WCD drivetrains of increasing impracticality

Over the corona-cation (specifically the last 3 days), I’ve had lots of time to do CAD, and I’ve used that time to hone my WCD skills in a variety of ways. I’ve created four drivetrains to various degrees of completion, documented below. None of these designs involve chain tensioners, a shortcoming I am aware of and would not include on a competition robot.

Firstly, I’ve created an 8WD drivetrain with 3.25" wheels, using a custom single-speed 2-NEO gearbox.

Secondly, a 10WD drivetrain with 4" Colson wheels and a different 2-NEO single-speed gearbox. This design is the most viable for a competition robot and resolves many of the issues I had with our competition robot from this year.

Stealth drive
Then we enter the realm of complete impracticality: a 14WD drivetrain using 2" stealth wheels, including a 3-775pro custom single-speed gearbox. A brainpan is necessary as the chain runs go below the bottom of the 2x1 side rail. The wheels on the ends have just over 0.15" of ground clearance. On the plus side, the bumper rails can mount directly to the top of the end rails since the wheels do not clear the top of the 2x1.

Finally, created completely on a dare by a team member, Camber drive. This design uses the 775pro gearboxes from the Stealth drive, but uses 18 1.625" Colson wheels as the drive wheels, cambered inward at an approximately 45 degree angle from the vertical. I put very little effort into this (it was done entirely between the hours of 11pm and 1am last night) so it is the least complete, and it is the only one where I had to resort to saying “just weld it” because I couldn’t think of another solution to attach the side rails. This is also easily the boatiest-looking drivetrain I’ve ever made.

All STEP files are available via Google drive at the link below:

If anyone has questions I probably don’t have answers but I’m happy to try.


Any reason for choosing 775 pros for the drive instead of sticking with the 2 NEO’s?


0/10 needs more decagonal wheels.


775s were less practical and therefore more appropriate. Also I wanted to design a 775 gearbox for fun.


This is going to be my design philosophy going forward, thank you for the inspiration.


Already preparing for a water game, I see.


Galaxy brain.

You should make one with bicycle wheels.


FWIW 1723 has used an 8 wheel WCD without chain tensioners for the past two years and had absolutely zero issues with the drivetrain. We added .018" to the center distance of the bearing holes. We used #35 chain so that probably had something to do with it working out alright. There was about a half inch of backlash at the wheel furthest from the gearbox (2 chain runs away) but we weren’t doing any odometry so that didn’t really matter.

IMHO chain tensioners aren’t strictly necessary and it’s a design tradeoff to consider if you’re confident in your machining capabilites. That said I certainly wouldn’t fault you for including them, especially if you plan to use #25 chain.

All of these designs look great. I’m particularly a fan of the camber drive :wink:


+1 for that. We’ve been using non-tensioned #25 chain on our drivetrains for the last three years, and never had any problems with it. We were inspired from 254 who (AFAIK) do this since 2017 or 2016. It really isn’t hard once you get the CC distance right - which might require some real life tests (we tested this in the offseason of 2017 and found the right amount to add to the CC distance for our mill).


I’m very glad I wasn’t drinking anything from a cup while I read that.


1993 Game. A team had very large wheels


I’m on mobile or I’d link a pic, but the camber drive is reminiscent of 116’s 2005 omni drive that was similarly heavily cambered.

Nice to see people living the #stancelife again.

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45 degrees of camber is nothing compared to 116’s 2005 robot. That thing had 82 degrees of camber.


Talk about timing. Was digging through 116’s archives a few days ago, and happen to have a few photos saved.

116-4 116-5


Why did they do that design? What advantage did it give (or supposed to give) over a traditional drive train?

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I like how you managed to reach the point where gear drive would be lighter than or comparable to chain/belt, even if you didn’t use it. Maybe an idea for future projects…? I hear banebots has some 1 3/8” wheels.

@Lil_Lavery can probably explain more (I’m pretty sure he’s in the picture with the team around the robot, but I’m not saying which one), or @dlavery can, but as I recall they wanted maximum stability in a full-omni drivetrain, which meant putting the wheels as far to the outside as they possibly could (kind of difficult when your wheels cross the corners). So they flattened the wheels to an absurd degree.

Funny note: The last picture was at IRI or I miss my guess. AFTER the robot had gone through a torrential downpour (OK, by coastal standards) in an open trailer (behind the robot) and had to be dried out.

You’d be right, assuming the photos were properly labeled. Would explain why the bot was soaked in some of the photos…

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Interesting design. How did you cad the pocketed belly pan? My laptop was screaming when I tried to do that :frowning:

You have not reached the level of ultimate impracticality until you make a round WCD robot with 16 drive motors (all PDP slots).

Take your inspiration from this.