[archiver]

Posted by Patrick Dingle at 05/01/2001 7:56 PM EST


College Student on team #639, Red B^2, from Ithaca High School and Cornell University.


In Reply to: ... the horror... HORROR.... AHHHHH
Posted by Gui Cavalcanti on 04/30/2001 9:35 PM EST:



Steel set screws holding a plastic sprocket to a shaft is a bad idea. if you really are convinced you want to use plastic, you need to find a way to distribute the driving force all the way around the plastic sprocket -- not in one spot. One method you might want to try is using about a 1/8 diameter pin, and machining a 1/8 diameter hole tangent to edge of the shaft. Then you machine a hole through the plastic sprocket such that it lines up with this dent in the shaft. In other words, this is a pin that goes all the way through the sproket and shaft such that it hits the shaft at a tangent. The center of the pin should be exactly tangent to the shaft. You can do this twice on the same sprocket, two parallel tangents on opposite sides of shaft. Unlike the set screw, this will distribute the forces two four spots on the sprocket, instead of one. Additionally they will be compression forces which are generally stronger than set screws.

Patrick

: I'm in no position to speak for my team, me being the programmer and all, but I now officially hate set screws. We have a reaaaaally simple 1:4 gear ratio drive train that propels us at a leisurely pace on treads... and we used set screws on the sprockets that were on the drive shafts. ::uncontrollable shivers::

: We literally snapped 3 plastic sprockets (right down the set screw line, no less) on our shafts before reverting to steel sprockets that were PINNED. No problems as of yet...

: Maybe this was off-topic with sprockets and everything, but still.

: -Gui Cavalcanti
: Team 422, Mech Techs