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Unread 24-02-2006, 01:28
sanddrag sanddrag is offline
On to my 16th year in FRC
FRC #0696 (Circuit Breakers)
Team Role: Teacher
 
Join Date: Jul 2002
Rookie Year: 2002
Location: Glendale, CA
Posts: 8,515
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Re: pic: 696 Gearbox Transmission

Ah yes, the 13 tooth gear. Most likely only Travis knows what I'm talking about, but I'll go ahead and say here. We ended up boring out the gear to O size (.316) and broaching in a 3/32 keyway to not quite full depth. So the gear is keyed to a .316 portion of the shaft. The very end of the shaft is turned down to 1/4" Since we already made the plates to fit a .875 OD (.375 ID) bearing, we put the 1/4" end of the shaft in a bronze bushing with .375 OD which rides in the .375 ID. For now, it is working, but we have not extensively tested it. We are in the process of finishing machining for the second robot's drivetrain.

The 13 tooth gear is one of a few things that keep me up at night. It is a tiny little sucker made from not the highest quality materials and it has the potential to undergo considerable stress.

The gearbox has many things that are kind of "on the egde" when it comes to design. For example, the primary reduction gear's teeth are about .025 away from the shifting dog which is spinning in an opposite direction at a much different angular velocity. We have standoffs that are very close to gear teeth. Our ground clearance is extremely low near the wheel. Approximately 3/16" There's quite a few things about it that just plain scare me, but we always overbuild everything, and instinct tells me (and the second set will comfirm) that it'll be okay. There's a lot of stuff that is real close, but it has no means and no reason to move. If it clears now, it will always clear. Anyhow, I don't think two speed dog shifting transmissions come too much smaller or lighter than this.

There is about a 3:1 difference between high and low. And the overall reduction is a bit more than an AndyMark shifter (allowing us to direct drive the wheel).

For getting up the ramp, you'll quickly notice that our wheels do not look capable. But design has speculated and testing has confirmed that indeed they are. Here's the reason why. If you look square on at the face of the wheel, you will not see a good portion of the bottom of the gearbox. In the side view of the robot, the lower portion of the gearbox is completely encapsulated by the wheel. In climbing the ramp at a roughly straight approach, there is no surface that can come into contact with the gearbox because it is in contact with the slighty larger wheel.
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Teacher/Engineer/Machinist - Team 696 Circuit Breakers, 2011 - Present
Mentor/Engineer/Machinist, Team 968 RAWC, 2007-2010
Technical Mentor, Team 696 Circuit Breakers, 2005-2007
Student Mechanical Leader and Driver, Team 696 Circuit Breakers, 2002-2004