10-10-2014 09:18

JesseK

Re: pic: Team 449 Hex Drive

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?

10-10-2014 09:24

Oblarg

Re: pic: Team 449 Hex Drive

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.

10-10-2014 09:42

Re: pic: Team 449 Hex Drive

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?

10-10-2014 09:51

JesseK

Re: pic: Team 449 Hex Drive

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.

10-10-2014 10:05

Re: pic: Team 449 Hex Drive

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

10-10-2014 11:27

449_PeterPeng

Re: pic: Team 449 Hex Drive

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.

10-10-2014 13:07

Chris is me

Re: pic: Team 449 Hex Drive

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?

10-10-2014 13:38

RonnieS

Re: pic: Team 449 Hex Drive

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

10-10-2014 13:38

Re: pic: Team 449 Hex Drive

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.

10-10-2014 14:03

Chris is me

Re: pic: Team 449 Hex Drive

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

10-10-2014 14:11

AdamHeard

Re: pic: Team 449 Hex Drive

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.

10-10-2014 14:31

nuclearnerd

Re: pic: Team 449 Hex Drive

I wonder if anyone has thought about anti-anti-tpinning frames 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

10-10-2014 17:02

hzheng_449

Re: pic: Team 449 Hex Drive

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.

12-10-2014 12:33

Oblarg

Re: pic: Team 449 Hex Drive

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.

12-10-2014 12:35

AdamHeard

Re: pic: Team 449 Hex Drive

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

12-10-2014 12:44

Oblarg

Re: pic: Team 449 Hex Drive

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

12-10-2014 16:46

aldaeron

Re: pic: Team 449 Hex Drive

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-

12-10-2014 16:49

Re: pic: Team 449 Hex Drive

Could you clarify what a 22.5 gusset is?

12-10-2014 17:12

aldaeron

Re: pic: Team 449 Hex Drive

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-

12-10-2014 18:00

Oblarg

Re: pic: Team 449 Hex Drive

449 doesn't have a sheet metal sponsor or access to a CNC mill, actually. We do all our machining by hand with a drill press, miter saw, and band saw.

However, we do have access to a laser cutter that can do delrin, which allows us to make precise templates for our gussets that we can then use to match-drill.

13-10-2014 16:00

Cash4587

Re: pic: Team 449 Hex Drive

My team this year had a cutout in the front bumper like you drew. It seemed to be somewhat effective to reduce the effects of teams hex drives. (our bumper cutout gap was 11" to make room for our arm when in the down position) However we really only had the chance to use it against 148 whose hex sides weren't as large as some other teams. In order to prove that the cutout really was effective in this aspect we would have liked to try it out on some different angled hex chassis. I don't know if any other teams can attest to this being an effective way to reduce the usefulness of a hex chassis, but please chime in if you have any other ideas on this.

13-10-2014 16:26

Oblarg

Re: pic: Team 449 Hex Drive

I think a hex chassis would still see some benefit in situations up against a wall, since they still have a point to pivot around where the frame contacts the wall (where a rectangular chassis would not).

Obviously, I have no way to test this at the moment. It'd be nice to play around with a few actual bots and see how the different situations pan out.