Searching For Swerve / Holonomic Drive Idea

[Roboshant]

I believe this is a hemispherical omnidirectional gimbaled drive or a HOG drive.

[Ari423]

Originally Posted by Roboshant

I believe this is a hemispherical omnidirectional gimbaled drive or a HOG drive.

No, according to its name a HOG drive uses a tilting hemisphere that spins in one axis (parallel to the hemisphere's circle), whereas these use a full sphere that can spin in 2 axes.

Swerve (and mecanum) technology has progressed a lot since 2003, so today there are much simpler and better ways of making a true omnidirectional drive compared to this pseudo-omnidirectional drive.

[Andrew Schreiber]

Originally Posted by CalTran

1717, 973, 16, and other swerve teams have done it before. It's possible, but as said, requires an absurd amount of coordination.

I've also done it numerous times with omni wheel based drives[1]. With a gyro it's fairly simple actually. Ether has posted enough of the math at this point that it's not bad at all. If you prefer to derive it yourself it's some basic trig.


[1] https://www.youtube.com/watch?v=TW6fR-bQFgI In this video the driver is simply commanding the direction to go (field centric) and a rotation rate. The robot figures out everything else. No coordination needed, this was, I think, Brando trying it out for the first time.

[Alan Anderson]

Originally Posted by Ari423

Swerve (and mecanum) technology has progressed a lot since 2003, so today there are much simpler and better ways of making a true omnidirectional drive compared to this pseudo-omnidirectional drive.

I'm still trying to find out what makes people call the ball drive something other than a "true omnidirectional" fully holonomic system.

[Ari423]

Originally Posted by Alan Anderson

I'm still trying to find out what makes people call the ball drive something other than a "true omnidirectional" fully holonomic system.

Since only the front wheels can impart a sideways force on the robot, the robot will turn (w/ CoR between the back wheels). If all 4 wheels were balls, it would be a true-omnidirectional drive. As it is now, the robot drives more like a car, where the front of the robot can go sideways, while the back of the robot doesn't.

[Andrew Schreiber]

Originally Posted by Ari423

Since only the front wheels can impart a sideways force on the robot, the robot will turn (w/ CoR between the back wheels). If all 4 wheels were balls, it would be a true-omnidirectional drive. As it is now, the robot drives more like a car, where the front of the robot can go sideways, while the back of the robot doesn't.

3 Wheels, you don't need 4.


Alan - I believe this system would have a difficult time translating and rotating at the same time, but, as I haven't built one or played with one I can't confirm this without putting in a bit more thought. But I think that's what folks are getting at. But I think that's based on my mental model of the wheels being the same as an omni wheel and I'm thinking that's not right.

[pwnageNick]

oh boy have I got something for you.

Remind me to revisit this thread in a month when all the craziness of the current season is over. I've got a fun project from a few years ago to share.

[Ether]

Originally Posted by Ari423

Since only the front wheels can impart a sideways force on the robot, the robot will turn

You can compensate for that by "tanksteering" the bot in the opposite direction. But that compensation is based on dynamics (forces) not simple kinematics.

With a true swerve it is straightforward to solve the inverse kinematics to get straight-line motion while simultaneously turning. Just make the direction command field-centric.

[IronicDeadBird]

I heard of a recently released design called the BB 8 don't know much about it but it could be worth looking into.

[Alan Anderson]

Originally Posted by Ari423

Since only the front wheels can impart a sideways force on the robot,...

Are we talking about the same thing? The front wheels on the TechnoKats 2003 "ball drive" 'bot are omniwheels, and can impart only forward/backward forces. The balls are the only thing that can produce a sideways force.

[Chris Endres]

Originally Posted by trumpthero786

I feel like steel would be very slippery on carpet. Traction would be difficult.

Well, purposeful metal-on-carpet is illegal in FRC (according to R6), if that is what you were referring. I would go for a hard rubber ball if I would design this, probably with a ~ 5" diameter.

[Ari423]

Originally Posted by Alan Anderson

Are we talking about the same thing? The front wheels on the TechnoKats 2003 "ball drive" 'bot are omniwheels, and can impart only forward/backward forces. The balls are the only thing that can produce a sideways force.

Oh then I was looking at the robot backwards. Make that the back wheels (the balls). The point is with this configuration, the drivetrain cannot travel in all three dimensions (x, y, r) at the same time. You could do it using three wheels set up with two balls in the front (or back) and at least one omni wheel facing horizontal (perpendicular to the front).

[CalTran]

Originally Posted by IronicDeadBird

I heard of a recently released design called the BB 8 don't know much about it but it could be worth looking into.

[ctt956]

Originally Posted by CalTran

Fire game!

[asid61]

Would not mecanums be easier to implement than a swerve drive and a ball drive? As an offseason project I like swerve drives more if you have the resources to do it, or mecanum if not.