Last fall we used SolidWorks tutorials I made to introduce new students to CAD. They worked well: each student worked alone or paired with a more experienced student, and I helped whenever they got stuck.
There’s plenty of room for refinement, but it was great for a situation where we had 1 mentor and 10 students for CAD.
Recently I’ve been working on a similar concept for a drivetrain tutorial, and would love to get feedback and ideas from the community. This tutorial focuses less on CAD and more on the research and design side of things - everything from searching for existing solutions, selecting a drive train type based on the game objectives and your team’s strengths (props to 1114 for that by the way) to stepping through engineering calculations and predicting speed and pushing force.
I think tutorials like this will be helpful for young teams and teams with higher student-to-mentor ratios. When it’s more mature I plan to do ones for other modules (arms, elevators, grabbers, conveyors, etc).
I’m open to ANY feedback, but am particularly interested in:
Relevant information that I missed in the Research section
Errors in any of my calculations (specifically GROSS errors - I know I’ve made some simplifying assumptions in an effort to make it digestible for high school students)
Sketches for concepts you have that I can add to the Concept Sketches page
Feedback (particularly from students) on which parts need better explanation.
Lastly, if you’re interested in collaborating with me on this, please PM me with your email address and I’ll give you editing privileges.
Thanks!
Alec Muller
Mechanical Engineer
Mech Mentor
Team 2342
p.s. If you’re interested in the SolidWorks tutorials, I link to them in the 1st page of the Detailed Design, and they’re also here:
I got further into the design this week so I thought I’d share some stats & pictures:
4" mecanum wheel (Agile Mode)
4" RoughTop plaction wheel (Traction Mode)
3 stages of gear reduction: 3.57:1, 1.55:1, and 4.2:1
Mecanum on Stage 2, i.e. 5.52:1 from CIM, 12.6 ft/s
Traction on Stage 3, i.e. 23.18:1 from CIM, 3.2 ft/s
Max pushing force ~170 lbs in Traction mode (limited by 120A breaker)
Dimensions: 8.00" long, 6.63" wide, 6.60" tall.
Weight: 6.28 lbs (includes CIM + pneumatic cylinder)
Mounting interface: 10-32 Tee Nuts on 1" spacing
Mecanum Wheels and wood stiffener plate are only left/right handed parts
(You’ll need a Left and Right version of this module to drive mecanum).
I can tell you put an immense amount of work into this and most of us could only beg our students to document their design process this well. I think our team would be happy to collaborate on this and expand the idea to other modules of the robot design process as well. It would at the very least help both teams get a lot more curriculum quickly.
Amazing design and incredible documentation! I’m a student, and I know I’d be too lazy to write this all down.
I see some opportunities for lightening holes.
I love how you’re documenting everything. We’re trying to move to that approach next year. Your process is far above what we’re aiming for, and the amount of effort in that spreadsheet is insane. Your tutorials are very in-depth and think outside the box and explain points that the average tutorial-writer would not even thing about; you essentially diagnose and fix problems before they even occur.
You may want to include Vex among your supplier list in the Overview tab.
In your “research” tab, you mention that robots rarely benefit from going faster than 13-15fps top speed. That is debatable.
In the same tab you mention that #25 chain is half as wide at 15mm HTD belt but 1.5x as strong. I think you’re thinking of #35 chain.
Thank you for mentioning sensors! All too often we forget to add sensors to CAD models.
You mention that speed and weight are independent of drive style, but I think it’s worth mentioning that unless you put a lot of effort into it, a swerve drive will be heavier than the other drive styles (and I love swerve, but most designs tend to be heavier than tank). As for mecanum, I have not found good records of them going over 15 or 16fps, and so you might want to find a solid source for that before thinking that it’s going to be as fast as a tank drive.
The stuff about absolute and relative references in spreadsheets is something I did not know, and should prove handy.
I am most certainly sharing this with the members I am training. It should prove to be a fantastic resource!
Feedback Incorporated
I’ve added VexPro as a supplier and changed the research page to say, “#25 chain is very common in FRC applications, and roughly the same strength as 15mm belt but only half as wide.” Originally I used the rated working loads for OEM chain suppliers (up to 154 lbs) instead of the McMaster-Carr chain (88 lbs) teams are more likely to buy.
Robot Speed
The design supports a variety of speeds if you swap out the Stage 2 sprockets. The current sprockets (34/22 = 1.55:1) give 12.6 ft/s, but you could easily go as high as (42/16 =) 2.625:1 for 21.4 ft/s, or as low as (32/22 =) 1.45:1 for 11.9 ft/s. We could also make tank mode faster (but at the expense of pushing force, obviously).
The main reason I lean towards 10-13 ft/s is that my team got burned in Aerial Assist by a 22 ft/s robot with HORRIBLE acceleration. Now I completely agree with the statement “The true measure of speed is the time it takes to go from A to B including acceleration”. For reference, I’ve calculated that a 10 ft/s robot is actually FASTER than a 16 ft/s robot for distances less than 10 ft. Every distance has a different sweet spot for gearing.
Level of Documentation Detail
While documenting our work is important, it obviously takes a lot longer: I think it’s taken me about 3X longer - starting from scratch - than it would have taken with bare-bones documentation. So creating tutorials like this is probably more appropriate during pre-season than the 45-day build season.
The counter-argument to that - which I’m VERY excited about - is the Wikipedia model: no one sits down (by themselves) and writes a high-quality Wikipedia article from scratch - it’s a collaborative effort that benefits from a lot of eyeballs, and each of the 100-odd edits takes far less time than building an article from scratch.
I can definitely see a team refining a tutorial like this (or adapting it to a different robot module) during the build season.
Thanks again and I look forward to working with you guys! Please email me at alecmuller@gmail.com if you’d like edit access to this tutorial.
The pneumatic actuators aren’t here yet, but it runs!
p.s. While I made this proof of concept with low-precision machining techniques, I would DEFINITELY recommend using a mill to get precise hole placements. Getting this to work required me to do things . . . horrible things . . . that would make most machinists cry.
