# Sign convention for angular velocities in 3D gear train

Consider a Humpage gear train shown above. We are viewing the gear train from right and gear B is rotating in clockwise direction. If we consider clockwise direction as positive what will be the sign conventions of gears D and C. Can you provide a reference for the same.

This is the question for your reference. They have considered the angular velocity of gears D and C positive here.

• I’m voting to close this question because the phrasing looks like a homework exercise.
– NMech
Sep 6, 2021 at 9:18
• Oh. Actual question is quite different. I will give the image of the question in case you need to refer it. Sep 6, 2021 at 9:26
• I think you're reading more into the question than it's asking for. I don't know of any way you can define CW or CCW as being positive or negative. The question just says "200 RPM" without a direction of rotation and asks for an output speed. The answer would be an RPM and whether H is rotating in the same direction as G or opposite. Sep 6, 2021 at 13:14
• Consider the axis gear B is rotating around is the "global axis", on which the CW and CCW are defined. Now, C & D are moving on a different axis which should be considered a "local axis", then the sign convention can be related out by looking at the motions on both sides of the interception point of the global and local axes - they shall agree for simplicity.
– r13
Sep 6, 2021 at 19:42
• My rule is to always assume rotation is mathematically positive defined for math like problems such as this…if it‘s something other than that, it should be specifically mentioned. Sep 7, 2021 at 15:01