Re-evaluate motor limit

This year we saw a new rule limiting the number of drive motors to 4. Apparently this was due to some teams experimenting with two drive motors per swerve module, and differential swerve.

This year we also saw some new motors released, including the Kraken X60, which has quite a bit more torque than the Falcon 500, particularly with FOC enabled.

We saw more damage this year, both to the field (mostly the source) and to robots (mostly to intake-end frame 1x2). Almost everyone I talked to blamed the Krakens. While that seems like an obvious conclusion, from what I’ve seen I’m not 100% convinced of this. It seems to me that the field damage was exacerbated through a combination of game design choices and a lack of reinforcement of the bottom of the field wall. As for the robot damage it’s important to note that inside-the-frame under-bumper intakes were common this year, and these robots didn’t have a belly-pan or internal structural members extending out to this intake side of the robot, and I think this was the largest contributing factor.

In our own tests (Kraken swerve) it seems to be that our acceleration is traction limited at low speeds and battery limited above a certain point. There doesn’t seem to be any point where we’re limited by the capability of the drive motors to output more torque or power. The battery can’t deliver more than about 1600W in real-world conditions and even a Falcon 500 with FOC is going to exceed 400W (1600W total) above about 600 to 700 RPM, and Krakens even earlier. Based on the stator current limits people are setting to prevent wheel slip, it’s still traction limited at that point.

So I don’t think the 4-motor limit is actually limiting robot speeds at all. I think the battery is already the primary limit.

I say this because, in limiting the number of drive motors to 4, we’ve removed a big creative element from the game. You can make so many more interesting robot drive base shapes with 5 wheels, compared to 4.

Yes, you could use an un-driven swerve module, or an omni-wheel for your 5th point of contact, but then it becomes a disadvantage because any un-driven wheel that’s supporting robot weight is reducing the available traction at the other wheels.

As long as we stay with this battery, I don’t believe we need any motor limit, but if people feel strongly about blocking double-motor swerves can we at least raise it from 4 to 5 to allow some creativity?

55 Likes

Replace it with a max amperage limit, enforced by the snap action breakers (yes, I know they allow more than their rated current, the limit can be picked appropriately with this in mind).

Differential swerve is a cool mechanism and it’s really dumb that it’s illegal.

45 Likes

inb4 3 normal mk4is and 1 3-motor mk4i becomes meta

6 Likes

Did you see hightide drive last year?

4 Likes

What’s the advantage of differential swerve if not more drive power/torque?

3 Likes

If we limit robot top speed directly, you can use all the motors you like. Every other energy-limiting rule has really poor control authority - like trying to turn a plane by sticking your hand out the window.

6 Likes

Sharing the drive load between two motors will give you higher efficiency (in theory), and it’s a fun project even if it’s not competitively optimal.

17 Likes

If your limit really is battery power, one could conceivably build a differential swerve with smaller motors which weigh less and still accelerate as fast.

2 Likes

5 module swerve was pretty great, that would be cool to do again

6 Likes

Or, hear me out, a game with regolith where everyone has to use the same wheels!
I know this sounds crazy, but no carpet means carpet won’t be torn up!

11 Likes

Robots breaking because of collisions is part of the game and will end up happening regardless of the number of motors allowed, or obstacles in the field, unless the amount of power a robot can use to drive is limited. I think we’ve all seen some pretty gnarly frame pieces after big collisions, in addition to electronics being broken as well. I see the reasoning behind a motor limit; slow teams town to help stop damage. having a 4-motor limit stops cool designs like team 2481 in 2022, diffy swerve, and other multi motor drives. Imo a hardware current limit (some kind of a breaker) is the way to go.

Or maybe, we don’t even use swerve next year since it is a water game after all…

3 Likes

You’re a lunatic :wink:

8 Likes

I think that many people don’t really understand why 12 motor swerve was good last year. It’s not because eight drive motors allows you to get more power into your motors, it’s because more motors allow you to run them at higher efficiency.

Having more motors decreases the amount of current each motor needs to draw. Motors have a higher efficiency when they draw less current, and create less heat per motor. When motors are at a higher temperature, they are even less efficient. The cycle continues through the match.

32 Likes

If you’re into insane amounts of static build-up, go for it I guess.
There were so many shorted electronics that year, not to mention the pain of drive team having to touch the robot after matches.

yeah it was beautiful :heart_eyes:
i need a heart opening gif that says hightide my beloved

2 Likes

Dissipate static by getting it to flow through the bumpers into the field walls?

Because heat exists, this doesn’t end up being true in practice. CIM class brushless motors already get hot when driving aggressively, and smaller motors don’t have the thermal mass or cooling capacity to handle the heat so you will see performance drops.

So it’s still battery limited, and 8 drive motors lets you get a higher percentage of that available battery energy converted into kinetic energy, at the cost of higher weight.

To me, that still means the battery is the true limiting factor. We can get asymptotically close to it, but we’ll never exceed it.

solution: water-cooled motors

1 Like

if only Kraken X60s and Falcon 500s had cooling ports :joy: /s

1 Like