18-08-2014 20:02

Arpan

Re: pic: 6-sided tank drive

Not sure if the 1*1 stuff supporting the bumpers is vexpro versachassis stuff, but if so I'd double layer it or use thicker material. That stuff is really thin for a bumper frame.

18-08-2014 20:24

evand4567

Re: pic: 6-sided tank drive

If it's welded together with 1/8" walls, it shouldn't be a problem

18-08-2014 20:28

Arpan

Re: pic: 6-sided tank drive

right; the 1*1 vexpro stock has much thinner walls. I'm not sure which it is.

18-08-2014 22:47

BBray_T1296

Re: pic: 6-sided tank drive

If I may ask, why are your angles "149.07 degrees" and "105.46"? You will never ever need that kind of precision in a FRC situation, especially on a frame which will be bashed and smashed into every 6 seconds anyways.*

Even with a chopsaw/bandsaw/mill/cnc mill/whatever, it is certainly a better real world design if you round those off to some amount. How critically important is it that you are exactly perfect? In your robot's frame, just about never.

Also, just a recommendation, While it is less pretty, using 1/32" (or preferably 1/16" or 1/8") increments instead of decimals is much less of a hassle for whoever will measure the parts, and just a couple clicks in CAD

Not trying to be a wet blanket on this design, it certainly is cool, but it would be beneficial for every party involved if you simply rounded to the most convenient dimensions, where there will be an immeasurable difference in performance, but a significant improvement in both engineering design quality, and manufacturing


*after all, the entire point of a 6 sided drive like this is for the very purpose of escaping trapping t-bones"

19-08-2014 07:13

evanperryg

Re: pic: 6-sided tank drive

The weird angles are the result of the not-weird side lengths. The tolerance should be pretty high.
Oh, and it's welded 1/8" aluminum tubing

19-08-2014 10:06

Rosiebotboss

Re: pic: 6-sided tank drive

Does it meet the 110" rule?

19-08-2014 10:14

g_sawchuk

Re: pic: 6-sided tank drive

Question for you, how exactly is this useful? I love the design, it looks pretty fancy, but in the long run it will amount to more work and not be worth it if doesn't have any specific benefits compared to a 4-sided tank drive.

19-08-2014 11:45

cxcad

Re: pic: 6-sided tank drive

This design is helpful for avoiding t-bone pins and defense in general. Also hexagons have a greater area to perimeter ratio.

19-08-2014 12:36

BBray_T1296

Re: pic: 6-sided tank drive

If you are going to forgo the square, a hexagon is really the best option for a traditional tank drive. For things like holonomic and 3 wheeled swerve, other n-gons may be appropriate.

Circles are mathematically the optimal perimeter-to-area figures, but would be difficult to make, and a nightmare to put bumpers on.

19-08-2014 12:41

AdamHeard

Re: pic: 6-sided tank drive

You can more efficiently optimize the use of the perimeter sizing by moving the front/rear wheels to inside the frame, and making the center wheel wider.

19-08-2014 12:45

g_sawchuk

Re: pic: 6-sided tank drive

Ah, good point, although T-Bone pins are rather rare. However, would the bot be able to play an effective defense? For example, if the objective was to T-Bone a bot of the other alliance, it would require rather exact precision as to hit the bot right in the middle of their side.

19-08-2014 12:52

BBray_T1296

Re: pic: 6-sided tank drive

I saw them happen quite a bit this season. Robots waiting for the ball from a human player after a truss were prime candidates for being bulldozed back to the inbound station

19-08-2014 12:53

AdamHeard

Re: pic: 6-sided tank drive

Not necessarily, if they are hit square to an angled face, at least the drivetrain is not perpindular to the t-boning robot.

T-bones happen a LOT at the high level of play in certain games.

19-08-2014 13:15

g_sawchuk

Re: pic: 6-sided tank drive

Fair enough. It is true that they happened this season a lot, but this was due to the lack of mobility some robots had as they waited for the ball from the human player. On a good driver, t-bones tend not to be effective as a good driver will stay in motion as much as possible.

19-08-2014 13:18

AdamHeard

Re: pic: 6-sided tank drive

There must have been some AWFUL drivers on Einstein this year.... and 2011... They were getting T-boned all the time!

Someone get these teams some better drivers

19-08-2014 13:24

g_sawchuk

Re: pic: 6-sided tank drive

It really depends on the game. It's true, this year was difficult to avoid being T-boned as most robots were incapable of driving right by the human player station without stopping and successfully getting the ball. Mixed with that and the fact that it's hard to move and pass the ball, it was one of the better years for t-boning, but still, t-boning is not what I would consider a very effective defensive strategy most years.

19-08-2014 13:32

Re: pic: 6-sided tank drive

Since Adam is too modest to boast about his team ( ), I'll be the one to inform you that that is a very dangerous and mostly incorrect statement to make.

