I was just messing around with some vex parts and I made this x drive. On the first look it looks pretty precise for the potential cost vs swerve drive and of course you get the benefit of going any direction without loosing much speed or torque like you would with mecanum drive. Considering this is vector addition there is also benefit of being hard to defend against as there is so much grip available. Is there any reason its not used as often in frc?
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the robots in FRC are much bigger so you will need more than 1 wheel on each side of the robot.
some teams use omni drivetrain by putting 3 omni wheels on each side of the robot and one wheel in the middle of the robot facing sideways which allows the robots to move left and right, but this type of drivetrain is much easier to defend against because you can push the robot easily to every direction.
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Well not necessarily need more than 1 wheel on each side. You can have a 4 wheel drive like how swerve is. This is the cad of my team’s this year drive train. With x drive you would just put a wheels on 45 degree on all 4 corners and direct drive them with planetary gearbox.
with omni wheels on 45 degrees you wont be able to move forward and to the right and left, it is not swerve, you will only be able to move in 45 degrees which will be very hard to drive
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It takes up a lot of robot real estate and gets easily pushed (like - easier than mecanum) under defense. It also doesn’t have a lot of COTS solutions like mecanum, this would require a custom drivetrain. That is why it is unpopular.
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This behaves exactly the same way a mecanum drive would behave, under ideal conditions. If you are “losing speed and torque” with a mecanum drive, then your wheels are slipping and you have to address that to get proper performance (e.g. with speed control, more wheels, etc)
All of those problems happen to X-shaped omni drives at full scale, and more, plus they have significant issues with climbing up over terrain. At this point you could almost argue a swerve drive is less work.
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This isn’t true at all. By varying the wheel speeds and using omni wheels you can move in any direction with this drivetrain. This driving is even shown in the linked video at the top of the post. If you don’t have the knowledge or experience to make claims like this, please don’t.
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This isn’t true. The kinematics are quite different.
…no they’re not? Like, not at all. A mecanum drive can use the same underlying code as an X shaped omni drive - presuming the wheels are at 45 degree angles in the corners of the chassis, as was commonplace when this drive was ever used in FRC. I’m not sure where you’re getting this from.
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They can use the same code, but the kinematics are indeed different. Draw out the free-body diagram.
Or: calculate the forward chassis speed relative to the motor speed for both drives.
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you are going to loose speed and torque and that wasnt the OP intention, and it still makes your robot realy easy to push around, it is bad substitute for swerve.
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The main points have already been covered I think.
- Mounting wheels/gearboxes at an angle is a hassle.
- Due to the orientation of the wheel, getting over obstacles is harder (no longer rolling over obstacles like a regular/mecanum wheel can.
- When driving at a 45 degree angle (ie diagonal), only 2 wheels are running but the normal force is split amongst all the wheels (ie less traction on driven wheels).
- Ability to push/not get pushed around goes down.
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Interesting you say that because I tested the amount of force it can output against a scale and this outputted a lot more force than mecanum did.
Also if you really think about it if you look at my video I was able to make it out of vex parts so I don’t know how much custom drivetrain it would take?
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I have driven mk4 swerves and frc mecanums on frc robots and I would say this felt like a lot more of swerve than driving mecanum
I mean obviously if you had the ability to go for swerve you would but for teams that don’t have budget for that and in future if there is a similar game like rapid react where swerve is really helpful this drive would be a interesting solution imo
We’ve really come full circle. X drives used to be somewhat more common before COTS swerve destroyed all other drivetrains, although even as a student from 2013-2016 I don’t think I ever actually saw more than a couple.
They tend to be easily pushed and have trouble going over obstacles. Omni wheels are fun to drive and easy to program, but that’s about where the advantages end. They might have some use in the hands of the right driver, but usually it’s better to save up and get a swerve, in case of games where pushing is hard to avoid.
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I would still prefer tank drive (west coast) as long as it is not 2015 but maybe it is only me.
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Ahh icic makes sense. Yeah definitely swerve is awesome. Imagine integrating some sort of suspension in swerve for years with obstacles.
Various forms of drivetrains featuring omni wheels have been utilized in FRC before. Not always with 4 wheels positioned in the “X” pattern, but the principles remain largely the same regardless of wheel quantity.
1114 in 2015 used a 3-wheeled omni drive. One of the advantages of only using 3 wheels, instead of 4 or more, is that it takes 3 points to make a plane. With 4+ wheels, there’s a chance that imprecision fabrication can cause not all four wheels to make contact (or the same degree of contact) as one another, which can lead to unequal amounts of force exerted by each wheel on the robot, which in turn can lead to errors with odometry and control. 3 wheels attempts to sidestep that issue, but can still have some concerns with weight distribution causing wheels with less weight on them to slip under less force than other wheels.
There are plenty of other examples of holonomic and omni-directional drivetrains utilizing omni wheels in FRC history. 857 in 2002, 116 in 2005, 1501 in 2010, etc. Prior to COTS Mecanum wheels being a thing (AndyMark first introduced them prior to the 2007 season), omni-wheeled drivetrains were somewhat common. Once mecanum wheels caught on, they phased out most omni-wheeled drives because of their superior ability to climb obstacles (such as the 2010 bumps or 2012 ramps) if you approached those obstacles perpendicular to the wheels. Now, with further expansions to the legal motor allowances, PDP slots, and the proliferation of COTS swerve modules, swerve reigns over all other forms of omni-direcitonal movements.
I do want to counter some half-truths presented in this thread. Omni wheels and mecanum wheels are equally resistant to being pushed. While some of the input/output kinematics vary slightly for rotation, the maximum force output (relative to motor input) and roller directions for these two drivetrains are identical. The reason some may anecdotally note that they think mecanums might be harder to push ties into the quality and assembly of mecanum rollers. If the rollers bind into the wheel housing, it will be harder to push. But this isn’t universally true of all mecanum wheels, and can also apply to omni wheels. It ends up being an implementation issue, rather than a theory issue.
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