Best Drivetrain For Starstuck Poll

What do you think the best drivetrain for starstruck is?

Poll Link

So that you know what I mean.

Tank drive example

H-drive example

X-drive example

Mecanum drive example

Swerve drive example

You didn’t allow for multiple choices in the poll, so I will say it here. Ideally the x-drive would be the best option, but based on problems with weight distribution, I think an H drive will work better. Though if I can, I will go for the x drive, for decreased motor count and increased maneuverability.

A “Kiwi drive” is always an option

Oh no.
I think that people are mixing up the tank drive and H drive’s names (Unless everyone really do think that an H-drive will be best for this year).

Tank drive: (Not tank treads)

H-drive:

I think if implemented correctly, a swerve drive will be a very solid option. Lots of issues that need to be resolved, but I will have my team prototype it at least.

H drive will be useful because it still allows for plenty of room at the front of the robot for the stars while still being able to move sideways for easy autonomous of knocking the stars off the fence, as well as lining up to intake a star.

I said that because at the time, five out of the five votes were for the H-drive.
I agree with you.

Fair enough

I meant to choose H-Drive.

So did I.

Everybody says mecanums are bad, but what makes them bad?

An H-Drive seems to be better than an X-Drive when you move diagonally more often than forward/back/left/right. That’s just due to the geometry of the drive. You get a larger opening in the front and back, but you need a bar across the middle or multiple sets of wheels to prevent turning when strafing. Otherwise, you will basically drive in a big circle or do some weird thing with your forward-facing wheels.

The biggest downside to me of an H-Drive is motor consumption vs. usage. An H-Drive made of a 4 motor tank drive and a 1 motor strafing wheel uses 5 motors (1 more than an X-Drive), and its strafing is still severely limited because it’s 1 motor trying to move the same weight that an X-Drive would use 4 motors to move. You can balance it and do more of a Plus Drive (2 perpendicular tank drives) with 1 motor on each wheel, but then you are basically recreating the X-Drive at a 45° offset.

I think moving forward, backward, or strafing will be more used in a match than moving diagonally, so an X-Drive is better there. I will try to work on some math to find at what angles of movement a Plus-Drive becomes better than an X-Drive.

Not the idea themselves, just VEX’s product essentially. The mecanum wheels are slow and bulky, and the design of the rollers allows for more “perfect” strafing at the expense of speed and power. If you have the time, you could prototype one and see for yourselves, but I think you’ll agree with the general consensus that mecanum is usually not the way to go.

If you have lots of time, however, you might want to check out the custom mecanum wheels made by one team (can’t remember the name, but Green Egg seems to pop into mind). By slicing apart a large HS gear, drilling holes into it, and inserting normal omniwheel rollers, the team was able to create custom mecanum wheels that were wayyy faster than VEX’s mecanum wheels.

I will post the link if I find it :slight_smile:

EDIT: Found it! https://www.youtube.com/watch?v=LVZR3NWYOik

So, it appears based on some math I just did that if the angle is less than 30° from forward/back/left/right, an X-Drive is faster. At 30°, they are the same, and at greater than 30°, an H-Drive is faster. This ignores speed losses due to torque and assumes that all wheels can spin at the same speed.

Out of 360° in a circle, at 240°, the X-Drive’s speed is greater than or equal to that of an H-Drive. At 120°, the H-Drive is faster than or the same speed as an X-Drive.

I can’t post a picture of my math from my phone and I’m not at a computer right now, but when I get a chance, I will post a picture of it so we can look for flaws in my math or logic.

I know from experience that they aren’t as efficient as omni wheels. My biggest guess to why this is the case is due to the cantilevered rollers. Due to the cantilever, any sideways movement will torque the roller. Since the roller is much longer than any omni roller, it leads to a higher force at the pivot. Higher force leads to higher friction. As for double supported mecanums, I believe a similar concept occurs because the rollers are longer than the rollers of the omniwheels, but it’s much less than the standard vex mecanum. The benefit of the current vex mecanum style is that due to the excess, it’s easier to strafe over bumps

double supported style: http://robu.in/wp-content/uploads/2014/03/100mm-aluminum-mecanum-wheel-left-14087-2.jpg

Assuming weight, and the number of motors are the same, and the center of gravity is centered, any drivetrain will have the same speed (conservation of energy). It’s just a matter of gearing it properly.

Now if you want to be practical about it, know that an X drive will be faster in the major directions, while H drive will be faster in the diagonals. However, if you compare the two, more than likely the H drive will be faster since the typical H drive uses 5-6 motors and an 8 motor X drive is usually overkill

Sorry, I think you misunderstood him. I believe he was saying that the X drive will be faster (in practicality) in 240 degrees of movement, while and H drive will only be more efficient in the other 120 degrees of the circle. This is because the way that the wheels are spinning, and the number of wheels that are powered at any given moment.

The only issue with an X-Drive this year is that you lose a good amount of space to the front 2 wheels on the drive. If you do a H-Drive, you may strafe a little slower, but you should have more space in the front for a lift/intake/catapult imo.

Honestly, I really feel like tank drive will again dominate for several reasons.

  1. The top teams other than a very few amount of X-drives always use tank
  2. Unless your driver is very skilled with an X drive and has a lot of practice, they can end up being over all less efficient because it always seems like we see people moving diagonally with only the power of two motors instead of just turning and going straight which would be so much faster
  3. yes, X drive does have a root two advantage, but a speed sprocket on tank is comparative
  4. tank leaves more room for parts and mechanisms
  5. H drive sacrifices motors and mecanum is just bad in general

Yeah I’m debating if strafing is worth it.
Edit: However, just because the experts do it doesn’t mean they do it because it is best. More likely they do it because they are spending more time on other bits of their robot that make it good.