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Design the robot.
@Declan Freeman-Gleason set the channel purpose: Design the robot.
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Design class starts tomorrow at BARN at 3:30 PM in the ETA Studio on the main floor.
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Here's the overview of the class..https://drive.google.com/open?id=1LA2bObLzm54Ic6VRHuU62UL2Y1OCLlp
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more documents from meeting #1
Lift Sketch https://drive.google.com/open?id=1dmaAeJ6zSrDDB5Es5vpqeCE-pqvyius
Week 1 Assignment https://drive.google.com/open?id=1IzUHNp9nmF6qGZVOGMK4RTVk13xZr53y
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Here's my homework for the first day with the scissor lift: https://docs.google.com/document/d/1D77VtIp5LiOXa1of8xANWdFu8B6OxKlD2C59mNS38Z8/edit
as an option to wheels & bearings for elevator is "linear guides"
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To the people designing elevators, this company makes kits for the bearing rollers
And actually, to everyone, this company makes a bunch of great brackets that are larger than the VersaFrame or Andymark ones
I wish I could make it to these classes, but the timing doesn't work. I've been trying to follow along with the assignments on my own, and here's what I have so far for my elevator + pivoting arm: https://docs.google.com/spreadsheets/d/1pJnPUGFvB9LkJB66Q1w3vSe-EgVw0w1mpmLmLb568/edit?usp=sharing
Looking at upcoming topics, I'm nearing the end of my comfort zone. I may need to borrow notes from the upcoming classes on strength, movement, etc. :persevere:
I have realized by studying other teams' past elevator designs and reading a couple Chief Delphi elevator design discussions that (mostly due to inexperience) I've inadvertently designed a 3-stage rather than 2-stage elevator. It's more complicated than a 2-stage, with half again as many bearings and probably a greater challenge to keep stiff and reliable. sigh So... I'm going back to the drawing board (better now than later) to create a 2-stage. The pivoting arm will not be able to be as simple to achieve the vertical operating range requirements, but a slightly more complicated (still 1-joint) arm is probably a worthwhile trade-off for the elevator simplification. I'll post an update when I complete it.
Alright, conceptual design v2 including geometry is done. I simplified from a 3-stage to a 2-stage elevator, and accepted the trade-off of a bit more challenging problem to solve with the am... I think it's worth it. I like the new design better. See the link in my original post if interested.
Also, I moved my 2D CAD over to the Design Class working area. It's inside a folder with my name. If anyone's interested in trying 2D geometry analysis like this, here are some tips:
- Getting the design to behave and move the way you want is all about setting up constraints.
- For example, when you sketch a 2-point rectangle, the default is for it to have vertical/horizontal constraints. If you need that rectangle pivot on one of its ends, you need to remove the vert/horiz constraints and add perpendicular constraints, plus add dimensions as appropriate.
- I've found that adding a point and then constraining it to the midpoint (using the midpoint constraint :)) of the short side of a rectangle turns it into a better "handle" for rotating the rectangle than by just trying to use the rectangle's corner (which sometimes doesn't work at all.
- The rectangle short-side midpoints mentioned above are also useful for creating linkages between rectangles using the coincident constraint.
- Sometime things will not move the way you want, and you cannot find the constraint causing the problem. I find it is often faster to just remove the item and recreate it with constraints I know will work rather than trying to hunt down the blocking constraint (after a while, there are a lot of overlapping constraints in the sketch).
- I'm also happy to demonstrate what I've learned so far about working with 2D sketches for geometry analysis. Maybe next meeting.
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Seeking advice. I now have a couple things: 1) a 2D sketch of a 2-stage elevator + arm and 2) the 3D CAD of the chassis shared with the class. What do you experienced F360 CAD folks think is the best workflow to proceed starting work on a 3D design & CAD of the elevator? I already copied the chassis CAD as a starting point.
Here's my current plan: I'm going to look at several elevator CADs to see how they're put together. I'll probably identify some elements from those designs to try with my design. And I'll do some hand 3D sketches or rough CADs & identify parts. I'll then go find CAD files for the off-the-shelf / generic pieces (e.g. 1x2 aluminum tube, gussets, motors & motor mounts, etc. - do we have a folder with basic stuff like that?), and I'll model the parts that will need to be custom. I may do some interim CAD files for specific assemblies. And then I'll pull the parts/assemblies into the overall CAD file and put it all together,,. sound right? Or is there a better way?
