Design and CAD
On Monday we split off a small Design and CAD team to prepare some “Crayola CAD” concepts.
Climber
Given that climbing is one of the hardest tasks, and will require a lot of space on the robot, we looked at the climber geometry in Onshape.
- The climber needs hooks that can raise up to ~4 ft (to climb on the sides of the chain), and lower to ~1 ft (to get the Trap mech up to the Trap).
- The robot CG should be between the hooks and the Stage Core so that it tends to tip towards the Core (after the bracing tower is extended)
- The climber needs a bracing tower with wheels that can roll up the wall of the Stage Core and support the robot from tipping when climbing. The chain will angle back to counter the pushing force from the tower, but they should balance without too much angle.
- The top of tower should carry the Trap mechanism to max height. Even then, we only get a few inches above the bottom of the trap door, so trap mech needs to be small.
- Ideally the hooks face towards the Stage to catch the chain as we drive in so we don’t have to place ourselves perfectly between the chain and the Core before climbing. The challenge is that chain can swing towards the core, leaving very little room to deploy the bracing tower.
- Another challenge is that chain needs to be pulled down as low as possible (right to the bumper), so the chain “path” has to cut right through the middle of the superstructure.
- A solution might be to have the CG location (relative to the hooks) change as the robot climbs so that the hooks pull the chain around the superstructure, and the robot tilts away from the core until the trap mech and tower are deployed, and then tilts back towards the Core. We’re still working on how that might work.
Gamepiece Manipulators (Shooter, Intake and Trap Mech)
Next we looked at our options for manipulating the game pieces. Decided there were at least two choices to make:
- We have a requirement to intake gamepieces from the floor. But do we do that over the bumper, or under the bumper?
- We have a requirement to score in the Amp and Trap. What mechanism do we use for that? The shooter, the intake, or a dedicated mechanism?
Those choices gave us a grid of 6 potential robot architectures. We looked at what a robot might look like for each cell in the grid, what advantages and challenges each might have.
| Under Bumper Intake | Over Bumper Intake | |
|---|---|---|
| Intake does Trap | Impractical. Robot would have to rotate to present bottom of bumper to Amp/Trap | Intake needs to lift to Trap height, as well as reaching over bumper so it needs 2 degrees of freedom |
| Shooter does Trap | Shooter needs a “cowl” to redirect the shot downward when scoring amp/trap. | Shooter needs 2DOF mechanism to lift from 2ft under-stage limit to 4’ trap height |
| Separate Trap Mech | Need two handoffs between intake and amp/trap mech. Could be a feeder switch, or shooter does the passing. Trap mech needs to elevate from 2’ tall max to 4’ tall max. | Same as left, but with a separate intake that pivots over the bumper. Intake could have separate handoff positions for each mech. Same intake disadvantages as above. |
The advantages of under bumper intakes are they’re faster to deploy, more damage proof in a collision, and might be able to intake from more than one direction. The disadvantages are that it is less “modular” for future upgrades, and may not have as wide a catch area if the game piece has to pass between the swerve wheels. On the whole though, the team decided the advantages outweighed the disadvantages. That left us with only two preferred architectures, which greatly reduces our solution space:
- Under Bumper Intake, Separate Trap Mech
- Under Bumper Intake, Shooter does Trap.
With that choice made, we split the CAD team into two groups to mock up our two preferred architectures using KrayonCAD (which is awesome btw @Nick.kremer). The sketches below aren’t anywhere near to final designs, they’re just a first attempt to communicate what each robot might look like, to help us identify any particular advantages or challenges. Each subsystem might end up looking completely different to what’s shown.
At the end of Friday’s meeting we conducted a “Conceptual Design Review” (CDR). Both design groups presented their concept to the full Celt-X team. This was a super fun moment, which took significant presentation and listening skill. We’re very proud of these students!
CX24 Robot Concept 1 Presentation.pdf (455.1 KB)
CX24 Robot Concept 2 Presentation.pdf (641.1 KB)
The team asked a lot of good questions, and they identified advantages and challenges of each concept:
| Advantages | Challenges | |
|---|---|---|
| 1) Separate Shooter and Amp/Trap Mech | More modular, with separate mechanisms for separate jobs. More stable shooter (since it doesn’t lift) | Climber needs 2DOF to move CG during climb. Extra mech might be heavier. Requires a feeder “switch” or a double-handoff. Handoff must be reversible so drivers can score either location quickly. |
| 2) Shooter does Trap | Might only need intake to shooter handoff. Shooter lifts out of the way of the climber hooks, can be used to shift CG during climb. Shooter lift axis could help take shots from a less defendable angle. Could be a candidate for “creativity award”. | More complex, heavier multi-function shooter Less stable base for accurate shots (Could be mitigated by having the lift axis be latched most of the match, and released for the climb only, but that would be a risky “one shot” mechanism.) |
Both concepts appear to have the potential to meet all of our design requirements, which is nice! The team identified several challenges that are common for both concepts:
- How will the under bumper intake package? Can it intake from the opposite end of the shooter for a pass-through? Can it intake from both ends maybe? Can it intake from all four sides maybe?
- Will the mechanisms interfere with each other once we give them more reasonable dimensions? Will the CG be balanced, or all on one side?
- How will intake interact with Swerve modules - can gamepiece get trapped under the robot?
- Where will the cameras mount? We need two cameras - one for april tags (looking in scoring direction at ~5ft elevation), and one for gamepieces (looking in intake direction at floor in front of bumper). Those will look in opposite directions for a pass-through shooter.
- Where will electronics mount (especially if under-bumper intake takes the traditions 5406 location)?
- What is the chassis size and design? We need to finalize that immediately to keep on AlphaBot schedule. That’s tough to do right now without all the answers for how the under-bumper intake and handoff will work
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We’ll try to answer those questions, and choose a preferred concept to develop further in the next meeting or two. Stay tuned!