Mecanum Specifics- Layout, Ratios, etc

[craigboez]

As a second year team, we're getting prepared to start experimenting with our first Mecanum drivetrain. We have a set of the 6" wheels from AM en route, and while we wait we were doing some digital design. I have a few questions that I was unable to answer from previous threads:

1. Does the layout of the wheels have a big impact on the overall performance of the bot? We could either lay them out in a square or rectangle - does it make a big difference (especially from a programming standpoint)?
2. Is maximizing the footprint a big deal? Put another way, should the wheels be pushed as far toward the corners as possible?
3. What have you used as a successful final gear ratio, and what type of gearbox did you implement. A few earlier posts suggested direct drive off a Banebots transmission, either 12:1 or 9:1. We don't have any of those, and rather than dropping $400 on some trannies we'll probably try to adapt the Toughboxes we've got. There are some good ideas floating around, just wanted to get a feel for what others have tried.

Thanks for the support.

[EricH]

Originally Posted by craigboez

1. Does the layout of the wheels have a big impact on the overall performance of the bot? We could either lay them out in a square or rectangle - does it make a big difference (especially from a programming standpoint)?
...
3. What have you used as a successful final gear ratio, and what type of gearbox did you implement. A few earlier posts suggested direct drive off a Banebots transmission, either 12:1 or 9:1. We don't have any of those, and rather than dropping $400 on some trannies we'll probably try to adapt the Toughboxes we've got. There are some good ideas floating around, just wanted to get a feel for what others have tried.

1. Layout doesn't seem to have a big impact. Main place might be in turning.

3. The team I worked with that used them in 2008 used something close to a 1:1 off of a Toughbox. I'm still not sure that was fast enough. I'm not sure what the ratio was off a 2005 KOP tranny (effectively a Toughbox, IIRC) when my team tried it in that year.

If you use a toughbox, I think there's a speed mod you can do pretty easily--you may want to do that.

[GUI]

Originally Posted by EricH

If you use a toughbox, I think there's a speed mod you can do pretty easily--you may want to do that.

We did this in 2008 (taking out a stage of reduction, though andymark sells gears for different reductions), and it reduces the gearing of the toughbox from 12.75:1 to 3.57. If you want help doing this let me know.

[pfreivald]

One might want to check if 3.57:1 is enough for a mechanum drive to get over the ramps. I know 12:1 works, but I'm not sure about 3.57:1.

[idahorobot]

Originally Posted by pfreivald

One might want to check if 3.57:1 is enough for a mechanum drive to get over the ramps. I know 12:1 works, but I'm not sure about 3.57:1.

Have you traversed the ramp with 12:1?

[dtengineering]

We used 12:1 banebots transmissions directly driving 8" AM mecanums in our Rack'n'Roll robot. It worked pretty well http://www.youtube.com/dtengineering#p/u/12/gyn9e0cT3-A and we were able to make it up a 30 degree incline.

The banebots trannies needed the long output shaft that is currently backordered, as are the BB P80 transmissions.

An AM toughbox with the long output shaft for each wheel should work well, too... although I'd highly recommend getting the aluminum gears to lighten it up, and maybe even speedholing them a bit. Four transmissions and ten pounds of wheels can start to add up quickly.


Jason

[MrForbes]

Originally Posted by craigboez

1. Does the layout of the wheels have a big impact on the overall performance of the bot?

It might have affect how tippable your robot is. See if you can understand why by reading this old white paper.

http://www.chiefdelphi.com/media/papers/1974

As for programming, I think it does not make much difference, although the "spinning" thing probably works best with the wheel/floor contact points in a square configuration.