Chief Delphi - Physics of T-boning

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Re: Physics of T-boning

Quote:

Originally Posted by DampRobot (Post 1387461)

I think the physical description of T boning described by this thread (including by me) is sort of incomplete. Why should it be easier for 971 with their octagonal frame to get out of pins than a rectangular bot of the same dimensions (and same drivetrain, same bumper fabric, etc)?

There's obviously some minimum torque needed to break off the bumper of the pinning robot, and shortening the length of the bumper against the pinning robot reduces this torque. But I'm still not sure exactly how it works.

One of the biggest advantages of a 971's octagonal frame is that they're a significantly smaller target for a defender. From what I've seen, any contact on any of the (4) angled surfaces doesn't seem to slow them down much if at all, so for them to be effectively t-boned someone has to get them exactly on the flat side.

Ignoring the smaller target aspect, the relatively short length of their 'flat' side means that it's relatively easy for their drive train to spin while being contacted on that side. This is one of those cases where drawing out a quick sketch of their drive train from above will do wonders for understanding.

Re: Physics of T-boning

Quote:

Originally Posted by DampRobot (Post 1387461)

On a rectangular frame perimeter when a robot goes to t-bone you, they are hitting you perpendicular to the direction your wheels roll (otherwise described as your wheel base). The portion of your bumper that they are in contact with is perpendicular to your wheel base, so as you try to drive out of the t-bone theoretically speaking 100% of the frictional force opposes your robot. In the case of 971, whose frame perimeter is not rectangular and have bumpers that are not perpendicular to their wheel base, 100% of the frictional force does not oppose their robot when contacted on one of the angled sides of the bumpers.

cos( Θ ) * frictional force = frictional force opposing your robot's motion

Θ = the angle between the plane of contact between the two robots' bumpers and the direction of your wheel base

Interestingly enough as a robot attempting to t-bone 971 on one of the angled sided of their bumper, you apply a force on their robot in the direction that they would be driving in to get out of the t-bone, effectively helping them escape the t-bone you are attempting to put them in.

Re: Physics of T-boning

Quote:

Originally Posted by rnewendyke (Post 1387504)

This is true, and explains why you can't pin them on their diagonal sides (or why you can't "T bone pin" a rectangular robot on its front or back either). But it's still much easier for 971 to escape when pinned on their "flat" side than a comparable robot with a rectangular frame similarly pinned from the side.

Re: Physics of T-boning

Quote:

Originally Posted by DampRobot (Post 1387514)

In the matches that I have seen of them, which at this point is a relatively small number, when other robots attempt to pin them on one of their flats, they turn whichever direction is more desirable to escape from forcing the pinning robot to contact them on one of their angled sides which allows them to then slip out of the pin. In this match between 0:52 and 1:00 they appear to be t-boned successfully on one of their flats until the t-boning robot eventually lets go. If you can find other instances where they do escape when contacted on one of their flats without turning out of the contact I'd be interested to see it.