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Originally Posted by Matt Adams
Secondly, having a tranmsission that you can easily modify is very ideal. For example: don't weld gears to shafts! If something strips or breaks, you'll have to replace the entire shaft. Bad news, especially if there are multiple gears on the same shaft! Not only obnoxious, but time consuming and expensive.
Matt
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Our team actually takes the opposite approach to this, we try to weld anything that we can but we start with robust materials that are highly unlikely to break. Welding the gears to the shaft after everything is the way you want it takes one more failure point out of the equations (Assuming you have someone who is excellent at welding versus other options such as set screws, pins etc) Again this past year in debug of the Team45 transmission it was a hare narrow and ended up being in high & low at the same time in a high power shift. This immediately locked up the transmission and send a shockwave through the gears, shearing the pinion off the drill motor, all other welded gears were unharmed and lasted the entire year and are still going strong. As stated above, many people use gears that are more than up to the task of anything the FIRST robot can throw at them. Personally, I like 20 pitch gears that have been lightened to an extreme amount, the teeth show little if any wear after a season. Since the drivetrain is arguably the most important part of the robot (Manipulation can be useless if you robot is stranded on the wrong end of the field) I try to have the team place a priority in power, modularity, and robustness there.
As for replacing a broken shaft, it should be a rule of thumb that you make a spare of anything that is custom and has a chance of failing. For transmissions I would strongly recommend making one that is similar left to right and fabricate a spare at the same time as you are fabricating the mains.