Inspired by the the group of #openalliance members. FRC 1675 (F4 Team 534) is going to try to document our team’s first foray into the world of CADathon. We’ve been having weekly OnShape/design lessons with a small group from our team, and this gives us the perfect way to stretch our design and CAD muscles.
During our most recent meeting we agreed on a plan as to how we’re planning to approach the CADathon such that it will maximize value to our team.
We are planning to design a robot that is within the ability of our team to build over the course of a standard FRC build season. We have limited access to our shop (MON/TUES/THURS 6:00 - 8:30 and SAT from 8:00 - 4:00). Our main machining resource is access to a CNC plasma cutter which allows us to accurately and reliably cut plate (and some tube, with challenges). Other than that we run with a chop saw, drill press, a variety of powered and non-powered hand tools.
We intend to develop a strategy that will allow us to be successful playing F4 GameDay within these constraints.
Skills for Football Manipulation:
Skills for Plate Manipulation:
Our Plan:
We are planning to design a Weight Plate specialist that will be under 36" tall to guarantee endgame points. Our discussion landed on the fact that the weight plates had quite a few advantages. We will be designing to take plates from the floors, as well as the retrieval zone and place them on the scoring peg.
First, scoring a single plate is the same value as 5 footballs. We felt given our design expertise footballs would be difficult to manipulate reliably such that scoring at that frequency would not be possible. The weight plates will be in a consistent orientation which (while not easy) will make them easier to manipulate.
Second, scoring weight plates creates a positive feedback loop making it harder for your opponents to score. Additionally, removing plates from the retrieval zone will limit (though not eliminate) your opponents ability to cross the field freely in most cases.
Third, as the ranking point is reliant on scoring 11 weight plates, this was a good place to spend our resources to maximize our chances to rank highly.
If we are able to design a weight plate mechanism that will meet our goals we will look at a simple football launcher. This will likely be a “shotgun” or catapult mechanism such that we do not have to worry about orientation. It will likely only load from the human player station to minimize its complexity.
Our goals for tomorrow are to have some design concepts for the plate manipulator to discuss in our meeting tomorrow. We would also like to have the basic chassis complete such that we have something to start building the plate manipulator on. We are trying to leave the chassis as flexible as possible at this point, and may have to make modifications depending on decisions around the other mechanisms.
There were two main focuses of the team for day two: get a basic chassis in CAD such that it could be used to build mechanism on, and to develop concepts for our weight plate manipulator.
For the chassis design we have chosen to iterate on our standard west coast setup that we have used for several years and improve it to match our manufacturing methods to (hopefully) produce a drivetrain with far less issues that we have had in the past.
For the past several years have been using the WCP Bearing Blocks in 2x1 tube. We have been moderately successful cutting the necessary hole patterns using our CNC plasma cutter on the tube, but have issues getting everything to align properly. (I think we tried to make at least 8 siderails before we produced one that was acceptable).
With that in mind, this chassis was developed such that all the bearing pockets would be cut directly into plate. Currently the plates are .125 and they are sandwiched around (3/4)“x(3/4)” 1/16th wall square tube. This combination creates the 1" width tube that works for the bearing blocks. We felt given our manufacturing capabilities this concept may be able to produce a more consistent chassis faster than we’ve been able to over the past few years. We’ll be looking to reduce weight on the plates with some pocketing, but so far we’re happy with the concept.
We’re current planning on a 4 Falcon drive with the WCP SS 1 Stage Gearbox. We’re planning to gear in the range of 16ft/s free speed and have a software limited speed when we’re placing plates.
Chassis still needs battery and bumper mounting solutions, as well as electronic panel layout and chain runs.
Manipulator Progress:
During our zoom meeting last night we discussed several different concepts for the weight plate manipulator.
It looks like we’re looking to build a 3 stage elevator (pending a bit of math) such that we can reach high enough to score at the 42" height while still being able to retract to under 36" to not limit our capabilities to move around the field. Our starting configuration is likely to be with the elevator extended such that we will not have to worry about the 12" vertical extension rule.
For the manipulator we’re looking at dropping our mechanism on top of the plate to act as a gauge to find an accurate distance. This will allow us to more easily pluck a single plate off of a stack. Once resting on the top of the stack we will actuate side grippers in combination with what we’re referring to a “stabbers” that will (hopefully) slip between the plates. This will give us enough contact area to collect the plate securely as we lift the plate off the stack (or ground). We currently plan to then rotate the plate to transport it in the vertical orientation to minimize additional loading on the “claw”.
Currently, we have several members working on more detail concepts for the gripper, and we should have a start on an elevator system which will be presented in our meeting tonight.
Lots of good work being done by the whole team. I’ve poked the other members of the team to come give some of their design insights and describe the work they’ve been doing.
Chassis and drivetrain is basically done. There is a little cleanup to do, and we will likely still add lightening patterns to the outside rails, but its at least presentable. We’ve even laid out a few electronics in CAD for the first time basically ever.
Joseph has taken the lead on the elevator design, basing the concept on our 2018 elevator, which in turn was heavily inspired by the GREYT lift.
Overall the design is intended to fit under the the 36" bar, and still be able to score the plates. This means the elevator will likely be stored in an up position to work around the vertical extension restrictions. Next steps will be to start the assembly and work out motors and how we intend to power the system.
We had a long discussion about the claw and grabber during our meeting last night. We began looking into whether there was value in being able to pickup the plates from the which causes additional complications with the design.
Noah and Ian have taken the lead on this design which will drop down on the plates from the top and then squeeze the plates from the side with a high friction material to pull them from the stack. They can speak to the specifics of what they’re working on.
Our meeting tonight will focus on the possible strategy change away from the ground pickup strategy which should significantly simplify the mechanisms.
Some of our geometry sketches as to a possible solution to ignore ground pickup (and not have to rotate our gripper to the vertical orientations. This would have us dump the plate directly onto some time of receiver on the chassis. (To be discussed).
my guess would be that the plates extend that far back to facilitate a pneumatic wrist.
and the orange frame they are attached to looks like it would be the carriage
I’m curious about the drivetrain. It looks like a wcd-style plate drive with small box beam reinforcing it, is there a reason that you’ve done this over just a taller size of box beam, like 1x3 or so?
The blue triangles at the time were going to be for a pneumatic lowering and raising system that we now have left. The orange rectangle was the third stage of the elevator. We are now going to be moving the elevator back and having almost everything inside the frame perimeter.
Yep. We’ve done tube 2x1 tube chassis that past few years. Most of our experienced machinists have left the team, so our precision manufacturing is done with a CNC plasma cutter that the school has. While we’ve been able to cut the side rails using this method, the table we have doesn’t have any way to properly zero to the edge of a part. This led to a lot of misaligned holes in the tube.
This chassis concept would allow us to not have to worry about zeroing on a part as the entire part will be cut from a larger plate. We’ve never actually built this type of chassis, and we were using the CADathon to work out some of the possible issues.
It was a busy last couple of days, incorporating a handful of design changes, but overall the strategy remained consistent.
The gripper was modified to just maintain a static angle which simplified the mechanism considerably. When loading from the human player station we will let the weight plates drop onto a pivoting roll cage on our chassis (which unfortunately did not make it into the CAD).
I’m very proud of all of the students that worked their tails off this week, especially considering they were all very green with CAD. We all worked collaboratively to put together something that both met our design criteria, and that we would be proud to field. This week-long version of the CADathon was an excellent way to get new designers immersed in CAD with far less pressure than the 3 day versions. It allowed a lot of learning and iteration.
Thanks to the organizers, and we’re looking forward to all of the reveals on the 28th.
