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View Full Version : Community vote: Classification of 'Twitch-likes'



Gertlex
01-13-2013, 01:49 PM
Hey folks,

I visited Trossen a couple of weeks ago, with Twitch (http://forums.trossenrobotics.com/robots.php?project_id=7), and in talking with Tyberius, it was decided to put it to the community as to how Twitch-likes should be classified for the Mech Warfare Competition. The fundamental issue comes down to the fact that the MW rules (http://forums.trossenrobotics.com/showthread.php?5454-Mech-Warfare-2013-Draft-Rules) are based on number of legs, but do not define anything based on the number of feet or style of feet.

At stake are three questions: (1)) Do these bots get put in the same league as quads and bipeds, or in the open league (which has not really existed, but is reserved rovers and hexapods)? (2) Which scoring panel configuration - 4 full panels like a quad, or 2 full, 2 half like a biped? (3) Bipeds receive 15% extra hit points. We can give this to Twitch-likes, or not, or even do the opposite: e.g. -15% hit points (17 total).

Twitch throws a bunch of wrenches into the rules.

As currently built, Twitch has six separate points of contact with the ground. This could be configured as 2, 3, 4, or 5 points of contact. These "feet" are in two groups, with feet in a given group being fixed relative to each other. You could choose to consider these groups to be legs - two legs.

To illustrate the various feet configurations, pictures!
4456
Top View

4457
Six points of contact with current Twitch

4458
Quad configuration - joining the lower legs

4459
Two-foot configuration - outrageously shaped joined feet

4455
Side view of making single feet for the quad.

The point to this is that while I can configure the feet in various bizarre ways so that it's technically 4-footed, or whatever, this kind of bot should probably just be classified separately.

There is also Jwatte's Little Walker (http://forums.trossenrobotics.com/robots.php?project_id=25#ad-image-0). This uses a different foot configuration, but is the same principle of 3 servos locomotion via large footprint. While different, there is continuum of possible designs between Twitch and Little Walker. Thus in my opinion, they should fall under the same umbrella in the rules.

This design also lowers the cost of entry for MW. A $500 Dynamixel bot is very possible... Probably not a bad thing.

Finally there's the spirit of the rules. The MW competition aims to emulate the MW games of yore (and the new nifty looking MW Online). There's nothing like Twitch, or hexapods, or rovers in the MW lore, and that has been an added basis for the separate Open League. You can choose to factor that into your opinion...

I'm sure others have thoughts (JWatte was in a rush to get his in ;) ). I encourage you to read others' thoughts, post your own. There's no rush to vote immediately on this, as discussion is good. I have however set the voting to end in 30 days... I'm planning on such a mech, and making a decision a couple months before MW gives me the chance to change my approach if needed :). Poll options were my first go at it with the new forum layout, and apparently I can't edit them. Worst case, a new thread gets made if a glaring omission was made in the options.

Thanks for reading!

(Note, I got lazy and didn't discuss/document the style of walking that Twitch uses... If some feel the definition of walking is also necessary for debate, I can better document that with vid, if needed...)

jwatte
01-13-2013, 02:36 PM
As built, Twitch has the benefit of a hexapod, that is has a triangle to balance on while moving the other triangle. It just happens to actuate each triangle separately.

Of course, you could do that with a biped, too. Just make the feet wide enough, and interlocking, and you get the same benefit. My "little walker" is something of a mutant between the twitch design, and a "wide hip" biped, and a "dead duck walking" :-)

I think the idea of the benefits of a biped is that something that has to balance for real, and is tall and ungainly, needs a bit of encouragement, because it's cool and we want to encourage it. Twitch is cool, but doesn't have those mechanical disadvantages, and thus I think it should count as a quad. Maybe the "biped" rule should be re-stated to talk about areas of balance, height vs covered area, center of gravity, etc :-)

Gertlex
01-13-2013, 02:40 PM
You missed the part where I'm not done with the post yet. (wasn't even going to submit it today) :tongue:

Gertlex
01-13-2013, 03:38 PM
Ok, I think I've said what I planned on saying. Voting is now open :)

gdubb2
01-13-2013, 04:30 PM
My opinion, for what it's worth. It's a biped.

