Swerve Central

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Revision as of 16:16, 5 May 2013 by MaiKangWei (talk | contribs) (Drawbacks of Swerve Drive)

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1640's 2013 pivot module
1640's 2012 pivot module
1640's 2011 pivot module
1640's 2010 pivot mechanism
This is a consolidation point for key and current information and engineering concerning swerve drive. It primarily deals with FRC 1640's swerve drive, but references to other systems and sources are included.

What is Swerve Drive

In FRC circles, swerve drive can be used for any drive train in which all drive wheels are steered. For this forum, the definition will be restricted to drive trains where all drive wheels are independently driven and steered.

Benefits of Swerve Drive

  • Agility - a true 2-d drive train in which drive direction is divorced from chassis orientation
  • Traction - high traction wheels may be employed without negative consequence; furthermore drive force may be vectored in any desired direction
  • Stealth - no need to telegraph intentions via chassis reorientation
  • Flexibility - with the drive direction and power controlled independently to each wheel by software, multiple drive modes, including game-specific drive modes, become possible
  • Dynamic Steering - for most FRC drive trains, driver joystick input maps 1:1 with drive train motor instructions; swerve steering directions to each wheel need not simply reflect driver joystick input, but may also reflect current "t" status in determining "t+δt" motor instructions; from a practical standpoint, this may be used as an agility force-multiplier
  • Minimal steering hysterisis - there is almost no need to overcome static friction in steering
  • Servicability - an independent wheel drive train just screams modularity; 1640 can swap out a pivot module in < 5 minutes (easy peasy)

Drawbacks of Swerve Drive

  • Complexity/difficulty - This is not an easy drive train to execute; mechanically or programmatically; not for the faint-hearted or impatient; it took us 4 years to realize all of the benefits (maybe, we think)
  • Mass - 1640's reduced the mass of 4 pivot modules to 31.6 lbm. Still a lot for a drive train
  • Time - CNC machining takes time; so does the assembly of complex mechanisms; as a result 1640 has finished swerve modules available to mount in chasses only at the start of week 5
  • Cost - Financial cost of swerve modules is a significant (but fortunately declining) portion of our build budget
  • Motor budget - 4-wheel swerve requires (4) drive motors and (4) steering motors; (8) motor controllers; (4) analog inputs; these leave less for other functions
  • Difficulty in driving straight - Not so surprisingly, an ultra-agile drive train has trouble driving a straight line; drivers compensate in tele-op, but this is a particular issue with autonomous
  • High use of cRIO resources -
  • Driver training is not optional with swerve

FRC 1640 White papers and CAD Design

Design Considerations

Value Engineering

1640 has always viewed swerve drive as a strategic investment. While not the best drive train solution for all situations, it is a very attractive drive train for many FRC situations.

But it's expensive (in many dimensions). 1640 therefore runs a value engineering project each year specifically for the swerve drive.

Value Engineering seeks to widen the gap between a device's value (to the customer) and its cost by:

  • increasing the value (performance, reliability, ease of maintenance,...);
  • reducing the cost (normally $s, but also mass, motors, time, driver training,...); or
  • both