Build Week Two General Update
Full Robot Design V1
Section authored by Design Subteam Lead Ari Grace
So far, we have settled for a 2-degree-of-freedom long arm with a universal manipulator attached to a wrist. Above all, we have prioritized a simple design with the ability to score both game pieces in all zones. We hope to primarily acquire the game pieces from the human player station, coupled with the ability to pick up fallen cones if necessary.
Central robot structure (electronics not included).
Master sketch depicting multiple arm positions.
Arm and Superstructure
We designed this superstructure to allow for the manipulator to pass through the base and remain stowed within the drivetrain at the start of the match. These constraints, along with a desire to keep the overall vertical profile as thin as possible, resulted in a rather interesting shape. Currently, the entire structure is bound together by gussets and tube plugs, but we would greatly appreciate suggestions for better reinforcement techniques.
Superstructure side and front views.
Right now, our arm is a single piece of 2x2 1/16” wall box tube with a hole drilled through each end for the manipulator wrist axle and the dead axle. In total the arm weighs in at 6.3 pounds, including the mechanism to drive the wrist, which consists of a MAXPlanetary 90 degree gearbox attached to the tube via clamping plates with a chain running to the wrist axle.
Arm side view.
The arm itself is driven by a dual neo chain run with an overall reduction of 115:1, which should be capable of achieving stowed to L3 speeds of roughly half a second. I chose to incorporate an intermediate stage rather than run a single, extremely long chain up the superstructure to prevent tensioning issues and an unbalanced center of gravity. Note that this gear reduction remains subject to change in response to data gathered from arm testing.
Arm driving mechanism.
Our initial idea for a manipulator was an adjustable roller claw that would interface well with both game pieces and minimize the precision needed to intake them, with an effective gap of 15 inches between the claws. A secondary advantage of this design is that it enables the shooting of cubes into desired goals to further reduce cycle times, and potentially even the shooting of cones if testing proves it effective. The claw’s actuation is driven by a Neo 550 with a gear reduction of roughly 237:1, allowing for a predicted actuation speed of less than half a second. The rollers are driven by a Neo on a 4:1 reduction, which, while likely on the fast side, will be what we stick with until testing actually proves the need for further reduction.
Roller claw in open position.
Our current design utilizes a Kit-of-Parts drivetrain in a 28” long by 26” wide configuration in order to strike a balance between having a small chassis and maintaining robot stability, with a cutout in the front plate to make space for the arm in its resting position. We’re using a quad-Falcon drive once again due to the success we saw with it last season. Our iconic half-inch HDPE brainpan with wired LEDs also makes its return in this design, but may be swapped out for a pocketed aluminum bellypan later on for ease of mounting electronics. Depending on how successful we are at getting a swerve drivetrain up and running, we might go all out and manufacture a swerve drivetrain for our final competition robot.
KoP drivetrain with ½” HDPE brainpan.
From Zero to Swerve in 30 Hours Flat
In the last programming update, we mentioned that our swerve modules would be arriving soon, and, while we would put some effort into getting them working, if we could not do spinning figure eights by the end of build week two we would not be using swerve this season. The six 3” REV ION MAXSwerve modules we ordered arrived the afternoon of Tuesday 1/17. By the afternoon of Wednesday 1/18 we had a fully functional prototype swerve drivetrain capable of doing spinning figure eights, as can be seen in the video we posted in the Open Alliance discord server. Before the modules arrived, we thought it could take us upwards of two weeks of work to perfect a swerve drivetrain, but thanks to the REV MAXSwerve Template it only took a few hours to implement full field-oriented driving. With the majority of our fabrication, electrical, and programming subteams working on the prototype simultaneously, it only took us roughly 30 hours to go from opening the module boxes to driving loop-de-loops around our practice field.
Prototype swerve drivetrain (bumperless).
Alpha Bot Progress and Setbacks
In our last update to this thread, we resolved to have a full alpha bot fabricated out of scrap box tube and ready for driver testing by the end of build week two. We did not achieve our goal as we spent both our weekly meetings this week working on swerve. Despite this departure from our schedule, we did get in a good few hours of work machining and assembling the arm on our meeting on Saturday 1/21. Pictured below is our current progress on the 2DoF arm and supporting superstructure.
2x2 box tube arm connected to a 48 tooth sprocket on a dead axle.
Vision Testing with Orange Pi 5
We have managed to get PhotonVision running successfully on the Orange Pi 5 using our recently-arrived Arducam OV9281 USB camera. The camera’s performance sits at about 50fps with less than 30ms of latency (measured by PhotonVision) but the accuracy is dodgy at best, so we’re still planning on buying a Limelight 3 when it releases. In the meantime, we’ll keep tuning our PhotonVision setup.
Well, I can safely say none of us expected we would get swerve capabilities up and running so quickly after receiving the modules. With this shocking development, there’s a good chance all y’all will get to see the first brand-shiny new 3636 competition ready swerve bot at the Wilsonville PNW district qualifier!
– Asa | 3636