Hypothetical CAD: Drivetrain Concept

So, in between study sessions, I was thinking of how to better stabilize a drivetrain while still allowing turning to be smooth. I cam up with this quick bit of CAD and was wondering if something like this would even be feasible

What do you guys think? My thought process here is with the wheels on both sides of the tubes, you essentially gain 4 “wheel lines” for more stability, due to the train covering more surface area. The “curve” you gain by placing wheels as such I expect also help in turning.

I don’t think this is even going to be built by my team, but it was an interesting thought to me. plus this gave me some practice CADing with VEXPro versachassis components


I guess that you’re planning on running chain in tube?
Edit: Wait never mind I see the sprockets.

I want to say I saw 118 run a drivetrain like this in 2016. I don’t think you’d have any issues as it should work just like any 8WD would.

If the question is if it would turn any better than in-line 8WD… I am not sure.

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I’m not sure what you mean by “stability”. If you mean resistance to tipping over, then you would want your wheels as close to the corners as possible. This gives you the longest moment arm between the CG and the “fulcrum point” of the wheel contact patch. By moving the corner omnis to the inside of the tube, you have made the robot more prone to tipping over, not less.

If you meant something else by “stability”, let us know.


I think you’re right about the curve.

We built something similar in 2017 but only used the inner-wheel option on one end. It helped our driver execute quick fish-hook turns at the end of gear scoring runs, and allowed a tapered bumper on that end so we slipped out of pins a little more easily. That taper also helped avoid the opponent loading zone, most of the time.

May I ask why you put the chain and belts outside the side rail?

I’m not sure about your team affiliation or technical background, so I don’t know how deep to go responding.

Basically, in this case the robot’s scoring geometry dictated drive rail spacing. Drive train elements outside the rail simplified access for maintenance. The downside is more cantilever load on the bearings, but that was not a major concern in 2017. The field was flat.

Not seen in the pictures: our climbing mech was PTO-driven through one of the rear wheels, which led us to over-build the drive train. That’s one of my team’s tendencies. We like safety factors so we always end up fighting to make weight.


This is a big benefit to the wheel layout described in the OP. By making the sides of your frame perimeter not flat, it’s much harder to be t-boned.


Teams used to run “hexagonal” chassis more often. 971 used it on their 2016 robot, and 118 also used in some years. T-bone resistance is a plus, with the turning performance being a possible side benefit.

Being able to change out the inboard wheels would be one area of concern. Especially if you were to use omnis at the corners and started from lvl 2 this year.

Why do you say that… you would just pull the shaft out partially and drop the wheel straight down.

I guess that’s slightly more time consuming than pulling the wheel straight off, but not by much.

Depending on how the wheel is secured to the shaft, you could have a tool access problem.

I am using shaft collars on all the shafts (our team does not have access to a lathe to make a channel for a c clip)

If the perimeter were to be hexagonal and therefore the robot were made wider than the rectangular profile, this would in fact increase the tipping stability.

The CAD posted does not show that, but could be easily modified by shortening the front and rear crossbeams.

Tap the shafts and stick a bolt and washer in there. Much less bulky and easier to maintain.


Harder to access from the inside of the frame depending on a few things, but definitely another way to go about it.

As others have said, there’s no reasin this drivetrain configuration wouldn’t work per se, and a number of teams have used something similar in previous years. But if you want any comments on “stability”, you’ll have to better define the term.

At least it doesn’t rely on the wheel being rotated the proper amount to access the tiny set screws :smiley:

Highly recommend these bolts if you go this route.

It also helps in the silly (but possible) situation of getting shoved such that the flat side of your robot is against a wall, leaving you unable to pivot out easily. Less of a problem in the “6 NEO” days than it was in the “2-4 CIM” days, but I’m sure it still happens every once in a while.