H-Drive or X-Drive

As the end of the summer season is nearing, our team will use the results of the prototypes built in the summer to help us construct a better robot for the rest of the season. The biggest debate our team has had is the debate on what drive to use. While making this decision we have thought of using either a 5 motor H-Drive or a 4 motor X-Drive. We also must keep in mind our design which is currently a dumper with a two motor hanging mechanism. Some pros of the H-Drive are, it is strong, and it is reasonably maneuverable and is also able to strafe. Some cons of the H-Drive are that it is slightly less maneuverable than the X-Drive, is slower than the X-Drive, and uses an extra motor. Some pros of an X-Drive are, it is extremely maneuverable, and fast. Some cons of the X-Drive are it is weak, and is difficult to build on.
Please comment on what system you think is better and if you have any better ideas.

Take the following considerations:

  1. H-Drives use minimum 5 motors, and X-Drives use minimum 4 motors.
  2. The center wheel in an H-Drive must drive the entire robot when driving sideways, an X-Drive’s wheels are more proportionally distributed
  3. The advantages of a Tank Drive still apply with an H-Drive, less so with the X-Drive.

Taking these into consideration:

  1. If your robot is heavier, using steel parts, etc. I would recommend an X-Drive over H. Having one motor move a 20-30 pound robot is not going to work out
  2. You said that you’re a dumper bot, and you hang. Dumper bots generally require less motors than catapults, so an H-Drive isn’t completely out of the question, as opposed to if you were a 6 motor catapult.
  3. In StarStruck, power in your drive is much less important than speed. H-Drives are generally able to provide more power, and X-Drives more speed, at the expense of the other.

I would recommend that you do an X-Drive, but’s that probably because I’ve had bad experiences with H-Drives. Also, if you’re a dumper, it might not even be that bad to go Tank Drive

Yeah, I was thinking the X-Drive would be slightly more efficient but thanks for bringing up the point of the center wheel on a single motor not being able to strafe efficiently as I have not thought of this yet. This would be a huge problem if our robot gets heavy as increasing the torque of the motors equals decreasing the speed which is bad and putting two motors on the center wheel is probably not an option.

Well the reason I am having a problem with gearing up the H-Drive to make it faster was because it would brown way to much. At our latest competition we used a 4 motor tank drive with turbo motors and our robot’s drive browned out constantly when attempting to push stars under the fence which, at the competition, mostly consisting of push bots was a large way of scoring. As to the internal and external gearing, yes, they would be the same for both drives but we could change them if needed.

Remember that High Speed and Turbo motors exchange speed for power. If you don’t have enough power, lower the speed, by moving to high speed or even just standard.

I know but I want my drive to be as fast as possible but when pushing stars under the fence I don’t want the drive to brown so I am thinking high speeds would probably be best.

In my opinion, I would prefer to have a dumper or catapult mechanism on a H- Drive since is is all straight and usually more reinforced. However, that being said, a X-Drive usually has more speed and it is more efficient. In your case, since you have a lifting mechanism, i would go with the x- drive. This is why: This year, the hanging pole is in the corner, meaning that a straight, square base may become time- consuming when trying to align. However, if u use a x-drive since the back left and right motor are 45 degrees, it will make an right angle allowing easier alignment. (This is true if u are making a traditional x drive with an octagonal perimeter) All you would have to do to align is to drive into the corner and make sure half of your back perimeter is touching the field perimeter.

My club has found that X-Drivetrains work incredibly efficiently only if built to absolute perfection. H-Drivetrains for my club has been the safer bet but if you can construct a strong build X-Drivetrain…I would choose that over the H-Drive.

I agree, the X-Drive will allow us to get in the corner better but no matter what drive we use, we will likely make it small as we are only using 2 motors to lift our entire robot so the less weight the better.

I would recommend a X-Drive with the 3.25 inch wheels all high speed motors. This gives you so much speed and enough torque to carry a mechanism made of aluminum. Does not work with steel.

We’re doing a turbo mecanum drive this year for maneuvering and speed. I don’t know the specifics of the gearing yet (we have one guy doing a bulk of the designing), but we will see how it works with us trying to drive into cubes and actually pick them up. I’m a bit skeptical, but we can’t get our hands on a kit until school starts in two weeks.

My only worry is that the drive will not be strong enough to push stars under the fence which posed a big factor at our last competition. I have no doubt the drive would be strong enough to carry itself it is just not strong enough.

Any tips on making an X-Drive better?

Gussets with lock nuts – a LITTLE bit of flex on the diagonals is good – take your time and make it well.

Shoulder screws are great, too. I would recommend just using extra crossbars to be completely certain the sides are 100% aligned, and then removing the extra crossbars once the base is finished. This will help prevent you from noticing your base is tilted after the rest of the robot has been built :slight_smile:

For the X-Drive, what type of PID Controller should be used?

In auton the PID should handle the X and Y axis independently. So two PID’s for each axis of movement.

In driver mode, it is much harder to have a PID on position as you are generally looking for speed control and direction control.