Spirit of the game:.. robots evolve.. games evolve.. this may be the next gen. of killer bots..:veryhappy: But I'm not a gamer, so have somewhat different ideas about this.

Several of us have tried different foot configurations to get better balance. Both with bipeds and quads. I see this as just a configuration that worked out. The number of legs vs the number of feet is what defines a biped in my way of thinking.

As for promoting bipeds, I'm not sure this is for the best. I've had bipeds, worked with them, got very frustrated and disappointed with them, before finally moving to quad designs. I see no real reason to continue with them.

Just my opinion
Gary

Th232
01-13-2013, 05:06 PM
I chose biped for the main reason that it has two legs, then * because of the interlocking nature of the feet. Perhaps a distinction can be made between a conventional biped where if it's standing in a "neutral" position the biped can't then lift one leg and continue to stand, while this sub-category can.

Gertlex
01-13-2013, 05:19 PM
That's a neat way to think of it, Th232. Seems like a valid way to distinguish...

tician
01-13-2013, 05:42 PM
I consider twitch and 'little walker' to be bipeds as they have two independently controlled legs, but since their designs render them statically stable at all times, they should not receive the HP bonus of larger DOF bipeds that can tip over.

Maybe some terminology clarifications?

Leg: an independently controlled structure that supports part, or all, of the weight of the robot for some time interval (e.g. a humanoid bot that frequently uses its arms for support to 'knuckle-walk' is classified as 4 legged); requires at least one actuator per leg; may not be controlled by a 'cam' based system (e.g. a single dc motor running continuously in a single direction to actuate one or more legs simultaneously);

Foot: structure that attaches to a leg and contacts the ground; may be as large or small, and with as many points of contact with the ground, as desired;

jwatte
01-13-2013, 06:47 PM
I did catch the post early but haven't voted yet. Listening to what everyone is saying.
So far I really like the idea of balance as a determining factor. Can it be knocked over? Then it's a biped :-)
I still think twitch should be allowed to compete in the regular league.

ArduTank
01-13-2013, 07:38 PM
It could, but it would have to be classified as a quad in my mind due to the large number of contact points. Did you see Giger using more than two parts of his body to walk at any given time??? No. Does Twitch? Yes. Twitch is therefore a quad.

tician
01-13-2013, 07:52 PM
It could, but it would have to be classified as a quad in my mind due to the large number of contact points. Did you see Giger using more than two parts of his body to walk at any given time??? No. Does Twitch? Yes. Twitch is therefore a quad.
But it has six points of contact, so why quad instead of hex? Little Walker has two C shaped feet, does it get called a quad or hex even though it only has two feet?

Th232
01-13-2013, 07:53 PM
It could, but it would have to be classified as a quad in my mind due to the large number of contact points. Did you see Giger using more than two parts of his body to walk at any given time??? No. Does Twitch? Yes. Twitch is therefore a quad.

Given that a quad, by definition, has four feet, why not classify Twitch as a hex instead?

Edit: Lol, just beaten to it.

lnxfergy
01-13-2013, 09:17 PM
I think we should look here at what the overall purpose of various rules were:

We ruled that hexapods should not be allowed to compete against bipeds/quads because the hexapod is too stable and easily carries much more payload.
We reduced the number of panels on bipeds because they are extremely payload limited and inherently less competitive.
We gave HP bonuses to bipeds because they are less competitive due to the complexity of walking/balancing.
Now consider twitch. Is it too stable? Can it easily carry the required payload? Is it inherently less competitive? I don't know these answers exactly, but I think it is probably yes, yes, and no.

I understand that there is an argument to be made for lowering the bar to entry, but I'd suggest we try to keep with the overall spirit of the rules. Perhaps if want to allow twitch, we should also consider allowing hexapods. Perhaps walkers which are easily balancing (hexapods, twitch, etc) take an HP penalty.

I can't seem to find the discussion, but I know at one point we had talked about including a clause that a biped with "overlapping feet" would not get the biped HP/target panel bonuses, as it is more stable.

-Fergs

Upgrayd
01-13-2013, 10:31 PM
The poll is a bit flawed. It should only contain the three options Biped, Quad or Other(open). We will not be adding any more of classifications that have new hp/target panel rules.

