pic: Inverted CIM 2-Speed Gearbox

[JesseK]

Originally Posted by KrazyCarl92

Interesting...I would have classified 2014 into School A given the prevalence of defense and the fact that just about every team would be playing D at one point or another. That is to say, sustaining a pushing match for 15+ seconds would be more valuable than shaving a few tenths of a second off of a 10 foot sprint. But like we were saying before, depends on which criteria you're aiming to meet.

(Apologies, just noticed this comment)
It seemed to me that the better defense for 2014 was a 'pillaring' technique. Pillaring is a tank warfare term, where the tank drives back & forth perpendicular to the cannon's aim. It requires planning & setup, but it makes the tank much harder to hit while making it relatively easy for it to maintain sighting on a target. This is prevalent in the Battlefield series of games.

This same concept works for defense on the FRC field. Sprint into position, then pillar back/forth and force the other team to either push you sideways or drive fast enough around you to get to their goal. The likelyhood of them pushing you is high - yet it's time consuming and usually not as effective as one would thing since it still doesn't solve the problem of them getting to their desired spot for an open shot.

Faster low gear speeds on an open field also give more opportunities to clip/turn a corner of a shooting bot - much more effective than raw pushing.

[Chris is me]

Originally Posted by JesseK

(Apologies, just noticed this comment)
It seemed to me that the better defense for 2014 was a 'pillaring' technique. Pillaring is a tank warfare term, where the tank drives back & forth perpendicular to the cannon's aim. It requires planning & setup, but it makes the tank much harder to hit while making it relatively easy for it to maintain sighting on a target. This is prevalent in the Battlefield series of games.

This same concept works for defense on the FRC field. Sprint into position, then pillar back/forth and force the other team to either push you sideways or drive fast enough around you to get to their goal. The likelyhood of them pushing you is high - yet it's time consuming and usually not as effective as one would thing since it still doesn't solve the problem of them getting to their desired spot for an open shot.

Faster low gear speeds on an open field also give more opportunities to clip/turn a corner of a shooting bot - much more effective than raw pushing.

While this is a great defensive technique for many years, 2014 included, it was a better technique for years such as 2013, when one had to navigate the length of the field, around obstacles, and pushing a robot into a specific area was a liability.

In 2014, pushing was much less risky as there were no safe zones. T-bone pinning a robot had a bit more risk than "pillaring" but a lot more benefit - the robot is essentially immobile for the duration of the pin. I don't think "pillaring" was definitively better in 2014 just because of the T-bone pin and the relatively wide space to drive around. It is an important part of a defensive strategy but not the end-all.

[JesseK]

Originally Posted by Chris is me

While this is a great defensive technique for many years, 2014 included, it was a better technique for years such as 2013, when one had to navigate the length of the field, around obstacles, and pushing a robot into a specific area was a liability.

In 2014, pushing was much less risky as there were no safe zones. T-bone pinning a robot had a bit more risk than "pillaring" but a lot more benefit - the robot is essentially immobile for the duration of the pin. I don't think "pillaring" was definitively better in 2014 just because of the T-bone pin and the relatively wide space to drive around. It is an important part of a defensive strategy but not the end-all.

When determining where to set low gear when executing defense is a consideration, is an effective T-bone pin mutually exclusive of an effective pillar defense?

Do (e.g.) sailcloth bumpers change this consideration at all?

This plays into the original topic a bit - shaft spacing is usually determined by the gear availability and the desired difference between high gear and low gear (e.g. the dog gear choices). School A wants a larger gearing difference, School B wants a smaller gearing difference.

[cbale2000]

Originally Posted by Chris is me

I wouldn't do either of those things, especially since you are cantilevering the first stage. You don't want the extra flex that these materials will add to your gearbox. Spend the few ounces of weight where it matters; I guarantee you something else will be on your robot that you would rather cut weight from than your gearbox plate. If you really want to minimize gearbox weight, pocketing the gears is where you could start shaving a few ounces.

To clarify my previous comment, you CAN use polycarbonate for gearboxes generally speaking, but you would probably not want to use your current design if you went this route.

A quick redesign using solid (not pocketed) plates and eliminating cantilevered shafts (by simply supporting them on both sides) might still be a worthwhile weight savings.

[Chris is me]

Originally Posted by JesseK

When determining where to set low gear when executing defense is a consideration, is an effective T-bone pin mutually exclusive of an effective pillar defense?

Not really.

Do (e.g.) sailcloth bumpers change this consideration at all?