As I've been designing the robot, I have been keeping a spreadsheet of the robot's weight. I think this project is a great chance to practice doing this before next build season.
I am not including nuts, bolts, or rivets in the spreadsheet yet
However, I am capping the robot's weight at 115lbs
If you include the locations of the weight items then you can keep track of the center of gravity as well as the weight. If we had been doing this with CHAOS this year, we would have moved the battery much earlier.
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Hi designers, would someone share a few highlights from class today? I have some work in progress (trying to follow along with the class), and I have the class outline, but I'm not sure if there specific things I need to cover in the context of the three things listed under the session 3 Strength topic. thanks
Topics today were stress, strain, and torque/moment arms. Wikipedia has a pretty comprehensive discussion https://en.m.wikipedia.org/wiki/Stress(mechanics) .... More than we covered today. The primary example was a vertical bar with a weight hanging from an arm attached to the top. There is a torque where the arm attached at the top, stresses in the form of compression and tension in the outer walls of the vertical bar and torque at the bottom where the vertical bar attaches to the base.
We also reviewed everyone's designs.
For aluminum, compression/ tension stress is about 10000 lbs per sq inch. Shear stress is less than that by a factor of sqrt(3)
Thanks. It seems like, for our most common building materials like 1x1 and 2x1 6061 Al tube, it would be good to have a list/table of examples of appropriate uses and limits. It would provide data points within which people could interpolate... For example, with 1x1 6061 of different wall thicknesses, how much weight could be handled by 1' and 2' lengths in the configuration of your primary example from today? From what I read, much of the time the top mech people on teams know what structural pieces they can use for different purposes based on experience, with the exception of something like triple climb that would get more thoroughly analyzed as Paul did our winch in 2018 (and determined 1/2-inch hex would not cut it :)).
I will not be at the session today
Neither will I
FYI. The material Paul is using for his slides is described here https://en.m.wikipedia.org/wiki/Ultra-high-molecular-weightpolyethylene. Pretty interesting stuff. Easily machined, tough, low friction, and self lubricating.
As far as arm/lift designs, looking at the class outline, it seems like we're at or getting close to the stage of selecting actuator types, gear reduction in the case of motors, etc. I'll be interested in seeing notes on that topic to stay in sync with the class. I also think the arm/elevator motor & gear ratio calculation & selection videos by Adam Heard from 973 Greybots posted to engineering channel on 4/14 are good supplemental material for this.
I'll be at the BARN tomorrow from 2pm to 5pm for open ETA studio. You're welcome to drop in and work on your designs, share tips on Fusion, etc.
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Hey, sorry I didn't let you guys know that I wasn't going to be at the meeting yesterday
I will be 15-30 minutes late to tomorrows meeting
I’ll be around 45ish minutes late because of my AP stat test
If people want to spend time working on their designs, I'll be at the BARN tonight from 7 to 9 pm for the open ETA studio. You can work by yourselves, work together, or however you like. I'll be happy to help with fusion or chat about your design.
I am also going to be about half an hour late today
I'm going to be late today
I am not going to be at the meeting today
Since we have a leadership meeting starting at 5:00 on Thursday May 30, are we planning on ending the design meeting early to accommodate for this?
I was not aware of the design class on Thurs 5/30. What time does it end ? Maybe we can start leadership meeting later like 5:30 or 5:45 ?
We can talk to Paul about it tomorrow 5/21
Usually the design meeting ends at about 5:30
How about we start leadership at 5:45 on 5/30 ? @Cruz Strom let me know after you speak to Paul on Tues.
There are three more sessions for the Spring Design Class: Tuesday May 21, Thursday May 23, and Tuesday May 28. The optional meeting on Thursday May 30 has been cancelled.
Thanks @Paul Vibrans . So we will stick with leadership at 5 pm for 5/30 as originally planned.
Hey, I think I left my camera at the barn, did you guys see it?
@Jake Benjamin has it.
Yes. Jake has it
I can get it to you tomorrow before school or during lunch, or today if you want
Thank you so much
I'll see you at lunch
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I will not be able to attend design class today due to homework and family obligations. Sorry for the late notice.
