THE Simplest WCD you'll ever see


Hope this will be helpful to everyone and FIRST community!

Hi everyone,
hope you all doing well,
for many years we were looking to make the simplest chassis/drivetrain possible inspired from the best teams and many others.
So basically the main goal is to reduce significantly the number of parts required without compromising on utilities and also adding lots of space to ease mechanisms integration.
we also fund out that with this configuration you can simply remove your tank drive system and changed for Swerve drive without doing any change to the frame!!

A normal WCD require a lot of parts such bumpers post that are used also to respect the (min 8" Rule bumpers support point ), beside that its don’t add any functionality in fact this even make your robot heavier and takes out volume and useful space on the robot.
by simply flipping the wheels on the inside of the frame dramatically help to get rid of all those cons aspect that as i mentioned before, not only that but you can use the inside of the 2"x1" side tube to fit the 25 driving chains to get even more out of it. in fact by doing so the chains are protected and easy to access for lubrification and work.
Plus we went even further by using the 2"x1" side members to kinda sandwich the gears in order to make the gearbox smaller and reduce needed parts to function, the reason we did so is because we come to conclusion that with new brushless motors 2 speed GBox is no longer needed.
Hope this will be helpful to everyone and to FIRST community!

Specs and parts:
Desired ratio is 8:1 reduction (can be modified)

  • 4x tube members.
  • 2x Lexan/3DPrinted gearbox plates.
  • 8x double sprockets 25 chain.
  • 16x 1.125" hex F-bearing.
  • 6x 7/8" F-bearing.
  • 4x pinions gears.
  • 6x reduction gears.
  • 6x Colson wheel 4"
    that all you need :slight_smile:
    I am eager to see your feedbacks!! :slight_smile:

Cool stuff, minimalism is a good design goal!

How do the different pieces of tube attach together?

This is a solid drivetrain. I wouldn’t call it a WCD since it’s lacking direct drive wheels and seems like it may be difficult to remove / easily access the wheels, which are core components of a WCD, but it still seems like a good drivetrain nonetheless.

To you, what are the advantages of a drive system like this over a versachassis?


You can use Vex gussets buy we prefer to attach them with block inside tube to minimize space occupation like so


Well the access to wheel will remain the same way of WCD so it is easy as WD to change wheels and the advantages of doing so is to reduce parts, weight, cost, more space to integrate modules and mecanisme.
You can read what i wrote up for more detai!

No? No

I can’t just take off the bumper and slide a wheel off to swap, now there’s robot guts in the way.


I did read what you wrote. I think with the drivetrain by itself you’ll have no trouble getting to the wheels, but consider what it would be like when you have a full superstructure and robot frame on top of it. What about a bellypan? These things can very easily get near if not in the way of where the wheels would come out, making it difficult to access the wheels, and potentially make them impossible to remove without sliding out the shaft.

I like the idea of designing things for minimal part counts, but I would be wary to say that a lower part count makes something inherently more simple. Some of the design choices made to reduce part count may also increase machining and assembly time. I would be willing to bet that a team with access to the resources needed to make this drivetrain could throw together a versachassis system and have it driving much faster than they could this custom drivetrain - would that not also be considered simple?

This drive style definitely has its place and it is ultimately up to each individual team to assess whether the tradeoffs of extra internal space and easier bumper mounting (the primary advantages that I see from this system) are worth the custom parts, increased machine time, and potential difficulty for serviceability. It’s a good drivetrain. I can’t say I agree with the title of “THE Simplest WCD” I’ve ever seen, but I would bet if you made this and took it to competition, you would be just as capable of seeing success with it as any other WCD-inspired drive system.


Depending on the game this can do a nice job of simplifying the design of your drivebase with respect to bumper mounting. That’s one advantage this system would have is that it carries some aspects familiar with a West Cost Drive, but its only four box tubing segments and can legally mount bumpers to.

Is it worth it? Depends on the team, although 118 has used a similar method of building their drivebases in recent years like 2017/2018.


Any reason you didn’t use bearing blocks? I can say from firsthand experience that trying to make a WCD-like drivetrain without them was not horribly simple to manufacture and maintain.

the access to wheel will be from underneath the robot lets assume that you have bench of part on the top well in order to change the wheel you need remove:

  1. the bumpers and the screw that is holding the wheel to the shalf
  2. pull the shaft from outside till the end of the shaft is no more inside the wheel hub
  3. pull the wheel from underneath then put the new one push the shalf till it’s inside the new wheel then put back the retaining screw and Voila!!

simply to minimize the number of parts, cost and weight !

yes that were the inspiration came from, i just took it to an other level of simplicity!!

What’s the plan on adding components to the top of the robot? Would the team need to construct a mezzanine on this?
How does the drive chain work? Is there a double sprocket on the gearbox and middle wheels? It looks like otherwise, chain could easily skip since it appears to be tangent to these components, instead of wrapping around them.
Is there any drop to the center wheel?
I presume there are some not-pictured standoffs between the gearbox plate and the chassis. Why don’t the holes line up?

I see, so now you’re requiring access to the bottom of the robot. Now you have to either tip the robot over or have it on a cart that gives you access to the bottom of the robot, plus you have to move shafts around. Seems much more complex than a standard WCD, where the process to remove a wheel is:

  1. Remove bumper (usually do it most matches to change bumpers anyways) and snap ring / screw holding wheel in
  2. Slide wheel off shaft
  3. Slide new wheel on shaft, put snap ring back on.

My pit crew can do this process for all 6 wheels in less than a minute.


If you can get an allen wrench in there to undo a bolt you could probably pull the whole shaft outward and let the wheel drop out. Probably not as easy access but still not awful if you design for it.


and the max drop center possible with this concept is 3/16" on each side but i preferer to use 4 colson wheel and 2 omni to maximize traction control. and yes chain are inside the tube.
my ssd crushed i lost every thing and the final version as well, fortunately i took some picture to share with my team the day before i will be doing an other cad and will release it!

yep exactly! and if you use colson wheels you don’t ever need to change them

Gotcha, nifty. This is a new-to-me technique, awesome! Thank you for teaching.

FWIW, I imagine that plate (swerve?) at the top of the picture also gives some rigidity (as Telly Monstor tells us, triangles are da bomb).

Despite the potential maintenance issues from having to get to the bottom of the robot for wheel work, I can definitely construct scenarios where this is the best possible alternative, so I definitely won’t dismiss the design over them. I like seeing a solid example of how to do wheels-on-the-inside, it’s not something I see all that commonly!

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I don’t know if I’d go that far, 4" ones certainly see more wear than 6" over a season.

Teams that prefer tread would probably just have a spare treaded wheel ready to swap.

I love the blocks on the end of joining your 2x1’s. I’ve considered producing these as a COTS item in the past but with so many thicknesses of 2x1 on the market is becomes hard to standardize.

There are some cool concepts here for sure. Bumper attachment would be a breeze. I’d consider maintenance of your chain in tube but usually those hold up okay. You could probably even use rivnuts in certain locations if you just wanted a threaded connection to bolt into from the top of the rail as long as it didn’t interfere with your chain in tube.

You’ll probably find there’s advantages and disadvantages to this style of setup. Some of those issues you’ll only find by building one out, let us know how it goes :slight_smile:


Yes thank you!
The blocks are very helpful they allow to save space and ease to dismount the tubing and are very solid.
we will likely prototyping it next back to school and for sure give our feedbacks on the results :slight_smile:

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