Somewhat, particularly if you're using solid core pool noodles with sailcloth. In that case, your bumper doesn't deform or grip enough to effectively T-bone anyone (or be T-Boned, which is the point), so you can only really play pillar defense.

This plays into the original topic a bit - shaft spacing is usually determined by the gear availability and the desired difference between high gear and low gear (e.g. the dog gear choices). School A wants a larger gearing difference, School B wants a smaller gearing difference.

I don't really get school B. The advantage in short acceleration is usually so minor that it's not important, and I feel like using low gear for more precise movement is using hardware to solve a software / controls problem. While pushing matches should be avoided, low gear to me exists so offensive teams have the option to push through defense if necessary and defensive teams can themselves push all day long against the strongest drivetrains. So it doesn't get used all that much, but it's more of a safety net.

[MichaelBick]

Originally Posted by Chris is me

While pushing matches should be avoided, low gear to me exists so offensive teams have the option to push through defense if necessary and defensive teams can themselves push all day long against the strongest drivetrains. So it doesn't get used all that much, but it's more of a safety net.

In our experimentation with a "school A" drivetrain, we've actually found that we like to t-bone and play the "pillar defense" both in high gear. We found that teams can create separation from the t-bone when we are t-boning in low gear. When we are playing "pillar defense", high gear allows us to keep up with opposing robots to effectively block the field. We now teach drivers to only use low gear in head to head pushing matches.

[JesseK]

Originally Posted by MichaelBick

In our experimentation with a "school A" drivetrain, we've actually found that we like to t-bone and play the "pillar defense" both in high gear. We found that teams can create separation from the t-bone when we are t-boning in low gear. When we are playing "pillar defense", high gear allows us to keep up with opposing robots to effectively block the field. We now teach drivers to only use low gear in head to head pushing matches.

Mind giving traction details? I would expect that sufficiently high traction & gearing, in combination, would lead to popped breakers. I have no experience here myself, but I've read plenty of it on CD from 2014.

[MichaelBick]

Originally Posted by JesseK

Mind giving traction details? I would expect that sufficiently high traction & gearing, in combination, would lead to popped breakers. I have no experience here myself, but I've read plenty of it on CD from 2014.

The robot was geared for 20FPS @ 100% efficiency, had 4 CIMs and 2 550s, and had 2" wide roughtop traction wheels. The robot never stalled while t-boning, which probably helped in preventing blown breakers.

[KrazyCarl92]

Originally Posted by MichaelBick

The robot was geared for 20FPS @ 100% efficiency, had 4 CIMs and 2 550s, and had 2" wide roughtop traction wheels. The robot never stalled while t-boning, which probably helped in preventing blown breakers.

To give an example where breakers DID pop...

Team 20's 2014 drive train had 3 CIM WCP dual speed shifters, with 4" colson wheels, and was geared for about 5.5 fps and 16 fps free speed (theoretical).

Here is video of our second match of the season: http://www.thebluealliance.com/match/2014nytr_qm13

In our pre-match strategy, we adopted the role of post-auto hounding of any opponents that missed their auto shots while our partners cleared missed auto shots of our own alliance. At the very start of teleop we go to play defense on 116 and set an open field T-bone pin on them which they fail to break free from for 26 seconds. The pin ends because we popped our main breaker.

Post-match after discussion with our drive team and some napkin math in the pits, we decided the following events likely led to the issue:
-The driver switched to low gear after the pin was initially set
-The shifting cylinder did not have sufficient force to shift the dog from high gear to low gear under the traction limit condition, so the dog remained engaged in high gear throughout the pin
-Our driver did not let up full throttle on the pin (we wanted to pin at full throttle without worrying about popping breakers as a design objective)
-We would have been pulling around 400 A or something crazy through the main breaker in this condition, which should only last a max of about 8 seconds according to the breaker spec sheet, so I am surprised we lasted this long before popping the breakers.

To mitigate the issue, we had the drivers always let up at the best opportunity early in the pin so the dog could shift. The very next match we popped the main breaker again, and after replacing it never saw a tripped main breaker the rest of the season (they tend to become easier to trip after tripping the first time).

When hounding teams on defense we could almost always maintain a pin once we set it, regardless of the fact that we were in low gear. The only exception that comes to mind is the Killer Bees being able to slip away well due to their drive train and driver skill.

Side note: I am unsure of whether we had changed this yet or not in the above scenario, but at one point early in the season we switched from 6 CIMs in the drive train to 4 CIMs and 2 MiniCIMs to up the torque in our catapult gearbox due to an increase in the pre-load of the torsion springs.