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Mecanum Wheels

The Yahboom Raspbot V2 uses mecanum wheels -- wheels with small rollers mounted at 45 degrees around the rim. By controlling the direction of each wheel independently, the robot can move sideways, diagonally, and rotate in place without changing its heading.

All mecanum methods are part of the Motors class and are accessed via Robot.motors.

Roller orientation

The Raspbot V2 uses the standard X-pattern:

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Front-left  (/): rollers at +45 deg
Front-right (\): rollers at -45 deg
Rear-left   (\): rollers at -45 deg
Rear-right  (/): rollers at +45 deg

Viewed from above with the front of the robot at the top:

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  FL (/)   FR (\)
  RL (\)   RR (/)

Movement table

F = forward, R = reverse, 0 = stopped.

Method FL (L1) RL (L2) FR (R1) RR (R2) Result
forward() F F F F Straight ahead
backward() R R R R Straight back
turn_left() R R F F Rotate left in place
turn_right() F F R R Rotate right in place
strafe_right() F R R F Slide right
strafe_left() R F F R Slide left
diagonal_forward_right() F 0 0 F 45 deg fwd-right
diagonal_forward_left() 0 F F 0 45 deg fwd-left
diagonal_backward_right() R 0 0 R 45 deg bwd-right
diagonal_backward_left() 0 R R 0 45 deg bwd-left

Methods

strafe_right(speed=150)

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def strafe_right(self, speed: int = 150) -> None

Slide directly right without rotating.

Parameter Type Default Description
speed int 150 PWM duty-cycle 0-255

strafe_left(speed=150)

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def strafe_left(self, speed: int = 150) -> None

Slide directly left without rotating.

diagonal_forward_right(speed=150)

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def diagonal_forward_right(self, speed: int = 150) -> None

Drive diagonally forward-right at 45 degrees. Only the front-left (L1) and rear-right (R2) motors are driven; the other two are stopped.

Note

Diagonal moves use only two motors so the effective thrust is lower than forward/strafe at the same speed. Increase speed by about 40 % to compensate if needed.

diagonal_forward_left(speed=150)

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def diagonal_forward_left(self, speed: int = 150) -> None

Drive diagonally forward-left at 45 degrees. Rear-left (L2) and front-right (R1) are driven.

diagonal_backward_right(speed=150)

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def diagonal_backward_right(self, speed: int = 150) -> None

Drive diagonally backward-right at 45 degrees. Front-left (L1) and rear-right (R2) are driven in reverse.

diagonal_backward_left(speed=150)

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def diagonal_backward_left(self, speed: int = 150) -> None

Drive diagonally backward-left at 45 degrees. Rear-left (L2) and front-right (R1) are driven in reverse.

Complete example

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import time
from raspbot import Robot

SPEED = 150
DURATION = 1.0

moves = [
    ("Forward",            lambda bot: bot.motors.forward(SPEED)),
    ("Backward",           lambda bot: bot.motors.backward(SPEED)),
    ("Rotate left",        lambda bot: bot.motors.turn_left(SPEED)),
    ("Rotate right",       lambda bot: bot.motors.turn_right(SPEED)),
    ("Strafe right",       lambda bot: bot.motors.strafe_right(SPEED)),
    ("Strafe left",        lambda bot: bot.motors.strafe_left(SPEED)),
    ("Diagonal fwd-right", lambda bot: bot.motors.diagonal_forward_right(SPEED)),
    ("Diagonal fwd-left",  lambda bot: bot.motors.diagonal_forward_left(SPEED)),
    ("Diagonal bwd-right", lambda bot: bot.motors.diagonal_backward_right(SPEED)),
    ("Diagonal bwd-left",  lambda bot: bot.motors.diagonal_backward_left(SPEED)),
]

with Robot() as bot:
    for name, move_fn in moves:
        print(name)
        move_fn(bot)
        time.sleep(DURATION)
        bot.motors.stop()
        time.sleep(0.3)

Troubleshooting

Strafe direction is reversed

The roller orientation of your wheels may be mirrored relative to the X-pattern. Swap strafe_right and strafe_left calls, or physically swap the front-left and front-right wheels.

Diagonal moves drift sideways

This is normal -- without encoders, wheel speed differences accumulate over time. Diagonal moves are best used for short bursts, not sustained navigation.

Robot rotates instead of strafing

The wheels are not in the X-pattern. Check that the roller axis on each wheel forms an X when viewed from above:

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  /  \
  \  /

If it forms an O (all rollers parallel), swap the left-side wheels front-to-rear.

See also