Revision as of 05:56, 20 October 2017

How to Design a Sprocket for Bulldozer Drive

The sprocket generator in OpenSCAD creates a proportionally correct sprocket.
How do we know how to scale it to match our specific case?
We first design the track. We settled on pin spacing of 3", and XXH 1.5" pipe (see Pipe Chart) for the roller, with 1" pins. Thus: roller = 1.9", pitch = 3". Ratio of 3/1.9=1.58. Ratio of pitch to the roller is constant.
Then we generate the sprocket:

Number of teeth
Roller (5 units)
Pitch - 1.58x the roller size as determined by our track geometry (looks sensible, and 3" pitch was selected as a convenient distance, and 1.9" OD roller was selected as a readily-available stock material
Thickness - that is the thickness of the plate material
Tolerance - play in the distance between rollers (pitch)?

Hint: The bulldozer from 2015 used an 8 tooth sprocket, generated with sprocket(8,5,7.5,2,0.2); in the last line of the Editor

Note: stock Export DXF does not work for 3D files - they need to be projected first.

To project - projection(cut=false) import("sprocket.stl"); STL file must exist in same directory

Sample file for exercise in OpenSCAD - the sprocket STL and the .scad file that loads the STL and does a 2D projection. Note that the directory must be correct. File:Sprocketexample.zip
Note: original srocket was generated using Parametric Sprocket Generator using sprocket(12,5,7.5,8,0.2);

Sprocket geometry for a correct sprocket pitch and roller diameter - example - File:Sprocketgeo.dxf

@@ Line 4: / Line 4: @@
 *The sprocket generator in OpenSCAD creates a proportionally correct sprocket.
 *How do we know how to scale it to match our specific case?
-*We note that the pin spacing on our track is 3"
+*We first design the track. We settled on pin spacing of 3", and XXH 1.5" pipe (see [[Pipe Chart]]) for the roller, with 1" pins. Thus: roller = 1.9", pitch = 3". Ratio of 3/1.9=1.58. Ratio of pitch to the roller is constant.
-*We note that the roller OD is 2.2"
+*Then we generate the sprocket:
-*The parameters we have control of are:
+:*Number of teeth
-:*the number of teeth,
+:*Roller (5 units)
-:*spacing between the rollers
+:*Pitch - 1.58x the roller size as determined by our track geometry (looks sensible, and 3" pitch was selected as a convenient distance, and 1.9" OD roller was selected as a readily-available stock material
+:*Thickness - that is the thickness of the plate material
+:*Tolerance - play in the distance between rollers (pitch)?
 =Bulldozer 2015 Usage=
 {{Hint|The bulldozer from 2015 used an 8 tooth sprocket, generated with sprocket(8,5,7.5,2,0.2); in the last line of the Editor}}