Re: Searching For Swerve / Holonomic Drive Idea
 

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

Re: Searching For Swerve / Holonomic Drive Idea
 

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.

Re: Searching For Swerve / Holonomic Drive Idea
 

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.

Re: Searching For Swerve / Holonomic Drive Idea
 

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

Re: Searching For Swerve / Holonomic Drive Idea
 

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.

Re: Searching For Swerve / Holonomic Drive Idea
 

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.

Re: Searching For Swerve / Holonomic Drive Idea
 

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.

Re: Searching For Swerve / Holonomic Drive Idea
 

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.

Re: Searching For Swerve / Holonomic Drive Idea
 

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

Re: Searching For Swerve / Holonomic Drive Idea
 

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.

Re: Searching For Swerve / Holonomic Drive Idea
 

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.

Re: Searching For Swerve / Holonomic Drive Idea
 

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).

Re: Searching For Swerve / Holonomic Drive Idea
 

Re: Searching For Swerve / Holonomic Drive Idea
 

Fire game!

Re: Searching For Swerve / Holonomic Drive Idea
 

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.