X-Drive or Chassis

  1. 3 weeks ago

    I’ve got a dilemma on my hands: whether i should use an x-drive or a normal chassis. On one hand, the x-drive would offer better shooting (which is a top priority)in order to control the flags as well as great positional defense on an open playing field with its precise and quick movements. I could maybe see this potentially dominating the field but would be a big risk to try. And yes x-drives can get on the platforms. On the other hand, the chassis has always been reliable through the years and wouldn’t be a bad option. Thoughts?

  2. josh_siegel

    Jul 24 Davis, California 162A alumni (2016-2018)

    I would never personally use an X-drive after having horrible experiences using them in the past. I have never made or played against a 4 393 motor drive train that didn't burn out like crazy. It is also just a pain to build around it.

  3. Edited 3 weeks ago by 675C Robotics

    @AstroNight Depends.
    If you are switching to v5, and you think you can shoot and pick up caps with 4 motors, then yes.
    But if you are not switching, do you think a 4 motor x-drive will be good enough?
    Even then, there are still a lot of other things to consider like torque output, what your strategy is, and what you have experience building

  4. NightsRosario

    Jul 24 Reisterstown/Catonsville, MD 3922A

    Please don't go X-drive. They have sqrt(2)x less torque than their tank drive counterparts. That loss of torque is pretty bad considering you have a crowded ball shooting area. That also eliminates your defense strategy idea. Another thing to consider is the amount of space you lose while building things. You can work around it, but if you want to do a top roller for the balls like a lot of people are doing you will have a harder time getting that to fit than if you were running a tank config.

  5. ItsAlex

    Jul 24 Taipei, Taiwan (ROC) 4253
    Edited 3 weeks ago by ItsAlex

    There isn't a best drive between each other. X drive and tank drive both have their own positives and negatives.

    If you want to focus on getting balls and waffles, then an x drive might be doable. X drives will be faster, but weaker.

    If you want to contest for center platform, tank drive will be the better choice as you have more torque compared to x drive.

    It all comes down to what kind of robot you want to make. An everything robot or a robot just made for a specific task

  6. [TVA]Connor

    Jul 24 South Texas 1814D
    Edited 3 weeks ago by [TVA]Connor

    A 4 motor V5 X-Drive should be able to easily handle an X-Drive considering It's both stronger and the motors are said to be more consistent. There's the existence of flip-out mechanisms for X-Drives that allow more space and workarounds. With V4, I was really close to being able to do everything with 4 motors while having an 8 motor X-Drive. I Won't share if I am going to continue with the X-Drive or not but I will say it is possible and, if built correctly, may be powerful.

  7. Thanks for the feedback. I’ll take everything into consideration.

  8. 2 weeks ago

    ZachDaChampion

    Jul 31 Fort Lauderdale, Florida 77788J

    @NightsRosario Please don't go X-drive. They have sqrt(2)x less torque than their tank drive counterparts.

    I know this thread is a bit old, but I want to clarify that X drives actually have effectively a speed ratio of 1:√2, so while they do lose torque, they gain it back in speed. If using standard torque motors, a 4 motor X drive has theoretically more torque than a 4 motor high speed tank drive (about 141 RPM, vs 160 of a standard HS chassis). Of course there is substantially more friction in an X drive than a tank, so you do lose some torque that is not redistributed, but it isn't just a plain torque reduction. I assume @NightsRosario knows this, I just wanted to clarify for those who may not.

  9. last week

    X drives burn out in a push fight and there will DEFINITELY be push fights in this game

  10. Carter

    Aug 3 Alabama 13907A

    @matthew_perry X drives burn out in a push fight and there will DEFINITELY be push fights in this game

    This will be false when a 4 motor x drive 100 rpm pushes a 4 motor tank drive set to 200 rpm.

  11. meng

    Aug 3 Singapore 8059

    @Carter This will be false when a 4 motor x drive 100 rpm pushes a 4 motor tank drive set to 200 rpm.