Today's class is the last class.
As a reminder, people are encouraged to continue working on designs over the summer. If you'd like help or assistance, you can let me know via this slack channel. Its easy for me to look at your Fusion 360 models if you place them in the SpartronicsCAD --> Design Class for 2019 folder. I can also forward them to Paul from there.
Another suggestion is to check the BARN ETA Studio for Fusion classes. There's an open "Fusion 360 user group" thing on the first and third sunday of each month. These are unstructured get togethers where people can help each other with using Fusion.
Finally a reminder -- If you want to get better at design, you need to do it. Practice is absolutely essential.
#engineering and #design-team -- I came across an interesting, inexpensive component for doing linear motion -- it's designed to work with aluminum extrusion, but it may be possible for us to generalize the design for use with other materials. We might be able to use these to build Paul's elevator for example.
One interesting and intriguing capability of modern CAD software, including Inventor and Fusion 360, is parametric design. I think it might be worth exploring now or in the future as a way for our team to save time. The way it would work:
1. Develop a set of reusable parametric designs for common types of mechanisms (2-stage elevator based on 2x1 tube, 2-joint robot arm using 2x1 tube, etc.) The designs are set up in a way that the tube lengths are adjustable using parameters. Joints between components, sketch constraints, etc. are set up in a way that the design doesn't break as parameters are changed (within reason: you would not expect a 1-inch long elevator member parameter value to result in a viable design).
2. Draw from the parametric designs to save time on general actuating mechanisms like drivetrains, elevators, arms, simple linear and rotary actuators.
3. Use the time saved on general mechanisms to invest in the novel aspects of the overall robot designs that interact with game pieces and field elements (e.g. intakes, gamepiece storage, placing/launching mechanisms).
Here's an example of a parametric drivetrain design created using Inventor: https://www.chiefdelphi.com/t/team-1510-parametric-drive-base-inventor-2017/161630
Sharing this here as well. I'm working on projects this summer to improve my Fusion 360 skills, starting very easy & moving up from there. Details below - let me know if you're interested. Thanks --Chris
Here's a well done CAD & design presentation by Annie Wang, a graduating senior from team 971. She goes through the process she's learned while on her team, including diving into a few specific techniques. While the CAD software she uses is Solidworks, a lot of what she explains applies in a general sense. Very impressive student designer... I think her mastery is a great indication of the opportunity we have in front of us as we focus on developing a design team. https://youtu.be/4Eg2b4-jtqA
Back in 2014, one of team 610's students, Ryan Tam, created this Design Tutorials document. It covers a lot of useful concepts and design aspects of FRC drive trains & mechanisms - good read. http://www.team610.com/wp-content/uploads/2014/03/Design-TutorialsRev10.pdf
You'll see, at the beginning, Solidworks is mentioned... Don't worry about that; the majority of what is covered is CAD software agnostic.
I've been playing around with combining 2D sketch analysis and parameters - seems like it could be pretty useful week 1. Here's a screen shot, and if you want to play around with it, you'll find it in the Parametric 2D Design folder within my Design Class Folder.
In case anyone’s interested in how one of those suction cup climbers was designed: https://www.chiefdelphi.com/t/694s-suction-cup-mechanism/362063
@Paul Vibrans Once when discussing the common practice of using butt-jointed tube with gussets (like with Versaframe), you said lap design was required to do it properly. Custom-designed “West coast drives” or WCD’s are probably as or more common now than the Andymark kitbot, and they often use tube+gussets, like this one just shared: https://www.chiefdelphi.com/t/off-season-wcd/364743. What kinds of changes would be needed to achieve the lap design approach, and how would it make a difference? I’m trying to learn from what you said, but I can’t find anything about anyone using that term with FRC robots. Would there be little tongues coming off the tube ends that went through slits in the tubes to which they’re mated, and then rivets would go through all layers? Thanks
Don't use tubes.
Because... channel of the same wall thickness will work sufficiently and is lighter and not any more difficult to work with? I assume weight isn’t the only reason to not use tube. Hundreds if not thousands of teams use tube like this. You’re saying they shouldn’t... still trying to understand why.
Channel is easier to use nuts bolts with because the back side is easily accessed, it's easier to route hose and wiring in the protected areas, it gives more room for components in the chassis base, it's easier to use backing plates where heavy components attach, the existing holes can be threaded because the wall thickness is adequate.. . And Paul probably has more reasons ...
