VEXpro Dog Geometry Questions

[Jared]

When I've done dog shifting mechanisms before, I've set up the gear and the pocket so that when the side of dog touches the side of the pocket, the two faces are parallel.

Vex's CAD seems to be different. The side of their dog isn't parallel to the side of the gear's pocket, so the dog only transmits torque through one edge.

See the gap highlighted in yellow in this section view:
http://imgur.com/17hgx7y

Is this really how vex pro shifting dogs work?

[asid61]

That's odd. It could just be a CAD error made to show the limits of the machining tolerances.
Some of my older cad models of wheels and gearboxes don't quite line up versakeys, for example. They're off by like 0.001".

[R.C.]

I'll take a look to see what we did, been using the same setup of dog/dog gear combo since 2011.

I'll post back with more info sometime this week when I get a chance

-RC

[Jared]

Originally Posted by asid61

That's odd. It could just be a CAD error made to show the limits of the machining tolerances.
Some of my older cad models of wheels and gearboxes don't quite line up versakeys, for example. They're off by like 0.001".

Vex's CAD models often include the actual clearances for parts, and I'm used to seeing these 0.001" or so gaps, but this is more significant.

I think that it could be a simple mistake in the modeling of the dog. I see no reason why this mismatched angle setup is any better than the typical approach, but I could be missing something.

[Jared]

Sorry to double post, but does anybody know if the error is with the dog model, or the gear model? We plan to use a vex pro dog with a custom dog gear, and we aren't sure what the actual pattern is.

If the side surface of the dog pocket (where the torque is transmitted) is extended, it goes through the center of the gear. On the dog, this is not the case, and the side of the dog doesn't lie on a diameter. When they hit each other in the CAD model, they only contact along one edge.

[R.C.]

Email me here.

I forgot to check last week and headed out of town atm. This way I remember to check when I get back.

Thanks