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This mecanum wheel 4WD robot physical build is now more or less complete, as shown above right, with the development emphasis now on a first full release of the software - its progress will continue to be documented here.

The 3D printed 'chassis plate' design was further developed so that there is an option for two L298N motor controllers to be installed for this mecanum-wheel build, since each of the four wheels must be separately/independently controlled.

The main aims of the project and it current status are:

• To use standard mecanum wheels that can be easily sourced: already obtained and shown in the images above.
• These mecanum wheels now have new motor control software developed for all the various mecanum wheel movement options (see below).
• For the wireless controller movement option 'standard' 4WD driving where the front + back, left or right wheels are driven the same is working using the controller's left joystick, and mecanum-based sideways movement using the right joystick has now been developed - other specialised mecanum-based movements still need further thought/development
• The sourced mecanum wheels also needed a custom 3D printed adaptor to connect a wheel to the standard YG2900 geared motor. This has been completed and is shown in the images above left and below. The adaptor's hexagonal wheel drive shaft goes through the wheel hub and is secured with a 20mm long M3 pan head screw through the centre of the adaptor with its nut held in a slot. The drive motor shaft is then fully secured in the adaptor's 'obround' slot using a 6mm M2 self tapping flanged pan head screw.
• The robot is controlled/managed by a Raspberry Pi 4 running Bullseye because the upgrade to a Pi 5 and Bookworm was considerd to be too significant at this time, as much of the underpinning software in Bookworm has changed (e.g. much of the camera functionality) - but all the existing control software continues to be reviewed/retested
• Additional functionality will also be developed to allow individual images to be captured and uploaded to a central Tiki repository, i.e. it will then have an IoT-like operational characteristic.
• Finally, since the wiring for all the various sensors and motor control was quite complex and because two L298N's are needed, this limits the space around the Pi 4 - so the new RPi-flex PCB has been used as it has very little overhang outside the Pi 4's footprint (as shown in the visualisation images below) - this PCB therefore simplifies all the interconnect.

More images for the build development are shown below:

The schematic below right, shows top views of a 4WD robot fitted with mecanum wheels and illustrates the wheel movements that can be 'set' to produce various overall robot movements.

Six pairs of ways of moving a robot therefore become possible which are described as follows:

a) FORWARD or BACKWARDS: where all four wheels, designated FL (front left), FR (front right), BL (back left), and BR (back right), are continuously rotated in the same direction.

b) SIDEWAYS-RIGHT or SIDEWAYS-LEFT: where the FL + BL and FR + BR wheels are continuously counter-rotated 'inwards' or 'outwards' to move sideways right or left.

c) GLIDE-RIGHT or GLIDE-LEFT: where only the FL and BR wheels are continuously rotated forwards to 'glide' forwards to the right or only the FR and BL wheels are rotated forwards to glide forwards to the left. To glide backwards these rotations are reversed.

d) TURN-RIGHT or TURN-LEFT: to do a simple TURN about a point on the side of the robot in which it is turning, to either the left or right, just the two front and back wheels on the opposite side to the turn direction are rotated forwards for a set period of time.

e) SPIN-RIGHT or SPIN-LEFT: to spin the robot clockwise around a point in its centre, for a set period of time the FL and BLwheels are rotated forwards while the FR and BR wheels are rotated backwards. To spin anti-clockwise the wheel rotations are reversed.

f) PIVOT-RIGHT or PIVOT-LEFT: a pivot as opposed to a TURN is defined as a rotation about a point at the rear of the robot - where pivoting to the right is achieved by, for a set period of time, rotating the FL wheel forwards and the FR wheel backwards. To pivot to the left the wheel rotations are reversed.

The image on the right shows an initial test assembly of the pair of L298N motor controllers, connected to an early version of the RPi-flex PCB installed on a RPi4.

 

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