Pros and Cons of x-drive for Turning Point

What are the Pros and cons of x-drive for Turning Point

Almost impossible to climb up the platforms, and much less pushing power.

Cons. you dont need to strafe, difficult to get on platform, heavier and more complicated drive, usually more friction in x drive, less robust than tank drive, difficult motor increments to work with
Pros. Strafing is cool to work with and it might get you an award if you do reasonably well.

True, 99 percent of the best teams don’t/won’t use strafing drives because it is never needed.


You can park, but it is hard. Strafing could be good for balls, but an optimized tank drive can do the same

I’ve built 3 X drive bots and tested them extensively.

The primary con is the platform. Mounting the center platform is nearly impossible, but KEEPING the platform is out of the question. By design, X drives don’t really grip the floor - they have to slide. On the platform, that’s a loser.

The second con is motor count. You can power a traditional drive with two channels even if you use 4 motors (for power, using Y’s), but you must have 4 separate channels for X drive.

Depending on your design, you’ll need a motor channel for ball intake, another for aiming the shooting mechanism, and a third for firing the ball. For the caps you need at LEAST one channel for elevating, one for grasping (passive intake is not working out well), and one for flipping (if you stand any chance of flipping a high scored cap). That’s 6 channels. If you’re using the older cortex, you still have enough for X drive, but not on V5.

That said, strafing is actually very useful (contrary to other posts here), but only if you’ve practice the tactic enough to notice WHY. Hint: it is much less accurate to aim a bot’s apparatus (firing a ball or mounting a cap on a pole) with pivoting than it is to advance left/right by strafing, especially if the apparatus extends well beyond the center of the bot - that is, rotation causes much more left/right adjustment on a longer “arm” than a shorter one, whereas with strafing it is the same no matter the apparatus’ length.

With X drive, using the Vex393 motors set to 160 RPM, the device is at least as fast as a standard tank drive running with 100 RPM motors. If the X drive is fitted with 100 RPM motors, it is considerably slower. 200 rpm settings may be too twitchy.

Bottom line, like others are saying, X drive is not well suited for Turning Point. If you like strafing for aiming, which isn’t a bad thought - consider mounting your apparatus SIDEWAYS.

Huh? X drives are faster mathematically. (under low load)

This doesn’t make any sense. X-drives are √2 (1.41421(141.4%)) times as fast as a tank drive at the same RPM.

Time to bring up a page that was previously mentioned
On the TVA instagram, we have done a vote on the meta design. Here is the result for the question regarding drivetrain styles:

As what I can tell when escalated on a larger scale, 63% of the teams will be simply doing a tank drive, while the other 31% will be doing some sort of drivetrain style that allows strafing (I’m not counting Other because it could be any style).
NOTE: This is based off of a public vote, and is simply used for predictions.

Please correct me if I am wrong but I can’t remember a World Champion team (I only know from Skyrise to now, please let me know if there was before) with an X-drive or any drive train able to strafe. I am not entirely sure why but I would believe it is for the annoying way a chassis is set up along with how little power it has.

44 Clean Sweep

@Brian_9605A as I said I don’t know that far back so thanks for letting me know.

44 didn’t win the tournament, but the alliance that won could strafe too.

So I’m kinda on topic for this thread, I don’t think strafing is useful in this game, as others have said.

Here are my quick thoughts on values:

  1. Strafing is far more useful this year than last year. This is due to both the flags and the poles all being lined up on the perimeter walls.
  2. Running around the perimeter with a tank drive with devices aimed sideways would seem to solve this, but a sideways arm for picking up caps would be difficult.
  3. Strafing is wasted effort/motor power for parking. So you have a big loss in one area for your gain in the other two.
  4. Motor considerations must factor in, as always.
  5. Overall, strafing is far more useful than last year, as last year nearly nothing was lined up so appropriately for strafing as things are this year. But that doesn’t mean it’s useful enough.
    Here are my quick thoughts on how this will drive teams. If teams don’t think parking will be so worthwhile compared to competing for flag/caps until the end, they’ll value strafing more and so we’ll see a decent amount of strafing as a result. Other teams will value climbing, and other teams will only want 2 V5 motors in their drivetrain, both of which will lead them toward tank drives. So I expect to see a much large mix this year. @[TVA]Connor 's post about question 4 doesn’t surprise me at all.

