Mechanum Gear Ratio Recommendations

[bakejame]

I have looked through the other posts about Mechanum wheels and the discussion about direct drive or chain drive to try to find my answer. I haven't had any luck.

What I would like to know is: what the best gear ratio supplied to the wheel should be for 8" Mechanum wheels? For last year's competition we had a GR of ~20:1 between the toughbox and the sprockets. We were very maneuverable, but we weren't very fast. That was mostly so we would have enough torque to get over the bumps. We don't have bumps this year, so torque won't be quite as necessary. We do think speed will be important though.

If someone knows of a formula we could use to calculate the GR we should use with our Mechanums, we would really, really, really appreciate it.

Thanks in advance.

[KHall]

Team 2171 won two regionals on 12:1 BaneBots planetary gearboxes (2008 and 2010). On 8 inch mechanum wheels (2008), I thought that the robot went a little too fast for easy control. On 6 inch wheels (2010) it was still very fast but much easier to control.

20:1 might be a bit slow for this league, depending on your wheel size.

Also, we noticed that there was a performance difference between different makes of motor drivers. You may want to experiment to see what works best for you.


Hope this helps.

Keith Hall
Mentor 2171

[Hawiian Cadder]

our team had a similar experience, that 12-1 is too fast, i think about a 14-16 to 1 would be about ideal

[Mr. Van]

I'm assuming you are using CIM motors.

Were these ratios overall (motor shaft to wheel shaft) or was there another reduction using chain and sprockets?

-Mr. Van
Robodox

[TubaMorg]

We've always just gone direct drive straight from the tough box (12:1) with no problems.

[bakejame]

Thanks everyone for your suggestions. I guess I need to order some larger sprockets for the wheels (we only have 26 tooth or smaller). We really want to use the CIMple Box due to its lower weight. With the 4.8:1 GR out of the box and a 12 tooth driver sprocket, I need to get a 28 to 30 tooth sprocket at the wheels to get close to the 12:1 GR.

By the way, how was it to strafe sideways at the 12:1 GR? Did it still perform pretty well?

[dtengineering]

Here's what 12:1 banebots direct drive to 8" AM mecanums looks like.

http://www.youtube.com/dtengineering#p/u/1/gyn9e0cT3-A

Heck... that thing even picks up tubes. Add a minibot and you're good to go.

Jason

P.S. If we rebuilt that machine all over again, I'd be tempted to consider the 16:1... the 12:1 had lots of speed, but I think the 16:1 would offer better acelleration and more precise control. I'd also use the Jaguar speed controllers to implement closed-loop speed control on the controller so you can take the PID loops and encoder reading out of the programming process. Not that it is hard to do that in labview... but back in the PIC days you actually had to have students who knew how to program in order to get 4 PID loops running! With labview and/or the jags, you just set your coefficients and go back to building the minibot.

[bakejame]

Originally Posted by dtengineering

Here's what 12:1 banebots direct drive to 8" AM mecanums looks like.

http://www.youtube.com/dtengineering#p/u/1/gyn9e0cT3-A

Heck... that thing even picks up tubes. Add a minibot and you're good to go.

Jason

P.S. If we rebuilt that machine all over again, I'd be tempted to consider the 16:1... the 12:1 had lots of speed, but I think the 16:1 would offer better acelleration and more precise control. I'd also use the Jaguar speed controllers to implement closed-loop speed control on the controller so you can take the PID loops and encoder reading out of the programming process. Not that it is hard to do that in labview... but back in the PIC days you actually had to have students who knew how to program in order to get 4 PID loops running! With labview and/or the jags, you just set your coefficients and go back to building the minibot.

We are definitely using the Jaguars, but will be using CIM motors. The larger motors should give us the extra torque needed for acceleration and, as a result, more precise control. By the way, I really liked the arm design you all came up with. Nice compact design.

[spiffyspleen]

we are planning on using four wheel mccannum and are deciding if we should use andy marks alternate gear ratios, our stratagy is pushing power great mobiity and acceleration whci of the following should we use?: 14.88:1(alternate), 12.75:1 (STANDARD), 12.5:1 (alternate), 10.71:1(alternate). which should we choose. thanks for the help. Go 2635! : )