pic: 649 Offseason Hexagonal Chain-in-Tube WCD

In the spirit of testing new designs, team 649 plans to build a hexagonal West Coast Drive over winter break. The design an concept is heavily inspired by 148’s X-009 offseason DT and 971’s 2014 octagonal drivetrain

It’s a chain-in-tube system, something we want to test before buildseason starts, mainly to determine if the lack of maintainance and tensioners are worth the extra effort to assemble the chain beforehand. We are also switching to chain for the first time in team history, previously using exclusively belts for our drivetrains (last year we had some serious issues with belts skipping and stripping. Mostly our fault, but we’d like to have some leeway for us making mistakes).

The drivetrain is designed so that the side rails can handle a 6 wheel or 8 wheel configuration (we left out 148’s 10 wheel config) without any additional machining. The render shows each configuration on each side of the drivetrain (we’re not going to make an asymmetrical drive, don’t worry)

With the assumption that next year’s game will be defense heavy, we wanted to test the usefulness of a hexagonal drive to prevent t-bones, and if we can even make the strange bumper shape.

This drivetrain will be used to test code, possible custom gearboxes, drivers’s practice, and prototypes when buildseason starts.

The CAD will be uploaded soon for anyone who wants a deeper look. Any input would be greatly appreciated

Very neat. I assume the bumpers will form the hexagonal sides? Very clever, and it performs the same function.
What made you opt for screw+washer and eclips to secure the shafts over circlips everywhere?
Is it just me, or are there 4 wheels on the far side and only 3 on the close side?

EDIT: Did you add any extra spacing for the chain? Apparently that’s a problem according to these tests.

yeah the bumpers form the sides we probably need a bit stronger bracing for the bumpers though, as these supports only touch the bottom of the bumper. And we used bolts and washers last year without too much problem, and its easier to machine for us than e-clip grooves are. we may do only e-clips or only only bolt and washers. we still haven’t decided.

Chain spacing is .1835 for the 6W config and .2 for the 8W config (cuz both designs share the outer holes, we couldn’t make everything a nice .186 like we would have liked)

It appears that the sides are set up so the near one would be for a 6 wheel drive and the far one would be for a 8 wheel drive

EDIT: just read the original post lol…

Going by the 2014 rules (as well as 2010-2013 I believe, don’t quote me) the bumper corners need to be supported. Because there are unsupported corners that overhang the wheels this drive base would not pass inspection in 2014.

Cool design otherwise.

I’m not sure what’s going on the bumpers, but we will definitely take that into consideration.

Meanwhile, we have uploaded a .STEP file to grabCAD for anyone who wants to see this drivetrain closeup on their CAD software. Link is found here: https://workbench.grabcad.com/workbench/projects/gcxZ6mpl3oBD-PyLoCJD-Qli9b91GRXN3BcSZKH-So9eF9#/space/gcLqs0BrcNAa6FSR5TBMBYGzUNm4er5A3ckfPNf6IoZmc9

Assuming 2016 game rules are similar to 2014, you can just have plates that touch the bumper in the corners for the required distance (1/2" in 2014 IIRC) to satisfy the bumper rules.

I think that is a nice design especially with the option for both 6 and 8 wheel drive. I was wondering why your side bumper supports are oriented horizontally instead of vertically. Additionally, it is pretty easy to cut a hole in the top of your change (where the chain is running) and put in a basic chain or belt tensioner if your end up having that problem. In the past, I have found 3D printer parts with a bolt to be great for tensioning.


Since the bumpers have to be 2 inches off the ground according to 2014 bumper rules, the bottom half of the boxtubing wouldn’t actually contact the bumper. so we turned it sideways to get some more contact area. But the bumper system is still a work in progress, so we may change it again if we think of something nicer.

and actually the design can be used with versablocks if we need to (the drop center is the same). we are just hoping to avoid spending money (and robot weight) on them.

I believe you will also be able to get a 4wd out of that system too!

Is this slightly better at turning due to the wheel that is on the outside (wider track width)

I think that is correct, but the main intentions of this drivetrain is to have the ability to work around t-bones.

I believe you will also be able to get a 4wd out of that system too!

Yup. However I don’t see any advantages of a 4wd as opposed to a 6wd or a 8wd, and I think the reason is because how many wheels are in contact with the ground (probably 99.99% wrong because of drop center).

Also, one time I saw a 4wd FTC chassis, and when it turns the entire thing shook, and I think that was because of the rubbing of the wheels. I think if we use a 4wd on this drivetrain, we will see the same thing happen, although I am not entirely sure.

why aren’t the two gearboxes parallel?

It’s just for show: we are trying to demonstrate that our system can be easily switched from a 6wd and a 8wd. That’s why the gearboxes aren’t parallel because of the position of the outputs shaft, but when we actually make this, both gearboxes will be parallel

This rendering is demonstrating a 8wd on the far side and a 6wd on the nearside. As a result, the gearboxes are in different places.

Wow, that’s really pretty. The bumper concept is simple and neat.

How are you dealing with the difficulties of adding a drop using the chain-in-tube system? Were you able to add a drop somehow or are the wheels different diameter? If so, how do you think that will impact the 6WD version, considering at all times the wheels touching the ground will be running at a different speed?

(or is that 3x1 tubing and I’m just missing it)

Haha Thanks! We had some fun with the rendering tools :cool:

And we’re actually using vexpro 16t sprockets, which lets us have a 1/8 inch drop. but because of that we had to make the side rails 2x1.5x.125 in order to be able to hold everything. we’re not a fan of that decision, but the drop center was worth it in our opinion.

And we may have to revise the bumper supports, because the 2014 rules somewhat mentions needing to support the corners (the wording is not very clear). We have a solution for this, its just slightly larger (it provides better support too, for a more defensive game.) When I get that finished I’ll put up another render.

Hi First_newbie. As someone new to First and CD, you should learn to read the threads before asking questions.

This is so because the chassis is set up on one side with a 6 wheel west coast drive, and the other with 8 wheels. This is only to demonstrate both on the model.