Finalizing the details of our prototypes and beginning to produce some advancements. Due to exams and a snowstorm, this week was a bit less productive than the other but still valid nonetheless. Detailed below is our third week of build season, as well as a quick summary. We will update our blog next week with our week 4 progress, so make sure to check our thread soon
We are so proud to share this Arm Simulation of our bot - See the “Programming” section for more details!
Intake & Design
To begin our week, we decided, as a team, to take a step back and decide once and for all on what intake design we would move forward with. Even though we had mostly decided on the pinch-roller intake, there was some miscommunication with the choosing of the designs, and in retrospect, some other prototypes still held some promise that could be looked into. The one other design that we managed to narrow down a comparison to was a 3-prong intake, with a rotating central disk that folds into half. 3 arms stick out of the disk that clamps down and grabs on to the cones and cubes. It’s a creative design that would increase strategic capabilities and could open up some more unique design choices. Some examples of how this intake grabs cones in any orientation are pictured below.
3-prong intake in action, taking an upright and fallen cone
We deliberated and debated, eventually coming down to a list of pros and cons for each intake and stances on why we should do one over another. The 3-prong roller intake would require pneumatics, which was a huge downside as our cad designs were built without that in mind, needing both subteams to have to adapt to the change. The pinch-roller intake has already been our plan for the past few weeks so has already had rough cad designs in the works. Having to redesign our plans and robot infrastructure to fit in the pneumatics would cause more work for the team, so the point goes to the pinch-roller intake.
Strategy-wise however, both had their pros and cons. The pinch-roller intake followed the Touch it, Own it philosophy for game pieces, which we found the 3-prong to have difficulty doing. Trying to configure the prongs to line up with the game piece during a match could waste valuable time and allow another robot to take our game piece in the middle of intaking. With swerve, we should be able to position ourselves in any manner around the game piece, which limits the usefulness of having the prong being able to adjust itself for the game piece in any form. The only way that this utility could come in handy is in the upper echelons of play, where opponents can find it difficult to predict our moves and we can quickly adapt and change how we intake the game pieces. Still, it’s hard to justify having such a complicated intake mechanism that could end up confusing us more than the opponent. Automating the intakes during auto is the same situation, where it could quickly become hard to solve for every situation and position we might find ourselves in. Once again, the pinch-roller seemed to make more sense.
Issues arose with the driver and operator controls with the 3-prong intake as well. We have laid down a general plan for how the driver and operator could move and what buttons they needed, leaving us with limited extra space. Having to fit in all of the different inputs would leave the controller being messy, and force the driver to only be able to intake with the operator, leaving matches ripe for miscommunication. The few seconds we can save by having the driver pick up the game pieces could make or break a match.
Rough copy of the button controls for driver and operator
With all of this in mind, the final choice with which we have decided to move forward with and use for our final design is the pinch-roller intake.
Having the design been chosen, we moved forward to refine the pinch-roller intake.
Our superstructure design intricacies were left unclear last week, and we found it important to share our design choices and our path on how we ended up with that design. Modularity and compartmentalization were our two main goals with the construction. Being as small as possible while accommodating the arm and the effector was a challenge, as we started at a 40+ inch height from pivot to chassis top and managed to eventually reduce it to 32 inches. It was also decided that it should have been able to be taken off the arm and the chassis with as little work done as possible to aid in repairs or incremental improvements.
Our result was a simple yet elegant superstructure that can be removed with only 4 bolts and an arm that can be removed with a couple of bolts and several wire/chain connections.
Initial CAD used a fair bit mix of 2x1 and 1x1, but was then simplified to mostly use 2x1
For our building and material components, we had extensive use of 2x1 due to its extremely high availability in our area and its cost advantage over having to buy other sizes. 2x1 used is 0.095 wall. We didn’t find a technical need for lightning holes (only saves us about 2lb) but decided to add them anyway due to the extrusions having to be processed in the cnc anyway and the team deciding that it looks nice.
(left) Initial Crossbar Configuration (right) revised chassis-based crossbar
We initially used a floating crossbar which was mounted to the top of the chassis in the middle but this left a cantilever in the design which there were concerns about its structural integrity, so it was decided to do away from that and use a chassis crossbar instead. However this complicated mounting interfered with the goal of modularity, so it was solved by using captive nuts inserted into the tube using printed tube blocks so that the superstructure can still be bolted onto the crossbar.