19-08-2014 16:08

evanperryg

Re: pic: 6-sided tank drive

That's how I had it laid out originally. Thankfully, I kept the other design around

A good driver should be able to avoid defense, yes, but a good defensive driver should be able to get a t-bone or two.

20-08-2014 03:18

tickspe15

Re: pic: 6-sided tank drive

If tbones were rare and could be easily avoided by good drivers you would not see teams like 254,971,973,148,1114,118,1730,33 and countless other elite teams dedicating engineering hours, money and weight to mechanical aids to get out of pins.

This year we were caught in pins constantly and it slowed us down significantly while simultaneously wearing down our wheels. Often less high scoring teams don't face the same level of defense as their higher scoring counterparts so their robots weaknesses are never exposed.

20-08-2014 10:42

Abhishek R

Re: pic: 6-sided tank drive

Wouldn't a hexagonal shape limit how close you can get to the outside walls of the field? I'd imagine if you skim the wall, you would end up being spun in some direction.

21-08-2014 07:08

evanperryg

Re: pic: 6-sided tank drive

In some cases, this is good. Some bumper materials have a lot of friction, so if you get caught up on the wall, it can be a pain to get away.

I agree that tbones are very common and drivers should be prepared for them, but I don't think I've ever seen a team make a mechanism specifically to break pins.

21-08-2014 12:18

Arpan

Re: pic: 6-sided tank drive

FRC 1114- drop down omni wheels

FRC 118- Drop down omni wheels

FRC 971 - Unique chassis shape

just 3 off the top of my head

21-08-2014 12:58

Zaque

Re: pic: 6-sided tank drive

I believe 1986 had a drop down omni wheel up front also.

21-08-2014 13:04

Boe

Re: pic: 6-sided tank drive

As well as a large number of teams using lower friction bumper materials, off the top of my head I can think of 971, 67, 1678, 1717, 254, 148, 1114, and 2056.

21-08-2014 13:30

Andrew Schreiber

Re: pic: 6-sided tank drive

In the 67 case I recall it was at least partially for their intake based on what my brother said.

22-08-2014 23:01

mrnoble

Re: pic: 6-sided tank drive

My students have spent a chunk of their summer designing a hex chassis 8WD because of this very problem; we saw lots of t-bones, and we contributed to a fair number of them. We finished 3D printing the narrow/wide wheels this evening. I've been researching new bumper materials, and the mixing of materials for maximum benefit whether defending or trying to avoid pins. Great stuff!

23-08-2014 15:13

evanperryg

Re: pic: 6-sided tank drive

If that's true, then 67 is the only example of a separate mechanism being used to break defense. The drop down omnis/chassis shape are drivetrain-related mechanisms.

24-08-2014 19:38

Aren Siekmeier

Re: pic: 6-sided tank drive

What? 67's choice of bumper material may have been unrelated to the drivetrain and pinning, and driven rather by the intake, is what Andrew is trying to say. And drop-down omnis are definitely a separate mechanism.

24-08-2014 20:00

Andrew Schreiber

Re: pic: 6-sided tank drive

The bumper material was primarily a function of their intake mechanism.

24-08-2014 23:55

Kevin Leonard

Re: pic: 6-sided tank drive

Drop-down omni wheels and alternate chassis shape are two attributes of a robot only present for the purpose of getting out of t-bone pins.
I guarantee 971's chassis shape wasn't there just to look cool.

254 switched to a sail cloth fabric for their bumpers this season just so they could get out of t-bones easier.

In a game like 2014, 2011, where defensive t-bones are prevalent and extremely effective, these mechanisms can be very important. However, there are some games, like 2012, where defense was unimportant and not prevalent.

It depends on the game, but after this year I see mechanisms like this increasing in popularity immensely.

25-08-2014 00:33

PayneTrain

Re: pic: 6-sided tank drive

987 had a drop down ball caster on their robot that tey would use to swing out of pins.

I didn't drive it myself so maybe they could tell you their exact experiences with it, but I thought it was pretty neat since it was probably had the highest simplicity to benefit ratio of a secondary mechanism I've seen in a while.

25-08-2014 00:37

AdamHeard

Re: pic: 6-sided tank drive

We copied this in 2013 and 2014.

In 2013 it worked great for us.

In 2014 we were forced to place it on our heavy side and it didn't work as well.

26-08-2014 13:33

wyrzykowskij1

Re: pic: 6-sided tank drive

Have you guys thought about the benefits of an equilateral hexagon? 2851 executed this in 2013 and it improved our offensive ability greatly. Now if only our shooter didn't jam

26-08-2014 17:15

PayneTrain

Re: pic: 6-sided tank drive

I'll be pointing some team members to this thread (and to the thread where you posted that super neat looking 6 wheel setup)