Defensive wedge done differently
 

Recently my team has been discussing ideas of what kind of drivetrain we might want to use next season. One discussion points that has often come up is traction. Wheels such as omni and mechanum provide great maneuverability but lack traction and usually void you of most defensive capabilites despite the setup of the rest of your drivetrain. Assuming you havn't built a wheel switching mechanic (that I find would likely take up a lot of space, weight, and time), it's difficult to be both very pushy and agile.

Tell me this: do you think there is any practicality behind a deployable wedge that would act as a traction device and a means of redirecting the force of an opposing robot? The concept would be similar to putting your foot behind you when pushing on something. In theory it could provide a simpler way of calling upon defensive capabilities while still maintaining a very agile robot.

Also, has anyone ever done anything like this before?

Re: Defensive wedge done differently
 

Do you mean a wedge that lifts other robots? They used to be allowed but the current rule set, normally makes them illegal.

If you mean something that brakes you into the ground when pushed a certain direction, then yes teams have used this before. In fact we helped a rookie team at Razorback this year that had trouble turning with the basic kit bot. We had them take off their back two wheels and add rough top traction to the frame where they used to be. All their weight was in the front of their robot so they could drive normally but if you tried to push them backwards the traction would engage and make them much harder to move. For a two CIM robot, it worked out very well and they played solid defense the rest of the tournament.

Re: Defensive wedge done differently
 

No, I don't mean to lift other robots, but your example is the concept I'm looking into.

[Edit] Did this modification make it easier to push other robots, or solely prevent other robots from pushing them, at the least?

Re: Defensive wedge done differently
 

One thing you need to be mindful of when creating this mechanism is that, in years past, there have been rules prohibiting robots from causing damage to the field. If you have some carpet similar to what is used on the field, I would test anything you design to make sure the mechanism does not dig itself into the carpet and damage it.

Re: Defensive wedge done differently
 

Your way of going about it is interesting, though the way I'd achieve what you're talking about its putting what amounts to putting a deployable jack just behind the corners of the frame with plaction tread on the plates that contact the ground. The thought being that you want to get as much of your robot's weight on the highest-traction surface you can.
That and it would just be useful to have built-in jacks on the robot for testing autonomous and such (just have a DIO on the driver-station determine whether the jacks are engaged or not during autonomous)

It's definitely something that we've even thrown around, and worth testing.

Re: Defensive wedge done differently
 

Hopefully some sort of treading will be sufficient in preventing damage to the field. I'm actually more concerned about drawing fouls from it.

Re: Defensive wedge done differently
 

I like the sounds of that. Do you think it would be beneficial to solely support the robot with a jack on both sides of the drivetrain (assuming there's 2 sides) or just in the front or back, etc?

Re: Defensive wedge done differently
 

Depends on how your frame perimeter. If you put jacks along the sides of the robot, they should be on the longer sides to be the most effective, as surface area is key.

Depending on how much traction you can get without damaging the carpet, it might work either way. A lot of robots that are geared low and have a 4CIM drive right now are capable of pushing with ~200-225 pounds of force. I'd find a good force gauge and see how much it takes to move it and try different tread and add surface area until you're satisfied. Also be sure to weight whatever test platform you use to a realistic robot weight (including bumpers and battery) if it isn't there already.

Re: Defensive wedge done differently
 

My only opposition to the jack strategy, as opposed to a wedge, is you would be unable to push back if your robot was completely jacked off of the ground.

Re: Defensive wedge done differently
 

Well, if you're running a mecanum drive you wouldn't be able to push back anyway. With most drivetrains, your best option might be the wedge setup, but keep in mind that you have to overcome the same traction your defender has to overcome to push you to move. Honestly, if you're interested in that setup, I'd look into a butterfly drive or octocanum setup, but that involves deploying wheels which you stated in your OP post you didn't want to have to deal with at the moment.

Re: Defensive wedge done differently
 

Thank you for the insight, this will be helpful when the team is designing in the coming season, and will give us some ideas to prototype beforehand.

Re: Defensive wedge done differently
 

But if you can't push back, the defense is still doing its job by keeping you in place. Especially if you are one of the top scorers. If you aren't, defense shouldn't be a problem anyways

Re: Defensive wedge done differently
 

If you want to get away from defenders, the first thing is a good driver. Watch 118 in match 60 of IRI this year. Our shooter got bent up after hitting 2468(that's what happens when you run into a wall of metal) so we had to play defence for the rest of the match. 217 and us were both defending 118, and they managed to get through us in a matter of seconds.

Re: Defensive wedge done differently
 

The goal is to use the stilts to play defense ourself, and an agile drivetrain to play offense.

Re: Defensive wedge done differently
 

A sensible and common goal. But I'd suggest watching some more match footage from as many different games as you can, as this goal doesn't really align with reality all that often.

While a mechanical brake will help you maintain position, in most cases there's enough room for a skilled offensive robot to avoid a fixed obstacle (like a team braked in position). Occassionally there are chokepoints (like next to the pyramids this year or the tunnel in 2010), but there are usually other options (under the pyramid this year or over the bumps in 2010) and most of the best offensive robots are capable of using those. If anyting, a braking device will be most helpful for maintaining offensive positioning during a lengthy scoring process in an unprotected area (such as most teams scoring tetras in 2005, tubes in 2007, or a bunch of balls in a single load in 2006).

Similarly, the concept a omni-directional offensive robot seems like it would more difficult to defend, but reality tends to disagree. Unless you have the option of goals in multiple directions (2005), the general path the offensive robot is going to take is predictable, regardless of how many different directions the robot can travel. A smart defender is usually able to position themselves between the offensive robot and their destination and force the offensive machine into at least some contact (a scenario that does not benefit mecanum or omni wheels). If you want to avoid this contact, the solution is typically having a higher acceleration and better drivers than the defender.