    Sigh... and your 100rpm x drive will go slower than the 200rpm tank drive....

  12. Carter

    Aug 3 Alabama 13907A

    @meng Sigh... and your 100rpm x drive will go slower than the 200rpm tank drive....

    This is correct. Besides from minor friction losses, the power of the system remains the same. It just drives me crazy that people think x drives magically lose a ton of torque, when in reality it is because people have been using 4 motor x drives, which lose most pushing matches. With the switch to v5, the motor distribution makes x drives interesting because it will win more pushing matches and not be at a loss in terms of motor power elsewhere if a 4 motor tank drive is meta. X drives still have major flaws, but the should at least be used in games that favor them.

  13. meng

    Aug 3 Singapore 8059

    @Carter This is correct. Besides from minor friction losses, the power of the system remains the same. It just drives me crazy that people think x drives magically lose a ton of torque, when in reality it is because people have been using 4 motor x drives, which lose most pushing matches. With the switch to v5, the motor distribution makes x drives interesting because it will win more pushing matches and not be at a loss in terms of motor power elsewhere if a 4 motor tank drive is meta. X drives still have major flaws, but the should at least be used in games that favor them.

    It’s not about that... you should compare Apple to Apple, I.e. 100rpm for x drive vs 100rpm for tank drive. Then we will be able to see the strength and weakness of each drive systems :)

  14. callen

    Aug 3 Braintree, MA, USA
    Edited last week by callen

    @meng It’s not about that... you should compare Apple to Apple, I.e. 100rpm for x drive vs 100rpm for tank drive. Then we will be able to see the strength and weakness of each drive systems :)

    Yes, apples to apples, but that's not what you have there. You've got apples to oranges. If you really want to compare them, you do something like the following:

    1. Gear them both so they free-travel linearly at the same rate with chassis of the same mass and mass distribution. With 393's 7:5 = 1.4:1, which is pretty close to 1.414... So this is manageable.
    2. Now compare how well they accelerate, maximum load they can pull, etc. linearly.
    3. Repeat 1 & 2 with them geared to free-travel rotationally at the same rate.

    What you should find is that the x-drive loses out linearly and wins out rotationally. Mostly we need linear since climbing and pushing battles are where we usually need the most strength, so the drive tends to be lossy, which is what it pays for to get the mobility it has.

    What @Carter was pointing out is that @matthew_perry 's comment was so general that it was just false. You can't just say one drive style is stronger, faster, similar. The drive style alone isn't any of those. It depends on the motors you're using, the internal and external gearing, how well it's built, and the drive style.

  15. NightsRosario

    Aug 3 Reisterstown/Catonsville, MD 3922A

    Just build a tank drive. Seems to have worked in the past.

  16. meng

    Aug 3 Singapore 8059

    @callen Yes, apples to apples, but that's not what you have there. You've got apples to oranges. If you really want to compare them, you do something like the following:

    1. Gear them both so they free-travel linearly at the same rate with chassis of the same mass and mass distribution. With 393's 7:5 = 1.4:1, which is pretty close to 1.414... So this is manageable.
    2. Now compare how well they accelerate, maximum load they can pull, etc. linearly.
    3. Repeat 1 & 2 with them geared to free-travel rotationally at the same rate.

    What you should find is that the x-drive loses out linearly and wins out rotationally. Mostly we need linear since climbing and pushing battles are where we usually need the most strength, so the drive tends to be lossy, which is what it pays for to get the mobility it has.

    What @Carter was pointing out is that @matthew_perry 's comment was so general that it was just false. You can't just say one drive style is stronger, faster, similar. The drive style alone isn't any of those. It depends on the motors you're using, the internal and external gearing, how well it's built, and the drive style.

    Believe me, I do know understand how x drive works.
    Apple to Apple means both should be geared in the same way. So minimally, both should be just using the torque setting for comparison.
    You can’t just gear one to 100rpm and the other to 200rpm and then conclude that the 100rpm has more torque. It is not a fair test.

