Virtual radius wheel (r = 4R ).  Square wheel. related Chebyshev Linkage (quasi-straight line).[br][br]Detailed explanation is described in [url=http://www5d.biglobe.ne.jp/~the_imai/etymology/Musashikoganei.html#Cassini_square]"[b]Cassini Wheel[/b]"[/url] .[br][br][color=#38761d][b]If this wheel edge were bigger than stair step, it's easy to climbing stairs (?).[/b][/color][br][br][b]■ about Planet orbit[/b][br]In this figure, If A were the earth, C were the moon, C rounds by θ speed, and C self-spins [= CC' round] by average θ/2 speed. i.e. θ : θ/2.[br][br][url=https://www.geogebra.org/m/UCkxPd6W]Reuleaux triangle approximation system[/url] is θ : θ/3 speed. [in this case, θ/3 is not average speed, is exact speed.][br][br][b]Tip:[/b] Reuleaux triangle Wheel was 2R virtual radius system, but this Cassini is 4R virtual radius system.[br]Reuleaux body was rigid, but this Cassini is amorphous body.[br][br][b]■ Is this a constant velocity?[/b][br]Please tell me.[br][br]■ 360゜: circle → 2π r ≒ 6r, square → 8r; [b]So, 4/3=1.33 times longer edge length.[/b] [br][br][b]■ Hybrid Reuleaux triangle[/b] ---- added on 2016/12/09[br]4 corners should be replaced by Reuleaux triangle corners. Corner's curve becomes more flat (i.e. 2R curve).[br]i.e. [b]blue is 4R arc, purple is 2R arc.[/b]