Robot Design Update
Woohoo it’s CAD!!
Design members have been hard at work and finished up CADing and reviewing the robot. Bar some prototyping for the Gripper which may change some distances, we now have a good idea of what our robot for this year will look like!
We ultimately decided to split our robot into four different subsystems: Drivetrain, Ground Intake, Lift, and Gripper. Overviews and design decisions for each subsystem can be found below
For the Drivetrain, we used a similar design to our 2022 robot with MK4i swerve modules and a 28.5” x 28.5” frame. Last year, we really enjoyed having a brainpan to maintain clean wiring and having an easy way to access the electronics. We were initially going to use a brainpan to mount electronics this year too, but due to our Ground Intake and Lift mounting needing a lot of cutouts on the brainpan, it was difficult for us to maintain sufficient space to mount electronics and wire effectively. Having good electronics placement (such as reducing the distance of the PDH → Main Breaker and PDH → SB120 path as much as possible to reduce the resistance in our system, see CD post here) was a top priority for us this year. Therefore, the brainpan became a less desirable option. Soon after, we switched to bellypan as we realized that it would not be terrible given the open space we have on our robot this year, it would also give us enough space to mount our electronics where we wanted.
To protect our electronics, we have velcroed-on polycarb plates which cover the open areas on our robot. These are also raised to be slightly above the bumpers so that game pieces would not get stuck in our robot.
One mistake we made this year was not finalizing the bellypan fast enough. Since we do not have the manufacturing capabilities to mill the large bellypan, we usually get our bellypans done through SendCutSend. We’ve been very satisfied with their work, but it is one of the first things we prioritize because of the time it takes to ship. However, given the switching from brainpan to bellypan as well as the desire to perfect electronics placement/making sure that things didn’t clip or interfere with anything, we ordered the bellypan later than we would have liked, which blocked our goal of getting the drivetrain wired early.
Our bellypan, finally here!
We went with a bumper cutout this season in order to accommodate how the Ground Intake intakes CUBES. This cutout is only for the bumper as we deemed a frame cutout to be unnecessary; we did not like how it affected the structural integrity of the drivetrain frame and where the center of gravity would be placed.
Going along with the theme of clean wiring, we added numerous grommet holes in the Lift mounting rails, as well as other places on our robot to allow for electronics in the bellypan to be wired easily.
On the corner of our swerve modules, we took inspiration from Spectrum and printed out 3DP corner pieces to push our frame perimeter out by 1/4” on each side. This allowed us to move our bumper mounting plates out of the corner, making them a lot smaller.
For the Ground Intake, we decided to use a motor-powered pivoting roller system with 4” mecanum wheels. This only intakes CUBES from the ground, as we decided intaking CONES was not worth the extra complexity. Although we do have a Gripper to intake both CUBES and CONES, we thought that a handoff system would speed up our CUBE cycles by a significant amount.
Our decision to use rollers instead of a gripper to intake CUBES off the ground was based on the logic of “touch it own it.” With this full-width intake, we are able to run into and intake CUBES without needing to precisely align with it.
The Ground Intake was one of the first things we prototyped, and we actually had a different original design. This design utilized two rollers: a set of 2” mecanum wheels and 2” compliant wheels to center and bring the CUBE into the middle of the robot’s frame. Aluminum tubing was used to ensure the intake was structurally sound because its planned resting state during the match was against the bumpers. However, after prototyping the position and CUBE movement with this design, we realized that the geometry of the two rollers was barely able to intake the CUBE. We iterated on this design, and after successful prototypes with the 4” mecanum wheels, decided on what we currently have.
In order to center the CUBES into an easily accessible position for the gripper to pick up, prototyping found that 4” mecanum and Thrifty Squish Wheels would work to center the CUBES into the bumper cutout.
The actuation of the ground intake is powered by a NEO Brushless motor on the right side of the robot, with a hex shaft spanning the robot to connect to the left. The NEO was geared with a 44:1 reduction, providing us with enough torque to lift the intake with only one motor.
The final stage of reduction is done through a 16T RT25 pulley belted to a 32T RT25 pulley on a dead axle. Originally, we had the pivot done with chain and sprocket, but we didn’t want to deal with chain tensioning or the extra weight. We hope that the belt and pulley will hold up to the torque, but if it doesn’t, the RT25 system was used so that we can just swap it out with #25 chain. The pulley is screwed directly to the arm, so as the pulley rotates, the arm will too.
