After sketching many different ideas and keeping in mind that adding degrees of freedom would add complexity and possibly require more motors or servos (ex: arm mechanism), we decided to go for a rotating flap to pick up the cans.
Looking at the previous year's competition, we knew this picking mechanism was great when combined with blind navigation (no can detection sensor). Considering the limited amount of time we had to build, we decided to compromise precision in can detection for robustness, efficiency and consistency in our robot. We thought storing more than 2 cans vertically while driving would still put us in a great position for competition.
First design, CAD by Alexandre Kneifel:
- Cans are vertical while driving (1 point for each). 4 holsters.
- Simple pick-up mechanism which does not require any can detection sensor (optimized tape following only).
- Large area covered with the front angled side arms.
- Backward parking manoeuver required for cans drop off.
- Longer than the allowable 2ft for competition.
- Very large robot (large dead angles during turns and higher polar moment of inertia for driving).
Explore different pick-up mechanism ideas and a side orientation slope instead to fit within the dimension requirement.
CAD by Braden Church:
- Fits the 2' x 2' dimension requirement.
- Keeping the simple pick-up mechanism.
- Possibility to keep the 4 holsters.
- No backward parking needed for cans drop-off.
- Still very large.
- Smaller area covered by the front angled side arms due to their new placement. By touching the box for cans drop-off, we could not extend the side arm past the holsters support wall.
Challenges faced during building
To be able to drop the cans in a 4" high box, our ramp needed to be quite high. Without a high ramp, the orientation slope just before the holsters would not have been steep enough and the cans would not have had enough speed to reach the different holsters (confirmed by prototype testing).
Because we were provided with cheap and low torque small motors, bringing the cans up the ramp without having a flap that would go over the 2ft dimension requirement was a real challenge. We spent many hours optimizing our flap.
We prototyped different variations and the one I used on Angel seemed to work best. It was a combination of a softer side to prevent cans from blocking at the entry and a shorter but stiffer side to push cans up with more force.
When not reaching the plateforme quickly, the cans were often propulsed back towards the front, outside of the robot. The two little angled roofs helped resolve this issue.
Due to time constraints, dimension limits and the space the wheel was taking on the side of our chassis during drop-off when touching the box, we chose to only have 3 holsters instead of 4 like initially planned.
Even though we were loosing the possibility to have 3 more points during competition, this desicion saved us a lot of time and allowed us to have a robust orientation system. We only needed a very simple orientation arm connected to a servo. It ended up working great and consistently.
Main learnings/takeaways from this project
- Planning and debugging circuits efficiently.
- Soldering electrical components on PCBs.
- Understanding when to use what type of battery.
- Preventing noise issues.
- Taking more time to plan properly (dimensions, part placement, chosen design...) ends up saving lots of time during building.
- When possible, it is nice to have parts temporarily fixed to test them before glueing permanently.
- Prototyping (virtual or physical) is so helpful to guide design choices.
- Great collaboration & clear communication leads to better design ideas.