3322 Pre Season Chassis

Team 3322, is proud to present our 2020 pre-season WCD and gearboxes. Our local offseason competition WAPUR was our first time running a WCD with custom gearboxes, and our first experience with a Chain in Tube setup. That drivetrain performed well, but there’s always room for improvement! I am the lead designer for the team and as part of my preparation for the season I have designed a couple west coast drives and custom gearbox pairs for a field requiring either 4 or 6 inch wheels.

The six inch wheel version uses a single speed double reduction 2 neo flipped gearbox, and 18 tooth 25 double sprockets driving AM aluminum wheels.

The four inch wheel version uses a single speed single reduction 2 neo gearbox, with the same sprockets, and AM extrusion wheels, but I might bump up the sprockets to 22t if it is deemed necessary.

We are hoping that Infinite Recharge will allow us to use this CAD and get a WCD done as early as possible. In order to make it as versatile as possible I opted to leave out the battery, bumper, and electronics mounting, Instead deciding to wait until the rest of the robot is at least conceptually done and mount those components then.

This CAD leverages fusion 360s admittedly slightly annoying parametric functionality to help achieve that goal, with the ability to be as short as 18 inches.

I put a majority of the time I spent on this project into optimizing the design of 2 and a half different gearboxes
A single reduction gearbox

And a double reduction gearbox

The last half is a chain in tube version of the single reduction gearbox, included in the imgur album linked here

Lots of random information:

It mounts to the frame using 3/8" long 1/4-20 SHCS threaded into the plate clamping it to the drive tube, the CiT version has the mounting bolts closer to mid line in order to clear the chain.

The Single reduction gearbox weighs 0.96 lbs without motors and has a gear ratio of 9:62, which works out to 14.9 ft/s free.
The flipped gearbox weighs 1.54 lbs without motors and you can swap out the pinion for 10, 11, and 12 tooth versions giving it a range of 14-17 ft/s free. The second stage reduction can also be changed from 22:40 to 20:42 if a slower speed is really needed

The main issues with our WAPUR chassis, now playing the role of a prototyping/code development chassis for build season, were ground clearance, and concerns with the CiT (chain in tube) setup. While I did not fully solve the ground clearance issues with the new 4 inch wheel WCD, if the game requires more than 0.4" of ground clearance we can just use the 6 inch wheel version.

The main reason I did not cad a CiT configuration is because 1) I ran out of time and 2) The chain limits design freedom with fastener placement when mounting above chassis elements, and the limitation of not being able to drill new holes, or drill out rivets in the drive rails (due to chips getting in the chains) would add more complexity that I do not think is worth the many benefits of CiT for our team. Of course, if the packaging constraints necessitate CiT I’ve already done the hard work so designing a CiT WCD in season should not be too time consuming or difficult.

I am aware that WCP basically just released both of these, but I cadded these before those came out leave me alone. I think I have a mounting system that better fits our goals, and these are cheaper for us to make.

The plan is to decide whether we can run one of these on kickoff day, and start CNCing them immediately, while the CAD and strategy team works rest of the robot.
Here’s a link to the various CAD downloads, PM me if you want the files in another format (f3d if you want parameters and use fusion) and feedback is appreciated.

Post to come about our CNC router setup.

I wish everyone the best of luck with the 2020 season, and happy new year!


These are great. Both gearbox options are nice and compact. Good luck in 2020!

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That 18 inch robot is beautiful. What does the bumper mounting look like?

You can also consider 32DP gears, which would let you have an all-steel geartrain.
These: https://www.andymark.com/products/steel-gear-15tooth-32dp-0-312-bore
plus these: https://www.therobotspace.com/ProductDetails.asp?ProductCode=vex-217-5869
gives 6.7:1 reduction in a single stage.

That gives a 3/8" hex output unless you broach it yourself.


I haven’t fleshed out what the bumper mounting looks like because the design is likely to change depending on how the rest of the robot ends up. Likely some c channel around the outside of the bumper support rails and then rivuts on the front and back rails.

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Hello BitSentinel,

I was looking for a drivetrain that I could draw inspiration from for my take on West Coast Drive Train. I managed to stumble on this post for your Pre Season Chassis. In post 6 of the thread, you mentioned that the bumper design “is likely to change depending on how the rest of the robot ends up.” As your team was able to win the Quality Award as well as seed 2nd at FIM District Kettering University Event #1, I was wondering if you would mind sharing how you mounted your drivetrain to the bumpers. Thank you, and congratulations on the success your team had this season!



That is a sweet drive train! I hope your team is able to build it soon.
Why did you choose not to use chain tensioners on your sprockets? I thought since chain stretches over the course of a season and it’s good to have one.
You mentioned chain in tube makes drilling out rivets difficult. If I put in a decently sized hole or two, do you think we could get the rivet bits to fall out? Are there any other ways to get around this problem?



casually chooses to ignore the actual question asked right before this

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3512 used these flipped gearboxes this season.

Very inspirational.

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Brings tears to my eyes

I can’t speak for the OP, but on drivetrains you can usually get pre-worn chain and use an exact c-c distance plus an adder value. As for rivets, it’s very possible to do, and there are threads on CD about CIT drives that address them, but it’s probably not worth it unless you really need the space

Hey BitSentinel the team and me got a few questions for you about your drive train


Good Afternoon BitSentinel,

I have some questions regarding your “inspirational” gearboxes.



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happy birthday


bump @BitSentinel


In light of 3322’s great performance this weekend, I wanted to come back to this thread to see if you had the time to explain the bumper mounting now. I was watching the event and there seemed to be robot handles on that were used to lift the robot and set it down. Hoping you could shed some light about how those were made or where you bought them from. Thank you so much for your help and congrats on the newest highest combined score record.


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