pic: Quick-Change Chassis 2

[Kevin Thorp]

Originally Posted by Rick

I hope this is a joke because isn't this the dream? A reliable drive train?

I would be looking at iterations of your previous (low maintenance) drivetrain, not designing something that is less robust so your pit crew has something to do.

Yes, I assumed our pit crew chief was joking. He loves to build & repair stuff, but he knows broken bots don't win.

Worm gearboxes are not as "forgiving" as traditional spur gear drives, but we've had 3 years of failure-free use out of these Nordex drives. Interesting development: We can now back drive some of the older units a bit.

I don't know if we'll use these gearboxes in 2017. Depends on the game & what strategy the team decides on.

Great discussion points here on CD!

[Ari423]

Originally Posted by Kevin Thorp

Yes, I assumed our pit crew chief was joking. He loves to build & repair stuff, but he knows broken bots don't win.

Worm gearboxes are not as "forgiving" as traditional spur gear drives, but we've had 3 years of failure-free use out of these Nordex drives. Interesting development: We can now back drive some of the older units a bit.

I don't know if we'll use these gearboxes in 2017. Depends on the game & what strategy the team decides on.

Great discussion points here on CD!

I'd be interested to know what size/kind of wheels you have used with the worm gearboxes and haven't had an issue with backdriving. Especially in 2014, which was basically one big pushing match in many regionals, I am surprised you haven't run into issues with the gearboxes breaking.

Also, the fact that some of your older gearboxes became backdriveable worries me. That means that either your worms or worm gears (or both) are wearing to the point that they have changed shape. I can only imagine that that means the gearboxes are less efficient. I wouldn't be surprised if this effects auto modes as the gearboxes wear throughout the season.

[cbale2000]

Originally Posted by Kevin Thorp

Worm gear efficiency is largely determined by the ratio. Yes, a high ratio (100:1) worm gear drive might be only 50% efficient, but at 10:1 they are 85-90%. Design World Article

True, which is why I said "as low as", but even at the high-end of that efficiency curve, at 90% efficiency you still have a less efficient drive system than virtually any other machine on the field, and that efficiency curve drops off fast if you opt to gear any slower.

The gearing on a worm drive is kind of a catch 22, if you gear high you loose torque and stall your drive motors in a pushing match, but if you gear low you loose efficiency and probably still stall your drive motors in a pushing match since you're fighting the other robot plus the added friction in the gearbox.

Originally Posted by Rick

I hope this is a joke because isn't this the dream? A reliable drive train?

I would be looking at iterations of your previous (low maintenance) drivetrain, not designing something that is less robust so your pit crew has something to do.

Not counting 2015 (we don't talk about 2015 ) our last two drive systems have been extremely reliable, so it's definitely not just a dream. The only maintenance we've had to do was replace wheel tread about once per event due to wear. Needless to say our pit crew was also quite board most of the time as a result. Both robots are iterations of the same design, so, when possible, I definitely recommend iterating on what works.

[Cothron Theiss]

Originally Posted by cbale2000

...at 90% efficiency you still have a less efficient drive system than virtually any other machine on the field...

I don't think that's accurate. I'd say if we actually hooked up everyone's robots to a dyno and tested their actual drivetrain efficiency, there would not be many with greater than 90% efficiency. I'm not saying worm gearboxes aren't less efficient than spur gearboxes, but 90% efficiency is nothing to complain about. I've always been impressed with Category 5's drivetrains in the past, so if they say it works well for them, I'm liable to believe them. Though I do agree with what someone said earlier (and maybe in another thread) about attaching the modules from the bottom, not the top of the frame rails.

[Kevin Thorp]

Originally Posted by Ari423

I'd be interested to know what size/kind of wheels you have used with the worm gearboxes and haven't had an issue with backdriving. Especially in 2014, which was basically one big pushing match in many regionals, I am surprised you haven't run into issues with the gearboxes breaking.

Also, the fact that some of your older gearboxes became backdriveable worries me. That means that either your worms or worm gears (or both) are wearing to the point that they have changed shape. I can only imagine that that means the gearboxes are less efficient. I wouldn't be surprised if this effects auto modes as the gearboxes wear throughout the season.

There are 2 threads discussing this gearbox/chassis concept. I described our wheels in the other thread: https://www.chiefdelphi.com/forums/showthread.php?t=152912

Maybe "in theory" right angle worm gearboxes are not the best choice, but in reality they've worked very well for Team 3489, including helping us win the Motorola Quality Award at Smoky Mountain in 2014.