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88 lines
3.8 KiB
OpenSCAD
88 lines
3.8 KiB
OpenSCAD
//
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// NopSCADlib Copyright Chris Palmer 2018
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// nop.head@gmail.com
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// hydraraptor.blogspot.com
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//
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// This file is part of NopSCADlib.
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//
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// NopSCADlib is free software: you can redistribute it and/or modify it under the terms of the
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// GNU General Public License as published by the Free Software Foundation, either version 3 of
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// the License, or (at your option) any later version.
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//
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// NopSCADlib is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
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// without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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// See the GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License along with NopSCADlib.
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// If not, see <https://www.gnu.org/licenses/>.
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//
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//
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//! Models timing belt running over toothed or smooth pulleys and calculates an accurate length.
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//! Only models 2D paths, so not crossed belt core XY!
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//!
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//! To make the back of the belt run against a smooth pulley on the outside of the loop specify a negative pitch radius.
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//!
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//! By default the path is a closed loop but a gap length and position can be specified to make open loops.
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//! To draw the gap its XY position is specified by ```gap_pos```. ```gap_pos.z``` can be used to specify a rotation if the gap is not at the bottom of the loop.
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//!
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//! Individual teeth are not drawn, instead they are represented by a lighter colour.
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//
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include <../utils/core/core.scad>
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use <../utils/rounded_polygon.scad>
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use <../utils/maths.scad>
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function belt_pitch(type) = type[1]; //! Pitch in mm
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function belt_width(type) = type[2]; //! Width in mm
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function belt_thickness(type) = type[3]; //! Total thickness including teeth
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function belt_tooth_height(type) = type[4]; //! Tooth height
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function belt_pitch_height(type) = type[5] + belt_tooth_height(type); //! Offset of the pitch radius from the tips of the teeth
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function belt_pitch_to_back(type) = belt_thickness(type) - belt_pitch_height(type); //! Offset of the back from the pitch radius
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//
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// We model the belt path at the pitch radius of the pulleys and the pitch line of the belt to get an accurate length.
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// The belt is then drawn by offseting each side from the pitch line.
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//
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module belt(type, points, gap = 0, gap_pos = undef, belt_colour = grey(20), tooth_colour = grey(50)) { //! Draw a belt path given a set of points and pitch radii where the pulleys are. Closed loop unless a gap is specified
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width = belt_width(type);
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pitch = belt_pitch(type);
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thickness = belt_thickness(type);
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part = str(type[0],pitch);
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vitamin(str("belt(", no_point(part), "x", width, ", ", points, arg(gap, 0), arg(gap_pos, undef), "): Belt ", part," x ", width, "mm x ", length, "mm"));
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len = len(points);
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tangents = rounded_polygon_tangents(points);
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length = ceil((rounded_polygon_length(points, tangents) - gap) / pitch) * pitch;
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module shape() rounded_polygon(points, tangents);
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ph = belt_pitch_height(type);
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th = belt_tooth_height(type);
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module gap()
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if(gap)
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translate([gap_pos.x, gap_pos.y])
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rotate(is_undef(gap_pos.z) ? 0 : gap_pos.z)
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translate([0, ph - thickness / 2])
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square([gap, thickness + eps], center = true);
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color(belt_colour)
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linear_extrude(width, center = true)
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difference() {
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offset(-ph + thickness ) shape();
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offset(-ph + th) shape();
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gap();
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}
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color(tooth_colour)
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linear_extrude(width, center = true)
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difference() {
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offset(-ph + th) shape();
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offset(-ph) shape();
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gap();
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}
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}
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function belt_length(points, gap = 0) = rounded_polygon_length(points, rounded_polygon_tangents(points)) - gap; //! Compute belt length given path and optional gap
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