pic: Team 449 Hex Drive



This is one of our preseason projects. It’s a 6 wheel West Coast style drive with 6 CIM, dual speed gearbox. The frame is 21x28 in. We are using 4 in Colson wheels in the center and Versa Wheels on the outside. Resting on top is a hexagon superstructure that is 35x28 in.

The link of CAD is below. Enjoy.

Wow, this is way more elegant that what I came up with for our offseason hex frame! I had really awkward plate mounts on the front/rear rails, and something similar on the sides.

Do you think rivnuts would work to mount the super structure frame to the side rails?

Having been there for the design discussions for this, I can assure you that our first few drafts were every bit as awkward/unsatisfying as whatever you had ;). It took quite a while (and input from four or five people) to get to a version of the design that we liked.

Peter, great job with this. Really. One of the best designs you’ve CADed, I wish I were half as good at this as you are.

What is the angle of inclination on your hex (the angle between a hex diagonal and the vertical)? Looks solid. Any reason you need all that structure just to get the shape? And why the different wheels on the ends?

I can’t speak for him, but given what we went through this past season I know we will want the hex to keep its shape through whatever the game throws at it. The extra structure should help with that.

It won’t hurt, but it’s definitely not necessary.

The angle of between front and side frame is 112 deg and between the two side frame is 137 deg. The odd angles are the tradeoffs from making the frame length whole numbers (24" and 15").

The extra verticle beams in the hex frame is not necessary but good to have. One it can diverge the side impact force from the gearbox. Second, it can serve as superstructure / mechanism mount.

As for the wheel, we choose colson in the center for its durability. But our drive subteams needed more traction. So we decided to use Versa Wheel on the side. However, it’s always possible to swap on other type of wheels, onmi or performance.

We mounted our superstructure with rivnuts in a similar way this year and it worked really well. Rivnuts are awesome for this kind of thing; we use them everywhere.

Can you elaborate?

How long does it take to swap the transmission? It looks to me that the bolts on the lower end of the transmission go through the inner wall of your 1x2 tubing and then a clearance hole on the outer wall to gain access to that bolt…I was wondering if anything will fall out of place in the gear box due to loosening the bottom half of the plates. Maybe I am wrong and the upper stand-off bolts will be enough to keep things in place for that short amount of time.
-Ronnie

While it does add a secondary (yet redundant) mounting interface, strength-wise it doesn’t displace much of the force. In our tests as long as you had sufficient backing from the diagonals to the main 2x1 frame, there would be no need for anything else to be done to displace force (especially useful considering it takes out a lot of unneeded weight).

Were you not getting enough traction with colson wheels before? We’ve had nothing but fantastic traction with them when needed. The Versawheels (while grippy at first) tend to wear a bit quickly, even if just on the edges of the drive.

Like I said above, the extra framing around the hex is nice, but redundant, and adds more weight than you need to accomplish the job.

In addition to strength, the inner rails are being used to mount the frame to the drive tubes.

I think Andrew’s point is best summarized as this drivetrain has two complete, independent frames that are likely strong enough on their own. If they were better integrated, a lot of framing could be eliminated.

The support for the angles also doesn’t even need to be a separate frame. For a very minimal (and very strong support), see what we did here.

I wonder if anyone has thought about anti-anti-tpinning frames :slight_smile: It seems to me that if your opponents front bumper were split in two (as shown on the top side of the diagram below), they might easily “straddle” the side points of your hexagon making it just as hard (maybe harder?) to get out of a T-pin as a straight side would be.

This isn’t a critique of your design directly - lots of teams have been experimenting with hexagonal bases recently

We considered integrating the angle supports into the base frame, but we didn’t like how much real estate the supports we considered would take on the 2x1.

Although having a raised secondary frame is heavier, we like the fact that it gives us more vertical space to place pneumatics and electronics. (Our robot for last season was a bit of a mess in terms of packing and that experience heavily influenced this drive’s design process).

Additionally, we’re at least trying to mitigate the weight gain from the hex superstructure by fabricating the base and inner rails on the superstructure with 2"x1"x1/16" and 1"x1"x1/16" (we normally use 1/8").

Also we’re using versawheels mostly to experiment with how well they perform compared to colsons. It’s an experimental offseason project, and we figured we may as well try out as many new features as possible.

These are good points, and we considered them while designing this.

Mainly, we decided that while a single frame is simpler, it makes it harder to really make use of the extra area provided by a hex frame (the picture you’ve linked shows this pretty well, as pretty much everything is contained in the inner rectangular frame. It also complicates wheel access, which is one of the primary selling points of a WCD.

You wouldn’t have to put the wheels internal like we did to do the simpler bumper support.

No, but you would have to make the inner rectangular frame smaller, shorten the wheelbase slightly, and complicate access.

Great post - thanks for sharing. Also thanks to all those sharing CAD archives that show off hex/oct chassis.

I asked Vex if they would add a 22.5 gusset offering to their VersaChassis line. It would allow those of us without a sheet metal sponsor to build something like this with minimal tools.

-matto-

Could you clarify what a 22.5 gusset is?

Apologies - can’t post a pic on a Pic thread apparently =P

http://imgur.com/dkk6jLg

I meant a 22.5 degree gusset. Put one on either end and the existing 135 degree gusset in the center, add some 2x1 VersaFrame and you have a quick hex chassis like the OP showed.

-matto-