pic: Concept 6W Drive Train

This is based from 469’s 2014 drive train, they always make beautifully simplistic machines. A custom single speed gearbox is in place of a Vexpro ball shifter.

After playing around with different drivetrain designs, this one seems the most appropriate for the resources on our team. Trying to stick with the keep it simple rule, and remove any unnecessary components. WCD systems consumed a lot of our machining resources the past few years, this should be quicker to make with the kids machining components.

Weight: 34.5 pounds

Any particular reason for cutting off the corners? Does it help much in giving more area for a given perimeter?

Definitely have to concur that simple is good.

Looks solid.

Looks a little too solid IMO. There’s a ton of 1x1 on there.
However, 34 lbs is still pretty light for six cims (actually that’s very light) so adding in a shifting gearbox would make good use of that drivetrain I think. It’s only a couple pounds more, and allows for safe top speeds of 18fps+ without worrying about main breaker trips.

What makes this drive train better than a kitbot with nitrile treads and 6 cim gearboxes? If you want to keep it simple why not go that route?

How is that any simpler than this?


It’s not.

Oh I just noticed:
Your main gearbox shaft is attached to the out frame member. If the outer frame becomes damaged in a collision and bends a little, it will damage the efficiency of the gearbox, and possibly render you immobile on one side.
Also, what’s the reasoning behind cutting the corners? It seems like extra work to me.

They are trying to work within their existing resources, and this is a simple design that fits within those resources. I would probably find it reasonable to assume that they don’t anticipate having the funding to buy Versa, or to buy Versa and still do X, Y, and Z that they want to or need to do. Or that they’re one of the teams that prefers making over buying (there are a few out there).

Is a WCD simpler? Maybe. But if you’re doing all the machining for it, there are some advantages to NOT doing a WCD (like having more time!). Even if you are thinking of buying one, there could still be advantages to not doing one (dead-axle setups tend to be a trifle easier than live-axle setups in terms of manufacturing, something about no keyway or hex).

Are the gussets at the corners supposed to be seperate strips or angle iron? If they are seperate strips, it looks like a hard hit to the upper member could severely bend it inwards.

Edit: The upper 1x1 above the wheels

A full versachassis can get expensive, I’ll admit that, but just using some of the parts can greatly simplify this design and make it not only more effective, but more reliable as well. You don’t need to buy an entire drivetrain setup, but using what your resources will allow can greatly simplify things.

You don’t need to break bank on COTS parts to make a great drivetrain, but ignoring the cost effective resources available to teams isn’t the answer either.

Is there a particular reason why the corners of the chassis are cut off?
The only reason I can think of is if you’re trying to make the chassis fit within the 112 inch frame perimeter.
Otherwise, I don’t see a structural benefit of cutting the corners off.

If I had to guess it would be that they’re trying to keep all the 1x1s the same length for convenience? Then cut ends to keep it flush. Personally though if that’s it then I might rather have the extra support from corners.


It gave about 4.5" inches in perimeter back, so the frame is at 28 x 30 with ~ .5" to spare. The small increase in bumper complexity seems worth the extra 4.5".

I think you are right depending on the game, but I would like to avoid the added complexity and cost if possible. Most games don’t require 18 fps imo.

Not much, it helps with bumper support and added area for mechanisms. I also like how the gear box gets packaged. We like to build as much as we can in house. The kitbot wouldn’t have the students machining the components.

You are correct with how we are thinking. I would argue once you add bumper support and interfaces for mechanisms to a WCD, it is more complex. This structure immediately supports the bumpers and provides a little better locations for mechanisms imo. We also try to build as much as we can in house. We are fortunate enough to use the manual lathes and manual mills in the school to build.

With the bumper outside of the frames protecting them, I am not to worried about it. The dead axles also act as cross members supporting the outside lower beam. If the upper beam needs more support, cross members could be easily added. The corners being removed reduces the frame perimeter, allowing more length or width to be added.

Using angle pieces to connect the beams, the corners have no structural benefit as they carry no load. Now if top and bottom gussets were used, then additional structural support would be provided. The statics and solid mechanics of the structure make the corners the strongest part. Angle pieces are susceptible to torsional loads, but the internal beams stiffen any torsional loading the structure would take. If you draw up a free body diagram it becomes clearer.

I can’t take much credit for this, I just copied it from 469 with a few tweaks. I would say it worked pretty well for them, world championship and such things. Not sure any one was questioning the reliability of their drive train, hats off to them, they are an inspiration to all teams.

We mill our WCD siderails on a manual mill for reference.

Also, bumper support on a WCDdoesn’t need to be complicated.

As for interfacing to mechanisms, how is it more difficult with a WCD?

Are there really no problems with only having a bumper support that low off the ground? As far as I can tell, that’s going to be contacting the bumper well below-center.

No problems at all.

We make one piece bumpers with strong corners. Any moment trying to bend the bumper over is reacted by the adjacent section.

Here is a good exercise…

Design a few drivetrains, give them all a good honest effort (otherwise you’re just wasting your own time and lying to yourself).

While designing, do your best to optimize all the variants for your resources. Publicly post them for review. Invite BRUTAL commentary, take this in stride and incorporate the feedback that makes sense. If you have enough experienced students, mentors and possible sponsors that can offer review, the public part could be skipped.

At the end do a fair comparison of the different options on the criteria that matter to you; fab time, difficulty, cost, etc…

Going into nearly every season we have designed a swerve, west coast, plate sandwich drive and the last few years butterfly/octonum. We constantly reassess them to better suit our ever changing resources, and compare them on the merits we care about.

It’s unreasonable to anecdotally link it to a drive a good team ran. Using that logic ANY drive can be proven to be the best.

Ah. We’ve never done one-piece bumpers. We probably should try it out, it seems. Thanks.

Edit: Out of curiosity, how do you do the corners on your bumpers?