It may also do better with our bumper mount technique because the metal is thicker at those points where the attach studs are. The frame surface also less likely to deform if the stud gets pushed or pulled sideways by bumpers or other heavy components attached to the frame's surface... (That's another reason backing plates may be needed).
In general there are use cases where for the same weight of material, tubes perform better. But I don't think those use situations really apply in the frame.
The other thing I noticed in the design you shared is that the main drive belts are exposed in the bed of the chassis. They are protected and shielded in the channel design.
I decided to spend some time reading the Off-Season WCD drive posting and many of the comments. It is clear that most people involved in this thread are extremely inexperienced in design and manufacturing. Few of the comments offer any complete insight on how to improve the design, just that the design needs work; perhaps it would take too much time and space to give a thorough critique but I think it is really a cultural problem.
The reason that hundreds if not thousands of teams use tube is because VEX has a packaged system that can be understood by mentors who are not engineers, or at least engineers with aircraft structural or marine structural experience, and teams are ill prepared to step outside the "box" to develop light weight structures that make the best robots. After much trial and error using these components, reasonable robots evolve. Probably the most common structural experience mentors have is wood frame construction of houses that uses dimension lumber and Simpson Strong-Tie attachments. The VEX tubes and brackets look a lot like all-metal house framing when assembled.
Wood has its place in high technology structures (Google "DH.98) but wood house construction should not be the pattern upon which a team bases its designs.
When we limit the team's designs to an all-COTS-all-the-time approach, we are limiting the creativity of our students and we are short changing them on experience. That means if we as mentors are limited in our understanding to just assembling COTS parts, we are an impediment to the advancement of our students and is our duty to overcome that. By doing what everyone else does, we guarantee that our robot will never be technically superior to any other robot and the only sure advantage we could ever have in competition will be from our driving or marketing efforts.
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Me too! Yours looks good. How’d you do it? I created a 1/2 cross-section sketch first, including several circles & lines, construction lines, application of several sketch constraints to generate the desired shape, and then some trimming of unneeded line segments. Then I revolved the remaining sketch around an axis to create a Body and hallowed it out using the Shell function, closing with some minor filleting.
Yeah, I did the same thing I think
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For the frisbee shooter assignment... Here's a quick CAD I did of a rough robot chassis + the low and high goals. My specs for the goals:
• Both 20 feet away from center of robot chassis
• Low goal is 4 feet wide and 2 feet tall, with the bottom of the goal 2 feet off the ground and the top of the goal 4 feet off the ground.
• High goal is 4 feet wide and 2 feet tall, with the bottom of the goal 10 feet off the ground and the top of the goal 12 feet off the ground.
Also, here's a picture of a stack of 7-inch frisbees. I was thinking frisbees in a cylinder might just work, but looking at the way the frisbees stack, I'm thinking about the helical storage approach instead. https://1drv.ms/u/s!AikCDwtdoW5LgYIHVmolVXyQ5XeReA
After significant thought, I realized that the Aegaeon intake doesn't work using only motors. The arms can be actuated by a snowblower type motor, but it would not be able to do what we need it to do. I have a redesign in mind that I will start in a week or so.
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I won't be able to make it to today's design meeting. I was just notified that I have a sailing banquet, the last one of my high school sailing career, tonight. However, I'm still working on a frisbee launching mechanism on my own time.
Just to let you know, the meetings are on Tuesdays and Saturdays from 7-9 pm.
Here's a link to the frisbee shooter design spreadsheet I shared last meeting. I've updated it as well as the CAD after a fair amount of work today. As Mark said, a spreadsheet can be a versatile way to keep track of notes, links to anything and everything, calculations, the progression of the design process, etc. Please take a look if you have a chance and consider whether or not something like this could be helpful to you. Feel free to copy, of course. https://docs.google.com/spreadsheets/d/1TlsQcyKvOu5T6DGl6J45bjS-vPHsDP1pUU-7YyNfAgk/edit?usp=sharing
Motor & gearbox selection blog post (Blue Alliance) that relates to what Paul explained about torque, speed, & identifying a gear reduction. It's a few years old, so there are newer motors than the ones referenced, but the fundamentals taught are spot on and presented in an FRC context... https://blog.thebluealliance.com/2013/06/24/behind-the-design-understanding-motor-and-gearbox-design/
I will be at the meeting hopefully by 8:30, my band practice went super late
@Parker Hutchinson Can you put your design in the Design Class Winter folder?