  17. callen

    Aug 3 Braintree, MA, USA
    Edited last week by callen

    @meng You can’t just gear one to 100rpm and the other to 200rpm and then conclude that the 100rpm has more torque. It is not a fair test.

    Right. But you also can't have both set to 100 rpm. That's just as unfair a test.

    @meng Apple to Apple means both should be geared in the same way. So minimally, both should be just using the torque setting for comparison.

    No, not exactly. Consider what the statements are. If you ask which is the fastest, you're asking in essence which can carry the same load the fastest. In that case you want try to match torques and loads and see which travels the fastest. If you ask which is the strongest, you're asking in essence which can push the strongest at whatever speed(s) you're trying to run. In that case you want to try to match speeds and see which can handle loads the best. But doing either one of these will inform about the other well, and matching free speeds is easier.

    The very reason so many people are so confused about the comparisons between x-drives and tank drives is because they keep comparing the two drives geared so that the motors rotate the wheels at the same rate. That's not comparing apples to apples.

  18. meng

    Aug 3 Singapore 8059

    @callen Right. But you also can't have both set to 100 rpm. That's just as unfair a test.

    No, not exactly. Consider what the statements are. If you ask which is the fastest, you're asking in essence which can carry the same load the fastest. In that case you want try to match torques and loads and see which travels the fastest. If you ask which is the strongest, you're asking in essence which can push the strongest at whatever speed(s) you're trying to run. In that case you want to try to match speeds and see which can handle loads the best. But doing either one of these will inform about the other well, and matching free speeds is easier.

    The very reason so many people are so confused about the comparisons between x-drives and tank drives is because they keep comparing the two drives geared so that the motors rotate the wheels at the same rate. That's not comparing apples to apples.

    Aahhh... I think I know the issue now - we are using different independent and dependent variables to test the similar thing.

    I am using the gear ratio as independent variable and then observe both the torque and speed of the drive.
    While you are using the torque itself as the independent variable and then observe the speed (or vice versa).

    Both approach are doable.
    But I would say that it is easier to match the gear ratio then to match the torque output or the speed.

    Why I said it is not a fair test is because if the drive is using different gear ratio, then obviously it will have different torque output.
    So if the question is solely about which drive has more torque, then it is not wrong to just use gear ratio as the independent and then the torque as dependent.

  19. callen

    Aug 5 Braintree, MA, USA

    @meng Aahhh... I think I know the issue now - we are using different independent and dependent variables to test the similar thing.

    Yes, and I'll explain why better...

    @meng I am using the gear ratio as independent variable and then observe both the torque and speed of the drive.

    There are three problems with this as I see it:

    1) Gears and sprockets/chain are not the only way to effectively mechanically build in the equivalent to a gear ratio. There are multiple other ways. Keeping the gear ratio as an independent while not similarly managing these other things means you're not fully keeping what you want to be independent actually independent. For example, what if I were to say tank drives are faster when you use 100 rpm on both a tank drive and an x-drive? I'm I wrong? You might think so, but maybe I'm saying it because with a tank drive I am using 6" wheels, while my x-drive's omni-wheels are limited to 4". Different wheel sizes as well as different wheel alignments are ways to mechanically build in the equivalent of gear ratio without using gears nor sprockets/chain. x-drives included a mechanical equivalent to gear ratio, essentially gearing for speed. While it's important to know about this to use the design, it's not useful to make comparisons.

    2) Gear ratio is not a performance (can't think of a good word there) part of the robot. For example, you do things like deciding to climb a hill. You need to make sure the robot has the strength to climb the hill. Then the fastest design is the one that provides the needed strength and carries the robot along the fastest. Or you have some speed you want your robot to be able to maneuver at in the field. You design tank and x-drives to perform at your desired speed. The one that can push stronger while doing so is stronger. Performance values are what are needed, so they are really what ought to be used.

