This basket-with-cover was designed for the FTC 2021-2022 Season (Freight Frenzy) to transport the cubes and balls picked up by the robot onto their destination platters of the Shipping Hubs, being attached to a telescopic arm. At the bottom of the page you can find a link to download the SolidWorks files for it.
One of our constraints was the reduced enclosing box — it had to fit inside the robot in a fairly narrow space, at the end of an internal hopper which was lifting the pieces once they were swept inside, with a rotating brush,and in between various internal rails and backbone structures.
It had to be able to receive the pieces from the side, accommodating both a cube or a larger sphere, securely hold onto them during transport, and reliably deliver them onto the Shipping Hub.
Another constraint was sturdiness, as the telescoping arm was moving very fast, with high accelerations.
Hence, after settling on the main idea of a parallelipipedic box we played with the shape of the “front teeth” for several iterations, using splines. The loading of the piece occuring at high speed as well, we had to minimize the bouncing around of the cube or sphere, while ensuring it would stay inside the basked as the cover-teeth was closing on it. The hole in the cover was made to better secure the sphere. For the same reason, the basked floor has a central depression.
For the delivery part, we had tried variants of a “trap-door” in the floor, which would let the piece fall down. However, it turned out difficult to control its opening, having had only a somewhat fragile lever, controlled by the opening and closing of the cover. We settled on a fixed solid floor, after also trying grooves or openings.
The back wall of the mobile cover-teeth, angled at 45 degrees, helps pushing the piece out when the cover opens.
We also did try tilting the basket, but it turned out too complicated to properly control, while also solidly attaching it to the telescopic arm sliding segments. Already, these segments had some twisting play, adding to the positioning error at the end of the long arm when fully extended.
For space economy considerations, we mounted the servo on the cover itself, thus on the mobile part, instead of the more natural choice of mounting it on the fixed wall-and-floor parts. The cover spins around one small axle fixed to the pillar and around the servo axle itself. The servo and cover being very light, there is very little transversal load on these axles. The vertical wall has an indentation shaped exactly as the negative of the servo standard attachment cross, which is thus simply sunk in the wall, and affixed with the appropriate screw from the other side.
This was done in SolidWorks after measuring the attachment cross with calipers, and we reinforced the top part on the back side, which also has the raised part with the holes to affix the basket to the telescopic arms, to have room for the cross, while not requiring a thick wall overall.
To finalize the dimensions, we first printed a shallow version of only the imprint, to adjust the exact numbers and to make sure the cross fits.
For the servo mounting shape, we had to solve a compromise between a secure mounting, mechanically solid, and not using too much material, in order to avoid too much weight, since the basket is at the end of a telescopic arm. So we picked a half-hugging shape, which has the servo partially sunk in, preventing it from moving in any direction except vertically, and then securing it with one screw on one of its mounting “ears”.
We had to carefully measure the servo dimensions with calipers, and then shape the top of the basket cover accordingly, reinforcing it right under the place of the servo.
Another very useful feature of SolidWorks is the ability to simulate to some degree what would be happening in reality once the parts are 3D-printed and assembled. As, thankfully, we can find the STEP files for FTC game parts online, we have downloaded the ones for the cube and sphere, and created an assembly with the basket and with them, which then we have moved around to see as best as possible how they would fit. This allowed us to fine tune the shape of the front teeth of the cover, the shape of the side of the arc, the placement of the top hole and the bottom indentation.
By clicking on BasketOnSlide you can download a zip archive with the SolidWorks files and the overall assembly.