pic: our octanem drive

[Alpha Beta]

We actually had a design similar to this in our initial brain storming session. We called it sextacanum, borrowing from the Latin prefixes. It will be great for the students who proposed this idea to see it in action. We'll have to check out some of your match videos from the PNW.

[Brandon Zalinsky]

We have pretty much the exact same system on our machine, with the same mecanum wheels. There are only a few differences. First, we have a 6:1 reduction to the traction wheel. Second, the auxiliary wheels are tractioned with Velcro (works incredibly well). To address this-

Any issues with wheel speeds being different? I'd think that could be abusive on the mecanum wheels- having them running at a different speed than the traction ones. Any jitterring or efficiency losses?

When we actuate the "drop drive", as we call it, down, it tips the bot forward so that we have the two traction wheels and the two mecanums not connected to them contacting the floor. There is then a function in code that drops the speed of the mecanum wheels to 1/6 of their normal speed to make sure that the mecanums and velcro wheels run at the same speed.

[zinthorne]

Originally Posted by Brandon Zalinsky

We have pretty much the exact same system on our machine, with the same mecanum wheels. There are only a few differences. First, we have a 6:1 reduction to the traction wheel. Second, the auxiliary wheels are tractioned with Velcro (works incredibly well). To address this-



When we actuate the "drop drive", as we call it, down, it tips the bot forward so that we have the two traction wheels and the two mecanums not connected to them contacting the floor. There is then a function in code that drops the speed of the mecanum wheels to 1/6 of their normal speed to make sure that the mecanums and velcro wheels run at the same speed.

We used transmissions which geared it down to 8:1 and then the extra big traction wheels with the 44 tooth sprocket helped give more power too. Same as in your design, our traction wheels lifted up the back mecanems about a half an inch.
This video has some pushing, and also a great upset win in finals.
https://www.youtube.com/watch?v=WbHHUtCGc1c

This link shows the shifting very well, and the pushing ability. You can see the front end lift up about an inch or two whenever I shift. You can also see how fast it is too.

[zinthorne]

Originally Posted by zinthorne

We used transmissions which geared it down to 8:1 and then the extra big traction wheels with the 44 tooth sprocket helped give more power too. Same as in your design, our traction wheels lifted up the back mecanems about a half an inch.
This video has some pushing, and also a great upset win in finals.
https://www.youtube.com/watch?v=WbHHUtCGc1c

This link shows the shifting very well, and the pushing ability. You can see the front end lift up about an inch or two whenever I shift. You can also see how fast it is too.

Sorry, forgot the other link, this is from the driver station, so you can see the shifting very well.
https://www.youtube.com/watch?v=m93XfLe4fj0

[tStano]

Can you strafe with 6 mecanums? How? The physics aren't working in my mind.

[EricH]

Originally Posted by tStano

Can you strafe with 6 mecanums? How? The physics aren't working in my mind.

It looks like it's a mecanum drive with drop-down traction wheels, rather than a 6-mecanum drivetrain.

Now, I think a 6-mecanum drivetrain could work, provided that the center mecanums were matched to opposite corners--that is, the FL and the RR mecanum wheels are matched to the CL and CR mecanums, and are oriented the same way, either via chain or via programming, or some similar setup.

[tStano]

Originally Posted by EricH

It looks like it's a mecanum drive with drop-down traction wheels, rather than a 6-mecanum drivetrain.

Now, I think a 6-mecanum drivetrain could work, provided that the center mecanums were matched to opposite corners--that is, the FL and the RR mecanum wheels are matched to the CL and CR mecanums, and are oriented the same way, either via chain or via programming, or some similar setup.

OHHHH. This robot's a square, I thought the left side of the picture was just cut off, and now it makes a whole lot more sense. Thanks!

And I think you're right, but I think it'd be a mess to get the powers ratios right, because you've got 2 wheels on the ground fighting one. The weight balance would have to be super weird, or there would need to be a lot of math with traction forces, power draw, motor controller and motor curves, and stuff so you could manipulate power ratios so the forward components cancel when you strafe(and the sideways components do when you don't).