Holonomic Drive

[kresty]

Thanks Oliver for showing him off on the stage and the talk, it was cool!

Here you can see its holonomic drive..  I mucked with the brightness so you can see the Lego details and the holonomic drive.  Note that the balls in the corners are just balls, they don't move and are a couple mm off the ground.  Like toy balls or something.  About the size of the Lego planets, (not sure), but I don't see a seam.

The Holonomic Drive means it can move any direction.  Oliver put a blue LED on one side so he knows which way's front.  It looks fun in person, he can spin it in circles and drives off in different directions.  It looks pretty fun to drive; a different kind of motion from the droids we're used to.

Also note that the Lego details are just cut where the wheels go.  Once you start using Lego as a building material and are willing to cut it, you have a bunch more possibilities. 



I have more pix of it on the stage I can post later.

[Lichtbringer]

Sweet. There seem to be castseams on the balls, or maybe just scratches or lighting?

Same size as the raquetballs used on Chewies OT bowcaster, maybe?

[kresty]

Hmm I didn't see the seam I'll have to look closer. It feels smooth, but not as soft as a kids ball pit ball

[Murasaki]

I am thinking the same drive system as CHiP ...

https://www.youtube.com/watch?v=8SiHxpoJVuw


I have just bought this for my son ... It is using the same wheels and I would say the same type of system.

[Lichtbringer]

Nice idea, i hope it´s a easy swap and works as planned. 

[savagecreature]

I am thinking the same drive system as CHiP ...

https://www.youtube.com/watch?v=8SiHxpoJVuw


I have just bought this for my son ... It is using the same wheels and I would say the same type of system.

Not the same wheels, not quite the same system, though similar in that they're both holonomic

CHiP is using Mecanums, a specific type of pseudo-omni wheel. For Mecanums to work properly they have to be attached to the chassis like the wheels would be attached to a car.

Omni wheels, which are what are on the Sentry droid are mounted perpendicular to each other when using 4, one at each corner at a 45 degree angle.


Though they both work similar enough that you could definitely get it to work the intent between the two systems is different. Omni wheels are used on robots that use each side of the chassis equally. That is to say, something that doesn't really have a front or a back. When used on remote control robots they often use IMU compensation systems so it doesn't matter which what it's facing, when you move the control away from you, the robot moves away, when you move the control to your left, the robot moves to your left.

Mecanum drives are intended for things that have a distinct front and back but will find great utility in the ability to move directly sidways when the need arises.

I'll put something in the wiki with images, explanations and examples sometime fairly soon for anyone that's interested. We've built more than one of both systems for the competition bots and for various research platforms. They're a lot of fun.

[kresty]

Savage (or anyone), do you happen to be able to identify the model of the wheels used (or motor?)  I managed to get a picture as it was lifted off the stage.

(excuse me for a moment while I use the new image shortcut thingy)

Underside of Sentry Droid

[kresty]

CHiP is using Mecanums, a specific type of pseudo-omni wheel. For Mecanums to work properly they have to be attached to the chassis like the wheels would be attached to a car.

Omni wheels, which are what are on the Sentry droid are mounted perpendicular to each other when using 4, one at each corner at a 45 degree angle.


Though they both work similar enough that you could definitely get it to work the intent between the two systems is different. Omni wheels are used on robots that use each side of the chassis equally. That is to say, something that doesn't really have a front or a back. When used on remote control robots they often use IMU compensation systems so it doesn't matter which what it's facing, when you move the control away from you, the robot moves away, when you move the control to your left, the robot moves to your left.

Mecanum drives are intended for things that have a distinct front and back but will find great utility in the ability to move directly sidways when the need arises.

I'll put something in the wiki with images, explanations and examples sometime fairly soon for anyone that's interested. We've built more than one of both systems for the competition bots and for various research platforms. They're a lot of fun.

Info in the wiki would be helpful. Maybe when you'd choose one over the other. I think of Mecanums as "loud" but maybe that's just 'cause the robot @ work that has them is huge. They also seem more annoying to my wee mind - like is the math more complicated?

[savagecreature]

The motors looks similar to an RS 500 series motor. I don't think they are, 'cause they have a plastic end cap on the rear and I've never seen a 500 with plastic, but then again, I haven't seen them all.  In any case, it's a similar motor in the same class, probably 12v, high RPM.





I say high RPM 'cause they've also got planetary gear boxes on the end of them, I'd bet reduction.



The green gives them away as most likely being VEX omnis, like these

[kresty]

If you look closely, you'll see a bar running across the middle of the bottom with a couple blocks.  I couldn't figure out why a block and bar was just sitting there, but figured it had to do something:

Underside of Sentry Droid

So, I asked The bar is for uneven floors, apparently it is so that each pair of omnis on the sides can pivot so that all 4 wheels might stay in contact on slightly uneven surfaces!