    3) We've seen repeatedly that people have trouble understanding what this method means. Many statements have been made with a caveat like "with the same gear ratio" when comparing the drives. Yet repeatedly people have misunderstood what is actually being said, entirely losing track of that caveat. So if approaching it this way hasn't worked so well in conveying the message, maybe we should use a different way that will show the actual gains and losses better.

    .

    Really, we should say it all differently anyway. X-drives have lower output power linearly and higher output power rotationally than do tank drives. While you probably don't need the same rotational power, x-drives are holonomic drives, which provides additional advantages, while their configuration makes things like driving over a bump harder. Once everyone understands the power part (I think the second is well understood.), the whole faster/slower/stronger/weaker thing and making choices based on performance will become clearer.

    This is why I really hate the statements I so often hear that x-drives are faster, which is based on this gear ratio comparison. Are they really? So if you're going to design robots for a straight-line race, would you choose an x-drive? We can even disallow multi-speed transmissions so that there is no need to worry about those complexities getting in the way of a comparison. If x-drives really are faster, shouldn't we use an x-drive for this? Or maybe we shouldn't be saying x-drives are faster?

  20. meng

    Aug 5 Singapore 8059

    @callen Yes, and I'll explain why better...

    There are three problems with this as I see it:

    1) Gears and sprockets/chain are not the only way to effectively mechanically build in the equivalent to a gear ratio. There are multiple other ways. Keeping the gear ratio as an independent while not similarly managing these other things means you're not fully keeping what you want to be independent actually independent. For example, what if I were to say tank drives are faster when you use 100 rpm on both a tank drive and an x-drive? I'm I wrong? You might think so, but maybe I'm saying it because with a tank drive I am using 6" wheels, while my x-drive's omni-wheels are limited to 4". Different wheel sizes as well as different wheel alignments are ways to mechanically build in the equivalent of gear ratio without using gears nor sprockets/chain. x-drives included a mechanical equivalent to gear ratio, essentially gearing for speed. While it's important to know about this to use the design, it's not useful to make comparisons.

    2) Gear ratio is not a performance (can't think of a good word there) part of the robot. For example, you do things like deciding to climb a hill. You need to make sure the robot has the strength to climb the hill. Then the fastest design is the one that provides the needed strength and carries the robot along the fastest. Or you have some speed you want your robot to be able to maneuver at in the field. You design tank and x-drives to perform at your desired speed. The one that can push stronger while doing so is stronger. Performance values are what are needed, so they are really what ought to be used.

    3) We've seen repeatedly that people have trouble understanding what this method means. Many statements have been made with a caveat like "with the same gear ratio" when comparing the drives. Yet repeatedly people have misunderstood what is actually being said, entirely losing track of that caveat. So if approaching it this way hasn't worked so well in conveying the message, maybe we should use a different way that will show the actual gains and losses better.

    .

    Really, we should say it all differently anyway. X-drives have lower output power linearly and higher output power rotationally than do tank drives. While you probably don't need the same rotational power, x-drives are holonomic drives, which provides additional advantages, while their configuration makes things like driving over a bump harder. Once everyone understands the power part (I think the second is well understood.), the whole faster/slower/stronger/weaker thing and making choices based on performance will become clearer.

    This is why I really hate the statements I so often hear that x-drives are faster, which is based on this gear ratio comparison. Are they really? So if you're going to design robots for a straight-line race, would you choose an x-drive? We can even disallow multi-speed transmissions so that there is no need to worry about those complexities getting in the way of a comparison. If x-drives really are faster, shouldn't we use an x-drive for this? Or maybe we shouldn't be saying x-drives are faster?

    First....why 100rpm... so that there isn’t any need for external gearing which will introduce frictions.

    And obviously I am assuming that everything else is held as controlled variables, eg. Size of wheels used, etc.

    It’s ok. I know you are concern that some readers might not understand the boundary of my comparisons, etc.
    But as you said, I do know all the “caveats” or boundary involved, so no.. I won’t get confused with that 3 problems.

    But appreciate your effort in trying to make it crystal clear for everybody though.

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