The rollers at the end are powered by another NEO, mounted directly on the left intake arm. We originally had this NEO on the gearbox plate with a double pulley on the dead axle. However, due to concerns over 3D-printed spacers under the double pulley melting due to fast speeds, we decided that mounting it directly onto the arm would be the simplest solution.
We are also trying out 3D printing these bearing retention hats to retain our bearings and make sure that they don’t pop out on the polycarb intake plate.
For the lift mechanism, we decided on using a tilted elevator to minimize arm extension length. We took heavy inspiration from 125’s 2018 design. We opted for a continuous design over a cascading elevator because we wanted to save weight through 3DP and belts as opposed to chain.
Since we pre-purchased a thrifty elevator kit, we wanted to use things we got from it even though we were opting for a continuous elevator. Both the base and the first stage of the elevator are similar to the original thrifty elevator, using the thrifty elevator bearing blocks.
For our carriage, we decided to mill our own plates and have standoffs in between the plates. The design of the carriage is very similar to 125’s carriage, but instead of 3D printing it, we milled a 0.25” aluminum plate. The 3DP carriage was a cool idea that would have saved weight, but we were concerned about its rigidity. Since it had to hold a mechanism with a linear extension at a tilted angle, we thought it was better safe than sorry and traded some extra weight for more rigidity.
For the left-right constraining bearings on the carriage, we half-pocketed enough space to fit an aluminum dowel pin with bearings on it (similar to 125’s carriage). An important thing to note is the “dogbone” corner relief, which we did because our CNC’s 4mm endmill would not be able to cut the corners needed to fit the dowel pin.
For the front-back constraining bearings, we used 1/2” 10-32 shoulder screws with a 3DP spacer to stop the bearing from moving. We plan on tapping the plate for 10-32 screws so that the shoulder screw can directly screw into the plate. We want to do this on the CNC to ensure that we tap the hole completely perpendicular to the plate. The holes for the shoulder screw are half-pocketed so that a portion of the shoulder part of the screw can rest inside the plate. If the elevator ever takes a hit, the shoulder screw wouldn’t be taking all the force and instead the carriage plate would take some of it.
We have 2 NEO motors with a 2.08 reduction (see reca.lc). We are using RT25 belts and pulleys just incase we may need to switch to chain, where we can just swap them for chain and sprocket without having to change center distance.
Similar to 125’s rigging, we have inline 3DP pulley blocks to allow for a 20mm wide HTD 5mm pitch timing belt to run through them. They are attached to the tube through screws that go through the tube and 3dp block. We also have an idler near the driving pulley to make sure that enough teeth are contacting the driving pulley that the belt won’t skip teeth.
We plan to drill a hole through and tap a 1/2” hex shaft for #4-40 screws to fasten the end of the belt to the shaft. For tensioning, we have a ratcheting system using a ratcheting wrench so that we can hand-tighten the system.
Originally, we were planning on using an energy cable, but we couldn’t get it to fit properly without interfering with other things on our robot. Instead, we are using a polycarbonate sheet that holds the wires on the inside and attaches to the carriage. As the carriage goes up, the polycarbonate sheet will bend up with it so the wires move up and down.
For the Gripper design, we took inspiration from team 3847, Spectrum. We aimed for a lightweight manipulator that attaches to our tilted elevator carriage. This would be able to intake CUBES and CONES from the human player station as well as extend outwards to grab CUBES from the Ground Intake in one mechanism. We are still prototyping the roller distances and will iterate based on what mechanical finds to work the best.
We are using a set of three 2” rollers connected by belts with the motor connecting to the middle roller which then connects to both of the other rollers through infinity belts to ensure that the rollers run in opposite directions. The motor in this case is a Neo 550, mounted far back, also for weight-saving purposes, attached to an UltraPlanetary gearbox for a 3:1 reduction.
For all of the rollers, we are using tubes mounted to custom pulleys with bearings on either end mounted on dead shafts to reduce the amount of weight in the Gripper.
All of this is mounted on a linear slide with a 10” extension, made using two 2”x1” tubes and two 2”x2” tubes with Thrifty Elevator bearing blocks in between (essentially just a horizontal, inverted Thrifty elevator). This linear slide moves using another Neo 550 motor mounted far back, also for weight-saving purposes, with another UltraPlanetary gearbox with a 9:1 reduction. All of this is then mounted on the Lift carriage plate.
Feel free to ask if there are any questions about our design, and until next time! (hopefully with more of the robot built )