Joe, good comments, these are all things we've been discussing and worrying about since we started trying to design the system. It's not an easy thing to build!
Just to clarify on our strategy for using this drivetrain, we do not plan to use the robot in a "suspension" mode for a majority of the match. We intend to lock the rocker mechanism into a "dropped center wheel" mode while driving on flat carpet and switch to the "suspension" mode only when crossing defenses (ideally we'll just be driving straight over defenses, so we won't be dealing with the scrubbing issues while turning like in the video).
With that in mind, here's where we currently stand w/regards to your comments:
1- We were anticipating the flex, but didn't have the resources to to accurately model it... It was faster for us to build this prototype with the components we were planning to use for the final design. The brackets shown are not final, they were made to let us do some testing and find the weak points of the design. The final bracket designs have some modifications based on what we learned, and lots of the high stress locations will be using bolted connections rather than rivets.
2- The frame contact (from the rocker) is something that was hard to work around using the components that we wanted to use. We saved a lot of manufacturing and design time by using Vexpro products, and tried to make the best geometry we could with them, but the dimensions of the wheels/versablocks/idler pulleys made it tricky to offset the wheel axles from the pivot location without making fancier brackets. We are still getting used to our new CNC, so keeping parts simple to speed up production was one of our priorities.
For our first tests of the concept, we literally just drove 39's robot from 2010 over our practice defenses to see how it would perform. It also had contact issues with the suspension members hanging up on the defenses, but it didn't seem to deter it (more importantly, it was still smoother than any other drivetrain concept we had tested at that point, despite the frame members contacting the defenses). It's not very pretty, but it still meets our requirement to cross the defenses in a controlled manner.
3- The torque provided by the belt on the rocker is a neat dilemma. Team 39's 2010 robot was designed so that the rocker mechanism is powered by one gearbox (attached to the rocker) and the trailing wheel is powered by one gearbox (attached to the trailing arm). This gets rid of that issue.... but we had decided pretty early on that two speeds would be pretty necessary for traversing the flat midsection and safe zone of the field quickly while maintaining the ability to push and drive over defenses in a controlled slower gearing.
We opted for the two-speed transmission with power transferred through an idler pulley at each of the suspension joints. Simple calculations showed that it would be able to push over the worst case defenses (with the rocker in front, not so much the other way around). The case we didn't look at was when the robot accelerates on flat ground in high gear, with the rocker at the back of the robot. The added torque on the rocker provided by the drive belt makes it pull some very large wheelies. This is another issue that is resolved by locking the rocker into 6wd dropped center mode.
I will see if we can run the suspension up against a wall in both directions with a scale to see how it reacts, that's a test we haven't done that should be interesting.
4- Shouldn't be an issue when we are locked into the 6wd dropped center mode. We never even tried to put it in high gear with the setup in the video, we knew it wouldn't turn.
