Tank Drive

20160902_141815

The tank drive is one of the most basic yet reliable drive system which can be made using the VEX IQ parts. This drive train style utilizes one or motors per wheel side. In the example drive train shown, the motors power both the front and back wheels; this is not necessary, as you can additionally choose to power just the front, or just the back wheels. All three options will yield different driving characteristics for your robot.

20160902_141824

Advantages

  • Easy to construct/troubleshoot.

Disadvantages

  • Cannot strafe left/right

5 Omni-Wheel Drive/ H-Drive

20160829_150841

The 5 Omni-directional wheel drive allows the robot to maneuver in more ways than compared to a standard tank drive wheel set-up. The middle omni-directional wheel allows the robot to strafe left and right, which can be very helpful in making minor robot position adjustments.

20160829_150909

Advantages

  • Can strafe/move in any direction.

Disadvantages

  • Requires 5 Omni-Directional wheels
  • Requires three motors on the drive, whereas the conventional tank drive only requires 2 motors

 X-Drive

20160830_135339The X-Drive is a type of base which can strafe left, right, up and down, similar to the H-Drive. This base consists of 4 omni-directional wheels, all placed at 45 degrees relative to each other. Simply by looking at the picture, it may be hard to visualize how it drives forward, so I’ll break it down for you.

20160830_135310

To drive forward (the direction of the green arrow), the wheels will rotate all at the same speed in the direction of the orange arrows. These orange arrows represent the force vector of each wheel. To add multiple force vectors graphically, we move the vectors in such a way that the vectors touch tip to end.

20160830_135310

The resulting force vector is the net resultant force vector. This means that the robot will move in the direction of the green arrow. To move in other directions, simply rotate the wheels in such a way that the resultant force vector is pointing to the desired direction of movement.

Advantages

  • Can strafe in any direction
  • Moves in a straight line faster than a traditional tank drive given that the motors on both systems rotate the wheels at the same speeds.

Disadvantages 

  • Requires four motors on the base.
  • Can be hard to offset wheels at 45 degrees

 Kiwi-Drive/ 3 Wheel Omni-Drive

iwi-drive-side

The Kiwi-Drive is similar to the X-Drive and H-drive in that they all have three degrees of freedom, meaning that they can move in any direction in the x-y plane, as well as rotate about its center. The Kiwi drive however only uses three motors and three omni-wheels, which is why some would prefer it over the other types of holonomic drives. The Kiwi Drive operates in the same fashion as the X-drive, in that the robot’s direction of motion will be in the same direction as the net resultant force vector.

kiwi-drive-with-arrows

In the picture above, the orange arrows represent the force vectors from each respective wheel, and the green arrow is the net resultant force vector. As you can see in the picture above, the x components of the orange force vectors cancel out, leaving you with a resultant force vector which has only a y component. If we were to rotate the wheels in this such manner, the robot would drive forward, in the same direction as the green arrow.  The robot shown uses three touch sensors for autonomous movement, and also has six touch LEDs to allow the user to interact with the robot without the use of the controller.

kiwi-drive-top

Advantages

  • Can strafe in any direction
  • Only requires three omni-wheels
  • Only requires three motors, as compared to the four motors of the X-Drive.

Disadvantages

  • Can be a challenge to build symmetrically
  • Has trouble going up the VEX IQ Starstruck ramp

Below is a video of the kiwi-bot autonomously driving around the playing field.

Design Challenges

  1. Design and build a robot base which can drive up the VEX IQ Starstruck bridge
  2. Design and build a holonomic drive base which can drive up the VEX IQ Starstruck bridge