pic: 2012 frc971 transmission

[Nuttyman54]

Originally Posted by MICHAELABICK

I'm wondering if you think that you would run this drivetrain again considering the following:

...

Out of all of these things there are a few pretty nice benefits(that still outweigh, at least imo, any negatives associated with them): less machining and less maintenance.

However you lost some one of the most important benefits of a classic WCD to me: the prototype with old drivetrain parts without keeping a large stock of parts(ie belts).

Did you think the trade off was worth it? Do you think for next years you would go with a more conventional belt drive, or maybe even a classic WCD?

I'll try to answer all this as best I can. Adam pointed out that we don't actually have an extra stage, we just moved the second stage external to the gearbox and onto the center wheel in a dead-axle setup, which in itself gives us some nice benefits as Roy mentioned.

One thing to keep in mind when you look at 971's designs and design choices with this drivetrain is that it is the result of many years of iteration, and we spent a lot of time trying to make it an integrated package with the team. Our decisions were not based solely on mechanical benefits, because we have some really great software mentors and have developed a driving style along with the physical robots over the years. This robot is the result of designing not just for the game, but for the team that would be using it, and playing to our own strengths. A lot of the tradeoffs and decisions make more sense in that context, such as the outboard motor effect on rotational inertia discussion above. Because we know that our drive style and code mitigates this factor, it benefits us more than it might some other team.

The team would definitely do this drivetrain again. It performed fantastically and we never really had any problems with it that I can remember. It was light, efficient and very easy to maintain.

It's also worth noting that 971 has not done a WCD since 2007. One of the hallmarks of WCD, and what makes it so easy to prototype on old drivetrains is the cantilevered setup and open layout which allows standard parts and easy swapping. In general, sheet metal construction encourages a more integrated approach to achieve an efficient design, but that makes it not great for prototyping. So in that regard, we don't consider it a "loss" because WCD has not been in consideration since the design didn't play to our fabrication strengths.

The 2012 design is the result of many years of various drivetrain iterations and innovations. Each is unique because of the game challenge, but there is a clear progression of eliminating problems while trying to maintain the improvements. One of the big driving forces behind the changes this year was the maintenance. On a traditional WCD, the cantilevered wheels are very easy to access and replace tread on because they are outboard of the frame. Due to our sheet-metal fabrication, cantilevered is not an optimal design so we switched to the dead-axle setup to allow drop-out wheels.

I'm not entirely sure what you mean by "conventional" belt drive, but we found this setup to be a nearly perfect driveline for us this year. We began working belts into our designs in 2011, with the elevator and roller claw both being belt-powered. Our experience with that gave us enough confidence to want to use it on the drive, and our experience this year means we will probably continue. As far as classic WCD, as long as 971 is building with sheet metal, I doubt we will ever run a "classic" WCD. It is far better suited to box tube construction techniques like 254, 1868 and 1323 use, and really isn't a good use of sheet metal resources. I don't think that our design is any better or worse performing than an equivalently designed WCD, but for 971 it's the right choice.