URDF only support STL and DAE file formats (as far as I know). If you can only find STEP files you can import those into most CAD programs and export it as a STL easily.
Solidworks is the most popular CAD software but it is expensive. If you don't already have access to it, there are some free ones you can try such as FreeCAD.
One small hiccup: if your STEP files don't contain color information then STL will work fine. But STL does not support colors so if your STEP DOES contain color you'll want to use DAE instead of STL, but most CAD packages don't export DAE. Most CAD software WILL export .wrl which can then be imported into Blender and then converted to DAE and color will be maintained.
To summarize:
if STEP file doesn't have color->import STEP into FreeCAD->export as STL
if STEP file does contain color->import STEP into FreeCAD->export as .wrl->import .wrl into Blender->export as DAE
(I know this works with Solidworks, I'm assuming FreeCAD can do it)
Originally posted by Airuno2L with karma: 3460 on 2017-05-22
This answer was ACCEPTED on the original site
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Original comments
Comment by pmuthu2s on 2019-02-05:
When I convert WRL format to DAE format using blender, color is lost. Any clue guys?