pic: Flipped CIM Drive Train

I designed an example chassis for the gearbox this time, because I was much happier with the results. There’s nothing really ground breaking about the chassis, but it fits in a 112" perimeter, and I think it would be strong enough to survive any game in recent history.

Maybe I’m wrong but it appears as if you could fit your outer wheels outside of the frame underneath the diagonal box tubing relatively easily. May need to switch them to a slightly thinner colson but doing so would open up quite a bit of room and use space that likely would go unused in the rest of the robot.

Purely out of curiosity, what effects would one get by having their wheels not in line? Obviously in this design it was more convenient with space, but in terms of turning, handling, and other big words deep in the Simbots presentation on drivetrains what changes?

Curiosity aside, cool gearbox with a sweet frame! Good stuff!!

In general, having that slight bulge in the middle can make it easier to escape from t-bone pins. Having just a bit more wiggle room to work with can make a big difference.

Also, there all sorts of specific scenarios where going with a hexagonal or an octagonal frame can provide benefits in regards to packaging or spacing or other nitty-gritty design details.

I love this design. I love how the shifting cylinders are also the gearbox standoffs. I love how the chain is tucked away in the tube. I love how putting the corner wheels on the inside gives you a hexagonal / octagonal frame for “free”. This is cool.

I like this design… A lot. Fantastic new iteration on the gearbox and I really like how, “slick” the shifting setup is. Very compact and saves a ton of space in the chassis. It’s also a pretty simple way of getting that hexagonal (well octagonal in this case) chassis. Overall a very nice design.

While it’s true that the space under the diagonal rails would normally go unused, putting the wheels outside would ultimately reduce the usable belly pan space for a given perimeter length. This is because there would be less bulge in the side of the drive, which would require the rails to move inward to maintain the same perimeter.

Cothron mostly covered the advantages of a bulged frame. I’ll add a few details on performance/ handling. Theoretically moving the outer wheels inward would increase the scrubbing forces while turning. (imagine the effect if the outer wheels were in the very center of the robot) However, that is negligible in most cases. It also gives the opportunity use wider wheels in the center without wasting space which can help the wheels wear more evenly. I personally think using wider middle wheels also reduces the amount of drop required to turn well, because there will inherently be less weight on the outer wheels.

Here is a video of a robot with an almost identical wheel layout for reference.

Thank you! I’m happy with how it came out. I can probably post the CAD if anyone is interested. Just let me know.

I get that, I’m saying leaving the frame as is, couldn’t you fit the inside wheels on the outside, in which case why not do so.

No, they wouldn’t fit there without a frame modification. They would stick outside the frame by about an inch.

Here is a top down view of what that would look like.

It looks like if you move the wheels slightly inwards and use the 7/8" wide wheels you should be good.

That doesn’t seem possible without making the chassis at least 1" thinner, even with 7/8" wide wheels.

I’ve done it several times before, hence why I’m bringing it up. ::safety::

The question isn’t whether it’s possible, but rather what effects it would have. If you bring the wheels closer to the center wheel, then you can make 7/8" wide work, but then you’re reducing your wheelbase length. For most games I don’t think having them in the inside is too big of a deal, and it’s easy to move the wheels in the design phase in-season anyway.

I don’t think it’s a huge deal either, but OP was mentioning bellypan space as a priority, in which case there would be situations where the space in the center of the robot may be more preferably allocated to something that isn’t the drivetrain.