CHAOS 131: Offseason CAD Concepts

I usually spend some time getting mentally ready for the FRC Season by designing something that would push our team’s boundaries. The goal of these designs isn’t necessarily to be a reasonable target for something to do in-season, but instead serve as a though exercise of “Could we actually do that if we REALLY needed to?”. Most of these designs have a limitation that is either tighter than practical or simply silly.

In the past, I have explored making things like:
A shifting 4x 775 Pro drivetrain gearbox using just an Inventables Carvey.
A Chassis that minimizes weight to a silly extent .(Onshape)

This offseason there were two designs. Neither of these is really complete or usable, but there are some ideas in there that may be recycled if the need arises.

The first was an attempt at a Swerve Drive Chassis that fixes some of the issues we experienced last year with the plates bending. This one extends the outer edges of the chassis rails into the corner allowing the corner of the gearbox to be anchored per the WCP recommendations. The other big change is that the bumpers will mount close to the gearbox plates to free up valuable drive rail space. Other iterative improvements include a belly pan that allows the wheel-bolt to be removed without pulling the bumpers off the bot.

The second design was a few takes at a passthrough linear lift, 'cause 'tis the season… I guess. The lift idea was inspired around these bearing blocks from Rev/CPR.

  1. Limit stage clearance to 1/8"
  2. No height loss per stage at the top end
  3. continuous rigging with the rigging hidden “behind” the vertical supports
  4. Have no more than one wrap around the spooling pulleys when extending to max height to make encoder counts “highly deterministic”
  5. Design with enough margin that it could foreseeably do a “buddy climb/alliance lift”
  6. include enough travel that the design would be applicable to any game (2005 anyone?)
  7. Maximize the open space through the center of the carriage.

There was some success here but the rigging leaves a lot to be desired. and there doesn’t appear to be a graceful way to integrate counter-balance springs into the structure. They either ended up being too big in diameter or too short to go at the top of the stages. There was an idea about wrapping them backwards around the drive shaft but that left all of the load in the rope and didn’t seem ideal. Combined with the fact that the slider stages required two machining ops and this concept seemed like it might be worth leaving for someone else to pursue.

Iteration 2 of the lift sacrifices stage clearance for manufacturing ease and follows the design language that we have been using for linear slides from 2019 and 2020. This version swaps the bushings for needle roller bearing in an attempt to improve efficiency. This design is based around a single thick plate and integrates configurable counterbalance springs and crossbar brace. The weight it a bit higher than the other option, but this is probably a more field-ready design.
Open todo items:

  1. Add rigging. This could use the holes that were included for redundant capture bearings on the bottom of the slider modules
  2. Move the counterbalance springs to the inside of the lift rather than the outside. This would simplify their attachment to the next stage
  3. Possibly switch to or include brackets for the stage corners
  4. Add soft-stops (bumpers) to the extents of travel
  5. Add the drive system. This probably looks similar to the V1 Drive system.

A final note:
There are a few lazy modeling techniques in here and some that I would highly recommend. please use an analytical eye if you are trying to duplicate something.

Feel free to comment on the design or leave feedback!

Also, to everyone who is contributing to the Open Alliance, Hats off to you! This post was already more blogging then I have in me. :face_exhaling:

Happy Kickoff!


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