Th232
01-13-2013, 10:49 PM
Good reminder on the intent of the rules Fergs.

If we have to go with Biped/Quad/Other, then I'd recast my vote for Other, based purely on Twitch/Little Walker's stability. That said, it does open up a can of worms regarding a more conventional biped with larger and/or interlocking feet. The balance distinction I suggested in my previous post could still work, but something still feels messy about it.

Heck, since I'll probably never be competing in MW thanks to the Pacific Ocean, why am I even posting in this thread?

CogswellCogs
01-13-2013, 10:52 PM
First of all, Twitch is a great design and implementation. I respect and admire the robotic acumen it took to build. It's not my intent to diminish the achievement by saying that it should not be allowed in the MW biped league.

I have two reasons. The Mech Warfare competition was inspired by games like MechWarrior and similar anime. Those represent the bipeds that Mech Warfare is striving to implement. Two legged, two footed robots that walk in way inspired by biology.

Second, let's look at the definition of 'biped'. Two feet, right ? A foot is where the end of the leg meets the ground. Twitch looks to have six of those. Calling it a hexapod seems more appropriate.

Gertlex
01-13-2013, 11:05 PM
Since Upgrayd and Tyberius are noting only 3 possible answers, the poll, were it more flexible, ought to ask two-fold:

1. Open league, or regular league?
2. If voted regular league: quad or biped?

I'm not sure what to do with the poll results that the current poll will give.



Second, let's look at the definition of 'biped'. Two feet, right ? A foot is where the end of the leg meets the ground. Twitch looks to have six of those. Calling it a hexapod seems more appropriate.

To me, the point is, what if I configure the feet like in the 'Two-foot configuration' image? (i.e. not make an evaluation solely on the basis of the actual Twitch bot.)

It was on this basis that I postulated that Twitch-likes be explicitly categorized

cire
01-14-2013, 03:54 AM
I think it should fall under the same category as quads because it doesn't have the associated challenges that make 2 legged robots so challenging.

Janis
01-14-2013, 08:09 AM
This is an interesting discussion. It made me think about this a little more.
I'm am going to participate in this years MW with this robot named HD2:
http://forums.trossenrobotics.com/showthread.php?5910-MechWarfare-entry-HD2
People unanimously called it biped.
By some of previous definitions it is an octoped as there are 4 points of ground contact for each leg.
Last year it had bars under the feet making it quad.

The problem is that current rules do not define biped precisely enough.
If any opponent thinks that biped advantage does not apply to HD2, I am perfectly fine to put the same amount of targets and HP as quads to participate.
But if by current rules it qualifies as biped then even better!

Let me try to state some definitions as I see it:
Foot: "Set of ground contacting surfaces which cannot be moved seperately"
Foot area: "Area of convex hull of all surfaces definig a foot"
By this definition both Twitch and HD2 are bipeds.

When it comes to "should balance itself" or "is easier to build" it becames tricky. What does it mean to "should balance itself"? Every bot should should balance itself.
For some it is easier for some it is harder to do.

I think what people here want to say is: Let's define biped as:
Biped:
1) It has two legs (possibly by the above definition) AND
2) To change the supporting leg while standing still on one leg requires movement of COG.
I'd give it some special name as it is a special case of all bipeds, say: "Humanoid Biped".

Requirement (2) is artifical in some sense. Why should I overcomplicate the design if the goal of two legged MW robot is achievable without it.
That would be the same as to require quads to be able to stand still on one leg or something.
Ok, maybe that's diverging from the spirit of the game somewhat but that was the main reason why I asked the biped question in the thread above.

Anyway, all this is to create some frame in which bipeds and quads could be compared in somewhat sane way just because quads are considered easier to build/operate.
But, why, really?
Maybe, first let's think, what actually makes _it_ harder independent of leg count?
I'd say, (putting all the technical stuff aside (materials, servo count, etc... ) the major components are 1) the height of GOG and 2) area of support. The bigger the ratio the harder the task.

