2015: Year of the Mecanum

[alopex_rex]

Originally Posted by TheJoe

Could it be possible that mecanum drivetrains are the ideal way to go because of their maneuverability?

We thought the exact same thing, after spending all of our off-season saying "well we're almost certainly doing tank drive, but if the game really wants something else..."

Our only experience with mecanum is with an off-season project, which had trouble going straight, we think because of wonky weight distribution. The programming was easy though: WPILib has a straightforward mecanum-drive function in the DriveTrain class.

[Ether]

Originally Posted by alopex_rex

Our only experience with mecanum is with an off-season project, which had trouble going straight, we think because of wonky weight distribution.

Weight distribution is only one of many factors which can cause unsatisfactory mecanum performance.

Here are some others:

• too much roller axial free play
  
  
• too much roller spinning friction
  
  
• wheel alignment (toe-in¹, camber¹, and axial offset²)
  
  
• excessive gearbox friction (improper assembly and/or lubrication)
  
  
• chain (or belt) too tight or not properly lubricated
  
  
• warped frame
  
  
• frame too rigid
  
  
• motor manufacturing tolerances
  
  
• motor controller calibration

¹Toe-in and/or camber of a wheel causes the wheel sprocket (or pulley) to be non-coplanar with the driving sprocket (or pulley), and thus contributes to friction between the chain (or belt) and the sprocket (or pulley). Toe-in also causes scrubbing friction with the floor surface.

²"wheel axial offset" in this context means that the wheel sprocket (or pulley) is axially offset from the plane of the driving sprocket (or pulley), causing the chain (or belt) to be non-coplanar, thus creating additional friction between the chain (or belt) and the sprockets (or pulleys).

[alopex_rex]

Originally Posted by Ether

Weight distribution is only one of many factors which can cause unsatisfactory mecanum performance.

Here are some others:
...

Thanks! This looks very helpful...and is also pretty intimidating, although I imagine a lot of those factors apply to any drive train one might make.

[oison75]

Our team is also considering using a mecanum drive train. We have never used mecanum before, but we firgured we have lots of resources to lean on and using mecanums will be very adventageous. Any suggestions for drive train layout, gearboxes, motors, bearings, etc? Also where're the best places to purchase mecanum wheels, I've only seen the Andy Mark ones and Vex ones... are those good? I'm extremely excited to start playing with a mecanum robot, but an also very nervous since our team is new to mecanum... Any suggestions?

[mfalk]

We used mecanum on our Rebound Rumble robot and had only slight problems getting on the bridges and that angle was much greater than 16-degrees. My thought is that robot drivers may underestimate their center of gravity when carrying loads up high and attempting to drive over scoring zones.