H-Drive Question

[M. Mohis]

We were discussing the pros and cons of H drive (4 omni's in tank and one in the middle sideways) and someone brought up that you couldn't do H drive in a U shaped chassis (no front plate). Thoughts?

[Joey Milia]

How far into the base is the opening? If it's less than halfway into the robot then I don't see any issues with an H drive. If it's more than that then you might have some issues, not only with the slide drive but with general frame stiffness.

[BryceKarlins]

With slide ("H") drives, it's not so much that the center wheel is in the middle of your robot; it's that the center wheel is under your center of mass. If your center of mass is in front, or behind the center wheel, you'll find yourself rotating slightly when you try to strafe.

So, teams that hold the totes in front of their robot will end up in trouble unless they do some maths.

[M. Mohis]

Currently the U is almost exactly half the base of the robot. But what if we were to put an omni at both the end of the U and the end of the actual robot? Would that reduce weird rotation?

[Team3266Spencer]

Originally Posted by BryceKarlins

With slide ("H") drives, it's not so much that the center wheel is in the middle of your robot; it's that the center wheel is under your center of mass. If your center of mass is in front, or behind the center wheel, you'll find yourself rotating slightly when you try to strafe.

So, teams that hold the totes in front of their robot will end up in trouble unless they do some maths.

In what direction would you rotate? Away from the mass?

[Amar Shah]

You could do two sideways wheels halfway along the sides of the U shape.

[z_beeblebrox]

Anyone have experience using a gyro to compensate for a center wheel offset from the center of mass?

[NewKid123]

What are the pros and cons of and and cons of an H-Drive system? Anybody have any ideas about the pros and cons of an H-Drive system?

[kartikye]

Pro:
Maneuverability
If it fails, you now have a tank drive

Cons:
Bit more expensive
Bit more complex

[eghazal]

How viable would an X drive be when used with a U shape Chassis?

[Nemo]

Originally Posted by z_beeblebrox

Anyone have experience using a gyro to compensate for a center wheel offset from the center of mass?

Our team did an offseason drive where the omni wheel was all the way at one end, so it had to compensate substantially in order to strafe straight. We used a gyro and managed to get it to strafe, but strafing was probably only 5 ft/s and we didn't stay with it long enough to get it to go really straight sideways. All we did was a simple proportional controller: we added an amount of turning to the joystick inputs / inverse kinematics equal to the gyro error times a tuning constant. Conceptually it isn't very complicated.

One of the things that does complicate life is that your strafe wheel isn't going to give you the same rate of angular acceleration as the drive does when it tries to spin the robot. That's what made our strafing a little shaky. I think that can be accounted for, but if those angular accelerations are different enough, it might take something fancy to really smooth things out.

If the center wheel was offset only somewhat from the center of mass, those problems get smaller, of course, and maybe you'd get by just fine with the simple proportional gyro feedback loop.

[Bruceb]

what will that center wheel to do robot balance when you are half way up the bump?
Seems it will get pretty wobbly.