For this year game, tower takeover which chassis will be better holonomic x chassis or holonomic h chassis? For advise.
I assume when you say holonomic H Chassis you mean using mechanum wheels? If that’s the case the more technical term is just simply mechanum drive.
My opinion would be the mechanum drive would be superior because it is faster. I don’t know the physics behind it but when you have wheels at 45 degree angle like that is slows down the whole robot.
So Holonomic drives are made with 4 Omni wheels. Mechanum drives are made with special wheels where the rollers are offset.
The H drive is not Holonomic, it has a 90 degree wheel mounted inthe H of the crossbar that lets the base strafe using the capability of the omni wheels.
On the original post of X vs +, it depends on where your object mechanism goes.
There is an often used frame that is a hexagon shape with the 1x5x1 channel as the walls with an open front. That’s my goto frame if I’m using Holonomic drive.
Terms are important.
Because it appears that double reverse four bars will be common this year, I would advise that you use a holonomic H drive, because it will allow for a better construction of a double reverse. Then again I personally don’t believe that holonomic drives will be necessary this year.
@nware49 So Holonomic H drive insn’t a thing. A H base with 4 omni wheels in a standard wheel pattern with a 90 degree omni wheel in the center is.
Terms are important, use the right ones for the right things.
oh. sorry to offend. i didnt realize that using the incorrect term to refer to the same concept would be such an issue. the creator of this post used the term “holonomic”, implying that the drive could move in any four directions without spinning, and “H chassis”, implying that there are 2 wheel wells and a crosspiece down the middle of the chassis with a 5th wheel on it to allow for the four directions of movement
It’s a new season with new people, trying to put our best foot forward. Otherwise it’s arm flail pointing and going ‘the thing-a-majig-callit’
An “H” style holonomic drive could allow a little more width between the chassis rails for collecting cubes.
An “H” style holonomic drive will be faster diagonally than a similarly powered “X” style. Conversely, the X-drive is faster in the X-Y directions than an H-Drive.
And yes, they are both holonomic. Even a mecanum drive is holonomic. Holonomic simply means that a drive train can be controlled in every degree of freedom it possesses. (X translation, Y translation, and rotation about the Z axis)
Here is a comparison chart for standard, x-drive, and mecanum that I’ve seen posted a few times.
This is really helpful! Thanks for sharing.
Important thing to note is that with teams building double reverse four bars and pushing a lot of cubes then there is a lot of wasted energy. Theoretically in an x drive if you look at all the force vectors half the energy is wasted and for mecanums it depends on the angle of the rollers, but i think vex’s are at 45 deg meaning half the work is also wasted there.
I think best case would be to use a 5 motor h drive and just use the center wheel for precision alignment. Practice is key
Yes, terms are important.
As @evasnphysics explained, the X-drive, the mecanum drive, and the tank drive with a 5th wheel turned at 90° to them (referred to here as “H-drive” even though it isn’t) are all holonomic drives. Meanwhile, a real H-drive (Yes, it’s a real term.) really isn’t holonomic and certainly does not have a wheel mounted at 90° from the others.
I think the OP was pretty clear by explicitly stating “holonomic” as well as both “X” and “H,” though.
Meanwhile, do you really use a hexagonal shape rather than an octagonal shape? Many “X-drives” use an octagonal shape. Even if there are no walls on some of the sides of the octagon, that doesn’t mean the shape isn’t octagonal, just like having a door in a square room doesn’t change the footprint from being square.
Sorry, it’s Octogon, sometimes my fingers get away from me.
What’s a “real H-Drive”
Take a look here: https://en.wikipedia.org/wiki/H-drive
Very cool and there are VEX parts that you could make that drive!
Sure, but you’ll go through a lot of effort to turn the four wheels for steering.
In engineering terms, holonomic drive normally means the total degree of freedom (DOF) is equivalent to the number of controllable DOF.
Bringing this definition into vex terms…
- mecanum drive is definitely holonomic. Controllable DOF = 2 (x and y axes), total DOF = 2 (x and y axes)
- a normal tank drive using omni wheels is not considered as holonomic. Controllable DOF = 2, total DOF = 1… meaning in order to go sideway, the robot has to turn to the side (i.e. the 2 controllable DOF at work) before moving towards the destination (i.e. total DOF = 1).
And side-note - think the h-drive issue is another example of how the industrial definition is different from vex definition. But for this case, I can totally understand why the originator of vex h-drive used this term to describe the drive. It is literally a H
So again, if we want to be taken seriously, then we should try our best to adhere to the industrial standard. So it is not about who gets offended or not.
Actually, the real definition of a holonomic drive in controls is any mobile robot drive with 3 axis degrees of freedom. (x, y, theta) This means any drive that can strafe is holonomic, ergo an H drive, and X drive, and a Mecanum driver are all holonomic.
“Terms are important, use them for the right things”