Yeah I'm working on it
I am going to be a half hour to 45 minutes late to the meeting tonight
Just to remind everyone, the next meeting is this Tuesday. We do not have a meeting today.
I will not be able to make tonight's meeting. Sorry for the inconvenience.
We used the smallest of these in the linear actuator for the flipper on the scissor lift. It didn't have enough load capacity for the application. They could be useful for guiding things if properly applied. They must run on hardened steel rods or tubes. Surface hardness should be 60 Rockwell C or more. I had to heat treat the guide rods we used to keep them from becoming grooved. Even then our applied load exceeded the capability of the linear bearings.
I started designing a 2-inch mecanum intake wheel on my flight back from visiting relatives in Indiana for Thanksgiving. The goal (other than just seeing if I could do it) was to design something mostly 3D-printable that is comparable to the purchasable options (which run $10 to $13 per wheel) like this: <https://www.thethriftybot.com/store/QTY-4-2-Inch-Vectored-Intake-Wheel-p158823700>
Everything should be 3D printable except the 3 nuts, 3 bolts, and six roller axles (which could be metal, carbon rod, open to suggestions - 3D printing won't cut it). I added threads to the rollers because I think they will add helpful "bite" when centering & intaking a game piece. I haven't printed or assembled yet, but I eventually will. If anyone has ideas / feedback, please let me know. Here's a link to the current design: <https://a360.co/2Pq2LdJ>
Here is an another option. I had Jack print one of these up just before thanksgiving break. I will bring it in on Wednesday. https://www.chiefdelphi.com/t/open-source-team-401-3d-printed-2in-vectored-intake-wheel/363438
Another thing to mention for these roller axles, we used bent paper clips as the axles.
In the thread Cruz shared, Nick Coussens from team 33 said they'll also be sharing their design, which has gone through a lot of testing and iteration apparently. They don't use axles for the rollers at all; rather, the rollers spin on bosses (i.e. little bump-outs in the design that protrude into each end of each roller). It looks to me like the thriftybot design may incorporate the same approach.
Here is a link to some videos of testing for the thriftybot 2in vectored intake wheels. The team has ordered these. https://photos.google.com/share/AF1QipOiTIl4jnuh3SNZ-cHKVpLiSGXoa1shVMsv7oTUdgyylXPL3mt7WlZYhoNjKhIw?key=ZWdKc0tRMkhIQ0d4eFBJUEkydW5saGpMenZUOTNB
1. Getting the spacing right vs. bumper and game piece (& compression is also part of that) is critical. In the second video, the bumper on the right was just a little bit further out (i.e. closer to the intake) than on the left, and the centering intake was much more effective on the left vs. the right. On the right, the intake seemed unable to get close enough to the ball.
2. Hard smooth plastic doesn’t grab onto hard smooth plastic very well. (Duh!) The rollers on those wheels are smooth 3D printed nylon, and they did not intake the 2017 fuel balls very well at all. No surprise really.
@Cruz Strom @Chris Rininger recently I've been thinking a lot about intakes, and I would like to test out an intake with mecanums and one without. I think they may end up hurting us. I wrote a paper on it last week, I'll try to upload it in a second.
I think it depends on the application. If game pieces are fairly scarce and high value (like 2016), then a wide intake + any edge enabling our robot to snag a game piece when even barely touching it with the edge of our intake is advantageous in my opinion. If game pieces are plentiful and not individually that valuable (like 2017), then a high volume intake with belts or normal wheels seems appropriate.
Here a source of linear motion solutions I was perusing recently: https://www.rollon.com/GLOBAL/en/products/. Team 3339 that had the similar climbing approach to us except they used motor-driven rack & pinion incorporated a solution like this X-Rail: https://www.rollon.com/GLOBAL/en/products/linear-line/2-x-rail/ Here's team 3339's BumbleB robot CAD - if you zoom in, you'll see these rails mated with the rack gears: https://grabcad.com/library/2019-bumbleb-3339-robot-cad-1