAML) · Model (MJCF)
