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Tank Drive

Over the years, we have developed and implemented a number of drive train designs, including:
  • Six-wheel skid-steer
  • Mecanum wheels
  • Tank treads
They all can have their place on a robot, depending on team capabilities, the competition objectives, and design priorities.  Here, we are going to focus on tank treads, as it is the drive train we get the most questions about.

Why do you use tank treads?

There a few reasons:
  • Overall simplicity.  While tank tread drives require more fabrication than some off-the-shelf skid-steer systems, the end result is among the simplest, having very few parts.  How?  The tank treads essentially drive all of the wheels, eliminating the numerous chains and sprockets required to drive a six-wheel skid steer system.
  • Terrain flexibility.  Having tank treads can be very beneficial for navigating uneven terrain.  It can also be beneficial for certain competitions where game pieces on the field could interfere with wheeled drive systems.

Is your tank drive system reliable?

Yes!  We have used tank treads on four competition robots and one off-season robot.  Reliability stats:
  • We have only broken one belt.
  • We have never had the tread delaminate.
  • We have never had a properly-tensioned belt jump off of the wheels.
  • We have never worn a belt out (includes many hours driving on concrete).

How is the robot able to turn ("skid steer") with so much traction?

While belts have considerable traction, we have found that we can turn quite easily by having the center idler wheels placed approximately 3/16" lower than the other wheels (the same tactic often employed in wheeled skid-steer systems).

How do you power your tank treads?

Tank treads can be driven in a variety of ways, typically similar to how a six-wheel skid-steer system would be.  It is generally easier to drive the end wheels, since there is naturally good belt-wrap there.

We typically use BaneBots P80 planetary gearboxes, designed in so they directly drive one of wheels.  Doing so provides a simple, reliable and low-profile solution.

We have run tank tread systems successfully with only two CIM motors (one per side) and a "typical" drive ratio (~12:1 gearbox ratio driving 5"-6" diameter wheels).

What belts and wheels do you use?

We use belts and wheels from BRECOflex.  Specifically:
  • Belts
    • We use the ATK10K13 belt profile for the following reasons:
      • While we have used the TK belt series, the "ATK" belt series is:
        • Significantly stronger.
        • As readily available.
        • Only slightly more expensive.
      • It has a raised center section ("K13") on the belt that mates with a center groove in the accompanying pulleys.  Doing so enables the belt to properly track on the pulley without flanges.

The tooth type/pitch is sufficiently large to handle the drive torque, while still being relatively lightweight.
    • The belt width is 50mm wide.  We have considered trying a narrower belt (25mm or 32mm), but doing so could make it easier for the belt jump off of the pulley when lateral belt forces are present (e.g., when the robot is skid-steering).
    • Our belt has the ends welded together ("V" option).  While not as strong as the truly endless belt construction ("BFX" option), it is readily available and sufficiently strong for our applications.
    • Our belt has steel tension members, which are readily available.
    • Belt backing
      • We have used the PVC White Herringbone belt backing successfully.

It has a high coefficient of friction, so tread carefully (pun!) to ensure the robot has sufficient driving force and proper wheel locations to ensure the robot is able to turn.
      • We have also used the Supergrip Green belt backing successfully.

It has a high coefficient of friction, so tread carefully (pun!) to ensure the robot has sufficient driving force and proper wheel locations to ensure the robot is able to turn.
    • Example p/n:  "50-ATK10K13/1600-V With PVC White Herringbone Backing"
  • Wheels (Pulleys)
    • We start with stock aluminum pulleys that mate with the above belt (readily available), then modify them to reduce weight (the wheel below is nickel-plated aluminum, FYI).
    • Example p/n:  "AL-55-ATK10-K13/48-0"

How do you keep the belts from jumping of the wheels?

There are few factors:
  • "K13" belt option
  • Sufficient belt width (50mm)
  • Proper belt tension
  • Aligned pulleys

How do you tension the belt?

Simple... We don't!  Well, here is the full story:

Actually, there is a small amount of tension, but we generally design the pulley positions for a zero-tension condition.
Our earlier designs used adjustable tensioners due to concerns of belts stretching or being too loose, but we have had success with designing for a zero-tension condition and not needing an adjustable belt tensioner (Case in Point:  Our 2012 and 2013 robots, which both had tank treads, never needed belt retensioning, even after driving practice, the Regional Competition and several robot demonstrations).