Also, I don’t want to damage my walls by banging a pointy corner of a robot into them. However, while simple, if a force were to be directly applied to one of the corners of the square, two of the wheels would be lifted up. The simplest design to understand is a robot with a square base with the wheels situated in the middle of each side. Therefore, the wheels cannot be mounted in the same manner as the aforementioned mecanum wheel. The result is a wheel that can roll like a normal wheel but also slide laterally very easily. Omniwheels have small rollers around their circumference that are perpendicular to the rolling direction. The horizontal axis of a second joystick controls the rotation of the robot. With arcade style control, the horizontal and vertical axes of a joystick specify the speed and direction of the robot.
User InterfaceĪ remote control was used to drive the robot using an “arcade style” control. If you’re building for a different platform, you may have to adjust accordingly for these factors. In ROBOTC, motor power levels also range from -127 to +127 other systems may use a different scale. In ROBOTC, the joystick axes have a range of -127 to +127 other products may provide a range of 0 to 255 or 0 to 1023. Convert joystick values to motor speedsĪ couple of notes on the code. Implement dead zones to compensate for joystick values
#Robotc ide code
Other platforms may have different code for this. Get value of three joysticks used for speed and Int deadband = 20 // Threshold value for deadzone Int Y1, X1 // Vertical, Horizontal Joystick Values
#Robotc ide software
Or, with ROBOTC, there’s a command (not shown) to have software implement a motor direction reversal: You can change this by reversing the two wires to the motor. If you’re building your own robot, you may find that one or more motors move in the opposite direction than intended. The software was written in ROBOTC - a dialect of the popular C programming language optimized for use with robots.
The actual power applied to each of the four motors is a simple formula of the three joystick axes. Since joysticks do not always return exactly to the center value of zero, a small dead zone is used to treat all values close to zero as zero. The complete program is barely 20 lines of code. The source code to control the robot is amazingly simple. If the motors cannot match each other, the motion of the robot will not be as expected. The mecanum works on the principle of combining and canceling vectors. Two of the wheels are mounted with the rollers at +45 degrees and two with rollers orientedĪnother important item to consider when using a mecanum drive system is weight distribution and build quality. Mecanum wheels are mounted on a 4WD robot as shown. This is an important rule to follow or else the behavior of the robot will not act as expected. Meanwhile, on the bottom the rollers should create a diamond. When putting on mecanum wheels, the rollers of the wheel should create an X when viewed from the top. This is the direction that the wheel would want to move. Rotation of a single mecanum wheel provides a "force vector" perpendicular to the rollers. This means that running all wheels in the same direction will result in a forward or backwards direction running one side in the opposite direction of the other will result in rotation and running the wheels on one diagonal in the opposite direction of the other diagonal will result in sideways movement. Different combinations of force vectors can combine/cancel to produce movement in all directions. This causes the motors to introduce force at 45 degree angles. Each wheel has rollers offset by 45 degrees from the wheel and the drive train. The robots are constructed using the VEX Robotics building system. This article looks at omnidirectional robots constructed with both types of wheels and includes software code for providing this control. The difference between the two types is the angle at which the rollers are mounted at. Both wheel types are similar in that they have rollers mounted around the wheel's circumference allowing for sideways movement of the robot.
A four wheel drive (4WD) omnidirectional robot can be built using either mecanum wheels or omniwheels. So, it's easy to move the robot in a congested area. Holonomic robots are omnidirectional robots that can move in any direction from any orientation, creating an incredibly mobile robot.
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