Maybe we should define HP count, traget count based on these measures. The problem is that those numbers chenge all the time. But maybe not that much.
Maybe we can take the barrel height from ground as one number (A) and support area when all feet are on the ground as other (B)?
And during the match the mech cannot lower turret below (A) and support area cannot exceed (B) at any time during the match. Which of course is not controllable but could give some good approximation.
For example, for HD2 these numbers would be A=37cm and B=340cm2
Define the handicap as A/B and translate it into bounus hitpoints and/or target area.
Maybe just (B) is enough? That way smaller mech designs would benefit over bigger ones.
This is a friendly competion at the end, so no obvious cheating is expected.

Thanks.

Upgrayd
01-14-2013, 08:36 AM
The way I look at it...

Leg count should be defined as a count of apendages that can be lifted vertically and moved laterally (side to side or forward and backwards) independantly of each other apendage while the body of the robot remains stationary.

So the test for a biped would be that if one foot was mechanically fixed to the ground the other foot should be able to lift, move to a new position, and lowered without the body moving.

Upgrayd
01-14-2013, 10:16 AM
In addition to my previous post...

Points of contact of a foot on the ground seem irrelevant to the classification.
With that being said I personally do not see how Twitch could be construed into being considered a quad as it clearly does not have 4 independent articulated legs.

The debate should really be what defines a biped.

gdubb2
01-14-2013, 10:38 AM
Dictionary says Biped = 2 feet.. BUT where does the definition of "foot" take us? Feet have toes, and some feet (Birds and reptiles) have very long toes. Twitch has long toes.

I think that within the current definition of biped, Twitch qualifies as biped. However if the defining factor was humanoid not biped, it would not qualify.

jwatte
01-14-2013, 01:47 PM
Let's worry less about the semantic definition and more about what we want a MW match to look like.
A quad is inherently unlikely to tip over because of its footprint. But bipeds are what Mech combat is built upon, and I don't think it will look like that without some"slant" to the rules.

CogswellCogs
01-14-2013, 01:52 PM
I'd hate to make 'humanoid' a requirement. A traditional mech warrior chicken walker would certainly qualify as a biped for MW. Is 'chickenoid' a word ?

This biped thing is a sticky question. I think it's like the Supreme Court said about pornography. We don't seem to be able to define a biped but we know it when we see it.

DresnerRobotics
01-14-2013, 04:04 PM
Just a few key points to consider:

Mechwarrior simply serves as an inspiration. Any argument that starts with "Well in Battletech/MechWarrior so and so is true..." is invalid.

The number of points of contact on a foot is not what should be debated here. A traditional biped could very well have a foot with multiple points of contact, it is still a biped so long as it has 2 joint-actuated legs. We'll not be defining humanoid vs biped either, because they're the same thing in terms of MW.

As Upgrayd said, perhaps clarification on how we define a limb is in order, ie: Can your limb be lifted individually and move in an X,Y,Z fashion?

Also, to play devils advocate:

If Twitch were defined as a biped, then would this be considered a Tripod? http://www.lynxmotion.com/images/html/build017.htm

byi
01-14-2013, 10:33 PM
I personally prefer the idea of focusing more on COG and/or overlapping feet, since it goes on the reasoning behind prior distinctions. however, i can definitely see how that might complicate things too much.

lnxfergy
01-15-2013, 01:28 AM
I believe the proper COG/stability test here might actually be the "is it more or less likely to fall over than Squidword".... hehe

-Fergs

ArduTank
01-16-2013, 03:32 PM
Just a few key points to consider:

Mechwarrior simply serves as an inspiration. Any argument that starts with "Well in Battletech/MechWarrior so and so is true..." is invalid.

The number of points of contact on a foot is not what should be debated here. A traditional biped could very well have a foot with multiple points of contact,it is still a biped so long as it has 2 joint-actuated legs. We'll not be defining humanoid vs biped either, because they're the same thing in terms of MW.

As Upgrayd said, perhaps clarification on how we define a limb is in order, ie: Can your limb be lifted individually and move in an X,Y,Z fashion?

Also, to play devils advocate:

If Twitch were defined as a biped, then would this be considered a Tripod? http://www.lynxmotion.com/images/html/build017.htm

There's a good definition!!!