Read the articles and test the drive yourself.

You’re probably thinking of this article, or something similar:

Notice the closing line before the asterisk, to quote: “However, an X-drive will usually have greater frictional losses than a tank drive because of friction between the omniwheels and the omniwheel rollers.”

This is a vast understatement. Further, in the body of the article, they make the claim that the bot is able to drive in TWO DIRECTIONS AT ONCE. That is how they misunderstand the physics involved.

The bot is NOT traveling in two directions at once. This represents a fundamental misunderstanding of how the bot is traveling in a “forward” direction (where all 4 wheels are driving at equal speeds).

The article completely ignores the fact that while two sets of wheel’s are attempting to travel at 45 degrees toward the left, the other two wheels are trying to drive toward the right, VECTORING those two forces through the rollers. There is some loss to friction, but that’s not the overriding factor. There is loss due to SLIPPING.

Think carefully about this. How is there any possibility that a wheel could travel FARTHER per rotation if it is SLIPPING at a 45 degree angle?

The two forces actually FIGHT AGAINST EACH OTHER, WASTING ENERGY. The drive works on VECTORED forces - not ADDITIVE forces. There is no “magnification” effect. Think, too, about how you found that article. Search the 'net for something like, “which is faster, X drive or tank drive”. How many SCHOLARLY articles do you find. ONE! That should tell you something. The article is deeply flawed.

They, and thus both of you, have the math EXACTLY INVERTED.

X-Drives are 1/1.414 the speed of a tank drive ( or about 0.702, or about 70% ).

Put another way, I observed in all 3 version of the drives I built that the drives always traveled FASTER DIAGONALLY than “forward”. All of them were evaluated with nothing else on them (no other equipment beyond the controller and battery). Two were built out of only 1 x 2 C-Channel, so the load was about as light as is possible.

Also, I’m new to the board, so let me point out two things about me.

  1. I’ve built 3 of these drives and tested them extensively. Never once have I seen an X drive faster than an inline drive. They’ve always been about 0.7 of the comparable speed (almost exactly 1/1.414 times).

  2. I’m not a student. I’m a teacher; an engineer (though a software engineer, I’ve worked consulting for film/video, architecture, manufacturing and game engine design). I’m here because I volunteered to teach programming at the robotics club at my son’s high school.

Here is a video of a shifting X drive built by AURA specifically to demonstrate that X drives are faster, this argument has been had to death, and more engineers, students, and student engineers than I can count have weighed in. The article by AURA that you linked explains it as clearly as it’s possible to do, so I’m not going to go over the same thing again. If experience matters then I guess I should point out that I’m a professional mechatronics (robotics) engineer and I have taken Vex X drives to the world champs finals, but that doesn’t matter, facts matter, and the fact of the matter is that mathematically X drives are faster with the same wheels and gearing (though as AURA also pointed out, that advantage decreases with frictional losses as the robot gets heavier). I would still encourage teams to build 2 otherwise identical robots and test them alongside each other, you get more building experience, and you’ll be more confident in the evidence if you build it yourself.

I am a little busy right now so I can’t debate this with you. Trust that you are not the first person to come to this “realization” and you wont be the last. You are not even the first to say “I am a professional engineer so you should listen to me” , the others were mechanical engineers and in the end admitted they were wrong.

I’m with Jason. An X-drive should be 1/1.414 the speed of a tank drive - before friction is even considered. Some of the power is used or “wasted” by the oppositional forces at play. What am I missing? And the video didn’t seem to demonstrate the an x-drive is faster than a tank drive.

Ur trolling … It’s super clear that X drive is faster in the video. Those who have taken Algebra II would also know it is true from math.