Rear end of the superstructure showing how close the pivot gearbox is to the pivot
The pivot gearbox was placed up as close as possible to the pivot instead of all the way down in the chassis. Although this results in a minor disadvantage from a CoG standpoint, it was decided that keeping the chain running as close as possible to eliminate issues regarding eventual chain wear and tensioning issues that will arise with using long chain runs. A discussion on the gearing for this pivot gearbox is shown in the Week 2 update.
Emphasis on using plate gussets instead of other methods like tube blocks, or welding for its assembly is due to the non-perpendicular angles our superstructure design requires, as well as the fact that we have a sponsor that can cut those particular gussets for us.
Superstructure as Week 3 wraps up
Another design choice that lacked explanation these past few weeks was the telescopic arm. We explored it pretty early on after kickoff and have taken a few weeks to refine it to a successful level. We thought that a telescopic arm would make an elegant solution to the long distance the arm must travel to L3 and an extent L2.
The existing designs we found were 2 stage pink arms, or traditional cf-spring driven telescopes for climbing. These were either too complex, incompatible with our machining capabilities, or too unproven and unoptimized for the application and forces it’s going to experience. Bearing blocks are usually made out of billet-milled aluminum, which our team does not have access to which quickly ruled that out. Existing telescope-bearing blocks were not sized for the dimension that we wanted the initial stage to be, leaving us with the question of how can we make a telescope that can be buildable to the team’s bounds, but also be reliable and efficient enough to help in scoring?
Telescoping Arm in its initial “pink arm” configurations
What we had theorized was initially a solution to a pink arm, but then as requirements changed and resolved into a direction, it was decided to forgo the Centre pink arm pivot and use a traditional arm pivot. This had many issues with how to properly power and gear the pivot, the discussion of which can be found in our week 2 post. The arm having 2 stages was forgone due to complexity, but ideating with geometry sketches showed that it was possible to build a 1 stage telescope while still being compact enough to fit inside the bot comfortably.
Eventually Resolved to have a rear pivot
Material-wise, the arm was made out of 4x4 and 2.5 x 2.5 Aluminum extrusions, with the 2.5 x 2.5’s spacing slightly offset to accommodate a partially external chain run. Pocketing them allowed us to save roughly 40% of their original weight. Having a partial external chain run was found to be easier due to easier simplicity and serviceability, with the added benefit of being able to take the hit of packaging trade-offs. An argument could be made on using a belt or rope instead of a chain, but we found that the team has grown accustomed to working with chains and its relative reliability when used properly. Belt and rope runs require systems that are uncertain to the team and the risks and potential issues we might face were not worth the effort for their weight and packaging advantages.
centre of mass with a 10lb intake mass simulator at the end.
Inner stage bearing setup
The overall assembly is about 15 lbs (with a notional intake it is about 20-23 lb). Bearing blocks and plates made out of 0.187 aluminum plates that are outsourced to a sponsor to reduce work needed to be cnc’d on our end, with the pivot being made out of 1-inch aluminum riding on high-load bushings.
Sprockets in pivot utilize both the 1.875 bolt hole found in typical plate sprockets but are also modified to accept a 3-inch 6 bolt pattern in order to add more robustness to the attachment points in the pivot.
To help with wire management up the arm, we have postulated a system utilizing a sheathed wire spool fed inside the telescope, with tension and wire return provided by cf-springs.
(left) Integrated wrist assembly with a neo550 + versaplanetary (right) same deal but with a NEO + maxplanetary
The intake ‘wrist’ has been integrated into the 2nd stage design of the telescopic arm, which will be powered by either a versa planetary or a max-planetary gearbox ( we have not yet decided on which we will be using ). One worry of ours is our uncertainty on how smooth or sloppy the bearing interface between the two stages is going to be, which should be solved and concluded by the time exam season is over and we get back into the groove of things.
Render of the Telescopic Arm as Week 3 wraps up
Overall, the telescopic arm has been a huge effort for our team, which should hopefully pay off during the season through our quick and efficient scoring of pieces on all levels of the grid.
Render of the Robot CAD as Week 3 wraps up
As always good luck to everyone building their bots and we wish you all the best. Make sure to check our week 4 thread next week for more Team 3161 progress. Cheers!